Elements are represented by 1,
2 or 3 letters e.g. oxygen-O, sodium-Na
Atomic Structure
An atom has a small central nucleus
containing sub-atomic particles called
protons and neutrons
The nucleus is surrounded by smaller
sub-atomic particles called electrons
Each proton and electron has an electrical charge
Protons have a positive charge (+1)
and electrons have a negative
charge (-1)
Neutrons do not have any
electrical charge; they are
neutral
The number of protons in an atom is
equal to the number of electrons,
therefore atoms have no electrical
charge
The atomic number (shown at the bottom) of an element is the number of
protons (and electrons) it has in one atom
The mass number (shown at the top) of an element is the
number of neutrons and protons a single
atom has
Electronic structure
Electrons in an atom occupy energy levels (or shells)
The first shell fills up first followed by the next
The first energy level can only hold 2
electrons, the second shell can only hold 8
and the third can only hold 8
The number of shells and the
number of electrons in the
outermost shell is relative to
the group and period an
element is placed in
E.g an element with 2 shells will be in period 2
and an element with 3 electrons in the outer
shell will be in group 2
The Periodic Table
There are around 100 elements and they are all listed and
arranged specifically in the periodic table
The horizontal rows are called periods and
the vertical columns are called groups
Elements in the same group have
similar properties
Elements are split into two types; metals (found on
the left of the periodic table) and non-metals (on the
right)
Most elements are metals
Elements found in the 1st group are all very
reactive metals
They are called Alkali metals
because they form alkaline
compounds
Lithium, sodium and potassium react
vigorously with water so all group 1 metals
must be stored in oil in order to stop them
reacting with the oxygen and water vapour
in the air
Lithium, sodium and potassium are
easily cut with a blade. The freshly cut
surfaces are silvery and shiny, but
quickly turn dull as the metal reacts with
oxygen in the air
Elements found in group 7 are all
very reactive non-metals
Elements found in group 8 are
very un-reactive and are called
noble gases
Chemical reactions
New substances are formed when chemicals react
When elements react, their elements join
with other atoms to make compounds
Compounds usually have different
properties from the elements they are
formed from
Ionic bonds
Compounds formed from a metal and a
non metal consists of ions
Ions are charged
particles that form when
atoms gain or lose
electrons
Metals lose
atoms to become
positively
charged ions
Ionic bonding is the force of attraction between negatively
and positively charged ions
Non metals gain electrons to
become negatively charged
ions
Covalent bonds
Covalent bonding occurs when two
non-metals share electrons between
each other
Chemical Formulas
The chemical formula of an atom
shows us which elements are in a
compound and how many atoms of
each element there are
The Conservation of Mass
No atom can be lost or made
during a chemical reaction
Therefore the total mass of atoms in the chemicals before a
chemical equation is always the same as the total mass of
atoms in the products of a chemical reaction