Transcript Chemical Bonding

Chemical Bonding
Chemical Bond
• The forces that hold groups of atoms together and
make them function as a unit
• Bonding involves only the valence electrons
• There are 2 types of bonds:
– Ionic: Transfer of electrons from a metal and to a nonmetal
– Covalent: Sharing of electrons between 2 nonmetals
– Note: When 2 metals bond an alloy is formed
• Electrons are transferred or shared to give each atom
a noble gas configuration (stable octet)
– This is known as the octet rule
Lewis Diagrams
• Valence electrons involved in bonding can
be represented by Lewis dot diagrams
• A chemical symbol represents the nucleus
and the core electrons (not involved in
bonding).
• Dots around the symbol represent valence
electrons.
Drawing Lewis Diagrams
Cl
1. Write the element symbol.
2. Draw dots, one for each valence
electron
3. Dots should be spread over 4 sides
•
It does not matter what side the dots are
placed, but do not start to pair dots until there
is one on each side
The number of valence electrons is equal to
the group number. With one exception.
• Lewis diagrams for the first 20 elements
Ionic Bonding
Ionic Bonding
• Metals
– Electron donors
– Donate their valence electrons to become a
positive ion (cation)
• Nonmetals
– Electron acceptors
– Accept valence electrons to become a negative
ion (anion)
Ionic Bonding
Ionic Bonding
The two oppositely charged
ions are attracted to each
other by a force called an
ionic bond
Monatomic
Cations
H+
Li+
Na+
K+
Mg2+
Ca2+
Ba2+
Al3+
Name
Hydrogen
Lithium
Sodium
Potassium
Magnesium
Calcium
Barium
Aluminum
Monatomic
Anions
F-
Name
Fluoride
Cl-
Chloride
Br-
Bromide
I-
Iodide
O2-
Oxide
S2-
Sulfide
N3-
Nitride
P3-
Phosphide
Properties of Ionic
Compounds
Structure:
Crystalline solids
Melting point:
Generally high
Boiling Point:
Generally high
Electrical
Conductivity:
Solubility in
water:
Excellent conductors,
molten and aqueous
Generally soluble
NaCl Crystal Lattice
Ionic compounds form solids
at SATP.
Ionic compounds organize in
a characteristic crystal
lattice of alternating positive
and negative ions.
All lattices are arranged so
that each ion has the
greatest possible number of
oppositely charged ions close
by, while keeping similarly
charged ions as far away as
possible
Representing Ionic Compounds
Lewis Diagrams
• Formation of sodium chloride:

]


 Na+ [ Cl

Cl

Na  +



Lewis Structures for Ionic
Compounds
• O•
••
2+ ••
Ba
O
••
2-
••
Ba•
••
••
Ba and O
•
BaO
••
••
••
2 Cl
• Cl
••
MgCl2
••
-
••
Mg
••
••
Mg •
2+
••
Mg and Cl
•
• Cl
••
Covalent Bonding
Covalent Bonding
• Electrons are shared
between two nonmetals
• Weaker attractive force
than ionic bonding
Properties of Molecular
Compounds
State at SATP
Structure
Typically gases & liquids,
but some solids
Variable (waxy to brittle)
Melting & Boiling Points Low
Electrical Conductivity
Nonelectrolyte
Solubility in Water
Variable (low to high)
Confused?? Don’t worry…more answers to come
Covalent Bonding
Lone pairs, valence electrons
not involved in covalent bond
• Formation of hydrogen chloride:
H Cl






Cl

H +


 H - Cl



Covalent bond, shared electrons
Structural Formula: H-Cl
(lone pairs are not drawn)
Lewis Structures
H  +  H  H H or H H




Cl
Cl
 
Structural Formula: Cl-Cl

or

Cl
Cl






Cl
+
Cl



Cl2:




H2:
Double and Triple Bonds
• Atoms can share 4 electrons to form a double bond or 6
electrons to form a triple bond.


N 2:
N N

O
=O



O 2:
• The number of shared electron pairs (covalent
bonds) that an atom can form is the
bonding capacity.
Multiple Covalent Bonds
•
•
••
••
N N
•
•
•
N N
••
••
•
N N
••
•
••
•N
•
N•
••
•
••
•
Multiple Covalent Bonds
•O
••
••
•
•
•
••
•
••
••
O C O
•
•
•
••
•
••
O C O
••
• C•
•
••
••
O•
•
••
••
••
••
O C O
••
•
••
•
Drawing Lewis Structures
1. Arrange the element symbols.
•
Central atoms are generally those with the highest bonding capacity.
•
Carbon atoms are always central atoms
•
Hydrogen atoms are always peripheral atoms
2. Add up the number of valence electrons from all atoms.
•
For polyatomic ions, add one electron for each negative charge and
subtract one for each positive charge.
3. Draw a skeleton structure with atoms attached by single
bonds.
4. Complete the octets of peripheral atoms.
5. Place extra electrons on the central atom.
6. If the central atom doesn’t have an octet, try forming
multiple bonds by moving lone pairs.