Atomic Structure and the Periodic Table Flashcards
What are atoms?
- Atoms make up all substances
- The smallest part of an element
- They contain Protons, Neutrons and Electrons
- They have a radius of about 0.1 nanometers (1 times 10 to the power of -10)
What is the nucleus like in an atom?
- The nucleus is in the middle of the atom
- The nucleus contains protons and neutrons
- This means the nucleus has a positive charge because of the protons
- The whole mass of the atom is concentrated in the nucleus
- It has a radius of around 1 x 10 to the power of -14m which is around 1/10000 of the radius of the atom
What are the electrons in an atom?
- Electrons move around the nucleus in electron shells
- They are negatively charged and tiny but can cover a lot of space
- The volume of their orbits determines the size of the atom
- They have virtually no mass (negligible 1/1840)
What are protons, neutrons and electrons all called?
Particles
What are the relative masses and charges of the three particles in atoms?
- Proton- relative mass of 1 and charge of +1
- Neutron- relative mass of 1 and charge of 0
- Electron- relative mass of very small (0 basically) and a charge of -1
What is the overall charge of an atom and why?
- Atoms are neutral (they have no overall charge)
- This is because they have the same number of protons and electrons
- Protons and electrons have opposite charges of the same size so they cancel each other out
What is the difference between an ion and an atom?
- In an ion the number of protons doesn’t equal the number of electrons
- An ion has an overall charge due to lost (+ve) or gained (-ve) electrons
- when atoms react they lose, gain or share electrons
- e.g. Ca2+ (lost 2 electrons)
- e.g. N3- (gained 3 electrons)
What is an atomic number?
- An atomic (proton) number tells you how many protons there are in an atom
- e.g. for Ca2+ atomic number is 20 (20 protons), therefore 18 electrons
- e.g. for N3- atomic number is 7 (7 protons), therefore 10 electrons
What is a relative atomic mass (RAM) number?
- A mass number tells you the total number of protons and neutrons that there are in an atom
What is an element?
- A substance made from only 1 type of atom - they have a fixed number of protons (same atomic number)
How are the types of atoms decided?
- Atoms can have different numbers of electrons, protons and neutrons.
- The number of protons in the nucleus decides what type of atom it is
What are isotopes?
- Isotopes are different forms of the same element
- They have the same number of protons but a different number of neutrons
- This means they have the same atomic number but a different mass number
How is the issue fixed in naming elements as they can be in the form of different isotopes?
Relative atomic mass is used when referring to an element as a whole
What does “Carbon-12” mean for example?
- This means there are 6 protons in this isotope as it is Carbon which is an element
- It also means there are 6 neutrons because the 12 is the mass number (12-6=6)
What is the formula for working out the relative atomic mass of an element?
relative atomic mass (RAM)
= sum of (isotope abundance x isotope mass number)
sum of abundances of all the isotopes
What are compounds?
- Compounds are substances formed from two or more elements
- The atoms are in fixed proportions throughout the compound and are held together by chemical bonds
How are the chemical bonds made?
- Making bonds involves atoms giving away, taking or sharing electrons.
- The Nuclei aren’t affected
How do you separate the elements out of compounds?
Through chemical reactions
What do compounds formed of a metal and non-metal element consist of?
- The compound consists of ions
- The metal atoms lose electrons to form positive ions
- The non-metal atoms gain electrons to form negative ions
What do the positive and negative ions in a compound consisting of a metal and non-metal element do?
They undergo ionic bonding due to the strong electrostatic attraction between the two polar charged ions
What do compounds formed of non-metals consist of?
- These compounds consist of molecules
- Each atom shares an electron with another atom, this is called covalent bonding
Do compounds have similar properties to the elements they are made of?
- No, they are usually totally different
How do we show what atoms are in a compound?
- We use formulas that are made up of elemental symbols in the same proportions that the elements can be found in the compound
What is the formula for a reaction between 1 carbon atom and two oxygen atoms?
