Atoms are the basic unit of
chemistry. They consist of 3
smaller things:
Protons - these are positively
charged (+)
Electrons - these are negatively
charged (-)
Neutrons - these have no
These 3 smaller particles are
arranged in a particular way. In
the center is the Nucleus where
you find the positive Protons
and neutral Neutrons.
In orbit around the nucleus are
the Electrons. These are found
in a series of orbits (depending
on the atom) with differing
numbers of electrons as seen
It's the electrons in orbit around the nucleus that allow one atom
to interact with other atoms so they can be linked together.
Sometimes atoms gain or lose electrons. The atom then loses or
gains a "negative" charge. These atoms are then called ions.
Positive Ion - Occurs when an atom loses an electron (negative
charge) it has more protons than electrons.
Negative Ion - Occurs when an atom gains an electron (negative
charge) it will have more electrons than protons.
The following image shows Na losing an electron and
Cl gaining an electron
Thus the Na becomes Na+
The Cl becomes Cl-
Molecules containin
g more than two
atoms are termed
polyatomic molecul
es, e.g., carbon
dioxide (CO2) and
water (H2O).
Polymer molecules
may contain many
thousands of
component atoms.
A water molecule is
made up of two
hydrogen atoms
and one oxygen
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