Covalent Bonding
Covalent Bonding
• 9.1 The Covalent Bond
• A covalent bond usually takes place
between two non-metal elements
• Covalent bonds generally occur
between elements that are close
together on the periodic table.
Covalent Bonding
• Octet Rule- When two
atoms both need to
gain valence
electrons to complete
the octet rule, they
share electrons in
order to gain the
configuration of a
noble gas : 8 valence
electrons.
Covalent Bonding
• A covalent bond is a chemical bond
that results from the sharing of valance
electrons.
• Covalent Bond- the shared electrons in
a covalent bond are considered to be
part of the complete outer level for both
atoms involved.
Molecule
A Molecule- is formed when two or more
atoms bond covalently.
A compound that is formed by molecules
is called a molecular compound.
Formation of a covalent bond
A valence orbital containing an electron
from one atom overlaps a valence orbital
from another atom. Because the nuclei of
both atoms have a positive charge, they
are attracted to the shared concentration
between them.
Diatomic molecules (Mr.
BrINClHOF)
• Diatomic molecules do not
occur in nature as single
atoms because the molecules
formed are more stable than
the individual atoms. Bromine
(Br2), iodine (I2), chlorine
(Cl2), hydrogen (H2), oxygen
(O2), and fluorine (F2) are all
diatomic molecules
Single Covalent Bonds
• When a single pair of electrons is
shared, e.g. hydrogen, a single
covalent bond is formed.
Lewis Structures
• Lewis structures - use
dot structures to show
how electrons are
arraigned in molecules.
• A shared pair of
electrons known as the
bonding pair, can be
represented as a pair of
dots or a line.
• a lone pair is a valence electron pair without
bonding or sharing with other atoms.
• They are found in the outermost electron shell
of an atom.
• Electron pairs are considered lone pairs if two
electrons are paired but are not used in
chemical bonding.
Multiple Covalent Bonds
Multiple Covalent Bonds - Many
molecules gain a noble gas configuration
by sharing more than one pair of
electrons, forming multiple covalent
bonds.
Carbon, nitrogen, oxygen, and sulfur
most often form multiple bonds.
Carbon, nitrogen, oxygen, and sulfur
most often form multiple bonds.
Multiple Covalent Bonds
• Double and triple covalent bonds are
examples of multiple bonds.
• A double bond occurs when two pairs
of electrons are shared. e.g. O2.
Multiple Covalent Bonds
• Double and triple covalent bonds are
examples of multiple bonds.
• A triple bond occurs when three pairs
of electrons are shared. e.g. N2.
Strength of Covalent Bonds
• The strength of covalent bonds
depends on how much distance
separates the bonded nuclei.
• This is called the bond length.
Strength of Covalent Bonds
• Since multiple bonds have a shorter
bond length.
• Single bonds (F2) are weaker than
double bonds (O2)
• Double bonds are weaker than triple
bonds (N2)
• Bond dissociation energy is the amount of
energy needed to break a covalent bond.
• Breaking bonds always requires the
addition of energy.
• Endothermic reactions occur when a
greater amount of energy is required to
break the existing bonds than is
released when the new bonds form in
the product molecules.
Exothermic reactions occur when more
energy is released forming new bonds
than is required to break the bonds in the
initial reaction.
9.2 Naming Molecules
• Naming Binary Compounds
• 1. The first element in the formula is always named
first.
• 2. The second element is named using the root of the
element and adding the suffix -ide.
• 3. Prefixes are used to indicate the number of atoms
of each type that are present in the compound.
• Note: One exception is that the first element never
uses the prefix mono- CO is carbon monoxide, not
mono carbon monoxide.
Common Names:
Naming Acids
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An acid is a compound that produces
hydrogen ion (H+) in solution.
Naming Binary Acids
Binary acid- contains hydrogen and one
other element e.g. HCl (hydrochloric acid)
1. Use the prefix hydro- to name the
hydrogen portion of the compound.
2. Use the root of the second element plus
the suffix -ic. e.g. HCl would be hydrochloric
acid.
Try These
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HBr
HF
H2S
HI
Try These
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HBr - hydrobromic acid
HF - hydrofluoric acid
H2S - hydrosulfuric acid
HI
- hydroiodic acid
Naming Acids
• Note: If the acid contains a polyatomic ion
that does not contain oxygen, the acid is
named the same way as a binary acid except
the root for the second part of the name is
the root of the polyatomic ion
• e.g. HCN, which is composed of hydrogen
and the polyatomic ion cyanide, would be
named hydrocyanic acid .
Naming Acids
• Naming oxyacids
• oxyacid- an acid that contains an
oxyanion (poly atomic ion that contains
oxygen).
Naming Oxyacid
• 1. Identify the anion present.
• 2. The name of the oxyacid consists of a form of the
root of the anion, a suffix, and the word acid.
• 3. If the anion suffix is -ate, it is replaced with the
suffix -ic. If the anion ends in -ite, it is replaced with
the suffix -ous.
• EX: The oxyacid HNO3 has nitrate (NO3-) as its
oxyanion. Following the rule it would be named nitric
acid.
• EX: The oxyacid HNO2 has nitrite (NO2-) as its
oxyanion. Following the rule it would be named
nitrous acid.