CO2 (Carbon dioxide)
What is the formula for Ammonia?
NH3
What is the formula for Sodium Chloride?
NaCl
What is the formula for Hydrochloric acid?
HCl
What is the formula for Calcium Chloride?
CaCl2
What is the formula for Sodium Carbonate?
Na2CO3
What is the formula for Sulfuric Acid?
H2SO4
How can you show a chemical reaction?
- With a word equation
- With a symbol equation
What are reactants?
- Reactants are the molecules and ions and elements on the left hand side of the arrow in a chemical reaction equation because they react with each other
What are products?
- Products are the molucules and ions on the right hand side of the arrow in a chemical reaction equation because they have been produced from the reactants
What are mixtures?
- Mixtures are formed of compounds and elements that have no chemical bond between them e.g. flour and sugar (before baking!)
Name the physical methods for separating parts of a mixture out:
- Filtration
- Crystallisation
- Simple Distillation
- Fractional distillation
- Chromatography
What are the properties of a mixture?
- The properties of a mixture are just the properties of the separate parts.
- The chemical properties of a substance aren’t affected by it being a mixture
What is paper chromatography?
A technique that can be used to separate different dyes in an ink
What is the set up for the paper chromatography process?
1) Draw a straight line near the bottom of filter paper using a pencil (pencil marks are insoluble)
2) Add a spot of ink to the line and place the paper in a solvent e.g. water or ethanol (some compounds dissolve well in water but others don’t)
3) Make sure the ink isn’t touching the solvent
4) Place a lid on the solvent container to stop the solvent evaporating
What should happen after setting up the chromatography process?
- The solvent will seep up the paper, carrying the ink with it
- Each different dye/pigment in the ink will move up the paper at different rates so the dyes will separate out and form a spot in a different place
- The insoluble inks in the dye will stay on the baseline
- The end result is a pattern of spots called a chromatogram
When can filtration be used?
- If an insoluble product needs to be separated from a liquid reaction mixture.
- It can also be used in purification
How is filtration carried out?
- The mixture is placed in cone shape filter paper which is in a funnel and a beaker.
- The liquid molecules are small enough to pass through the filter paper but the solid product does not and thus, separating them.
What proprty does a solid have if it can be dissolved?
soluble
How are soluble salts separated from a solution?
Using evaporation or crystallisation
How is evaporation carried out?
1) The solution is poured into an evaporating dish
2) The solution is slowly heated. The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form 3) The dish is heated until dry crystals are left
What is an advantage and disadvantage of using evaporation to separate parts of a soluble salt?
The method is quick but can only be used if the salt does not decompose when it is heated unlike in crystallisation.
How is crystallisation carried out?
1) The solution is gently heated in an evaporating dish.
2) Once some of the solvent has evaporated or when crystals start to form, remove the dish from the heat and leave to cool
3) The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4) Filter the crystals out of the solution and leave them in a drying oven or desiccator to dry
What is distillation?
- A process used to separate mixtures which contain liquids.
- The main two types of distillation are fractional and simple.
What is the simple distillation process?
1) Solution is heated. Part of the solution which has the lowest boiling point evaporates first.
2) The vapour is cooled by cold water flowing around the tube (condenser) in which the vapour is travelling through from where it evaporated
3) The vapour condenses and is collected
4) The rest of the solution is left behind in the flask
What is the disadvantage of the simple distillation process?
It can only be used to separate things with very different boiling points
What is the fractional distillation process?
1) The mixture is put in a flask and a fractionating column is put on top. It is then heated.
2) The different liquids evaporate at different temperatures
3) The liquid with the lowest boiling point evaporates first and when the temperature on the thermometer matches the boiling point of this liquid it will reach the top of the column.
4) It will then go through a condenser and be collected
5) The liquids with higher boiling points will only get part the way up the column before condensing and running back down towards the flask
6) Once the first liquid has been collected, the temperature is raised until the next liquid reaches the top of the column and so on
What were atoms described as at the start of the 19th century?
