Chemical Bonding
Chapter 7
Chemical Bonds
 Chemical
Bond – a link between
atoms resulting from the neutral
attraction of their nuclei for
electrons
 force of attraction between atoms
Ionic bond
 Ionic
Bond – chemical bond
resulting from the transfer of
electrons from one bonding
atom to another
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Ex. NaCl
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Ionic Bonds form ionic compounds
which are composed of ions.
Characteristics of an ionic bond
 -high
melting points (shows a
strong bond)
 -brittle
 -dissolve in water
 -good conductors of electricity in
solution
Octet Rule
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Octet Rule – atoms tend to gain, lose, or
share electrons in order to acquire a full
set of valence electrons.
Example of an ionic bond:
Consider NaCl – (table salt)
Na – 1s22s22p63s1
Cl – 1s22s22p63s23p5
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What happens?
Na loses 1e- to form an octet
becomes Na+ ion
called CATION
Cl gains 1e- to form an octet
becomes Cl- ion
called ANION
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Using Lewis Dot diagrams
used to show valence electrons
dot represents valence electrons (or x’s
and o’s)
random order
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Na
Cl
-> Na+ + Cl -
Formulas
 Empirical
Formula – chemical
formulas which gives the simplest
whole number ratio of atoms of
elements in a compound.
 -cation ALWAYS written first
 -total “+” must equal total “-“
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Monoatomic ions – made of ONLY 1
element
Must remember the charge of the ion
Cations:
Anions:
Group 1: +1
Group 17: -1
Group 2: +2
Oxide: -2
Silver: +1
Sulfide: -2
Zinc: +2
Nitride: -3
Aluminum: +3
Phosphide:-3
Polyatomic ions
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ions which consist of more than one
atom
they act as a whole and carry a net
charge
Examples of Polyatomic Ions
 Hydroxide - OH- ,Acetate – C2H3O2 Hypochlorite – ClO- ,Sulfate – SO4-2
 Nitrate – NO3,Carbonate – CO3-2
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Bicarbonate – HCO3-,Phosphate – PO4-3
Binary Compounds
 Binary
Ionic Compounds
 - contain ions of only 2 elements.
 - Need to know the ratio of
elements in the compound
Writing formulas: Criss-Cross
method
write symbols of the elements or
polyatomic ions putting the charge as
a superscript
 put parenthesis around only the
polyatomic ion
 crisscross the numbers not the
charges and represent as subscripts
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Writing formulas….
 reduce
if possible
 eliminate and rewrite any
subscript of 1 and any
parenthesis whose subscript is 1.
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Example: Na and O form
Na2O
Covalent Bonds
 Covalent
Bond – chemical bond
resulting from the sharing of
electrons between bonding atoms
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Ex. CO2
7.2 Covalent Bonds
 Molecule-
a group of atoms
grouped together by covalent
bonds.
 Molecular substance – a
substance made up of molecules.
Molecular vs. Empirical
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Molecular formula – tells you how many
atoms are in a single molecule of the
compound.
Ex. C6H12O6 glucose
The empirical formula can be written for
molecular formulas.
Ex. CH2O glucose
Properties of covalent bonds
 Properties
of Covalent Bonds
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Bonds can be polar depending
on the Electronegativity of the
atoms.
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If one atom is significantly
more electronegative than the
other, the electron density will
change.
The atom that is more
electronegative will pull the
electrons closer to it and cause a
partial negative on that atom.
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**Electronegative difference
must be between 0.5 and 1.9
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If the electronegatives are
similar, the bond will be nonpolar
(electronegative difference less
than 0.4)
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Ionic bonds
Involves transfer of electrons
 Forms ions
 Usually forms between metal and
nonmetal and/or polyatomic atom
 substances usually soluble in
water
 high melting point
solutions are usually good
conductors of electricity
 compounds are brittle
 formulas are expressed as empirical
formulas
 9.Electronegativity difference
greater than 1.9
 10.strong bond
 11. criss cross
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