Topic 1- Atomic structure and the periodic table Flashcards
What are all substances made of?
All substances are made of atoms.
What is an atom?
An atom is the smallest part of an element that can exist-so it cannot be divided.
What is the radius of an atom?
Atoms have a radius of about 0.1 nanometers
thats 1 x 10-10 m
What do atoms contain?
Atoms contain a NUCLEUS-
1) It’s in the middle of the atom.
2) It contains PROTONS an NEUTRONS.
3) The nucleus has a radius of around 1 x 10-14 m).
4) It has a positive charge because of the protons.
5) Almost the whole mass of the atom is concentrated in the nucleus.
and ELECTRONS-
1) Move around the nucleus in electron SHELLS.
2) They’re negatively charged and tiny, but they cover lot of space.
3) The volume of their orbits determines the size of the tom.
4) Electrons have virtually NO mass.
What is the relative mass and charge of protons, neutrons and electrons?
Particle Relative Mass Charge
Proton 1 +1
Neutron 1 0
Electron Very small -1
What is the overall charge of an atom which contains and equal number of protons and electrons and why?
1) Atoms are NEUTRAL- they have NO CHARGE overall (unlike ions).
2) This is because they have the SAME NUMBER of PROTONS as ELECTRONS.
3) The charge on the electrons is the SAME size as the charge of the PROTONS, but OPPOSITE- so the charges CANCEL OUT.
What is an ion?
An ion is an atom or group of atoms that has lost or gained electrons.
What is the charge of an ion?
In an ion, the number of protons DOESN’T EQUAL the number of electrons. This means it has an OVERALL CHARGE.
For example, an ion with a 2- charge, has two more electrons than protons.
How are atoms represented?
Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, Na represents an atom of sodium.
What can you learn from the chemical symbol?
The chemical (or nuclear) symbol of an atom tells you its ATOMIC (proton) NUMBER and MASS NUMBER.
What does the mass and atomic number tell us?
Tip- the mass number is always larger than the atomic number except from hydrogen.
1) The ATOMIC NUMBER tells you how many PROTONS there are.
2) The MASS NUMBER tells you the TOTAL number of PROTONS AND NEUTRONS in the atom.
3) To get the number of neutrons, just subtract the atomic number from the mass number.
What is an element?
An element is a substance that contains only one type of atom.
So an element is a substance made up of atoms that all have the same number of protons in their nucleus.
N.b - all elements of the same type have the same atomic number i.e. the same number of protons.
How do atoms differ?
Atoms can have different numbers of protons, neutrons and electrons.
It’s the number of PROTONS in the nucleus that decides what type of atom it is.
E.g. an atom with one proton in its nucleus is hydrogen and an atom with two protons is helium.
What must a substance contain the same number of to make it an element?
A substance must only contain atoms with the same number of protons to make it an element.
How many elements are there?
Where are they shown?
There are about 100 different elements.
Elements are shown in the periodic table.
What are isotopes?
1) ISOTOPES are different forms of the same element, which have the SAME NUMBER of PROTONS but a different number of NEUTRONS.
2) So isotopes have the same atomic number but different mass numbers.
N.B- the number of neutrons is just the mass number minus the atomic number.
What is a common example of an isotope?
A very popular example of a pair of isotopes are carbon -12 and carbon-13.
Carbon-12 contains 6 protons
6 neutrons
12 6 electrons
C
6
Whereas Carbon -13 contains 6 protons
6 electrons
7 NEUTRONS 13
C
6
Therefore the IDENTITY of an atom depends on the number of PROTONS in its nucleus.
What is relative atomic mass and what is it used for?
Because many elements can exist as a number of different isotopes, RELATIVE ATOMIC MASS (Ar) is used instead of mass number when referring to the element as a whole.
The relative atomic mass (Ar) of an element is an average value that takes account of the abundance of the isotopes of the element.
In other words, the Ar is an average value for all the isotopes of that element. Numerically it is the same as the mass number.
How can you work out the relative atomic mass of an element?
Example:
Bromine atoms exist as the isotopes 79 and 81- there are 50% of each present in the universe, which is why in the periodic table, an average mass number of 80 is quoted.
Other isotopes are 35 with 37
Cl Cl
In this case, 25% are the 37 isotope, and 75% are the 35 isotope, and that is why the periodic table quotes the relative atomic mass number of Cl as 35.5:
% x mass % x mass
(25 x 37) + (75 x 35)
__________________ = 35.5
100
What is the relative atomic mass (Ar) formula?
relative atomic
mass =
(Ar) (isotope abundance x isotope mass number)
____________________________________
100
What are compounds?
How are they bonded?
Compounds are substances formed from TWO OR MORE elements, the atoms of each element are in fixed proportions throughout the compound and can be represented by formulae using the symbols of the atoms from which they were formed.