John Dalton concluded atoms were solid spheres and different spheres made up the different elements
What did JJ Thomson in 1897 discover about atoms?
He discovered that atoms were not a solid sphere. After measuring the charge and mass of an atom, he found that an atom must contain even smaller, negatively charged particles called electrons.
What theory did JJ Thomson devise?
- JJ Thomson’s theory was known as the plum pudding model.
- The theory stated that an atom was a ball of positive charge with electrons stuck in it
Who proved that the ‘plum pudding model’ was wrong and how?
Ernest Rutherford and his student Ernest Marsden using the famous alpha particle scattering experiment
What is the alpha particle scattering experiment?
It is the firing of positively charged alpha particles at an extremely thin sheet of gold.
What did the Ernests expect to happen in the Gold Leaf Experiment?
- They expected the particles to pass straight through the sheet or be slightly deflected at most.
- This was because the ‘plum pudding’ theory led them to believe that the positive charge of each atom was spread out throughout the ‘pudding’ of the atom.
What actually happened in the Gold Leaf Experiment?
- Most the particles did go through the gold sheet but some were deflected more than expected.
- A small number were also deflected backwards.
- The plum pudding model couldn’t be right
What theory did Rutherford come up with to explain this new evidence?
He came up with the nuclear model of an atom
What is Ernest’s nuclear model of an atom?
In the model, there is a tiny positively charged nucleus at the centre, where most the mass is concentrated. A ‘cloud’ of negative electrons surround the nucleus so most the atom is empty space.
How did Rutherford’s model explain what had happened in the experiment?
- It showed that when the alpha particles came near the concentrated, positive charge of the nucleus, they were deflected.
- If they were fired directly at the nucleus, they deflected backwards, otherwise they just passed through the empty space.
What was the flaw in Rutherford’s model?
Scientists realised that the electrons in a ‘cloud’ around the nucleus of an atom, would be attracted to the nucleus, causing the atom to collapse.
Who developed Rutherford’s theory to fix the flaw in it?
Niles Bohr
How did Niles Bohr develop the model of the atom?
- In his model, the atom suggested that the electrons were contained in shells.
- He proposed that the electrons orbit the nucleus in fixed shells and aren’t anywhere between.
- Each shell was a fixed distance from the nucleus.
Was Niles Bohr’s theory supported?
Bohr’s theory was supported by many experiments and it also helped explain the observations that scientists were seeing at the time
How was the existence of the proton discovered?
The likes of Ernest Rutherford and others, found through experiments that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus.
These particles were named protons.
How was the existence of the neutron discovered?
- About 20 years after scientists accepted that atoms have nuclei, James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.
- The nuclear model for the atom was similar to the modern day accepted version after this discovery.
What are the Electron shell rules (electron configuration)?
- Electrons always occupy shells (also called energy levels)
- The lowest energy levels are always filled first
- Only 2 electrons are allowed in the first shell
- only 8 are allowed in the second and third shells
- atoms like to have full electron shells e.g. noble gases (group 0)
- in most atoms electron shells are not full and this makes the atoms want to react
What is the electronic structure of an atom?
- The number of electrons in each shell of an atom
- e.g. Nitrogen has an atomic number of 7 so it must have 7 protons and 7 electrons.
- The first shell in the atom can only take 2 so the other five go into the second shell.
- Therefore,the electronic structure is 2,5
How were elements arranged in the early 1800s?
- They were arranged in order of relative atomic mass.
- A periodic pattern was noticed in the properties of the elements. Hence why it was called the periodic table (Newland’s Theory of Octaves)
How did Dmitri Mendeleev overcome some of the problems in the first periodic table in 1869?
- He took the 50 known elements and put them into his Table of the Elements with various gaps.
- However, some of the elements were not arranged in order of atomic mass but were switched if they had a similar property to another element (like iodine and tellurium)
Why were gaps left in Mendeleev’s table?
- Some of the gaps indicated the existence of undiscovered elements and allowed Dmitri to predict what those properties.
