GCSE Chemistry Paper 1 Notes
Chemistry Basics
Atom: The smallest neutral part of an element that can take part in chemical reactions.
Ion: A charged particle formed when an atom, or group of atoms, loses or gains electrons.
Element: A substance made from atoms with the same
unique atomic number [number of protons in the nucleus].
Diatomic Elements: The formula for most elements is just
their symbol, but there are some non-metal elements known
as diatomic elements. They contain 2 atoms of the same
element covalently bonded together.
Molecule: A particle consisting of 2 or more atoms
covalently bonded together.
Compound: Contain 2 or more different elements
chemically joined together.
Isotopes
Isotopes are atoms of an element with:
The same number of protons.
Different number of neutrons.
So they have the same atomic number but a different mass
number.
Isotopes of an element have the same chemical properties
because they have the same number of electrons.
Ions
An ion is an atom or a group of atoms with a (+) or (-) charge.
In general:
Hydrogen atoms and metal atoms lose electrons to form positively charged ions [cations].
Non-metal atoms gain electrons to form negatively charged ions [anions].
Oppositely charged ions in solution may join to form an insoluble solid, called a precipitate.
In all ionic equations:
All substances are shown by their formulae.
The number of atoms of each element in the reactants and products are the same.
The total electrical charge is the same on both sides of the equation.
Spectator ions: Ions that are present during the reaction but remain unchanged [so don’t change state].
, Ionic Compounds:
o Bonding:
Ionic bonds are strong electrostatic forces of attraction between oppositely charged ions.
o Structure:
The ions in an ionic compound form a lattice structure which has:
A regular arrangement of ions.
Ionic bonds between oppositely charged ions.
o Melting & Boiling Points:
Ionic compounds usually have:
High melting points.
High boiling points.
As a result, they are solid at room temperature. In terms of bonding and structure:
There are many strong ionic bonds.
Large amounts of energy must be transferred to the lattice structure to break these
bonds.
o Solubility:
Ionic compounds are often soluble in water. They dissolve to form aqueous solutions.
o If a compound is made from a metal and a non-metal, its bonding will be ionic.
Covalent Bonds
A covalent bond is formed when a pair of electrons is
shared between two atoms.
Covalent bonds:
o Are strong.
o Form between non-metal atoms.
o Often produce molecules, which can be
elements or compounds.
, A hydrogen atom can form one covalent bond. Usually, for atoms of other non-metals:
o Number of bonds = [8 – group number].
When drawing dot-and-cross diagrams:
o Draw overlapping circles to represent the outer shells.
o Draw a dot to represent an electron from one atom, and
a cross to represent an electron from the other atom
[ensure that each bonding pair of electrons is between
the two atoms].
o Ensure that each atom [apart from hydrogen] has eight
electrons in its outer shell.
If a compound is made from 2 non-metals, its bonding will be
covalent.
Simple molecular substances
Bonding:
o A simple molecule consists of just a few atoms joined to each other by strong covalent bonds. They
can be:
Non-metal elements, such as H2, 02, Cl2.
Compounds of non-metals, such as HCL, H2O,
CH4.
o Simple molecular substances usually have:
Low melting points.
Low boiling point.
o They are usually gas or liquid at room temperature
because of this.
o Simple molecular substances with relatively large
molecules, such as wax, are in the solid state at room
temperature.
Non-conductors of Electricity:
o Simple molecular substances do not conduct electricity when solid, liquid or gas. This is because their
molecules:
Are not an electrically charged.
Do not contain electrons that are free to move.
o Conducting in a solution:
Most simple molecular substances do not conduct electricity when in solution. However:
Some of them breakdown when they dissolve in water, forming ions.
These ions can move around, so the solution conducts electricity.
Solubility in Water:
o Many simple molecular substances are insoluble in water. The intermolecular forces between water
and these substances are weaker than those between:
Water molecules.
Molecules of the substance itself.
o Simple molecular substances dissolve in water if they can form strong enough intermolecular forces
with water molecules:
Hydrogen and oxygen are sparingly soluble [very little dissolves].
Chlorine, carbon dioxide, sulphur dioxide and ammonia are soluble in water.
Ethanol and Ethanoic acid are soluble in water.
