CHEMICAL BONDING

1
Chemical Bonds
2
CHEMICAL BONDING

• Cocaine

3
Electron Shells

• Atomic number number of Protons in the Nucleus
• Which also happens to be the number of Electrons
• Electrons vary in the amount of energy they
  possess and they occur at certain energy levels
  or electron shells.
• Electron shells determine how an atom behaves
  when it encounters other atoms

4
Electrons are placed in shells according to rules

• The 1st shell (orbital) can hold up to 2
  electrons and each shell thereafter can hold 8
  electrons

5

• Octet Rule atoms tend to gain, loose or share
  electrons as to have 8 electrons
• C would like to Gain 4 electrons
• N would like to Gain 3 electrons
• O would like to Gain 2 electrons

6
(No Transcript)
7
Electron Dot Structures
Symbols of atoms with dots to represent the
valence-shell electrons 1 2 13
14 15 16 17
18 H? He ?
? ? ? ?
? ? ? ? ? ? Li? Be?
? B ? ? C ? ? N ? ? O ?
F ? Ne
? ?
? ? ? ? ? ?
? ? ? ?
? ? ? ? ? ?
? Na? Mg? ? Al? ? Si ? ?P?
?S? Cl ? Ar
? ?
? ? ? ? ? ?
8
Learning Check
? A. X would be the
electron dot formula for 1) Na 2) K 3)
Al ? ? B. ? X ? would be the
electron dot formula ? 1)
B 2) N 3) P
9
Forms of Chemical Bonds

• There are 2 extreme forms of connecting or
  bonding atoms
• Ioniccomplete transfer of 1 or more electrons
  from one atom to another
• Covalentsome valence electrons shared between
  atoms
• Most bonds are somewhere in between.

10
Formation of Ions from Metals

• Ionic compounds result when metals react with
  nonmetals
• Metals lose electrons to match the number of
  valence electrons of their nearest noble gas
• Positive ions form when the number of electrons
  are less than the number of protons
• Group 1 metals ?? ion 1
• Group 2 metals ?? ion 2
• Group 13 metals ?? ion 3

11
Formation of Sodium Ion

• Sodium atom Sodium
  ion
• Na ? e? ??? Na
• 2-8-1 2-8 ( Ne)
• 11 p 11 p
• 11 e-
  10 e-
• 0
  1

12
Formation of Magnesium Ion

• Magnesium atom Magnesium ion
• ?
• Mg ? 2e? ?? Mg2
• 2-8-2 2-8 (Ne)
• 12 p 12 p
• 12 e-
  10 e-
• 0
  2

13
Some Typical Ions with Positive Charges (Cations)
Group 1 Group 2 Group 13 H Mg2 Al3 Li
Ca2 Na Sr2 K Ba2
14
Learning Check
A. Number of valence electrons in aluminum 1)
1 e- 2) 2 e- 3) 3 e- B. Change in
electrons for octet 1) lose 3e- 2)
gain 3 e- 3) gain 5 e- C. Ionic charge
of aluminum 1) 3- 2) 5- 3)
3
15
Solution
A. Number of valence electrons in aluminum 3)
3 e- B. Change in electrons for octet 1)
lose 3e- C. Ionic charge of aluminum 3)
3
16
Learning Check
Give the ionic charge for each of the
following A. 12 p and 10 e- 1) 0 2)
2 3) 2- B. 50p and 46 e- 1) 2 2)
4 3) 4- C. 15 p and 18e- 2) 3 2)
3- 3) 5-
17
Ions from Nonmetal Ions

• In ionic compounds, nonmetals in 15, 16, and 17
  gain electrons from metals
• Nonmetal add electrons to achieve the octet
  arrangement
• Nonmetal ionic charge
• 3-, 2-, or 1-

18
Fluoride Ion
unpaired electron octet ? ?
? ? 1 - F ? e? F
? ? ? ? 9
p 9 p 9 e- 10 e- 0
1 - ionic charge
19
Ionic Bonds