- The gaps were also made to make sure that the elements with similar properties stayed in the same groups.
Did the newly found elements fit the gaps of Mendeleev’s table?
- They did fit the pattern and it helped confirm Mendeleev’s ideas.
- Mendeleev made really good predictions about the chemical and physical properties of Ekasilicon which we know today as Germanium.
What are the columns in the periodic table made up of?
The columns are made up of elements with similar properties
What are the columns called?
The columns are called groups
What does the group number tell you?
The group number tells you how many electrons are in the outer shell
What are the rows called and what do they symbolise?
The rows are called periods and each period number represents the number of shells of electrons.
What type of ions are formed when metals react?
Positive ions
What do atoms usually react to form?
A full outer shell made via gaining, losing or sharing electrons
Why are metals at the bottom of the groups easier at losing electrons?
- Metals to the bottom have outer shell electrons that are a long way from the nucleus, so have a weaker attraction.
- Less is needed to remove the electrons at the bottom
- Electron shielding makes it easier to lose the electron too
What are the similar properties of all metals due to metallic bonding?
- Strong and malleable
- Good at conducting heat and electricity
- Have high boiling and melting temperatures
What are transition metals?
- The metal elements between group 2 and 3 (don’t have a group)
- Typical metal properties(dense, strong, shiny)
- They can have more than one ion
- Transition metal ions are often coloured and so compounds that contain them are colourful
- Often good catalysts
What are the alkali metals?
All of group 1
Lithium, Sodium, Potassium, Rubidium, Caesium, Francium
Form alkalies when reacted with water
What are the similar properties of the group 1 elements?
- Have one electron in the outer shell which makes them very reactive and gives them similar properties as they all want to lose the 1 outer electron as they WANT A FULL outer shell
- reactivity increases down the group as the distance is greater from the nucleus (weaker attraction so easier to lose the electron) and there is higher shielding from more shells between outer shell and nucleus so easier to lose
- Soft and have low density
What are the trends for the alkali metals as you go down group 1?
- 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 happens when group 1 elements are put in water?
- They react vigorously to produce hydrogen gas and metal hydroxides (salts that dissolve in water to produce alkaline solutions).
- The more reactive the element, the more violent the reaction
How does the energy output vary down the group when alkali metals are reacted with water?
- The amount of energy as you go down the group increases ie. potassium releases enough energy to ignite hydrogen
How do group 1 elements react with chlorine gas?
- Vigorously to form white metal chloride salts.
- Reactivity increases down the group so the reaction with chlorine gets more vigorous
Why do Group 1 metals tarnish in the air?
Because Group 1 metals react with the oxygen in the air to form a dull metal oxide layer
What do lithium and oxygen react to make?
Li(2)O- lithium oxide
What do sodium and oxygen react to form?
a mixture of sodium oxide and sodium peroxide
Potassium reacts with oxygen to from what mixture?
A mixture of potassium peroxide and potassium superoxide
What are the different properties that Group 1 elements have compared to the transition metals?
They are more reactive e.g. react more vigorously with water, oxygen or Group 7 elements Much less dense, strong or hard and have lower melting points
What are halogens?
Non-metals
group 7 elements: Fluorine, Chlorine, Bromine, Iodine and Astatine
What are the trends between group 7 elements (they all have 7 electrons in their outer shell)?
- Going down the group, the halogens become less reactive (outer shell is further distance way from the nucleus), have higher melting and boiling points and have higher relative atomic masses.
- They react in fairly similar ways because they all have seven electrons in their outer shell (all form diatomic molecules e.g. most reactive is F2)
Halogen atoms can share electrons via covalent bonding. What structures do the compounds that form when halogens react with non-metals have?
Simple Molecular Structures
What do halogens form when they bond with metals?
ions called halides with ionic structures
What do the more reactive halogens do to the less reactive ones when in an aqueous solution of its salt?
They will displace the less reactive ones e.g chlorine gas displaces iodine from potassium iodide
What are the properties of noble gases (group 0 elements)?
