Chemical
Bonding
Chemistry 1-2
Mr. Chumbley
Modern Chemistry: Chapter
6
Introduction to Chemical
Bonding
Chapter 6 – Section 1
EQ: In what ways can atoms of different elements
combine to form chemical compounds?
Chemical Bonding
A
chemical bond is a mutual electrical
attraction between the nuclei and
valence electrons of different atoms that
binds atoms together
 There


are two types of chemical bonds
Ionic Bonds
Covalent Bonds
Ions

Atoms are capable of either gaining or losing
electrons

Ions are atoms that have gained or lost one
or more electrons

Cations are atoms that have lost electrons
and are positively charged

Anions are atoms that have gained electrons
and are negatively charged ions
Ionic Bonds
 Ionic
bonding results from the electrical
attraction between cations and anions
 In
ionic bonds, atoms completely give up
electrons to other atoms
 Ionic
bonds form between metals and
nonmetals
Covalent Bonds
 Covalent
bonding results from the sharing
of electron pairs between two atoms
 Covalent
bonds typically form between
nonmetals
Chemical Bonding
Covalent Polarity

Electrons are not always shared equally in a covalent
bond

Compounds are considered polar if there is an
uneven distribution of charge

Nonpolar-covalent bonds are covalent bonds in
which the bonding electrons are shared equally by
the bonded atoms

Polar-covalent bonds are covalent bonds in which
the bonding atoms have an unequal attraction for
the shared electrons
Chemical Bonding
Electronegativity and Bonding

Electronegativity is a
measure of the ability of
an atom to attract
electrons from another
atom

The difference in the
electronegativity (ΔEN)
between the atoms within
the compound
determines the type of
compound
Electronegativity Table
Rules for Determining Bond
Type
1.
If the ΔEN is less than 0.4, then the bond is nonpolar
covalent.
2.
If the ΔEN is between 0.4 and 1.6, the bond is
considered polar covalent.
3.
If the ΔEN is greater than 2.0, then the bond is ionic.
4.
If the ΔEN is between 1.6 and 2.0 and if a metal is
involved, then the bond is considered ionic. If only
nonmetals are involved, the bond is considered
polar covalent.
Sample Problem 6A (p. 167)
Use electronegativity differences to classify
the type of bond formed between sulfur, S,
and the following elements:
Electronegativity
difference
Bond type
hydrogen, H
2.5 – 2.1= 0.4
Polar-covalent
cesium, Cs
2.5 – 0.7 = 1.8
Ionic
chlorine, Cl
3.0 -2.5 = 0.5
Polar-covalent
Electron-Dot Notation

Electron-dot notation
is an electronconfiguration
notation in which
only the valence
electrons of an atom
or a particular
element are shown,
indicated by dots
placed around the
element's symbol
Charge by Group
1+
4+
2+
3+ 4-
2+
1+ 2+
0
3-
2-
1-
Covalent Bonding and
Molecular Compounds
Section 2
p. 168 – 179
EQ: What are the key characteristics of
covalent bonding?
Basics of Covalent Bonds

Previously we had introduced the idea of the
molecule and formula unit, and had used the
terms interchangeably

A molecule is a neutral group of atoms that
are held together by covalent bonds

A molecular compound is a chemical
compound whose simplest units are
molecules
Shared Electrons

As mentioned previously, covalent bonds result
from the sharing of electrons

This can be difficult because different parts of
different atoms either attract or repel
Electron-Dot Notation

Electron-dot notation is an electron-configuration
notation in which only the valence electrons of an
atom or a particular element are shown, indicated
by dots placed around the element's symbol

Lewis structures are representations of formulas in
which the atomic symbols represent the nuclei
and inner-shell electrons, dot-pairs or dashes
between two atomic symbol represent electron
pairs in covalent bonds, and dots adjacent to only
one atomic symbol represent unpaired electrons
Octet Rule
 Electrons
around atoms tend to follow
something called the octet rule

The octet rule states that chemical
compounds tend to form so that each
atom has an octet (8) of valence
electrons
Lewis Structures