The elements are held together by chemical bonds.
How are compounds formed and how are bonds made?
Compounds are formed from elements by chemical reactions. When elements react, atoms combine with other atoms to form compounds.
Making bonds involves atoms giving away, taking or sharing ELECTRONS. Only the ELECTRONS are involved, the nuclei of the atoms aren’t affected at all when a bond is made.
How can compounds be separated?
It’s usually difficult to separate the original elements of a compound out again-compounds can ONLY be separated into elements by CHEMICAL REACTIONS (breaking and making bonds). Compounds cannot be separated using physical processes.
N.b- during a chemical reaction at least one new substance is made. You can usually measure a change in energy such as temperature change.
How can Chemical reactions be represented?
Chemical reactions can be represented by word equations or equations using symbols and formulae.
How are compounds made of metals and non-metals formed?
A compound which is formed from a metal and a non-metal consists of IONS. The METAL atoms LOSE electrons to form POSITIVE IONS and the non-metal atoms GAIN electrons to form NEGATIVE IONS.
The OPPOSITE CHARGES (positive and negative) of the ions mean that they’re strongly ATTRACTED to each other. This is called IONIC BONDING.
What do compounds made of only non-metals consist of?
How are they formed?
A compound formed from non-metals consists of molecules. Each atom SHARES an ELECTRON with another atom- this is called COVALENT BONDING.
What are the properties of compounds?
The PROPERTIES of a compound are usually TOTALLY DIFFERENT from the properties of the ORIGINAL ELEMENTS.
Compounds can be small molecules or great bug structures called lattices.
What is used to display the different types of atoms in a compound?
Compounds can be represented by formulas. The formulas are made up of elemental symbols in the same proportions that the elements can be found in the compound.
What occurs during chemical reactions?
During a chemical reaction, bonds between atoms break and the atoms change places- the atoms from the substances you start off with (the reactants) rearrange themselves to form different chemicals. These new chemicals are called the products. You can show what happens in a chemical reaction using equations.
What do word equations show?
These show what happens in a chemical reaction using the full names of the substances involved. They show the reactants and the products.
What do symbol equations show?
Symbol equations show exactly the same as word equations but using chemical symbols and formulas. However, when balanced correctly they also show the ratio of the amounts of substances involved in the reaction.
What are valencies?
The valence of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. It can be used to work out the formula of compounds.
How can you work out a valency?
The valencies of metals are found by which group number they are in. So hydrogen is in group 1 so has a valency of 1.
However, to find the valency of a non-metal between group 5-8 you have to subtract their group number by 8. So oxygen has the group number 6 so has 6 electrons in its outer shell. The valence of oxygen is 8-6 which is 2. So oxygen needs to gain 2 electrons to have a full outer shell and become stable.
Why is it necessary to balance equations?
Equations must be balanced because mass doesn’t disappear during a reaction- there are always the same atoms present at the end of a reaction as there are at the start. This is known as the law of conservation of mass.
How do you balance equations?
The number of atoms on the left hand side must equal the number of atoms on the right hand side. Rules:
1) Write the different types of elements below the left and right hand side.
2) Count up the numbers of atoms on each side and write them in.
3) Look for something that doesn’t balance and add large numbers to the equation so that it does balance.
4) Recount the number of atoms again and return to rule 2 until all the elements are balanced.
Tip-symbol equations show how many atoms of one element there are compared to the number of elements. So it’s fine to double, or triple, or quadruple the number of atoms in a balanced equation, as long as you do the same to every term in the equation.
Tip- You don’t have to use whole numbers to balance an equation.
What is a molecule?
A molecule is two or more atoms chemically bonded together. The atoms may be the same type (an elemental molecule) or of a different types (a compound e.g. H2O).
What is a mixture?
1) Unlike in a compound, there’s NO CHEMICAL BOND between the different parts of a mixture.
2) The parts of a mixture can either be ELEMENTS or COMPOUNDS, and they can be easily separated out by PHYSICAL METHODS such as filtration, crystallisation and chromatography.
N.b- a physical method is one that doesn’t involve a chemical reaction, so doesn’t form any new substances.
What are the properties of a mixture?
The PROPERTIES of a mixture are just a MIXTURE of the properties of the SEPARATE PARTS- the chemical properties of a substance aren’t affected by it being part of a mixture.
What is chromatography?
CHROMOTOGRAPHY is a method to separate mixtures made up of liquids of different colours. An example of this is the use of paper chromatography to separate different dyes in an ink?
How do you carry out paper chromatography?
1) Draw a LINE near the bottom of a sheet of FILTER PAPER.
2) Add a SPOT of the ink to the line and place the sheet in a beaker of solvent, e.g. water.