Helium
Neon
Argon
Krypton
Xenon
Radon
- They all have eight electrons in their outer energy level, apart from helium which has two, giving most of them a full outer-shell.
- They don’t react much at all because their outer shell is energetically stable (more or less inert), strong intermolecular force.
- Monatomic gases (individual atoms)
- Colourless gases at room temperature
- Non flammable
What are the patterns to the properties of noble gases?
- The boiling point and relative atomic mass increases down the group
- Boiling point increases due to the increase in the number of electrons in each atom leading to greater intermolecular forces
What is ionic bonding?
The electrostatic attraction between oppositely charged ions
What is covalent bonding?
The electrostatic between a shared pair of electrons and the nuclei of the bonding atoms
Why was Newland’s Theory of Octaves Rejected by some scientists?
- His theory only worked for the first 20 elements known at the time
- New elements had nowhere to go
- Copper was in the same group as Li, Na and K which react with water but copper does not react with water
Define soluble
A property where the substance can dissolve in a certain solution
Define insoluble
A property where the substance cannot dissolve in a solution
Define a solute
A solute is a substance(solid) which is dissolved
Define solvent
The liquid that dissolves the solute
Define solution
A combination of a solute dissolved in a solvent
What is the relative molecular formula mass?
The sum of all the individual atomic masses for atoms present in the formula of the molecule
What are the two phases in chromatography?
- Mobile (where molecules can move (liquid or gas))
- Stationary (where molecules can’t move (solid or thick liquid)
What happens to the sample in chromatography in relation to the phases?
The substances in the sample constantly move between phases and an equilibrium is formed
How do different chemicals separate out in chromatography?
Different chemicals are distributed differently between the two phases, whether it spends more time the stationary or mobile phase
What is the mobile phase in paper chromatography?
The solvent
What is the stationary phase in paper chromatography?
The filter paper
What two things determine how long the molecules spend in each phase?
- The solubility of the molecule in the solvent
- How attracted the molecules are to the filter paper
Each substance on a chromatogram has an RF value, what is an RF value?
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
What does a larger RF value imply?
The substance moved further through the stationary phase
How do you work out an RF value?
distance travelled by substance
RF = ———————————————–
distance travelled by solvent
How do we see if carbon dioxide is present?
The gas will bubble through limewater and make it go cloudy
How do we see if hydrogen is present?
A lit splint will make a squeaky pop
How do we see if oxygen is present?
A glowing splint will be relighted
Why did some scientists suggest that Mendeleev’s table was incorrect?
- Some chemists thought all elements had been discovered so there was no need for gaps
- He put some metals in the same group a non-metals (Bromine with Manganese)
What is the definition of relative atomic mass?
An average atomic mass value which takes into account the abundance of the isotopes of an element.
what is the RAM of chlorine?
Chlorine has two isotopes (same protons / different neutrons) each with a different abundance.
The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.
35.5
% isotope 1 % isotope 2
—————– x mass isotope 1 + ——————— x mass isotope 2
100 100
Reactions of Group 7 give appearance of:
Cl2
Br2
I2
Cl2 = faint yellow /green
Br2 = yellow
I2 = orange/brown
F2 and Cl2 are:
Br2 is a :
I2 and Al2 are:
give the boiling point in 0C and K of Group 0 elements (noble gases)
Helium
Neon
Argon
Krypton
Xenon
Radon
what are the uses of these elements and how many protons do they have?
Helium
Neon
Argon
Krypton
Xenon
Radon
Halogen equations
Lithium + chlorine =
Potassium + Iodine =
Rubidium + Astatine =
Group 1 metals plus oxygen
name the word and balanced equations for
Lithium + Oxygen
Rubidium + Oxygen
Sodium + Oxygen
Group 1 metals plus water
Potassium + water
Lithium + water
Caesium + water
what do the all follow?
Displacement reactions
a more reactive halogen will …….
e.g. write word and symbol equation for
Chlorine + Potassium Bromide