Electron-dot notations can be used to
represent compounds

Lewis structures are representations of
formulas in which the atomic symbols
represent the nuclei and inner-shell electrons,
dot-pairs or dashes between two atomic
symbol represent electron pairs in covalent
bonds, and dots adjacent to only one atomic
symbol represent unpaired electrons
Central Atoms in Covalent
Bonds
 The
atom with most amount of unpaired
electrons tends to be the central atom in
a molecular compound
Determining Central Atoms
A
general set of rules for the location of
atoms within molecules:
1.
2.
3.
If a carbon-group element is present, it is
always the central atom
If no carbon is present, the atom with the
lowest electronegativity will be central
Hydrogen is never at the center of a
molecule
Sample 6C
Draw the Lewis structure for methane, CH4.
Sample 6C
Draw the Lewis structure for iodomethane, CH3I.
Sample 6D
Draw the Lewis structure for formaldehyde, CH2O.
Shared Electron Pairs
A
single bond is a covalent bond in which
one pair of electrons is shared between
two atoms
A
multiple bond is a covalent bond in
which more than one pair of electrons is
shared between two atoms
Resonance
 Some
molecules cannot be represented
adequately by a single Lewis structure
 Different
structures indicate atoms
bonded together in different ways
 Resonance
refers to bonding in molecules
or ions that cannot be correctly
represented by a single Lewis structure
Polyatomic Ions
A
polyatomic ion is a charged group of
covalently bonded atoms
 When
drawing the Lewis structure for
polyatomic ions, the number of electrons
present changes based on the charge
Sample 6D-2
Draw the Lewis structure for Nitrite, NO2-.
Ionic Bonding and Ionic
Compounds
Section 3
p. 180 – 184
EQ: What are the key characteristics of ionic and
metallic bonding?
Basics of Ionic Bonds
 An
ionic compound is composed of
positive and negative ions that are
combined so that the numbers of positive
and negative charges are equal
A
formula unit is the simplest collection of
atoms from which an ionic compound’s
formula can be written
Formation of Ionic Bonds

In general, atoms are the most stable when
they have electron configurations that are
the same as noble gases

Atoms gain or lose electrons to obtain a noble
gas configuration to electrically charged

The attraction between the positive and
negative ions results in an ionic bond
Ionic Bonding Structure
 Ionic
compounds tend to form to make
the most efficient use of energy
 Ionic
compounds form a crystal lattice as
a result of the positive and negative
attraction between adjacent ions
Crystal Lattice of NaCl
The ion’s arrangement is shown with
the electron clouds just touching
one another
When the distance between the
atoms is exaggerated, it is easier to
see the regular pattern of the
crystal lattice
Crystal Lattice of NaCl
NaCl can be
considered a
structure where six
sodium atoms
surround each
chlorine atom, or
vice-versa
Bond Strength and Chemical
Properties

The force of attraction between individual formula units as
well as the intermolecular forces of attraction gives ionic
compounds unique properties

Ionic compounds tend to have high melting points and
boiling points

Ionic compounds are typically very hard, but very brittle


Slight shifts in the arrangement of the atoms turns the strong
attractive force into a strong repulsive force
Most ionic compounds are electrical insulators as solids, but
can conduct electricity as liquids or when dissolved in
water
Metallic Bonding
Section 4
p. 185 – 186
Metallic Bonding

Most metals have vacant orbitals in their
highest energy levels

The energy levels of each metal atom will
overlap, allowing the few electrons from each
atom to move freely from one atom to
another

Metallic bonding is the chemical bonding
that results from the attraction between metal
atoms and the surrounding sea of electrons
Metallic Bonding
Metallic Properties

Electrical and thermal conductivity relate to
the sea of electrons

Metallic luster is a result of absorption and
emission of light

Metals are malleable and ductile


Malleability is the ability of a substance to be
hammered or beaten into sheets
Ductility is the ability of a substance to be
drawn, puller, or extruded to produce a wire