1. Bonding and Molecules

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

10. Element Bonding Formula
Hydrogen H-H H2
Oxygen O-O O2
Nitrogen N-N N2
Fluorine F-F F2
Chlorine Cl-Cl Cl2
Bromine Br-Br Br2
Iodine I-I I2

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