3) The SOLVENT used depends on what’s being tested. Some compounds dissolve well in WATER, but sometimes other solvents, like ethanol are needed.
4) Make sure the ink isn’t touching the solvent-you don’t want it to DISSOLVE into it.
5) Place a LID on top of the container to stop the solvent EVAPORATING.
6) The solvent SEEPS up the paper, carrying the ink with it.
7) Each different DYE in the ink will move up the paper at a DIFFERENT RATE so the dyes will SEPARATE OUT. Each dye will form a SPOT in a different place- 1 spot per dye ink.
8) If any of the dyes in the ink are INSOLUBLE (won’t dissolve) in the solvent you’ve used, they’ll stay on the BASELINE.
9) When the SOLVENT has nearly reached the TOP of the paper, take the paper out of the beaker and leave it to DRY.
10) The end result is a pattern of spots called a CHROMATOGRAM.
N.b. - The point the solvent has reached as it moves up the paper is the solvent front.
How can you interpret chromatograms?
On some chromatograms, the number of spots you end up with tells you the number of different substances there were in a mixture. For example , if you end up with two spots, that might mean the ink contains two dyes.
This isn’t always the case though-sometimes the umber of visible spots on the chromatogram does’t match the number of dyes in the ink. For example, two dyes could travel the same distance up the filter paper so would only show one spot.
So all we can say is there are at least as many substances in the mixture as there are spots on the chromatogram.
What is filtration?
Filtration is often used if your desired product is an INSOLUBLE SOLID that needs to be separated from a LIQUID mixture. It’s also a useful technique for purification. For example, solid impurities in a reaction mixture can be removed using filtration.
Explain the process of filtration…
1) Fold a piece of filter paper into a cone.
2) Place the filter paper point down into a filter funnel that is sitting in the neck of a container such as a conical flask.
3) Pour the mixture containing the insoluble solid into the funnel lined by the filter paper. Make sure that none of the mixture goes over the top or down the side of the filter paper.
4) The liquid will pass through the filter paper but the solid won’t - it will be left behind.
Tip-insoluble means the solid can’t be dissolved in the liquid.
What two methods can be used to separate a soluble solid and a solution?
If a solid can be dissolved it is said to be soluble.
There are 2 methods used to remove a soluble product from a solution- EVAPORATION and CRYSTALLISATION.
What is evaporation and how long does the process take?
Evaporation is a really QUICK way of separating a soluble salt from a solution, but you can only use it if the salt DOESN’T DECOMPOSE when it is heated. Otherwise you’ll have to use CRYSTALLISATION.
Explain the process of evaporation…
1) Pour the solution into an EVAPORATING DISH.
2) Place the evaporating dish on top of a TRIPOD and gauze and place a BUNSEN BURNER underneath.
Tip-if the solvent is flammable you shouldn’t use a Bunsen burner to heat it, as it may catch fire. You’d need to use a different heating method, such as using a hot plate.
3) Slowly HEAT the solution. The SOLVENT will evaporate and the solution will get more CONCENTRATED. Eventually the SOLID CRYSTALS will start to form.
4) Keep heating the evaporating dish until all you have left is dry solid crystals.
What is crystallisation and how long does the process take?
Crystallisation takes more time than evaporation, however it can produce nice big crystals, that would decompose if heated.
Explain the process of crystallisation…
1) Place an EVAPORATING DISH on top of a TRIPOD with a GAUZE MAT. Place a BUNSEN BURNER underneath the TRIPOD.
2) Pour the solution into the EVAPORATING DISH and gently HEAT it. Some of the SOLVENT will evaporate and the solution will get more CONCENTRATED.
3) Once some of the solvent has evaporated, or when you see crystals start to form (the POINT OF CRYSTALLISATION), remove the dish from the heat and leave the solution to COOL.
Tip-Make sure you use tongs when removing the very hot evaporating dish.
4) The salt should start to form CRYSTALS as it becomes INSOLUBLE in the cold, highly concentrated solution.
5) FILTER the crystals out of the solution, and leave them in a warm place to dry. You could also use a DRYIN OVEN or a DESICCATOR.
Tip- the longer you the solution is left to cool following heating, the larger the crystals will be.
Exam tip- You may be asked to suggest what technique could be used to separate a certain mixture, so you need to know which techniques separate what.
Tip-You can use crystallisation INSTEAD of evaporation to form salt crystals. This is useful if you want to form large salt crystals.
What is rock salt and which technique is used to separate the mixture?
ROCK SALT is:
simply a MIXTURE of SALT and SAND (they spread it on roads in winter).
Salt and sand are both COMPOUNDS-but SALT DISSOLVES in water and SAND DOESN’T. This VITAL DIFFERENCE in their PHYSICAL PROPERTIES gives a great way to separate them.
