C1 - Atomic structure and the periodic table Flashcards
What is an Atom?
- atoms which are the tiny building blocks of all matter. Each atom is made of subatomic particles called protons, neutrons, and electrons
What is an Element?
A atom or molecule of the same type.
An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
What are the diatomic molecules?
Some non-metal elements exist as molecules that are made up of two atoms joined together.
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For example:
- Iodine, I2
- Hydrogen, H2
- Nitrogen, N2
- Fluorine, F2
- Bromine, Br2
- Oxygen, O2
- Chlorine, Cl2
What is a compound?
Are there properties different?
A compound is a pure substance made up of two or more DIFFERENT elements chemically combined and which cannot be separated by physical means.
- The properties of compounds are usually quite different from the elements that form them
What is a pure substance?
What is Mixture?
The meaning of pure
- a pure substance consists only of one element or one compound
- a mixture consists of two or more different substances, not chemically joined together
The substances in a mixture can be elements, or compounds, or both. Being part of a mixture does not change the chemical properties of the substances that are in it.
Mixtures can be separated by physical processes so no new substances are made.
Naming non-metal compounds?
- Ionic compounds contain metal and non-metal elements joined together as particles called ions
- The metal element’s symbol is always written first
- The non-metal element always takes on the name ending ‘– ide’ unless oxygen is also present,
- For example, PbS is called lead sulfide and MgCl2 is called magnesium chloride
- When oxygen is present the name ending is usually ‘-ate’
- For example, CuSO4 is copper sulphate, KClO3 is potassium chlorate and Na2CO3 is sodium carbonate
- Some formula names are similar so be careful with spelling
- For example, NaNO3 is sodium nitrate and NaNO2 is sodium nitrite
- The ending ‘-ite’ will always have less oxygen than ‘-ate’
- The number of oxygen atoms varies, so you cannot tell how many oxygen atoms are present from the name ending
What is the Conservation of Mass?
- The law of conservation of mass states that no atoms are lost or made in a chemical reaction. Instead, the atoms join together in different ways to form products. Atoms cannot be created or destroyed.
- This is why, in a balanced symbol equation, the number of atoms of each element is the same on both sides of the equation.
How does the conservation of mass allow us to balance chemical equation?
- The Law of Conservation of Mass enables us to balance chemical equations, since no atoms can be lost or created
- You should be able to:
- Write word equations for reactions outlined in these notes
- Write formulae and balanced chemical equations for the reactions in these notes
What is a molecule?
A collection of two or more atoms held together by chemical bonds.
What are Half Equations?
- Half equations and ionic equations are specific types of equations for showing some of the fine details going on in chemical reactions
- Half equations are used to show what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons
- They are called half equations, because they represent only half of what is happening in a reaction involving electron transfer
- One species gains electrons
- Another species loses electrons
Examples of half equations are:
Pb2+ + 2e- →Pb
2Br-→Br2 + 2e-
What are Ionic Equations?
- Ionic equations are used to indicate what happens to ions during reactions
- They help to simplify complicated processes where many substances are present, but only certain ions are actually reacting with each other
- For example, we can use ionic equations to show what happens when an acid neutralizes and an alkali:
HCl+ NaOH → NaCl + H2O
- Written out as an ionic equation would be
H+ + OH- → H2O
- This is because sodium and chloride ions were present at the beginning and also at the end of the reaction, so they are unchanged
- Ions which are present but do not take part in reactions are called spectator ions
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What is Filtration and how does it work?
Filtration is used to separate an insoluble solid from a liquid. It is useful for separating sand from a mixture of sand and water, or excess reactant from a reaction mixture.
Filtration works because the filter paper has tiny holes or pores in it. These are large enough to let small molecules and dissolved ions through, but not the much larger particles of undissolved solid.
- A piece of filter paper is placed in a filter funnel above a beaker
- A mixture of insoluble solid and liquid is poured into the filter funnel
- The filter paper will only allow small liquid particles to pass through as filtrate
- Solid particles are too large to pass through the filter paper so will stay behind as a residue
What are the four physical separation techniques?
Filtration
Crystallisation
Chromatography
Distillation
What is Crystallisation and what is is used for?
It is used to separate a soluble solid(dissolved) from a liquid.
Crystallisation is used to produce solid crystals from a solution. When the solution is warmed, some of solvent evaporates leaving crystals behind. For example, crystallisation is used to obtain copper sulfate crystals from copper sulfate solution
- A solution is placed in an evaporating basin and heated with a Bunsen burner.
- The volume of the solution has decreased because some of the water has evaporated. Solid particles begin to form in the basin.
- All the water has evaporated, leaving solid crystals behind.
