IGCSE Combined Sciences Summary Chemistry C1 The particulate nature of matter Atom: the smallest particle in which you can divide a substance in which it’s still keeps its
characteristics. Molecule: the smallest possible amount of a particular substance that has all the characteristics of
C2 Experimental techniques Separation Methods:
● Filtration: This is used when trying to separate a insoluble solid from a liquid.
● Distillation: Used to separate mixtures that are homogenized, this can be done by heating one
substance till the point it turns into a gas, leaving only the other remaining liquid.
● Recrystallization: Used to purify chemicals, this is done by dissolving the impurities and a
compound in an appropriate solvent. Either the wanted or the unwanted substance can be
removed from the solution.
● Chromatography: Used to separate mixtures of colored compounds. This is only done with
inks, dyes and food agents.
C3 Atoms, elements and compounds
Chemical VS physical change: chemical changes make new substances whereas physical changes do
Element: one of the basic substances that are made of atoms of only one kind and that cannot be
separated by ordinary chemical means into simpler substances. Compound: pure substances made of atoms of two or more elements chemically combined in fixed
● Homogeneous: uniform composition that doesn't readily separate. Every part of a
homogeneous mixture has the same properties.
● Heterogeneous: does not exhibit uniform properties. It's often possible to see the particles in
the mixture and separate them from each other.
Proton Number (atomic): the number of positive charges or protons in the nucleus of an atom of a
given element. Mass Number (nucleon): the sum of the number of protons and neutrons of an atomic nucleus. Electron Configuration:
Noble gases: the least reactive of all known elements. That’s because with eight valence electrons,
their outer energy levels are full. As a result, noble gases cannot become more stable by reacting with
other elements and gaining or losing valence electrons. Therefore, noble gases are rarely involved in
chemical reactions and almost never form compounds with other elements.
Relative charges and masses of electrons, protons and neutrons:
Periodic table related to electronic structure
The diagram shows a section of the periodic table, with the elements arranged as usual in the order of
their atomic number, from 2 to 20. The red numbers below each chemical symbol show its electronic
Moving across each period, you can see that the number of occupied energy levels is the same as the
As you go across each period from left to right, an energy level gradually becomes filled with
electrons. The highest occupied energy level contains just one electron on the left-hand side of the
table. It is filled by the time you get to the right-hand side.
Ionic Bonding: a type of chemical bond that involves the electrostatic attraction between oppositely
charged ions. They happen in metals and nonmetals.
● Cations are formed when atoms (usually metals) lose electrons.
● Anions (negative) are formed when atoms (usually nonmetals) gain electrons.
Covalent Bonds: forms between two atoms and is the attraction of two atoms to a shared pair of
electrons. It happens between two nonmetals. Small groups of covalently bonded atoms can join
together to form molecules. Formation of ionic bonds between elements from Groups I and VII:
When elements in Group I and VII react, the atom of the Group I element loses the electron from its
outer shell. This can be transferred to the outer shell of eight electrons (or two for lithium).
Formation of ionic bonds between metallic and nonmetallic elements:
Electrons are transferred from a metal atom to a nonmetal atom. The outer shells will have become
complete. Metal atoms will become positive ions because they loose electrons, whilst non-metal ions
will become negative ions because they gain electrons.
Cross and Dot diagram:
H2 Cl2 H2O
N2 C2H4 CO2
C4 Stoichiometry Formulae of simple compounds: For example, in iron sulfide, every iron atom is joined to one sulfur
atom, so we show its formula as FeS. Formula of a simple compound from the relative numbers of atoms present: For example, a unit
of Na2SO4 contains two sodium atoms, one sulfur atom and four oxygen atoms joined together.
Formula of a simple compound from a model or a diagrammatic representation:
Construct and use word equations: copper + oxygen = copper oxide Determine the formula of an ionic compound from the changes on the ions present:
2 Cu + O2 → 2CuO
Construct and use symbolic equations with state symbols, including ionic equations:
s = solid
l = liquid
g = gas
aq = aqueous (dissolved in water)
For example, the state equation for sodium and water, this would be the equation with the state
2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) Deduce the balanced equation for a chemical reaction, given relative information:
Total mass of products at end of reaction = total mass of reactants at the beginning (this is because no
atoms are created or destroyed during chemical reactions)
However, finding out the total product may not always be possible for a variety of reasons:
1. Reversible reactions may not be completed
2. Some product may be lost when it is removed from the reaction mixture.
3. Some of the reactants may react in an unexpected way.
Steps to balancing equations:
1. Write the element symbols
2. Write the masses
3. Write the Ar values
4. Divide masses by Ar
5. Divide by the smallest number
6. Write the formula.
Define the mole: A specific number of particles called Avogadro's constant, 6.02 x 10^23.
Use the molar gas volume, taken as 24 dm3 at room temperature and pressure.
C5 Electricity and chemistry