Chemists don’t usually use one of these techniques in isolation, but will often use two or more in oder to separate a mixture.
Explain the process of separating rock salt using filtration and evaporation…
1) GRIND the mixture to make sure the salt crystals are small, so will dissolve easily.
2) Put the mixture in water and stir. The SALT will DISSOLVE, but the SAND WON’T. (Tip-heating the mixture will help to dissolve the salt).
3) FILTER the mixture. The grains of SAND won’t fit through the tiny holes in the filter paper, so they collect on the PAPER instead. The SALT passes through the filter paper as it’s part of the solution.
4) EVAPORATE the water from the salt so that it forms DRY CRYSTALS. (Tip-you could also use crystallisation here if you wanted nice big crystals).
What is distillation?
Distillation is used to separate mixtures which contain LIQUIDS. There are 2 different kinds- simple and fractional distillation. (page 40)
What is simple distillation?
SIMPLE DISTILLATION is used to separate out a liquid from a mixture. (It’s used in industry to get pure water from sea water).
Explain the process of simple distillation…
- Set up apparatus. Attach a clamp stand to a flask of sea water and place a safety mat, bunsen burner, tripod and gauze under it. Then place a thermometer inside the flask and attach a condenser. Heat the mixture.
Tip- the thermometer will show the boiling point of the vaporised liquid. The condenser turns the vapour back into a liquid as it it cooled by the water. - HEAT the solution. The part of the solution that has the lowest boiling point EVAPORATES first.
- The VAPOUR is the COOLED, CONDENSES (turns back into a liquid) and is collected.
- The rest of the SOLUTION is left behind in the flask.
- You can use simple distillation to get PURE WATER from SEAWATER. The WATER evaporates and is condensed and collected. Eventually you’ll end up with just SALT left in the flask.
What is a disadvantage of using simple distillation to separate out solutions?
The PROBLEM with simple distillation is that you can only use it to separate things with VERY DIFFERENT boiling points- if the temperature goes higher than the boiling point of the substance with the higher boiling point, they will MIX again.
So if you have a MIXTURE OF LIQUIDS with SIMILAR BOILING POINTS you need another method to separate them- like fractional distillation.
what is fractional distillation used for?
When would you use this technique?
How is the process used in industry?
Fractional distillation can be used for SEPARATING a MIXTURE of different LIQUIDS.
It is especially USEUL when the BOILING POINTS of liquids are CLOSE together.
Although fractional distillation is a technique commonly used in industry to separate liquid mixtures, e.g. SEPARATING CRUDE OIL into different groups, it is also used in the lab.
Explain the process of fractional distillation…
- You put your MIXTURE in a flask and stick a FRACTIONATING COLUMN filled with GLASS RODS on the top. Attach a CONDENSER to the column. Then you heat it.
- The DIFFERENT LIQUIDS will have DIFFERENT BOILING POINTS- so they will evaporate at DIFFERENT TEMPERATURES.
- The liquid with the LOWEST BOILING POINT evaporates first. When the temperature n the thermometer matches the boiling point of this liquid, it will reach the TOP of the column.
- Liquids with HIGHER BOILING POINTS might also start to evaporate . But the column is COOLER towards the TOP. So they will only get part of the way up before CONDENSING and running back down towards the flask.
- When the first liquid has been collected, you RAISE THE TEMPERATURE until the NEXT ONE reaches the top.
Why is experimental evidence important to science?
New experimental evidence may lead to a scientific model being changed or replaced.
What were atoms thought to be at the start of the 19th century before the discovery of the electron?
At the start of the 19th century JOHN DALTON described atoms as TINY SOLID SHERES, that could NOT be DIVIDED and said that different spheres made up different elements.
Who discovered the electron?
How did he come to this conclusion?
In 1897 J J THOMPSON concluded from his experiments that atoms WEREN’T solid spheres.
His measurements of CHARGE and MASS showed that an atom must contain even smaller, negatively charged particles- ELECTRONS.
What is the plum pudding model?
Tip- MODELS are used to predict the outcome of experiments. If the prediction is proved wrong the model may need to change.
The ‘solid sphere’ idea of atomic structure had to be changed. The new theory was known as the ‘PLUM PUDDING MODEL’.
The plum pudding model suggested that the atom is a BALL of POSITIVE CHARGE with negative ELECTRONS EMBEDDED in it (like dried fruit).
Who conducted the alpha particle experiment?
In 1909 ERNEST RUTHERFORD and his student MARSDEN conducted the alpha particle scattering experiments.
What did the alpha particle scattering experiment involve?
They fired positively charged ALPHA PARTICLES at an extremely thin sheet of gold.
