1:01 understand the three states of matter in terms of the arrangement, movement and energy of the particles
Solid
Arrangement: Particles are close together and regularly packed.
Movement: Particles vibrate around a fixed point.
Energy: Particles have less kinetic energy than both liquids and gasses.
Liquid
Arrangement: Particles are close together but irregular.
Movement: Particles are free to move.
Energy: Particles have less kinetic energy than gasses but more than solids.
Gas
Arrangement: Particles are far apart and there are no forces between them.
Movement: Particles are free to move.
Energy: Particles have more kinetic energy than liquids and solids.
1:02 understand the interconversions between the three states of matter in terms of: the names of the interconversions, how they are achieved and the changes in arrangement, movement and energy of the particles
Melting: When a solid is heated, the energy makes the particles vibrate fast enough so that the forces of attraction between the particles break. For example H2O(s) –> H2O(l)
Freezing: When a liquid is cooled, the particles move slow enough so that the forces of attraction between them will hold them into a solid. For example H2O(l) –> H2O(s)
Boiling: When a liquid is heated strongly, the energy makes the particles move fast enough so that all forces of attraction are broken. For example H2O(l) –> H2O(g)
Condensing: When a gas is cooled, the particles move slow enough so that the forces of attraction between them will hold them as a liquid. For example H2O(g) –> H2O(l)
Sublimation: A small number of substances have the ability to change directly from a solid to a gas when heated. For example CO2(s) –> CO2(g)
1:08 understand how to classify a substance as an element, a compound or a mixture
Element: The simplest type of substances made up of only one type of atom.
Compound: A substance that contains two or more elements chemically joined together in fixed proportions.
Mixture: Different substances in the same space, but not chemically combined.
Note: elements such as oxygen (O2) are described as diatomic because they contain two atoms.
The full list of elements that are diatomic is:
- Hydrogen (H2)
- Nitrogen (N2)
- Fluorine (F2)
- Oxygen (O2)
- Iodine (I2)
- Chlorine (Cl2)
- Bromine (Br2)
Harry Potter does The Elements – video
Watch Daniel Radcliffe sing the names of all the elements – it’s just a shame there are now more elements than were written into Tom Lehrer’s famous song…..
1:14a know what is meant by the terms atom
Atom: An atom is the smallest part of an element.
1:15 know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles
An atom consists of a central nucleus, composed of protons and neutrons.
This is surrounded by electrons, orbiting in shells (energy levels).
Atoms are neutral because the numbers of electrons and protons are equal.
| Mass | Charge | |
|---|---|---|
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | negligible (1/1836) | -1 |
Atomic structure – Tyler de Witt video
This video explains the basics of atomic structure, telling you what is inside an atom:
Build an atom – interactive
This is a good interactive demonstration showing how subatomic particles make up the atoms in the Periodic Table.
1:16a know what is meant by the terms atomic number, mass number and relative atomic mass (Aᵣ)
Atomic number: The number of protons in an atom.
Mass number: The number of protons and neutrons in an atom.
Relative atomic mass (Ar): The average mass of an atom compared to 1/12th the mass of carbon-12.
1:18 understand how elements are arranged in the Periodic Table: in order of atomic number, in groups and periods
The elements in the Periodic Table are arranged in order of increasing atomic number.
Columns are called Groups. They indicate the number of electrons in the outer shell of an atom.
Rows are called Periods. They indicate the number of shells (energy levels) in an atom.
1:20a understand how to use electrical conductivity to classify elements as metals or non-metals
Metals
- conduct electricity
Non – Metals
- do not conduct electricity (except for graphite)
1:21 identify an element as a metal or a non-metal according to its position in the Periodic Table
Metals on the left of the Periodic Table.
Non-Metals on the top-right, plus Hydrogen.
1:25 write word equations and balanced chemical equations (including state symbols): for reactions studied in this specification and for unfamiliar reactions where suitable information is provided
Example:
Sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).
Word equation:
sodium + water –> sodium hydroxide + hydrogen
Writing the chemical equation
A chemical equation represents what happens in terms of atoms in a chemical reaction.
Step 1: To write a chemical equation we need to know the chemical formulae of the substances.
Na + H2O –> NaOH + H2
Step 2: The next step is to balance the equation: write a large number before each compound so the number of atoms of each element on the left hand side (reactants) matches the number on the right (products). This large number is the amount of each compound or element.
During this balancing stage the actual formulas for each compound must not be changed. Only the number of each compound changes.
2Na + 2H2O –> 2NaOH + H2
If asked for an equation, the chemical equation must be given.
State symbols are used to show what physical state the reactants and products are in.
| State symbols | Physical state |
|---|---|
| (s) | Solid |
| (l) | Liquid |
| (g) | Gas |
| (aq) | Aqueous solution (dissolved in water) |
Example:
A solid piece of sodium (Na) reacts with water (H2O) to produce a solution of sodium hydroxide (NaOH) and hydrogen gas (H2).
2Na(s) + 2H2O(l) –> 2NaOH(aq) + H2(g)
Balancing equations – Tyler de Witt videos
This excellent Tyler de Witt video is an introduction to balancing equations:
And here’s another of the lovely Tyler’s videos with some practice questions and answers on equation balancing:
Balancing equations – interactive
This is useful to help you to practice how to balance equations:
1:26 calculate relative formula masses (including relative molecular masses) (Mᵣ) from relative atomic masses (Aᵣ)
Relative formula mass (Mr) is mass of a molecule or compound (on a scale compared to carbon-12).
It is calculated by adding up the relative atomic masses (Ar) of all the atoms present in the formula.
Example:
The relative formula mass (Mr) for water (H2O) is 18.
Water = H2O
Atoms present = (2 x H) + (1 x O)
Mr = (2 x 1) + (1 x 16) = 18
Calculation of relative formula mass – Tyler de Witt video
Here’s an excellent Tyler de Witt video explaining how to calculate the relative formula mass of compounds with:
- a simple formula
- a formula which includes brackets
- a formula which includes a dot (water of crystallisation)
3:01 know that chemical reactions in which heat energy is given out are described as exothermic, and those in which heat energy is taken in are described as endothermic
Exothermic: chemical reaction in which heat energy is given out.
Endothermic: chemical reaction in which heat energy is taken in.
(So, in an exothermic reaction the heat exits from the chemicals so temperature rises)