GCSE Chemistry notes. Many topics included. Concise and precise for effective revision. Targetted at AQA but can be used by other exam boards. Includes mindmaps, diagrams and summaries.
Topics included:
Atomic structure,
The periodic table,
Structure and Bonding,
Chemical calculations,
Chem...
Methods to separate a soluble solid from a solution: Paper chromatography- practical:
Evaporation: 1)Draw a line near the bottom of the sheet of filter paper, using a pencil.
(can only be used if the salt doesn’t decompose (break down) when its heated, otherwise (pencil marks are insoluble and won’t dissolve in the solvent.
crystallisation will have to be used). 2) Add a spot of the ink to the line and place the sheet in the solvent
1. Pour solution in an evaporating dish/water bath/electric heater. (solvent- able to dissolve other substances), e.g. water.
2. Slowly heat the solution. The solvent will evaporate and the solution will get more 3) Make sure the ink isn’t touching the solvent so it doesn't dissolve into
concentrated. Eventually crystals will start to form. it.
3. Keep heating the evaporating dish until all that is left is dry crystals. 4) Different inks will move up the paper at different rates. If the ink is
Crystallisation: insoluble it will stay on the baseline.
1. Pour the solution into an evaporating dish and gently heat the solution. Some of the 5) When the solvent has nearly reached the top of the paper, take the
solvent will evaporate and the solution will get more concentrated. paper out and leave it to dry.
2. Once some of the solvent is evaporated or when crystals start to for (point of 6) The end result is a pattern of spots called a chromatogram.
crystallisation), remove the dish from the heat and leave to cool.
3. The salt to start to form crystals as it becomes insoluble in the cold, highly Law of conservation of mass:
concentrated solution. No atoms are lost or made
4. Filter the crystals out of the solution, and leave them in a warm place to dry. In
during a chemical reaction.
History of the atom
• The ancients Greeks were the first to have ideas about atoms.
•
Chemistry-C1
In the early 1800s, John Dalton described atoms as tiny, solid
spheres, and said that different spheres made up the different
elements. The atoms could not be divided or split. Mass number= pro
• In 1897 J J Thomson discovered a tiny negatively charged
Atomic number= p
particle called the electron. Thomson proposed the plum
pudding model for the atom. The ‘plum pudding’ model Atomic structure
suggested that negative electrons were embedded in a ball of Atoms have a neutral c
positive charge. of protons and neutron
• In 1909 Ernest Rutherford and his students Geiger and Simple distillation is used for separating a liquid from a In an ion, the number o
Marsden conducted the alpha particle scattering experiment. solution: the same as the numbe
They fired alpha particles at a very thin piece of gold foil. A 1. The solution is heated. The part of the solution that has means it is an atom tha
few alpha particles were repelled showing that there must be the lowest boiling point evaporates first. charge. E.g. an ion with
a tiny spot of positive charge in the centre of the atom. 2. The vapour is then cooled, condenses and is collected. electrons than protons
Rutherford then proposed the nuclear model. 3. The rest of the solution is left behind in the flask. Fractional distillation is used to separate a mixture
• In the nuclear mode, electrons orbit around a nucleus. The 4. Can be used to get pure water from seawater. The of liquids:
nucleus contains positively charged protons. 1. The mixture is put in the flask and a Element: made from o
water evaporates and is condensed and collected. Salt
• Bohr then suggested that electrons were orbiting the nucleus will be left behind in the flask. fractionating column is put on top. It is then Compound: when two
in energy levels (or shells). The electrons were a set distance 5. Problem with simple distillation: can only be used with heated. are chemically joined
from the nucleus. things that have different boiling points. 2. The different liquids will have different dioxide).
• In 1932, James Chadwick provided evidence that showed the boiling points- so they will evaporate at Mixture: two or more
existence of uncharged particles called neutrons in the different temperatures.
