Chemical Bond Formation
some bonds share (covalent), some
transfer electrons (ionic)
therefore bonds formed depend upon:
1) electron configuration
2) attraction for electrons
1
Electronegativity
tendency of an atom to attract electrons
to itself when bonded
recall periodic trend of
electronegativity....
most active metals (low left) have the
lowest electronegativity
Francium-least electronegative (0.86)
most active nonmetals (top right) have
the highest electronegativity
Fluorine-most electronegative (4.10)
2
Electronegativity
Definition: A measure of the ability of an atom in
a chemical compound to attract electrons
o Electronegativity tends to increase across a period
o As radius decreases, electrons get closer to the
bonding atom’s nucleus
o
Electronegativity tends to decrease down a group
o As radius increases, electrons are farther from
the bonding atom’s nucleus
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Periodic Table of Electronegativities
4
Periodic Trend:
Electronegativity
5
Summary of
Periodic Trends
6
try these...
Arrange the following elements in order of increasing
electronegativity
1. antimony, fluorine, indium, selenium
A: indium, antimony, selenium, fluorine
2. francium, gallium, germanium, phosphorus, zinc
A: francium, zinc, gallium, germanium, phosphorus
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Electronegativity
The greater the difference in electronegativities
(Δ), the greater the strength of the bond
between atoms
Bond strength-measure of energy needed to
break bond between atoms
greater bond strength, the more energy
required to break the bond
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Electronegativity
H-F
Bond Strength
(kJ/mol)
568.1
1.90
H-Cl
431.95
0.63
H-Br
366.25
0.54
H-I
298.32
0.01
Bond
Δ
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Bond Character
electrons are transferred when electronegativity
difference is high
electrons are shared when electronegativity
difference is low
At what point does sharing switch to
transferring?
1. electronegativity varies slightly depending on
atoms in bond
2. number of atoms
not an easy answer..it is a continuum
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Bonding Character
Ionic Bonds
atoms combine via
TRANSFER of electrons
ions are produced and
attraction of opposite
charges holds compounds
together
Δ≥ 1.67
the large electronegativity
difference means one atom
pulls electron(s) completely
away from the other atom
Covalent Bonds
atoms combine via
SHARING of electrons
no ions are produced and
sharing electrons holds
compounds together
Δ< 1.67
the small electronegativity
difference means neither
atom pulls electrons
completely away; they share
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Bond Character
To determine which type of bond:
1. Find Δ = |electronegativity of atom 1 electronegativity of atom 2|
2. Classify the bond; 1.67 or higher = ionic;
less than 1.67 = covalent
Mg-O
Δ = |3.50-1.23|= 2.27 ionic
B-N
Δ = |3.07-2.0|=1.06 covalent
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Try this:
Calculate Δ and classify the following bonds as
ionic or covalent based on electronegativity
differences
B-P
Hydrogen-Iodine
Be-Si
Astatine-Beryllium
C-Na
Cobalt-Fluorine
Li-O
Chlorine-Tellurium
Mg-N
Bromine-Cerium
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Ionic Bonds/Ionic Compounds
ex. NaCl
Δ = |1.01-2.83| = 1.82
Characteristics:
1. high melting points (MP)
2. conduct electricity in molten state
3. soluble in water
4. crystallize as sharply defined particles
Occur between a metal and nonmetal, so we do
not have to find Δ every time
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15
Ionic Bonding
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Electron Dot
Notation
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Ionic Bonding with Lewis Dot Diagrams
Show how the compound MgO is formed using Lewis Dot
Diagrams
Try KF
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Covalent Bonds
atoms with the same or nearly the same
electronegativity (low Δ) react by sharing electrons
Characteristics
1. usually occur between atoms of nonmetals
2. typically have low MP
3. do not conduct electricity
4. can be brittle or gases
Occur between a nonmetal and nonmetal (or
metalloids), so we do not have to find Δ every time
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 Covalent compounds tend to form so that each
atom, by sharing electrons, has an octet of electrons in
its highest occupied energy level.
 Covalent compounds involve atoms of nonmetals
only.