What results were they expecting from the experiment and why?
From the plum pudding model, they were EXPECTING the particles to PASS STRAIGHT THROUGH the sheet or be SLIGHTLY DEFLECTED at most.
This was because the positive charge of each atom was thought to be very SPREAD OUT through the pudding of the atom.
What did the results show?
Most of the particles DID go STRAIGHT THROUGH the gold sheet, some were deflected MORE THAN EXPECTED, and a small number were DEFLECTED BACKWARDS.
So the plum pudding model COULDN’T be right.
What theory did Rutherford come up with which explained his evidence?
Tip- For a theory to be accepted there must be experimental evidence to support it.
Rutherford thought there was a tiny, positively charged NUCLEUS at the centre, where most of the MASS is concentrated.
A cloud of negative electrons surrounds this nucleus- so most of the atom is EMPTY SPACE.
when alpha particles came near the CONCENTRATED, POSITIVE CHARGE of the NUCLEUS, they were DEFLECTED. If they were fired directly at the nucleus, they were deflected BACKWARDS. Otherwise, they passes through the empty space.
What was the new atom model called?
It was called the NUCLEAR MODEL and replaced the plum pudding model.
What fault did the nuclear model of an atom have?
Scientists realised that electrons in a cloud around the nucleus of an atom, as Rutherford described, would be attracted to the nucleus, causing the atom to COLLAPSE.
Who adapted the nuclear model?
What was his theory?
What evidence did he have to support his theory?
Niels Bohr adapted the nuclear model by suggesting that electrons ORBIT the nucleus at SPECIFIC DISTANCES in FIXED SHELLS.
The theoretical calculations of Bohr agreed with experimental observations. It helped to explain lots of other scientists’ OBSERVATIONS at the time.
Who discovered the proton and how?
Further experiments by Rutherford and others showed that the nucleus can be DIVIDED into smaller particles, which each have the SAME CHARGE as a HYDROGEN NUCLEUS. These particles were named PROTONS.
Who discovered the neutron?
What evidence did he have to prove his theory?
The EXPERIMENTAL WORK of JAMES CHADWICK provided the evidence to show the existence of neutrons within the nucleus.
THIS WAS ABOUT 20 YEARS AFTER THE NUCLEUS BECAME AN ACCEPTED SCIENTIFIC IDEA.
Tip- protons, electrons and neutrons are called sub-atomic particles because they are smaller than atoms (sub means less).
Tip- both protons and neutrons can be called NUCLEONS because they both exist in the nucleus, therefore the mass number is sometimes called the nucleon number.
What is chemistry about?
Chemistry is about the movement of ELECTRONS.
What happens in a chemical reaction?
When a chemical reaction occurs, electrons are either lost, gained or shared between one atom and another, with the result that chemical bonds are formed.
How can you predict/consider how an element reacts?
The arrangement (configuration ) of electrons in an atom is vital when considering how an element reacts, or wether it will react at all.
What are the rules for electron configuration?
1) Electrons always occupy SHELLS (sometimes called ENERGY LEVELS).
2) The LOWEST energy levels are ALWAYS FILLED FIRST- these are the ones closest to the nucleus.
3) Only A CERTAIN NUMBER of electrons are allowed in each shell:
1st shell: 2 2nd shell: 8 3rd shell: 8
4) Atoms are much happier when they have a full electron shells- like the noble gases as they are stable and less reactive.
5) In most atoms, the OUTER SHELL is NOT FULL and this makes the atom want to REACT to fill it.
How can the electronic structure of an element be represented?
The electronic structure of an atom can be represented by numbers or by a diagram. For example, the electronic structure of sodium is 2,8,1 .

Development of the periodic table…
What two ways could the elements be categorised in the periodic table before the discovery of sub-atomic particles?
1) Their PHYSICAL and CHEMICAL PROPERTIES.
2) Their RELATIVE ATOMIC MASS.
How was the first periodic table organised by Dobereiner?
How many elements were discovered when the first periodic table was made?
What is Dobreiners method of organisation of the periodic table known as?
Scientists had NO IDEA of ATOMIC STRUCTURE or of PROTONS, neutrons, or ELECTRONS, so there was no such thing as ATOMIC NUMBER to them.
- Dobereiner spotted that SOME ELEMENTS shared SIMILAR properties. He began to put them in groups of 3, calling each group a TRIAD.
He also noted that the atomic weights of the middle element was approx the average of the atomic weights of the top and bottom element.
Dobereiner’s organisation is known as DOBEREINER’S TRIADS.
Remember- the relative atomic mass is the average mass of one atom of one element.
What was wrong with Dobereiner’s Triads?
As new elements were discovered it was difficult to fit them into triads, so his theory only partially worked, and was abandoned.
