Chemical Bonds & Molecular
Attractions
Chapter 12
Student Learning Objectives
• Determine the type of chemical bond &
the chemical formula
• Describe molecular attractions & provide
examples
What is a chemical bond?
A chemical bond is an attraction between atoms.
The chemical bond puts each atom in a lower energy
state.
Water H2O
Ibuprofen C13H18O2
What is conserved in chemical reactions?
 Mass and charge are
conserved in chemical
reactions.
 The formula mass of the
product is equal to the
formula mass of the
reactants.
 The relative mass of a
substance is always the
same. (law of definite
proportions)
H2O
Practice
Calculate the formula mass for each of these
compounds, & determine the relative mass.
1. CO2
2. HCl
3. NH3
4. CH4
How does an electron dot structure compare
to the shell model?
The Lewis electron dot
symbols represent the
valence electrons of the
main group elements.
Shows unpaired e–
The electron dot
structure is based on the
octet rule.
Practice
Draw the electron dot structures. How do the dot
structures compare to the group number?
1. H
2. C
3. Ar
4. Na
What is an ionic bond?
Ionic bonds form between positive and negative ions.
 Electric force establishes bond
 Strongest chemical bond
Outer Shell Electrons
Ion
Mostly Full
Gained Negative
Mostly Empty
Lost
Positive
Ion charges must balance to give a net charge of zero
when atoms bond.
Na + Cl
Be + N
Practice
1) Ionic bonds are usually formed between metals from
the left side of the periodic table and nonmetals from
the far right side of the periodic table. Why?
2) Determine the chemical formula, and then name the
compound.
1. Mg + S
2. Ca + Br
3. Rb + Se
What is a metallic bond?
Metallic bonds form in metals as all electrons are
shared among all the nuclei in the metal.
e
e
e
Cu
e
e e
e e
e
e
Cu
Ni
e
e
Ni
e
e e
e
Sharing of all electrons establishes bond
Results in conductivity and malleability of metals
Ions homogeneously distributed in alloys
Weakest chemical bond
What is a covalent bond?
Covalent bonds are formed between atoms that
share pairs of electrons in the inter-nuclear region.
Covalent Sharing of e—
 Sharing of electron pairs establishes the covalent bond.
 There can be 1, 2, or 3 pairs of electrons shared.
H–H
CO
NN
2e
4e
6e
single bond
double bond
triple bond
Polar Molecules
 In general, the farther apart (left↔right) two atoms are on
the periodic table, the more polar the bond will be.
Practice
1) Which are polar molecules? Which bond would be
the most polar?
a) CO
b) CO2
c) H2O
d) NH3
2) Polar molecules tend to have high boiling points.
Why?
Molecular Attractions
Molecular attractions occur as a result of polarity.
Ion-Dipole
– Sodium cation and the chloride anion attract to waters
– Charged species as a rule dissolve readily in water
– Ionic substances are very hydrophilic (water-loving)
Ion-Dipole Attractions
Cl– Anion
Na+ Cation
Dipole-Dipole
– Water molecules are dipoles
Intermolecular force
between dipoles
 Ion-Induced Dipole
 Dipole-Induced dipole
Soda Pop
(Dipole-Induced Dipole)
Induced Dipole-Induced Dipole
Instantaneous
Uneven
Distribution
of e–
Carbon Dioxide Molecule
Vibrates
Practice
1) Which of the molecular attractions is the strongest?
Why?
2) List the molecular interactions in order from
strongest to weakest.
3) What, specifically, causes the surface tension
exhibited by water?
Hydrogen Bonding
Hydrogen bonding is a special form of a dipoledipole molecular attraction.
This is not a chemical bond
(no new substance produced)
H is part of the bond pair
Very uneven sharing of e−
Results in high Lf and Lv for water
A hydrogen bond is the attraction between the
positively charged hydrogen and a negatively charged
lone pair of electrons.
Practice
1) Why does it take a while for the bubbles to leave
your soda?
2) Why does it take a relatively long time for water to
boil?