UNIT 6 -
CHEMICAL BONDING
INTRODUCTION
TO CHEMICAL BONDING
I. Types of Chemical Bonding
A. ____________________: mutual electrical attraction
between the nuclei and valence e- of different atoms
that binds the atoms together
B. Why do atoms bond together?
1. Atoms by themselves have
_______ potential energy
2. Want to have _______ P.E.
(this is what happens in nature)
3. Atoms are ______ stable
alone than combined with other atoms
C. Electrons are ____________________ during bonding
D. Types of chemical bonding
1. ____________________:
results from attraction between large numbers of cations and anions; involves
the transfer of electrons
a.
____________________: positive ion; atom that has lost e-
b.
____________________: negative ion; atom that has gained e-
2. ____________________:
results from sharing of e- pairs
between two atoms
E. Determining Ionic or Covalent Bond (Official Way)
1. Remember
__________________________________? (how much an atom wants to gain an e-)
2. Difference in EN tells
whether bond is ionic or covalent
a. EN
difference ____________________ (50% or less ionic character) = COVALENT
1. _______________COVALENT: EN difference ______ to
______ (5 - 50% ionic character)
2. _______________ COVALENT: EN difference ______ to ______
(< 5% ionic character)
b. EN
difference greater than ______ (> than 50% ionic character) = IONIC
F. Determining Ionic or Covalent Bond (Easy Way)
1. ____________________: metal
& nonmetal in formula
2. ____________________: 2 or
more nonmetals
a.
____________________: 2 different nonmetals
b.
____________________: 2 of the same
nonmetal
COVALENT BONDING AND MOLECULAR COMPOUNDS
I. Molecules & Molecular Formulas
A. ____________________: neutral group of atoms held
together by covalent bonds
B. _________________Molecule: molecule that
contains only two atoms (of the same element)
--> there are only 7
of them; they are
II.
Formation of a Covalent Bond
A. 2 separate atoms far enough away
____________________________________________ on each other
B. As they move ______________, the _______________ (+
chrg.) attracts the ______________ from the
other atom & vice versa
(________________ P.E.)
C. When atoms get too close, the + chrgs. in nucleus
repel each other; + chrgs. from other nucleus & e-
repel each other also
(increase in P.E.)
III.
Characteristics of the Covalent Bond
A. ____________________: distance between 2
bonded atoms at their minimum P.E.
1. In other words, avg.
distance between 2 bonded atoms
2. Measured in _______________
(pm) = 1 x 10- m
B. Amt. of energy released when a bond is formed is
______________ to the difference in P.E. from separate
atoms to the minimum P.E.
C. Same amt. of energy must be added to
_________________________________
D. _____________________________: energy required to
break a chemical bond & form isolated atoms
1. measured in _______________
2. kJ = _________ J (J =
Joule, measure of energy)
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LEWIS
STRUCTURES:
formulas which symbols represent nucleus & inner shell electrons; dot
pairs or dashes represent electron pairs in covalent bonds
1. ______________________________: (lone pair) pair of
electrons that is not involved in bonding &
belongs to only one atom
2. _______________________________: shows atoms, bonds,
& arrangement, but not lone pairs of e-
3. _______________________________: produced when one pair
of e- is shared b/n two atoms
4. MULTIPLE BONDS: stronger & shorter than
single bonds
a. Double Bond:
produced when ______ pairs of e- are shared b/n two atoms
1) shown by
either 2 side-by-side pairs of dots
2) or by 2
parallel dashes
b. _______________ Bond:
produced when 3 pairs of e- are shared b/n two atoms
1) shown by
either 3 side-by-side pairs of dots
2) or by 3 parallel
dashes
STEPS
FOR DRAWING LEWIS STRUCTURES
1.
Count the total number of valence electrons in the compound.
EXAMPLE: CCl4
C: 1 x 4 e- = 4
Cl: 4 x 7 e- = 28
32
2.
Draw the symbols for the elements with the central atom in the middle.
(The central atom is the one that is written first,
except hydrogen will never be central.)
3.
Connect the surrounding atoms to the central atom with a pair of electrons.
Had
32 e- to start (step 1)
Used 8 e- to
connect
Have 24 e- left
4.
Put electrons around surrounding atoms until all have 8 electrons around them.
(Exception: Hydrogen will only have 2 e- around
it.)
Have 24 e- left
Used 24 e- to complete surrounding
Have 0 e- left to use
5. If
there are any electrons left over, put them on the central atom.
6.
Check to make sure that all atoms have 8 electrons around them.
7. If
there are not enough electrons to give all atoms 8 electrons around them, try
multiple
bonds.