What is the difference between relative atomic mass (Ar) and atomic weight?
Key Difference: Atomic mass is defined as the total mass of protons, neutrons and electrons present in an atom of an element. Atomic weight is defined as the ratio of average mass of the atom present in an element. It is calculated to 1/12th of the mass of carbon atom. It is also referred to as relative atomic mass.
Both the terms, atomic mass and relative atomic mass read the same, but technically there is a big difference in the meaning of both the terms.
Atomic mass is the average mass of a single atomic particle or molecule. It is the sum of protons and electrons present in the atom of an element.
How did John Newland arrange the 64 elements?
HE ARRANGED the elements with the only thing they could measure which was RELATIVE ATOMIC MASS, and so the elements were arranged in oder of increasing ATOMIC MASS (which was the same as the mass number p + n).
What did Newland notice when ordering the elements?
He found similar properties amongst every EIGHTH element.
He noticed that some patterns were repeated; this is called periodicity e.g. the reactive metal Na was followed eight elements later by K another reactive metal.
What did he call this pattern?
He called this the LAW OF OCTAVES.
What was wrong with his atomic mass method of ordering the elements?
Newlines did NOT LEAVE GAPS FOR UNDISCOVERED ELEMENTS so this UPSET THE ORDER.
Some elements were placed in the WRONG GROUP and some ended up occupying the same spot.
Who overcame these problems?
Dimitri Mendeleev ordered the elements differently.
How did Mendeleev order the elements?
In 1869, DIMITRI MENDELEEV overcame some of the problems of early periodic tables by taking 50 known elements and arranging them into his table of elements- but leaving GAPS.
MENDELEEV put the elements MAINLY in order of ATOMIC MASS but did switch that oder if the properties meant it should be changed.
This enabled him to PREDICT the existence of UNDISCOVERED elements, and to group elements with SIMILAR PROPERTIES.
What confirmed Mendeleev’s periodic table?
When new elements were found and they FITTED THE PATTERN it helped confirm Mendeleev’s ideas.
Knowledge of ISOTOPES made it possible to explain why the order based on ATOMIC WEIGHT was not always CORRECT.
What new knowledge explained why elements were not always grouped strictly by atomic weight?
The discovery of ISOTOPES in the early 20th century confirmed that Mendeleev was correct to NOT to place elements in STRICT ORDER of atomic mass but to also take account of their PROPERTIES.
Isotopes of the same element have DIFFERENT ATOMIC MASSES but have the same CHEMICAL PROPERTIES so occupy the same position on the periodic table.
What is the periodic table?
The PERIODIC TABLE is a table that contains all the known elements.
How many elements are in the modern periodic table?
About 100 elements are in the periodic table, which all materials are made of.
How is the modern periodic table organised?
The discovery of protons, neutrons and electrons allowed the periodic table to be rearranged in order of INCREASING ATOMIC (PROTON) NUMBER.
Because the number of protons = number of electrons in a neutral atom, the modern periodic table is an arrangement of the elements ELECTRONIC CONFIGURATION.
What is the advantage of organising elements like this?
Arranging elements like this means there are REPEATING PATTERNS in the PROPERTIES of the elements. So elements with similar properties are in the same group.
It is also useful for working out which elements are metals and which are non-metals.
Why is the table of elements called the periodic table?
The word periodic describes something that happens at regular periods. For example, sunrise is periodic.
The table is called periodic because similar properties occur at regular intervals.
What are groups?
Elements with SIMILAR PROPERTIES form COLUMNS. These VERTICAL COLUMNS are called GROUPS.
What does the group number tell you?
The GROUP NUMBER tells you how many ELECTRONS there are in the OUTER SHELL. For example, GROUP 1 elements all have ONE electron in their outer shell.
The exception to the rule is GROUP 0, for example Helium has two electrons in its outer shell. Group 0 elements all have a full outer shell of electrons, but the number of electrons needed to fill each shell is different.
How can you predict the way in which an atom will react?
- The way atoms react depends upon the NUMBER OF ELECTRONS in their OUTR SHELL. So all the elements in the same group react in a similar way.
If you know the PROPERTIES of ONE ELEMENT, you can PREDICT properties of OTHER ELEMENTS in that GROUP.
- You can make predictions about trends in REACTIVITY.
E.g. in Group 1, the elements react more VIGOROUSLY as you go DOWN the group. And in Group 7, REACTIVITY DECREASES as you go down the group.
What are the rows in the periodic table called?
The ROWS are called PERIODS.
What does each period represent?
The number of the period that an element’s in tells you how many electron shells it has.
What is the goal of all atoms?
Chemistry is all about atoms passing/sharing electrons between each other in order to obtain a FULL OUTER SHELL, i.e. A STABLE ARRANGEMENT OF ELECTRONS; this is the ultimate goal.