- The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
To obtain large, regularly shaped crystals from crystallisation:
- put the solution in an evaporating basin
- warm the solution by placing the evaporating basin over a boiling water bath
- stop heating when crystals begin to form around the edge of the basin
After the remaining solution has cooled down, pour the excess liquid away (or filter it). Dry the crystals using a warm oven or by patting them with filter paper.
What is Simple Distillation?
Simple Distillation is used to separate a liquid from a solid if we want to keep the liquid.
Simple distillation is used to separate a solvent from a solution. It is useful for producing pure water from seawater but this process requires a lot of energy.
Simple distillation works because the dissolved solute has a much higher boiling point than the solvent. When the solution is heated, solvent vapour leaves the solution. It moves away and is cooled and condensed. The remaining solution becomes more concentrated as the amount of solvent in it decreases.
- The solution is heated, and pure water evaporates producing a vapour which rises through the neck of the round bottomed flask
- The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
- After all the water is evaporated from the solution, only the solid solute will be left behind in the flask.
What is Fractional Distillation?
Fractional distillation is used to separate different liquids from a mixture of liquids. It is useful for separating ethanol from a mixture of ethanol and water, and for separating different fractions from crude oil.
Fractional distillation works because the different liquids have different boiling points. When the mixture is heated:
- vapours rise through a column which is hot at the bottom, and cooler at the top
- vapours condense when they reach a part of the column that is below the temperature of their boiling point
- each liquid is led away from the column
- The solution is heated to the temperature of the substance with the lowest boiling point
- This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
- All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
- For water and ethanol
- Ethanol has a boiling point of 78 ºC and water of 100 ºC
- The mixture is heated until it reaches 78 ºC, at which point the ethanol boils and distills out of the mixture and condenses into the beaker
- When the temperature starts to increase to 100 ºC heating should be stopped. Water and ethanol are now separated
What happens if you use fractional distillation on substances with similar boiling points.
What is Chromatography and how does it work?
- This technique is used to separate substances that have different solubilities in a given solvent (e.g., different coloured inks that have been mixed to make black ink)
- A pencil line is drawn on chromatography paper and spots of the sample are placed on it. Pencil is used for this as ink would run into the chromatogram along with the samples
- The paper is then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent, so the samples don’t wash into the solvent container
- The solvent travels up the paper by capillary action, taking some of the coloured substances with it
- Different substances have different solubilities so will travel at different rates, causing the substances to spread apart
- Those substances with higher solubility will travel further than the others
- This will show the different components of the ink / dye
- If two or more substances are the same, they will produce identical chromatograms
- If the substance is a mixture, it will separate on the paper to show all the different components as separate spots
- An impure substance will show up with more than one spot, a pure substance should only show up with one spot
Why have models of the atoms changed?
What did John Dalton say?
- The atomic model developed by scientists has changed over time as experimental evidence has improved our understanding of the structure of atoms
- In 1803 John Dalton presented his atomic theory based on three key ideas:
- Matter is made of atoms which are tiny particles that cannot be created, destroyed, or divided
- Atoms of the same element are identical, and atoms of different elements are different
- Different atoms combine together to form new substances
- At the time, the theory was correct but as science developed some parts of Dalton’s theory were disproved
- This is a fundamental feature of science: new experimental evidence may lead to a scientific model being changed or replaced
What was the Plum pudding model?
- In 1897 physicist J.J. Thomson discovered the electron
- Using a cathode-ray tube he conducted an experiment which identified the electron as a negatively charged subatomic particle, hence proving that atoms are divisible
- Based on his investigations Thomson proposed a model of the atom known as the plum pudding model which depicted negative electrons spread throughout soft globules of positively charged material
What was the Alpha scattering experiment?
In 1909 Ernest Rutherford designed an experiment to test the plum pudding model. In the experiment, positively charged alpha particles were fired at thin gold foil. Most alpha particles went straight through the foil. But a few were scattered in different directions.
This evidence led Rutherford to suggest a new model for the atom, called the nuclear model. In the nuclear model:
- the mass of an atom is concentrated at its centre, the nucleus
- the nucleus is positively charged
- Most of the atom is empty space
What was the Bohr model?
- In 1913 Niels Bohr further developed the nuclear model by proposing that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus
- Each orbital has a different energy associated with it, with the higher energy orbitals being located further away from the nucleus
- Bohr’s theory and calculations agreed with experimental results
- Further investigation and experimentation revealed that the nucleus could be divided into smaller particles, each one having the same mass and charge
- This work led to the discovery of the proton
How was the Neutron discovered?
