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9 Sci - Chemistry
A group of the same atoms are called elements
Periodic Law - The properties of elements aren’t
random. They follow a distinct pattern and have similar
chemical and physical properties at certain intervals.
In your periodic table:
» Elements are shown by order of size (atomic weight)
» Rows of elements are known as Periods
» Columns of elements are known as Groups (I to VIII)
Chemical symbol/formula –
The letter(s) that represent the
element. Most elements are just the
first letter of their name, but
this isn’t the case for all elements.
Atomic Number – Number of Protons/Electrons in the atom in
its neutral state.
*In any neutral atom: No. Protons = No. Electrons
Relative Atomic Mass
The total mass of the atom (relative to Carbon-12)
Mass Number
Total number of protons and neutrons (not shown)
Electrons are found within specific electron shells.
» The first shell holds max 2 electrons
» The second shell holds max 8 electrons
» The third shell holds max 18 electrons
» The fourth shell holds max 32 electrons
Valence Electrons – The electrons in the outer shell.
This determines the chemical properties of elements
Octet Rule – Atoms are most stable and want to have
8 electrons in their outer shell (Valence electrons)
Period number will tell you how many electron shells
the atom has.
Group number (I to VIII) will tell you how many
electrons are in the outer shell (Valence electrons)