VSEPR THEORY
VSEPR Theory: (Valence Shell Electron
Pair Repulsion)
valence electrons in an atom will orient themselves to be as far apart as
possible
* CLASSES OF MOLECULES
A
= central atom
B = surrounding atoms
E = unshared electron pairs on central
atom
*** subscript tells how many of each you have ***
EXAMPLE
1: CH4 
1 central atom, 4 surrounding atoms, no unshared e- prs. on
central atom
CLASS = AB4
EXAMPLE
2: NH3 
1 central atom, 3 surrounding atoms, 1 unshared e- pr. on
central atom
CLASS = AB3E
* SHAPES OF MOLECULES
CLASS
SHAPE
AB2
linear
AB2E
bent
AB2E2
bent
AB3
trigonal planar
AB3E
trigonal pyramid
AB4
tetrahedral
MOLECULAR POLARITY vs.
BOND POLARITY
BOND POLARITY
~ refers to the equal (______________) or unequal (______________)
sharing of electrons
~ What makes a bond polar (covalent)?
* If the bond
occurs between two _____________________ nonmetals
MOLECULAR POLARITY
~ refers to the symmetry (______________) or asymmetry
(______________) of a molecule
~ What makes a molecule asymmetrical?
* If there are
______________________________________ around the central atom.
and/or
* If the
surrounding atoms are different ____________________________________
POLAR MOLECULE WITH POLAR
COVALENT BONDS
unshared
e- pair on central atom makes the molecule polar
bond
is between 2 different nonmetals – so bond is polar covalent
NONPOLAR MOLECULE
WITH POLAR COVALENT BONDS
no
unshared e- pairs on central atom
bond is between 2
AND surrounding atoms are same different nonmetals, so bond
element, so molecule is NONPOLAR. is polar covalent
Special Cases Regarding Molecular Polarity:
~ When there are only 2 atoms in the compound or ion…
*
examples: F2 or HF
*
POLARITY OF MOLECULES (symmetry of molecules) – different from bond polarity
A MOLECULE
is nonpolar if...
- there are no unshared e- pairs around the central atom
AND
- the surrounding atoms are all the same element
A BOND is nonpolar (covalent) if…
- it occurs between two atoms of the
same element
IT IS POSSIBLE, EVEN LIKELY, THAT A NONPOLAR
MOLECULE HAS POLAR COVALENT BONDS!
Ionic
Bonding & Ionic Compounds
A. ____________________: composed of + and - ions
whose charges cancel each other
out; electrons are
_______________
1. Most exist as
____________________
2. __________ network of + and
- ions; not composed of individual uunits
B. Formation of Ionic Compounds
. .
1. Na .
+ : Cl : -->
.
2. Characteristics
of Ionic Bonding
a.
minimize P.E. by organizing into _______________
b.
____________________: energy released when 1 mole of ionic crystalline cmpd.
is formed from gaseous ions
IONIC
VS. COVALENT (MOLECULAR) COMPOUNDS
Ionic
Compounds
Covalent (Molecular) Compounds
~ formed by transferring
electrons
~ formed by sharing electrons
~ occurs between positive and
negative
~ occurs between nonmetals
ions (metal & nonmetal or metal &
polyatomic ion)
~ smallest unit = "formula
unit"
~ smallest unit = "molecule"
~ exist as solids, usually crystal
shape
~ exist as liquids, gases, or non-crystal
solids
~ have high melting
points
~ have low melting points
~ most dissolve in
water
~ few dissolve in water
~ melted or dissolved in water
conduct
~ melted or dissolved in water does not
electricity
conduct electricity
~ fixed + and - parts; anions &
cations
~ may have slightly + and - parts or
totally neutral
~ EXAMPLES: KCl, NaF, KNO3
~ EXAMPLES: NH3, CO2, CH4
Polyatomic Ions
1. ____________________: charged group of covalently
bonded atoms
2. Combine with ions of _______________ charge to form
ionic compounds
3. Compounds with polyatomic ions have
____________________________ bonding
4. Lewis Structures
a. Negatively charged
polyatomic ion = _____ e- to total number of valence e- for cmpd
b. Positively charged
polyatomic ion = ________ e- from total # of valence e- for cmpd
-------------------------------------------------------------------------------------------------------------------------------------------INTERMOLECULAR
(IM) FORCES
*without them, all matter would be gases*
intermolecular
forces:
forces of attraction between molecules
4
TYPES OF IM FORCES (in order from strongest to weakest)
1.
HYDROGEN "BONDING"
* occurs between molecules that have
hydrogen & nitrogen, hydrogen & oxygen, and
hydrogen &
fluorine
* accounts for the unusually high
boiling point of NH3, H2O, and HF
2.
DIPOLE-DIPOLE FORCES
* occurs between polar molecules
(dipoles)
* the slightly positive end of one
polar molecule is attracted to the slightly negative end
of another polar
molecule
3.
DIPOLE-INDUCED DIPOLE FORCES
* occurs between a polar molecule
(dipole) and a nonpolar molecule or between a polar
molecule and a
noble gas
* the slightly positive end of a
polar molecule temporarily attracts the electrons from a
nonpolar molecule
or noble gas
4.
LONDON DISPERSION FORCES
* occurs between all molecules
* only force that acts between
nonpolar molecules and noble gases
* moving electrons (in electron
cloud of an atom) temporarily attract the electrons from
another atom
** COVALENT BONDING IS STRONGER THAN ANY OF
THESE IM FORCES. **