 The term “molecule” is used exclusively for covalent
bonding
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Covalent Bonds
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Covalent Bonding with Lewis Dot Diagrams
Covalent bonds result from the sharing of electrons
Using Lewis Dot Diagrams, show how bonding
occurs between a fluorine molecule, F2
Show how the bonding occurs in water, H2O
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Completing a Lewis Structure -CH3Cl
 Make carbon the central atom (it wants the most bonds, 4)
 Add up available valence electrons:
 Join peripheral atoms
to the central atom with electron pairs.
H
C
..
..
..
..
H
..
..
H
 C = 4, H = (3)(1), Cl = 7 Total = 14
Cl
..
 Complete octets on
atoms other than hydrogen with remaining
electrons
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Covalent Naming
There are 7 elements commonly found in
nature as diatomic molecules - made of two
atoms of the same element
hydrogen molecule - H2
nitrogen molecule - N2
oxygen molecule - O2
fluorine molecule - F2
chlorine molecule - Cl2
bromine molecule - Br2
iodine molecule - I2
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Covalent Prefixes
Often the final
vowel of the prefix
is dropped if the
element name
begins with a
vowel
subscript #
1
2
3
4
5
6
7
8
9
10
prefix
monoditritetrapentahexaheptaoctanonadeca-
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Covalent Naming
Follow the order of the chemical formula
Name the first element using the exact element
name
Name the second element as though it is an
anion (stem with the -ide ending, oxide)
add Greek prefix to each element name to
denote subscript
mono is usually NOT used, unless we have to
differentiate between two compounds of the
same elements
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Covalent Naming
Given the following formulas of covalent
compounds, identify the correct name
N2O3
first element name: nitrogen
second element name with -ide ending: oxide
add prefixes: dinitrogen trioxide
P4O6
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Naming Binary Compounds
P2O5 = diphosphorus pentoxide
CO2 = carbon dioxide
CO = carbon monoxide
N2O = dinitrogen monoxide
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Compound Name
Carbon dioxide
Carbon monoxide
Diphosphorus pentoxide
Dinitrogen monoxide
Silicon dioxide
Carbon tetrabromide
Sulfur dioxide
Phosphorus pentabromide
Iodine trichloride
Nitrogen triiodide
Dinitrogen trioxide
Compound Formula
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Answers – Write the Formula
Compound Name
Carbon dioxide
Carbon monoxide
Diphosphorus pentoxide
Dinitrogen monoxide
Silicon dioxide
Carbon tetrabromide
Sulfur dioxide
Phosphorus pentabromide
Iodine trichloride
Nitrogen triiodide
Dinitrogen trioxide
Compound Formula
CO2
CO
P2O5
N2O
SiO2
CBr4
SO2
PBr5
ICl3
NI3
N2O3
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Practice – Name the Compounds
Compound Formula
N2O4
SO3
NO
NO2
As2O5
PCl3
CCl4
H2O
SeF6
Compound Name
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Answers – Name the Compounds
Compound Formula
N2O4
SO3
NO
NO2
As2O5
PCl3
CCl4
H2O
SeF6
Compound Name
dinitrogen tetroxide
sulfur trioxide
nitrogen monoxide
nitrogen dioxide
diarsenic pentoxide
phosphorus trichloride
carbon tetrachloride
dinitrogen monoxide
selenium hexafluoride
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Covalent Naming
Try to determine the names of these
covalent compounds:
N2O4
Cl2O6
SF4
CO
CO2
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Covalent Naming
Write the formula of the following covalent
compounds from their name
disulfur trichloride
tetraphosphorus trisulfide
carbon disulfide
sulfur trioxide
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Polarity and Covalent Bonds
In a covalent bond between different elements,
one element attracts the shared pair of electrons
more strongly than does the other
This creates a polar-covalent bond
The atom with the higher electronegativity
attracts electrons more strongly and acquires a
slight/partial negative charge (δ-), leaving the
opposing end with a slight/partial positive
charge (δ+)
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Polarity and Covalent Bonds
δ+H
Examples
δ-
Nδ
O
H
δ+
H
H
δ+
δ+
δ-
F H
-
H+
δ
δ+
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