Introduction to Bonding
Key Terms:
Chemical Bond
Ionic Bond
Covalent Bond
Electronegativity
Metallic Bond
Why Form Bonds?
 Single atoms are not how most
of the elements in nature exist
 Atoms “seek” the lowest energy
state possible
 In the dissociated stated, aka
individual atom state, most atoms
are at a higher energy
 When the atoms combine it
lowers the total energy of the
system, which means it is more
favorable
Chemical Bonds
 A chemical bond forms when 2
or more atoms rearrange valence
electrons to increase stability
 Remember the term valence
electron, what was considered a
“magic number” of valence
electrons?
 Most atoms prefer 8 valence
electrons to fill their s- and porbitals
 Two ways for atoms to share
electrons:
1.
2.
Completely transfer
Share the electron(s)
Octet Rule
 A chemical rule of thumb
in which atoms that
combine seek to have 8
electrons as their valence
electrons
 An atom that is surrounded
by 8 electrons that only
contain s- and p-orbitals as
valence orbitals will be
stable
Ionic Bonding
 Ionic bonding forms when
valence electrons are
transferred from one atom
to another
 When an ionic bond is
present the compound is
considered an ionic
compound
 One of the most common
examples of an ionic
compound is that of
common table salt, NaCl
Ionic Bonding
Anions and Cations
 Ionic compounds are
comprised of:
 Cations An atom or molecule that
loses an electron to become
positively charged
 Anions An atom or molecule that
gains an electron to become
negatively charged
Properties of Ionic Compounds
 Ionic Compounds are
arranged in crystal lattice
structures to put the atoms in
the lowest energy state
possible
 Strong forces hold the ions
together
 High melting and boiling
points
 Hard- not easily crushed
 Conduct electricity when
melted or dissolved because
ions are free to move
Pure Water vs Salt Water
 If you are sitting in a pool
of pure water and someone
drops a plugged in toaster
in with you. What will
happen to you?
 Nothing
 Now, if someone adds salt
to the pool before you get
in what would happen once
the plugged in toaster is
added?
 Zap!
Covalent Bond
 A covalent bond occurs
when electrons are shared
when forming molecules
 Formation of molecules
causes increased stability
 Covalent compound have
weaker forces holding
them together compared to
that of ionic bonds
Properties of Covalent Bonds
 Covalent compounds have:
 Lower melting and boiling
points
 Many covalent compounds
are volatile liquids or gases
 Soft- easier to crush
 Are not conductors of
electricity
 Ex.
 Methane is a covalently
bound molecule that is a
gas or a volatile liquid
Electronegativity
 Electronegativity is a property
that tells how strong an atom’s
attraction is for electrons
 Electronegativity is a property
of an atom that can be found
using a chart or table
 What do you think happens
when one atom has a stronger
pull on an electron than
another?
 Think of a large dog and a
smaller dog playing tug of war
 Unequal sharing
Polar Covalent Bonds
 Polar covalent bonds occur when
electrons are shared unequally
giving these molecules charged
ends or poles
 Since oxygen has a higher
electronegativity than hydrogen,
oxygen holds onto shared
electrons more, giving the
oxygen a partial negative charge
and the hydrogen a partial
positive charge
 This type of unequal sharing is
denoted by a ∂+ or ∂- to say
slightly more positive or negative
at that atom
Nonpolar Covalent Bonds
 Nonpolar covalent bonds occur
when electrons are shared
equally because the atoms have
the same or close
electronegativities
 Nonpolar compounds tend to
have weaker interactions
between molecules while polar
compounds have stronger
interaction between molecules
 This idea of molecules interacting
with each other will be covered
in a later lesson
Determining Bond Type
Electronegativity Difference
Type of Bond
Greater than or equal to 1.7
Ionic bond
Between 1.7 and 0.3
Polar Covalent
Less than or equal to 0.3
Nonpolar covalent
Metallic Bond
 Metallic Bonds form in
metals because the
electrons are delocalized,
giving metals a “sea of
electrons”
 Due to this “sea” metals
have the following
properties




Luster
Conductors
Malleable
Ductile
Practice Problems
 Determine the type of bonds for the following compounds:
Mg and F
1.

4.0 – 1.2 = 2.8 ionic
S and O
2.

3.5 – 2.5 = 1.0 polar covalent
Na and Cl
3.

3.0 – 0.9 = 2.1 ionic
N and O
4.

3.5 – 3.0 = 0.5 (slightly) polar covalent
B and F
5.

4.0 – 2.0 = 2.0 ionic