- In 1920 Rutherford put forward the idea of the existence of large, neutral particles within the nucleus
- His idea was based on the differences between the atomic mass and the atomic number of atoms
- In 1932 James Chadwick published a paper based on an experiment carried out by Frédéric and Irène Joliot-Curie which provided evidence for the existence of these neutral particles which were called neutrons
what is the Size of atom and nucleus?
This is surrounded by electrons arranged in shells. The nucleus is tiny compared to the atom as a whole: the radius of an atom is about 0.1 nm (1 × 10 -10 m) the radius of a nucleus (1 × 10 -14 m) is less than.
How do calculate the number of subatomic particles?
The symbol for an atom can be written to show its mass number at the top, and its atomic number at the bottom.
To calculate the numbers of subatomic particles in an atom, use its atomic number and mass number:
- number of protons = atomic number
- number of electrons = atomic number
- number of neutrons = mass number - atomic number
What are Isotopes?
Do they have the same charachteristics?
- Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
- The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number
- So, C-14 is the isotope of carbon which contains 6 protons and 6 electrons, but the 14 signifies that it has 8 neutrons (14 - 6 = 8)
- It can also be written as 14C
- Isotopes display the same chemical characteristics
- This is because they have the same number of electrons in their outer shells, and this is what determines their chemistry
- The difference between isotopes is the neutrons which are neutral particles within the nucleus and add mass only
How do we represent Electrons in Electron shell diagrams?
- Electrons orbit the nucleus in shells and each shell has a different amount of energy associated with it
- The further away from the nucleus, the more energy a shell has
- Electrons first occupy the shell closest to the nucleus which can hold a maximum of 2 electrons
Why is the Electronic structure important?
eThe arrangement of electrons in shells can also be explained using numbers
- This method consists of writing down the number of electrons in each shell and separating each number with a comma
- There is a clear relationship between the outer shell electrons and how the periodic table is designed
- The number of notations in the electronic configuration will show the number of shells of electrons the atom has, showing the period in which that element is in
- The last notation shows the number of outer electrons the atom has, showing the group that element is in
- Elements in the same group have the same number of outer shell electrons
How are elements ordered in the modern periodic table?
- There are over 100 chemical elements which have been isolated and identified
- Elements are arranged on the periodic table in order of increasing atomic number
- Each element has one proton more than the element preceding it
- This is done so that elements end up in columns with other elements which have similar properties
- The table is arranged in vertical columns called groups and in rows called periods
- Period: These are the horizontal rows that show the number of shells of electrons an atom has and are numbered from 1 - 7
- E.g. elements in period 2 have two electron shells, elements in period 3 have three electron shells
-
Group: These are the vertical columns that show how many outer electrons each atom has and are numbered from 1 – 7, with a final group called group 0 (instead of group 8)
- E.g. group 4 elements have atoms with 4 electrons in the outermost shell, group 6 elements have atoms with 6 electrons in the outermost shell and so on
What is the difference between Metals and non-metals in terms of ions?
Differences in chemical properties
Most elements are metals. In their chemical reactions, metal atoms lose electrons to form positive ions. For example:
- when magnesium burns in air, each atom loses two electrons to form a Mg2+ ion
- when sodium reacts with chlorine, each sodium atom loses one electron to form a Na+ ion
Elements that do not form positive ions in their chemical reaction are non-metals.
The chemical properties of the compounds of metal and non-metal elements are also different:
- most metal oxides are basic
- most non-metal oxides are acidic
What is the difference between Metals and Non metals?
Where is Group 0 on the periodic table and what are they also called?
Group 0 contains non-metal elements placed in the vertical column on the far right of the periodic table. The elements in group 0 are called the noble gases. They exist as single atoms.
- They are all non-metal, monatomic (exist as single atoms), colourless, non-flammable gases at room temperature
- The group 0 elements all have full outer shells of electrons; this electronic configuration is extremely stable
What is the trend in boiling point in Noble gases and why?
Boiling points
This is because, going down group 0:
- the atoms become larger
- the intermolecular forces between the atoms become stronger
- more energy is needed to overcome these forces
Why do group 1 electrons become more reactive as you go down the group?
Explaining the trend in reactivity
When a group 1 element takes part in a reaction, each of its atoms loses its outer electron to form a positively charged ion. The more easily the ions form, the more reactive the metal.
Going down group 1:
- the atoms become larger
- the outer electron becomes further from the nucleus
- the force of attraction between the nucleus and the outer electron decreases
- Less energy is required to overcome the force of attraction as it gets weaker, so the outer electron is lost more easily
- So, the alkali metals get more reactive as you descend the group
How do Alkali Metals react with water?
