Chapter 13: Bonding: General Concepts Chapter 13: Phenomena Phenomena: Scientists measured the bond angles of some common molecules. In the pictures below each line represents a bond that contains 2 electrons. If multiple lines are drawn together these are double or triple bonds and contain 4 and 6 electrons respectively. What patterns do you notice from the data? H H N H H H N H H + O C O O C N H Cl Cl C Cl Cl B F Bond Angles: 107˚ Bond Angles: 109.5˚ Bond Angles: 109.5˚ Bond Angles: 120˚ C O Bond Angles: 105˚ Bond Angles: 119˚ Bond Angles: 120˚ Bond Angle: 117˚ Bond Angles: 180˚ Bond Angles: 180˚ a) b) c) d) g) e) h) f) i) j) S O
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Chapter 13: Bonding: General Concepts
Chapter 13: Phenomena
Phenomena: Scientists measured the bond angles of some common molecules.
In the pictures below each line represents a bond that contains 2 electrons. If
multiple lines are drawn together these are double or triple bonds and contain 4
and 6 electrons respectively. What patterns do you notice from the data?
H HN
H
H HN
H
H +
O
CO
O
CN H
Cl ClC
Cl
Cl
B
F
Bond Angles: 107˚
Bond Angles: 109.5˚ Bond Angles: 109.5˚
Bond Angles: 120˚
C
O
Bond Angles: 105˚
Bond Angles: 119˚
Bond Angles: 120˚ Bond Angle: 117˚
Bond Angles: 180˚
Bond Angles: 180˚
a) b) c)
d)
g)
e)
h)
f)
i)
j)
S
O
Chapter 13
Bonding:
General Concepts
o Types of Bonding
o Electronegativity
o Lewis Structures
o Strength/Length of
Covalent Bonds
o Shapes of Molecules (VSEPR)
o Polar Molecules
2
Big Idea: Bonds are formed from
the attraction
between oppositely
charged ions or by
sharing electrons.
Only the valence
electrons participate
in bonding. The shape
of the molecules
maximize the distance
between areas of high
electron density.
Chapter 13: Bonding: General Concepts
Types of Bonding
Ionic Bonds: Formed when a lower
energy can be achieved by the
complete transfer of one or more
electrons from the atoms of one element
to those of another; the compound is
then held together by electrostatic
attraction between the ions.
Covalent Bonds: Formed when the lowest
energy structure can be achieved by
sharing electrons.
3
Chapter 13: Bonding: General Concepts
Types of Bonding
Ionic Bonds: Tend to be between a
metal and a non metal.
Metals: Usually lose their electrons.
Nonmetals: Usually accept additional
electrons.
4
Note: In general, atoms gain or lose electrons until they have the same number of
electrons as the nearest noble gas
Chapter 13: Bonding: General Concepts
Types of Bonding
Element
Electron
Configuration
(Atom)
Gain/Lose
Electrons
Ion
Formed
Electron
Configuration
(Ion)
S
K
I
5
What ions do atoms form?
Chapter 13: Bonding: General Concepts
Types of Bonding
Ionic Solids: Assembly of cations and anions
stacked together in a regular array.
Ionic Compounds are represented with formula
units (lowest ratio of types of atoms in the
compound).
Ionic Compound
Covalent Compound
6
AB2 2AB2 3AB2
CD 2CD 3CD+ -+ -
+-
+ -+-
+ -
Note: Ionic solids are example of crystalline arrays in which the overall charge on
an ionic solid is neutral.
Chapter 13: Bonding: General Concepts
Types of Bonding
Steps to calculate the energy needed to form an ionic bond:
Step 1: Standard states to gaseous single atom state
Na(s) Na(g) 97 𝑘𝐽𝑚𝑜𝑙
½F2(g) F(g) 80. 𝑘𝐽
𝑚𝑜𝑙
Step 2: Both atoms have to form ions
Na(g) Na+(g) + e-(g) 494 𝑘𝐽𝑚𝑜𝑙
(ionization energy)
F(g) + e-(g) F-(g) -323 𝑘𝐽𝑚𝑜𝑙
((-)electron affinity)
Step 3: The ions need to come together to form a
crystal (Lattice Energy)
Na+(g) + F-(g) NaF(s) -923 𝑘𝐽𝑚𝑜𝑙
Total Reaction
Na(s) + ½F2(g) NaF(s)
97 𝑘𝐽
𝑚𝑜𝑙+ 90. 𝑘𝐽
𝑚𝑜𝑙+ 494 𝑘𝐽
𝑚𝑜𝑙+ −323 𝑘𝐽
𝑚𝑜𝑙+−923 𝑘𝐽
𝑚𝑜𝑙= −575 𝑘𝐽
𝑚𝑜𝑙
7
Note: When energy is
released, the sign is negative
because no work is needed to
make the reaction happen.
Chapter 13: Bonding: General Concepts
Types of Bonding
What is holding ionic solids together?
Coulombic Potential Energy
𝐸𝑃,12 =𝑍1𝑒 𝑍2𝑒
4𝜋𝜀∘𝑟12= +𝑍 −𝑍 𝑒2
4𝜋𝜀∘𝑑=−𝑍2𝑒2
4𝜋𝜀∘𝑑
Z1 & Z2 = charge of ions
The total potential energy is the sum of all the
potential energies
𝐸𝑃 =1
4𝜋𝜀∘−𝑍2𝑒2
𝑑+𝑍2𝑒2
2𝑑−𝑍2𝑒2
3𝑑+𝑍2𝑒2
4𝑑⋯ = − 𝑍2𝑒2
4𝜋𝜀∘𝑑1−
1
2+1
3−1
4+⋯
𝐸𝑃 = −𝑙𝑛 2𝑍2𝑒2
4𝜋𝜀∘𝑑
Need to multiply by 2 to account for the other half of the
line.
𝐸𝑃 = −2𝑙𝑛 2𝑍2𝑒2
4𝜋𝜀∘𝑑
8
Note: 𝑙𝑛 2 = 1 − 1
2+ 1
3− 1
4+⋯
Chapter 13: Bonding: General Concepts
Types of Bonding
Once neighboring ions come into contact they
start to repel each other.
𝐸𝑃∗ ∝ 𝑒− 𝑑 𝑑∗
d=0 𝑒− 𝑑 𝑑∗ = 1 max repulsion
d>1 𝑒− 𝑑 𝑑∗ = 1 repulsion decreases
The potential energy of an
ionic solid is a combination of
the favorable Coulombic
interaction of the ions and the
unfavorable exponential
increase which results when
the atoms touch. The ideal
bond length occurs at the
minimum potential energy.
Energy Minimum Occurs: 𝐸𝑝,𝑚𝑖𝑛 = −𝑁𝐴 𝑍1𝑍24𝜋𝜀∘𝑑
1 − 𝑑
𝑑∗𝐴
9
Note: d* is a constant
that is commonly
taken to be 34.5 pm
Chapter 13: Bonding: General Concepts
Types of Bonding
Covalent Bond: A pair of electrons shared
between two atoms (occurs between
two non metals)
10
Note: In covalent bond formation, atoms go as far as possible toward completing
their octets by sharing electron pairs.
Chapter 13: Bonding: General Concepts
Electronegativity
Electronegativity (χ): The ability of an
atom to attract electrons to itself when it
is part of a compound
11
Note: The atom with
higher electronegativity
has a stronger
attractive power on
electrons and pulls the
electrons away from the
atom with the lower
electronegativity.
Chapter 13: Bonding: General Concepts
Electronegativity
The dividing line between ionic and covalent bonds is hazy.