Why atoms form bonds
Electrons are in energy levels around
the nucleus (electron cloud).
The higher the energy level, the more
energy is required for an electron to
occupy that part of the cloud.
The outermost part of the electron
cloud contains the valence electrons
– that is the valence shell.
Maximum number of valence
electrons in an atom is 8.
Atoms are stable
when they have 8
When the atoms
have 8 electrons, it
is called an octet .
Atoms must lose,
gain or share
electrons to attain
Atoms that form bonds with other atoms by sharing
them or transferring them is known as the Octet
There is always an exception!
Hydrogen and Helium
Hydrogen needs only
one more to fill its
Helium has a full
valence shell – it is
stable and does not
bond with other
So what about Lithium?
Is it easier for
Lithium to gain 7
electrons or lose
Bond…. Chemical Bonds
They are formed when atoms gain or
If the compound has a metal, then it
is an ionic bond.
When atoms gain or lose an electron, they
become an ion.
A Na atom has 11 positively charged protons
and 11 negatively charged electrons.
When it loses 1 electron to become more stable, it has 11
protons (+) and 10 electrons (-) and has a +1 charge.
Cl has 17 protons.
When Cl gains 1 electron to complete the octet, it has 17
protons (+) and 18 electrons (-).
It is now an ion with a –1 charge.
Since the Na has a + charge and the Cl has a –
charge, the two atoms are attracted together
and form an ionic bond.
They have a 1:1 ratio when they combine…..
Atoms that share electrons form covalent
If the atoms have a covalent bond and are the
same type of atom…. They are diatomic
So you ask…. “How do I
know if it is covalent or
Ionic bonds are formed
attraction of two oppositely charged
Covalent bonds are formed when
atoms share electrons.
Typically bonds between metals and
nonmetals form ionic bonds.
Bonds between two nonmetals form
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