- The reactions of the alkali metals with water get more vigorous as you descend the group, as with the other reactions
The alkali metals react with water to produce a metal hydroxide and hydrogen. For example, sodium reacts with water:
sodium + water → sodium hydroxide + hydrogen
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)
Sodium hydroxide is an alkali. It is a base that dissolves in water to form an alkaline solution. This solution:
- has a pH greater than 7
- turns universal indicator solution blue or purple
- Rubidium, caesium and francium will react even more vigorously with air and water than the first three alkali metals
- Of the alkali metals, lithium is the least reactive (as it is at the top of group 1) and francium would be the most reactive (as it’s at the bottom of group 1)
How do Alkali Metals react with Oxygen?
- The metal oxide produced is a dull coating which covers the surface of the metal
The group 1 elements react with oxygen from the air to make metal oxides which is why the alkali metals tarnish when exposed to the air
At room temperature, oxygen reacts with the surface of the metal. This forms a white oxide, which covers the surface. The metal below the surface does not react.
The alkali metals burn vigorously when heated and placed in a gas jar of oxygen. The oxide forms as white smoke.
For example:
sodium + oxygen → sodium oxide
4Na(s) + O2(g) → 2Na2O(s)
The reactivity of the group 1 elements increases down the group, so their reactions with oxygen get more vigorous.
How do alkali metals react with Chlorine?
- All the group 1 metals react vigorously when heated with chlorine gas to form salts called metal chlorides
The group 1 elements react vigorously with chlorine. The products of the reactions are chlorides. At room temperature the chlorides are white solids. They dissolve in water to form colourless solutions. For example:
sodium + chlorine → sodium chloride
2Na(s) + Cl2(g) → 2NaCl(s)
The reactions with chlorine get more vigorous going down the group.
Where is Group 7 on the periodic table and what are they also called?
- The elements in group 7 are known as the halogens
- These are fluorine, chlorine, bromine, iodine and astatine
- These elements are non-metals that are poisonous
- All halogens have similar reactions as they each have seven electrons in their outermost shell
- Halogens are diatomic, meaning they form molecules made of pairs of atoms sharing electrons (forming a single covalent bond between the two halogen atoms)
- When halogen atoms gain an electron during reactions, they form -1 ions called halide ions
What are the Physical Properties of Chlorine?
Green gas which is very reactive and poisonous
What are the Physical Properties of Bromine?
Orange liquid
What are the Physical Properties of Iodine ?
Grey solid
What is the trend in mp and bp in Halogens?
- The melting and boiling points of the halogens increase as you go down the group
- This is due to increasing intermolecular forces as the atoms become larger, so more energy is required to overcome these forces
At room temperature (20 °C), the physical state of the halogens changes as you go down the group
* Fluorine and chlorine are **gases**, bromine is a **liquid** and iodine is crumbly **solid** * The colours of the halogens also change as you descend the group - they become darker
What happens when halogens react with Metals?
- Chlorine, bromine and iodine react with metals and non-metals to form compounds
Metal Halides
- The halogens react with some metals to form ionic compounds which are metal halide salts
- The halide ion carries a -1 charge so the ionic compound formed will have different numbers of halogen atoms, depending on the valency of the metal
- E.g., sodium is a group 1 metal:
- 2 Na + Cl2 → 2 NaCl
- Calcium is a group 2 metal:
- Ca + Br2 → CaBr2
- The halogens decrease in reactivity moving down the group, but they still form halide salts with some metals including iron
- The rate of reaction is slower for halogens which are further down the group such as bromine and iodine
Half equations for displacement reactions?
- You could be asked at Higher Tier to provide ionic equations to show what is happening during displacement reactions of the halogens
- These are:
Cl2 + 2Br- → 2Cl- + Br2
Cl2 + 2I- → 2Cl- + I2
Br2 + 2I- → 2Br- + I2
Compare Alkali Metals with Transition Metals
- The transition elements are located between Groups 2 and 3 in the centre of the periodic table
- They have all of the typical properties of metals but there are some key differences between them and the Group 1 metals
All of the group 1 metals form ions with a +1 charge while the transition metals can form ions with variable charges
- For example iron can form an Fe2+ ion or an Fe3+ ion
- The transition metals are much harder, stronger and denser than the group 1 metals, which are very soft and light
- They have much higher melting points e.g. titanium melts at 1,688 ºC whereas potassium melts at only 63.5 ºC, not far off the average cup of tea!
- The transition metals are much less reactive than the group 1 metals
- The alkali metals react with water, oxygen and halogens while the transition metals either react very slowly or do not react at all
- A classic example of this is the reaction with oxygen
- A group 1 metal will tarnish in the presence of oxygen as a metal oxide is formed
- When cut with a knife, the shiny appearance of the metal disappears in seconds as it is covered by the dull metal oxide
- Iron on the other hand can take several weeks to react with oxygen to form iron oxide (rust) and requires the presence of water