Try these acids
• HNO3
• HNO2
• H2CO3
• H2SO4
• H2SO3
Try these acids
• HNO3
• HNO2
- nitric acid
- nitrous acid
• H2CO3
- carbonic acid
• H2SO4
• H2SO3
- sulfuric acid
- sulfurous acid
Naming Acids Hints
• Ic I ate an oxyacid,It was dangerous, but
I’m ite
Naming Acids Hints
• Do not use prefixes (mono, di, tri etc)
• The most common polyatomic ions are the
ones that end in ate. They contain 3 or 4
oxygens. If the first letter of the (ate)
polyatomic ion begins with A-O it contains
3 oxygens, if the first letter of the (ate)
polyatomic ion begins with P-Z it contains
4 oxygens. E.g NO3, ClO3, CO3; PO4, SO4.
Naming Acids Hints
• The ite polyatomic ions have one less
oxygen than their ate counterparts. e.g.
ClO3 is chlorate and CLO2 is chorite, NO3
is Nitrate and NO2 is nitrite, PO4 is
phosphate, PO3 is phosphite, SO4 is
sulphate, SO3 is sulphite
Acid Naming Game
• Rules.
1. Roll one die and combine with hydrogen
to get acid.
2. Write correct formula and name of acid.
3. Other players will check for correctness.
1st player to get 3 acids correctly wins.
Dot Diagrams For Molecules
and Polyatomic Ions
Step 1- Sum the valence electrons for all
atoms in the molecule. (Use Periodic
Table)
• For Anions - Add an electron for each
negative charge.
• For Cations – Subtract an electron for
each positive charge.
• Step 2 – Write the symbols for the
atoms to show which atoms are
attached to which, and connect them
with a single bond.
– Single bond – represents 2 electrons
• Step 3 – Complete the octets of the
atoms bonded to the central atom (
hydrogen can have only 2 electrons).
• Step 4 - Place any leftover electrons on
the central atom, even if doing so
results in more than an octet.
• Step 5 – If there are not enough
electrons to give the central atom an
octet, try multiple bonds.
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Dot Diagrams For Molecules and Polyatomic Ions
Step 1- Sum the valence electrons for all atoms in the molecule. (Use
Periodic Table)
For Anions - Add an electron for each
negative
charge.
For Cations – Subtract an electron for
each positive
charge.
Step 2 – Write the symbols for the atoms to show which atoms are
attached to which, and connect them with a single bond.
– Single bond – represents 2 electrons
Step 3 – Complete the octets of the atoms bonded to the central atom (
hydrogen can have only 2 electrons).
Step 4 - Place any leftover electrons on the central atom, even if doing
so results in more than an octet.
Step 5 – If there are not enough electrons to give the central atom an
octet, try multiple bonds.
9.4 Molecular Shape
VSEPR Model- Valence Shell Electron Pair Repulsion model
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– Linear
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– Trigonal planer
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– Tetrahedral
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– Bent
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– Pyramid
Polar Covalent Bonds
• If a covalent bond formed between atoms
of different elements does not have equal
sharing of electron pairs, it is said to be
polar covalent.
• When a polar bond forms, the shared pair
of electrons is pulled towards one of the
atoms and a partial charge forms at the
end of the atom.
Polar Covalent Bonds
Polar Covalent Bonds
Molecular Shape
• VSEPR Model- Valence Shell Electron
Pair Repulsion model
• Many chemical reactions, depend on
the ability of two compounds to come
in contact with each other.
• The shape of a molecule determines
whether or not molecules can get close
enough to react.
•
Linear
Trigonal planer
Tetrahedral
Bent
Pyramid
• The repulsions among electron pairs
results in atoms exhisting at fixed angles
to each other.
• The angle formed between two terminal
atoms and the central atom is the Bond
Angle
Molecules that contain no lone
pairs
• When two pairs are shared off the central
atom the bond angle is 180o and the
shape is linear (BaCl2)
Molecules that contain no lone
pairs
• Three bonding pairs will seek the
maximum separation forming a bond angle
of 120O (AlCl3) and the shape is trigonal
planer.
Molecules that contain no lone
pairs
• When the central atom has four bonding
pairs (CH4) the shape is tetrahedral with
bond angles of 107.3O
Molecules with lone pairs
• Lone pairs take up a greater amount of
space than shared pairs. The geometry of
PH3 is trigonal pyramidal
Molecules with lone pairs
• A water molecule has two single covalent
bonds. And two lone pairs. The water
molecule has a bent shape with a bond
angle of 104.5O
Bonding
Bonding
Bonding
Bonding
1. If the electronegativity difference (usually called ΔEN) is less than 0.5, then the
bond is nonpolar covalent.
2. If the ΔEN is between 0.5 and 1.6, the bond is considered polar covalent
3. If the ΔEN is greater than 1.6, then the bond is ionic.
Use the electronegativity
difference ΔEN to
• Predict the type of bond that forms
between.
• K and O
H and F
• H and O
Fr and F
• Mg and N
N and O
• Mn and Cl
Al and Cl
• Pb and O
C and I
Solubility of Polar Molecules
Surficant
Properties of Covalent Compounds
Intermolecular forces (van der Waals forces)
Properties of covalent bonds
• Molecules are either polar or non polar
one way to distinguish between polar
and non polar is that non polar
molecules are not attracted to an
electrical field
Solubility of Polar Molecules
• Like dissolves like
• Non polar molecules are only soluble in
non polar substances.
• Polar and ionic substances are usually
soluble in polar substances
• oil and water don’t mix, why?
Intermolecular forces
• The weak forces of
attraction between
molecules are called
intermolecular forces
(van der Waals).
These forces are
much weaker than
the forces holding the
molecule together.
Intermolecular forces
• Many properties of
molecules are due to
intermolecular forces.
• Low melting and boiling
points
• Hardness- many covalent
compounds are relatively
soft when in solid form e.g.
paraffin wax.
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