Atoms consist of a nucleus which contains
positive protons (relative mass 1, charge 1+)
and neutral neutrons (relative mass 1,
charge 0). The nucleus is surrounded by a
series of shells which contain the negative
electrons (relative mass 0, charge 1-).
The arrangement of the electrons
in their shells is called the
electron configuration.
The first (inner) shell can
hold up to 2 electrons, the
next two shells can hold up to 8
electrons. The shells are filled
from the inside out.
Atoms are neutral because the number of positive
protons and negative electrons is always the same
in an atom.
When atoms lose electrons, they become positively
charged ions (metal atoms lose electrons). When
atoms gain electrons, they form negatively charged
ions (non-metal atoms gain electrons).
Elements are substances that contain only
one type of atom.
Gold
Oxygen
Helium
The atomic number (6) represents the
number of protons.
The mass number (12) represents the
number of protons + neutrons.
The atomic number of an atom also reveals
the number of electrons.
The Periodic Table is an arrangement of the
elements in atomic number order. Atoms of elements
that are in the same group (column) have the same
number of electrons in their outer shell. Atoms of
elements in the same period (row) have the same
number of electron shells.
All atoms in group 0 have a full outer
shell of electrons. All atoms in group 1
have 1 electron in their outer shell.
All equations are balanced because no
atoms can be destroyed or created.
Atoms form compounds by giving or
taking electrons (making ionic compounds)
or sharing electrons (making covalent
molecules).
Atomic Structure
Ionic bonding
Covalent bonding
Balancing equations
Videos
Add whole numbers in front of the formulae
to ensure you have the same number of
each atom on each side of the equation:
Questions
Answers
N2 + 3H2 -> 2NH3
2Na + 2H2O -> 2NaOH + H2