A chemical reaction is simply what happens when electrons are being moved around so that atoms can achieve this goal.
What are metals?
Metals are elements which can FORM POSITIVE IONS when they react. This means metals lose their electrons.
Where are metals found on the periodic table?
They’re towards the BOTTOM and to the LEFT of the periodic table.
What are the majority of elements in the periodic table metals, or non-metals?
MOST ELEMENTS in the periodic table are metals.
How can you tell if an element is a non-metal?
Non-metals DON’T generally FORM POSITIVE IONS when they react. So they often gain electrons becoming negatively charged.
Where are non-metals found?
NON-METALS are at the far RIGHT and TOP of the periodic table.
How do atoms react?
Atoms generally react to form a FULL OUTER SHELL. They do this via LOSING, GAINING or SHARING electrons.
Explain the relationship between the electronic structure of metals and non-metals, and their positions in the periodic table?
1) Metals to the LEFT of the periodic table DON’T have many ELECTRONS TO REMOVE and metals towards the BOTTOM of the periodic table have outer electrons which are a LONG WAY from the nucleus so feel a weaker attraction.
BOTH these affects means that NOT MUCH ENERGY is needed to remove the electrons so it’s FEASIBLE for the elements to react to FORM POSITIVE IONS with a full outer shell.
2) For NON-METALS, forming positive ions is much MORE DIFFICULT. This is as they are either to the right of the periodic table- where they have LOTS OF ELECTRONS to remove to get a full outer shell, or towards the top- where the outer electrons are close to the nucleus so feel a STRONG ATTRACTION. It’s far more feasible for them to either SHARE or GAIN electrons to get a full outer shell.
What type of bonding do metals and metals have?
All metals have METALLIC BONDING which causes them to have SIMILAR basic physical properties.
What 3 physical properties do metals have?
1) They’re STRONG (hard to break), but can be BENT or HAMMERED into different shapes (malleable).
2) They’re great at CONDUCTING HEAT and ELECTRICITY.
3) They have high BOILING AND MELTING POINTS.
What 4 properties do non-metals have?
Non-metals don’t have metallic bonding, so they don’t tend to exhibit the same properties as metals:
1) They tend to be dull looking and more brittle than metals.
2) They generally have lower boiling and melting points than metals, so aren’t always solids at room temperature.
3) They don’t generally conduct electricity.
4) They often have a lower density than metals.
What are elements in group 1 known as?
Elements in group 1 are known as the ALKALINE METALS.
What physical properties do alkali metals have?
The alkali metals are all SOFT and can be cut with a knife to show a SHINY interior that becomes dull on reaction with oxygen in the air.
They have LOW DENSITIES.
What are the 3 trends for alkali metals going down the group?
- Increasing reactivity- the outer electron is MORE EASILY LOST as the attraction between the nucleus and electron decreases, because the electron is FURTHER AWAY from the nucleus the further down the group you go.
- LOWER MELTING and BOILING points.
- HIGHER RELATIVE ATOMIC MASS.
What is the electron configuration and chemical properties of alkalis metals?
*Tip- they have characteristic properties because of the single electron in their outer shell.
The group 1 elements all have 1 electron in their outer shells.
The group 1 elements are keen to LOSE THIS SINGLE OUTER ELECTRON and must do so by reacting with something else. This is why they are all so very reactive and react in similar ways as each other.
*So the outer shell of electrons determines the properties of the Group 1 elements.
How do alkali metals react with non-metals?
1) The Group 1 elements don’t need much energy to lose their one outer electron to form a full outer shell, so they readily form 1+ IONS.
2) They only ever react to form IONIC COMPOUNDS. These compounds are generally WHITE SOLIDS that dissolve in water to form COLOURLESS SOLUTIONS.
How do alkali metals react with water?
1) When Group 1 metals are put in WATER, they react VIGOROUSLY to produce HYDROGEN GAS and METAL HYDROXIDES- salts that dissolve in water to produce ALKALINE SOLUTIONS.
2) The MORE REACTIVE (lower down the group) an alkali metal is, the more violent the reaction is.
3) The amount of ENERGY given out by the reaction increases down the group- the reaction with potassium releases enough energy to ignite hydrogen.
What is the equation for the reaction of an alkali metal with water?
Alkali metal + water ——-> metal hydroxide + hydrogen
How do alkali metals react with chlorine?
1) Group 1 metals react VIGOROUSLY when heated in CHLORINE GAS to form white METAL CHLORIDE SALTS.
2) As you go down the group, reactivity increases so the reaction with chlorine gets MORE VIGOROUS.
