2. Why atoms form chemical 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.
3. Atoms are stable
when they have 8
valence electrons.
When the atoms
have 8 electrons, it is
called an octet .
Atoms must lose,
gain or share
electrons to attain
the octet.
Atoms that form bonds with other atoms by
sharing them or transferring them is known as
the Octet Rule .
4. There is always an exception!
Hydrogen and Helium
Hydrogen needs only
one more to fill its
valence shell.
Helium has a full
valence shell – it is
stable and does not
bond with other
atoms.
5. So what about Lithium?
Is it easier for
Lithium to gain 7
electrons or lose 1
electron?
6. Bond…. Chemical Bonds
Ionic Bonds
They are formed when atoms
gain or lose electrons.
If the compound has a metal,
then it is an ionic bond.
Ex.
xx
Na Cl x x
x
xx
7. When it loses 1
Ionization electron to become
more stable, it has
11 protons (+) and
When atoms gain 10 electrons (-) and
or lose an electron, has a +1 charge.
Cl has 17 protons.
they become an
When Cl gains 1
ion.
electron to complete
A Na atom has 11 the octet, it has 17
positively charged protons (+) and 18
protons and 11 electrons (-).
negatively charged It is now an ion with
electrons. a –1 charge.
8. Opposites Attract
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…..
9. Covalent Bonds
Atoms that share electrons form
covalent bonds.
If the atoms have a covalent bond
and are the same type of atom….
They are diatomic molecules.
Ex. xx xx
x
x Cl Cl
xx
x
x
x
x
xx
11. Metallic Bonding
Metallic bonds - electrons are distributed
equally through a metallic crystal.
The electrons in metals can be thought of
as being property of all the atoms.
The positive nuclei are surrounded by a
"sea of electrons" that are all attracted by
the nuclei at the same time.
12. So you ask…. “How do I know
if it is covalent or ionic?”
Ionic bonds are formed by the attraction of
two oppositely charged particles.
Covalent bonds are formed when atoms
share electrons.
Typically bonds between metals and
nonmetals form ionic bonds.
Bonds between two nonmetals form
covalent bonds.
13. Isn’t it ionic, don’t you think
Electron pairs sometimes share
unequally in covalent bonds.
The attraction an atom has for the
shared pair of electrons in a covalent
bond is called electronegativity .
14. High Electronegativity
(need to gain
electrons)
Low Electronegativity Atoms in Column 17
(need to lose have high
electrons) electronegativity.
Atoms in Columns 1
and 2 have low
electronegativity. Cl F Br
H K Li