Filtration separates insoluble solids from liquids. (elements or compou
nucleus. 3. The liquid with the lowest boiling point
Filtration and crystallisation can be used to separate rock chemically joined toge
evaporates first. When the temperature on
salt: the thermometer matches the boiling point
1. Grind the mixture to make sure the salt crystals are small. of this liquid, it will reach the top of the
2. Put the mixture in water and stir. The salt will dissolve, but the column. Atoms are so small (
sand won’t. Salt and sand are both compounds, but salt 4. The column is cooler towards the top. Isotopes: atom of
dissolves in water and sand does not. When the first liquid has been collected, with different numbe
3. Filter the mixture. the temperature is raised until the next amount of protons).
4. Evaporate the water from the salt so that it forms dry crystals. liquid reaches the top.
, Trends Development of the periodic table Group 7
• Going down a group, there are more occupied • In 1864, Newlands proposed ‘law of octaves’. He • Halogens – (non-metallic elements).
energy levels and the atoms get larger. As the based the order on atomic weight and said • Exist as small molecules made up of pairs of atoms
atoms get larger, the electrons in the highest every eighth element was similar. However, new • There is a single covalent bond between the halog
occupied energy level are less strongly attracted elements were being discovered and didn’t fit molecules.
by the nucleus. his table. • Low melting and boiling points, increases going do
• • Reactivity decreases going down the group.
Reactivity increases going down group 1 • In 1869, Dimitri Mendeleev placed the known
• At room temperature:
because the outer electron is less strongly elements in order of their atomic weights so
Fluorine: pale yellow gas
attracted to the nucleus as the number of that a pattern in their properties could be seen. Chlorine: green gas
occupied energy levels increases and the atoms In some places he changed the order of the Bromine: red-brown liquid
get larger. elements so that elements with similar Iodine: grey solid, easily vaporises to a violet gas
• The reactivity of the halogens decreases going properties were in the same group. He left gaps • Poor conductors of thermal energy and electricity.
down the group because the attraction of the for undiscovered elements. He used his periodic • Form 1- ion.
outer electrons to the nucleus decreases as the tale to predict the properties of the • Halogens bon covalently with non-metals, formin
number of occupied energy levels increase. undiscovered elements. • A more reactive halogen is able to displace a less r
an aqueous solution of a halide compound:
Group 1 Chlorine + potassium iodide -> potassium chloride + io
• Alkali metals
• Soft solids at room temperature. Transition metals
• Low melting and boiling points that decrease going • Central block on periodi
down the group. group 2 and 3.
• Going down the group, reactivity increases. • Good conductors of elect
Questions energy.
• Reacts quickly with oxygen in the air. A layer of Group 0 1) Why is sodium more reactive than • Hard strong with high de
oxide forms on the surface of the metal: • Noble gases lithium? (group 1) • Have very high melting p
Sodium + oxygen -> sodium oxide • Colourless gas A sodium atom has more occupied with group 1 metals.
• Reacts quickly with water to produce hydrogen gas energy levels, so its outer electron is •
and metal hydroxide that is an alkali:
• Non flammable further from the nucleus, and so can be
Harder, stronger, and mu
that group 1 metals.
Sodium + water -> sodium hydroxide + hydrogen • Very unreactive more easily lost when it reacts. • Much less reactive than g
• The metal hydroxides are all soluble in water. They • Stable arrangement of 2) Why is fluorine more reactive than metals only react slowly,
form colourless solution with a high PH. electrons (8 electrons in chlorine? (group 7) oxygen and water at ord
• Forms +1 ion. A fluorine atom has fewer energy levels, temperatures.
outer most shell). Except so its nucleus has a greater attraction for
• React with halogen to form salts that are white or • Compounds of transition
for helium which has 2 electrons in the highest energy level, so it brightly coloured.
colourless crystals: attracts electrons more easily when it
Sodium + chlorine -> sodium chloride
electrons in the outer • Many transition metals a
reacts.
• Compounds of alkali metals dissolve in water, most shell. compounds are catalysts
reactions.
forming solutions that are usually colourless.
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