What is the equation for the reaction of alkali metals with chlorine?
alkali metal + chlorine —–> metal chloride
Tip- The alkali metals also react with the other halogens in similar reactions.
How do alkali metals react with oxygen?
The Group 1 metals react with OXYGEN to form a METAL OXIDE. Different types of OXIDE will form depending on Group 1 metal.
All metal oxides formed are WHITE SOLIDS.
What are the elements in group 7 known as?
The elements in Group 7 of the periodic table are known as the halogens.
what are the physical properties of halogens?
The halogens are non-metals and consist of molecules containing pairs of atoms.
What is the name given to pairs of atoms?
Pairs of atoms are known as diatomic.
What is the electronic configuration of halogens and why do they react similarly?
The group 7 element all have 7 electrons in their outer shells.
The halogens are keen to GAIN one more outer ELECTRON and must do so by REACTING with something else. This is why they all react in similar ways.
How do halogens react down the group and why?
1) REACTIVITY - REACTIVITY DECREASES DOWN THE GROUP, so elements at the bottom of the group are less reactive than elements at the top of the group.
This is because halogens react by gaining an electron in their outer electron shell- its HARDER TO GAIN an extra electron, because there is LESS ATTRACTION from the NUCLEUS pulling electrons to the atom.
What are the trends in melting and boiling points for the halogens?
The melting and boiling points of the halogens INCREASE DOWN THE GROUP.
What are the trends of relative atomic mass in group 7?
The relative atomic masses of Group 7 elements INCREASES as you go DOWN the group.
Tip-why is it useful to know and understand the trends in group 7?
Theses trends can be used to predict properties of halogens.
How do halogens react with non-metals?
Halogen atoms can SHARE electrons via covalent bonding with other NON-METALS so as to achieve a FULL OUTER SHELL.
The compounds that form when halogens react with non-metals all have SIMPLE MOLECULAR STRUCTURES.
How do halogens react with metals?
As halogens have 7 electrons in their outer shells, it is easy to gain one electron and fill up their outer shell.
So when halogens gain one electron from a metal they form 1- IONS called HALIDES for example Na + Cl -
How do halogens react with other halogens?
DISPLACEMENT REACTIONS occur between a more reactive halogen and the salt of a less reactive one.
E.g. chlorine is more reactive than bromine, so chlorine will displace bromine from an aqueous solution of its salt (a bromide).
chlorine + potassium bromide –> bromine + potassium
chlorine
Tip- astatine is the least reactive halogen so it can’t displace any other halogen.
What are the elements in group 0 known as?
The elements in group 0 are called THE NOBLE GASSES.
What are the physical properties of the noble gasses?
1) They exist as MONATOMIC GASSES- single atoms NOT bonded to each other.
2) The noble gasses are all un-reactive- NON-FLAMMABLE.
3) All elements in group 0 are COLOURLESS GASSES at room temperature.
What is the electronic configuration of the noble gasses?
They all already have energy levels of EIGHT ELECTRONS, apart from helium which has two, giving them a FULL OUTER-SHELL.
This is why they DO NOT REACT AT ALL.
What are the patterns in the boiling point and relative atomic mass down group 0?
The BOILING POINTS and RELATIVE ATOMIC MASS of the noble gasses INCREASE as you move DOWN the group.
Why do the boiling points increase as you go down the group?
The INCREASE in boiling point is due to an INCREASE in the NUMBER OF ELECTRONS in each ATOM leading to GREATER INTERMOLECULAR FORCES between them which need to be overcome.
Where are transition elements located?
The transition elements (transition metals) are found between groups 2 and 3.
What are transition elements?
The transition elements are typical metals with similar properties which are different from those of the elements in Group 1.
What are the typical properties which transition elements and metals share?
- Good CONDUCTORS of HEAT and ELECTRICITY.
- Very DENSE, STRONG and SHINY.
- Easily bent or hammered into shape (malleable)
What special properties do transition metals have?
- Transition metals can have MORE THAN ONE ion. E.g. Fe 2+, Fe 3+, Co 2+, Co 3+.
- Transition metal ions are often COLOURED, and so COMPOUNDS that contain them are COLOURFUL e.g. CuSO4 is blue and KMnO4 is purple.
- Transition metal compounds often make good CATALYSTS. For example, a Ni (NICKEL) based catalyst is used in the hydrogenation of alkenes, and an IRON catalyst is used in the HARBER PROCESS for making ammonia.
How are transition metals different to group 1 metals?
- The transition metals have higher DENSITIES and MELTING POINTS (except mercury).
- They are HARDER and mechanically STRONGER.
- Transition metals are much LESS REACTIVE and DO NOT REACT as vigorously with WATER, OXYGEN or HALOGENS (the group 7 elements).
E.g. copper Cu is used for water pipes, nickel is used in coins.