Sugar is soluble in water.
Chemistry Basics
Atom: The smallest neutral part of an element that can take part in chemical reactions.
Ion: A charged particle formed when an atom, or group of atoms, loses or gains electrons.
Element: A substance made from atoms with the same
unique atomic number [number of protons in the nucleus].
Diatomic Elements: The formula for most elements is just
their symbol, but there are some non-metal elements known
as diatomic elements. They contain 2 atoms of the same
element covalently bonded together.
Molecule: A particle consisting of 2 or more atoms
covalently bonded together.
Compound: Contain 2 or more different elements
chemically joined together.
Isotopes
Isotopes are atoms of an element with:
The same number of protons.
Different number of neutrons.
So they have the same atomic number but a different mass
number.
Isotopes of an element have the same chemical properties
because they have the same number of electrons.
Ions
An ion is an atom or a group of atoms with a (+) or (-) charge.
In general:
Hydrogen atoms and metal atoms lose electrons to form positively charged ions [cations].
Non-metal atoms gain electrons to form negatively charged ions [anions].
Oppositely charged ions in solution may join to form an insoluble solid, called a precipitate.
In all ionic equations:
All substances are shown by their formulae.
The number of atoms of each element in the reactants and products are the same.
The total electrical charge is the same on both sides of the equation.
Spectator ions: Ions that are present during the reaction but remain unchanged [so don’t change state].
, Ionic Compounds:
o Bonding:
Ionic bonds are strong electrostatic forces of attraction between oppositely charged ions.
o Structure:
The ions in an ionic compound form a lattice structure which has:
A regular arrangement of ions.
Ionic bonds between oppositely charged ions.
o Melting & Boiling Points:
Ionic compounds usually have:
High melting points.
High boiling points.
As a result, they are solid at room temperature. In terms of bonding and structure:
There are many strong ionic bonds.
Large amounts of energy must be transferred to the lattice structure to break these
bonds.
o Solubility:
Ionic compounds are often soluble in water. They dissolve to form aqueous solutions.
o If a compound is made from a metal and a non-metal, its bonding will be ionic.
Covalent Bonds
A covalent bond is formed when a pair of electrons is
shared between two atoms.
Covalent bonds:
o Are strong.
o Form between non-metal atoms.
o Often produce molecules, which can be
elements or compounds.
, A hydrogen atom can form one covalent bond. Usually, for atoms of other non-metals:
o Number of bonds = [8 – group number].
When drawing dot-and-cross diagrams:
o Draw overlapping circles to represent the outer shells.
o Draw a dot to represent an electron from one atom, and
a cross to represent an electron from the other atom
[ensure that each bonding pair of electrons is between
the two atoms].
o Ensure that each atom [apart from hydrogen] has eight
electrons in its outer shell.
If a compound is made from 2 non-metals, its bonding will be
covalent.
Simple molecular substances
Bonding:
o A simple molecule consists of just a few atoms joined to each other by strong covalent bonds. They
can be:
Non-metal elements, such as H2, 02, Cl2.
Compounds of non-metals, such as HCL, H2O,
CH4.
o Simple molecular substances usually have:
Low melting points.
Low boiling point.
o They are usually gas or liquid at room temperature
because of this.
o Simple molecular substances with relatively large
molecules, such as wax, are in the solid state at room
temperature.
Non-conductors of Electricity:
o Simple molecular substances do not conduct electricity when solid, liquid or gas. This is because their
molecules:
Are not an electrically charged.
Do not contain electrons that are free to move.
o Conducting in a solution:
Most simple molecular substances do not conduct electricity when in solution. However:
Some of them breakdown when they dissolve in water, forming ions.
These ions can move around, so the solution conducts electricity.
Solubility in Water:
o Many simple molecular substances are insoluble in water. The intermolecular forces between water
and these substances are weaker than those between:
Water molecules.
Molecules of the substance itself.
o Simple molecular substances dissolve in water if they can form strong enough intermolecular forces
with water molecules:
Hydrogen and oxygen are sparingly soluble [very little dissolves].
Chlorine, carbon dioxide, sulphur dioxide and ammonia are soluble in water.
Ethanol and Ethanoic acid are soluble in water.
Sugar is soluble in water.
