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Pearson Edexcel GCSE Chemistry Revision Notes
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Chemistry All Units RevisionChemistry Unit 1 Revision (Principles of Chem)
States of Matter:
States:
Solid: Particles are regularly arranged at fixed positions that have very strong Forces of attraction. They
have a fixed shape and volume. Particles vibrate around fixed positions. Have a low amount of energy and
can’t be squashed
Liquids:Particles are close together but not in fixed positions and are randomly arranged and are free to
move past each other (Can’t be squashed). Have a fixed volume but no definite shape and fills container.
Particles moving in constant and random motion. Have a moderate amount of energy. Weak forces of
attraction between particles
Gases: Particles are far apart. No fixed shape or volume. Particles have high energy. Quick lots of
movement. Lots of energy. Can be squashed
Interconversions between States:
Condensation: When heat in a liquid is taken away, the particles start to lose energy and they move around
less and lose energy until the forces of attraction get stronger.
Freezing: When even more heat is taken away, the liquid starts to contract and the particles stop moving,
forming a solid.
Melting: When heat is applied to a liquid, the particles start to vibrate more quickly in all directions and they
gain energy until the bonds holding the particles get weaker.
Evaporation: The liquid then gains even more energy and start to expand even more, where the liquid
starts bubbling and a gas is formed
Diffusion:
Diffusion is the movement of particles from an area of high to low concentration. Eg, in bromine, it diffuses
from high to air (low). Diffusion takes time as the particles have to move around the other gas particles.
Speed of gas depends on Mr, the higher the slower.
Solution Definitions:
Solvent: The substance that the solute is dissolved into which then forms a solution.
Solute: The substance that is dissolved
Solution: The product formed from the reaction
Saturated Solution: A solution in which no more solute can be dissolved, as it's reached its maximum
capacity.
Elements, Compounds and Mixtures:
Elements, Compounds and Mixtures:
Element: A substance that has only one type of atom and can’t be broken down into anything simpler
Compound: A compound is made when 2 or more different atoms of elements joined together by chemical
bonding.
Mixture: Is when different elements or compounds that are not chemically bonded together
Melting and Boiling Points:
A pure substance has clear fixed melting point as their composition is the same throughout so every part
melts at the same temperature. Mixtures have a range of melting and boiling points as the composition isn’t
the same throughout and so parts melt at different points.
Separating Techniques:
Filtration: is used to separate solid substances from liquid substances. The large solid particles (residue)
cannot fit through the tiny pores in the filter paper but the liquid and anything dissolved in the liquid (filtrate).
Crystallisation: is where a substance is dissolved in a minimum amount of hot solvent so that it becomes
saturated on cooling and crystallises to form a solid which we can collect by filtration.
Simple Distillation: is used to get pure liquids from solutions. The solution is heated until it boils. The pure
vapour is then condensed back into a liquid (called the distillate) by the cold condenser.
, Fractional Distillation: is used to separate liquids with different boiling points, for example a mixture of
ethanol (bp 78oC) and water (100oC) can be separated as the ethanol boils first and water second. A
special fractionating column is added to the apparatus which is full of glass beads. These increase the
available surface area to give a better separation and purer distillate.
Chromatography:
Used to separate the colours in a mixture of dyes. The mixture is applied to a pencil line near the bottom of
the pape and then the paper is placed in a jar with a small layer of solvent. Paper is the stationary phase
and the solvent is the mobile phase.
Rf values are used to identify the components of mixtures. The Rf value of a particular compound is always
the same. Calculating the Rf value allows you to identify unknown substances as it can be compared with
Rf values of known substances under the same conditions.
Rf value = distance moved by compound spot/ distance moved by solvent
Atomic Structure:
Atoms and Molecules:
Atom: The smallest particle of an element that consists of electrons surrounding a nucleus that contains
protons and neutrons
Molecules: Smallest particle of a substance that is formed when atoms join together by chemical bonds
Atom Structure:
Subatomic Mass Charge Position
Particle
Proton 1 + Nucleus
Neutron 1 0 Nucleus
Electron Negligible - Electron
Shells
Isotopes and Ars:
Atomic Number: Number of protons/electrons in an atom
Mass Number: Number of protons + neutrons in an atom
Isotope: Atoms of the same element with the same number of protons but a different number of neutrons
Relative Atomic Mass: The average mass of an atom of isotopes of an element compared to carbon 12.
RAM Calculation:
(abundancy * mass number) + (abundancy * mass number)
RAM = 100
The Periodic Table:
Arrangement of Elements:
Elements are arranged in order of increasing atomic number. Group number tells you how many electrons
are in the outermost shell. Period number tells you how many electron shells the atom has.
Electronic Configurations:
Electronic configurations show us the arrangement of electrons of an atom in its shell.
Metals and Non-Metals:
Metals: Basic (react with acids), Giant Ionic Lattices (high melting points, conduct electricity
when molten), (Left of PT)
Non Metals: Acidic (reacts with bases), Simple Molecular (low boiling points, don’t conduct
electricity), (Right of PT)
Group 0 Reactivity:
Noble gases are very unreactive/inert as they already have a full outer shell of electrons and they don’t
want to lose or gain any .Elements in the same group show similar chemical properties. This is because
they have the same number of electrons in their outer shell.
Chemical Formulae, Equations and Calculations:
, Mr and Ar:
- Ar: Calculated from the mass number or RAM of an element
- Mr: Calculated by adding up the RAMs of all the atoms in a formula
Mole:
- A mole is a measure of the amount of substance
- 1 mole is the amount of substance that has 60 * 1023 (Avogadro’s Number)
- M ass (g) = M r * M oles (mol)
Reacting Masses:
- Calculate the mass of MgO that can be made by completely burning 6g of M in O
-
Magnesium Oxygen Magnesium Oxide
Equation 2Mg o2 2MgO
Mass 6 10
Mr 24 40
Moles 0.25 0.25
Ratio 1 1
Percentage Yield:
- Percentage Yield: % of yield obtained from the theoretical yield
- Percentage Yield (%) = (Yield Obtained / Theoretical Yield) * 100
- There are 3 reasons why we don’t get 100% yield:
- Incomplete Reaction (Uneven mixing, limiting reactant)
- Loss of Product (Leaks, Spills, evaporation)
- Unwanted Products (Side Reactions)
Empirical Formula:
- Measure Crucible and lid mass
- Add metal to crucible and measure mass with lid
- Heat crucible over a bunsen burner and lift lid occasionally to allow oxygen through
- Continue heating until mass is constant
- Measure mass of crucible and contents
- Mass of Metal: (Empty crucible + Metal) - Crucible
- Mass of Oxygen: (MgO mass - mass of metal)
- Find moles then ratio
Concentration:
- Concentration (mol/dm3) = Moles (mol) / Volume (dm3)
Gas Volumes:
- Moles of Gas (Mol) = Volume (dm3) / 24
- Avogadro’s Law: At room temperature and normal atmospheric pressure, 1 mole of any gas has a volume
of 24dm3
Ionic Bonding:
Ions Definition:
- Ion: Electrically charged atom that is formed by the loss or gain of electrons
- Cations: Metals that lose electrons and become positively charged
- Anions: Nonmetals that gain electrons and become negatively charged
Dot and Cross Diagrams:
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