• Complete electron transfer from an element
  (metal) to an element of high affinity for
  electrons (nonmetal)
• 2 Na(s) Cl2(g) ---gt 2 Na 2 Cl-
• Ionic compounds exist primarily between metals at
  left of periodic table and nonmetals at right

20
Ionic Bonds

• Between atoms of metals and nonmetals with very
  different electronegativity
• Bond formed by transfer of electrons
• Produce charged ions. Conductors and have high
  melting point.
• Examples NaCl, CaCl2, K2O

21
Ionic Bonds One Big Greedy Thief Dog!
22
1). Ionic bond electron from Na is transferred
to Cl, this causes a charge imbalance in each
atom. The Na becomes (Na) and the Cl becomes
(Cl-), charged particles or ions.
23
Covalent Bonding

• The bond arises from the mutual attraction of 2
  nuclei for the same electrons. Electron sharing
  results. (Screen 9.5)

Bond is a balance of attractive and repulsive
forces.
24
Covalent Bond

• Between nonmetallic elements of similar
  electronegativity.
• Formed by sharing electron pairs
• Stable non-ionizing particles, they are not
  conductors at any state
• Examples O2, CO2, C2H6, H2O

25
2. Covalent bonds - Two atoms share one or more
pairs of outer-shell electrons.
Oxygen Atom
Oxygen Atom
Oxygen Molecule (O2)
26
Electron Distribution in Molecules

• Electron distribution is depicted with Lewis
  electron dot structures
• Valence electrons are distributed as shared or
  BOND PAIRS and unshared or LONE PAIRS.

27
Bond and Lone Pairs

• Valence electrons are distributed as shared or
  BOND PAIRS and unshared or LONE PAIRS.

This is called a LEWIS ELECTRON DOT structure.
28
Bond Formation

• A bond can result from a head-to-head overlap
  of atomic orbitals on neighboring atoms.

Note that each atom has a single, unpaired
electron.
29
Valence Electrons

• Electrons are divided between core and valence
  electrons

30
Rules of the Game

• of valence electrons of a main group atom
  Group number

31
Building a Dot Structure

• Ammonia, NH3
• 1. Decide on the central atom (the atom with
  lowest electron affinity) never H.
• Hydrogen atoms are always terminal.
• Therefore, N is central
• - Generally Symmetrical
• 2. Count valence electrons
• H 1 and N 5
• Total (3 x 1) 5
• 8 electrons 4 pairs

32
Building a Dot Structure

• 3. Form a single bond between the central atom
  and each surrounding atom

4. Remaining electrons form LONE PAIRS to
complete octet as needed.
3 BOND PAIRS and 1 LONE PAIR.
Note that N has a share in 4 pairs (8 electrons),
while H shares 1 pair.
33
Sulfite ion, SO32-

• Step 1. Central atom S
• Step 2. Count valence electrons S 6
• 3 x O 3 x 6 18
• Negative charge 2
• TOTAL 26 e- or 13 pairs
• Step 3. Form bonds

10 pairs of electrons are now left.
34
Sulfite ion, SO32-

• Remaining pairs become lone pairs, first on
  outside atoms and then on central atom.

Each atom is surrounded by an octet of electrons.
35
Carbon Dioxide, CO2

• 1. Central atom _______
• 2. Valence electrons __ or __ pairs
• 3. Form bonds.

This leaves 6 pairs.
4. Place lone pairs on outer atoms.
36
Carbon Dioxide, CO2

• 4. Place lone pairs on outer atoms.

5. So that C has an octet, we shall form DOUBLE
BONDS between C and O.
37
Double and even triple bonds are commonly
observed for C, N, P, O, and S
H2CO
SO3
C2F4
38
Urea, (NH2)2CO
39
Urea, (NH2)2CO

• 1. Number of valence electrons 24 e-
• 2. Draw single bonds.

40
Urea, (NH2)2CO

• 3. Place remaining electron pairs in the
  molecule.

41
Urea, (NH2)2CO

• 4. Complete C atom octet with double bond.

42
Bond Order of bonds between a pair of atoms
Acrylonitrile
43
Polar Covalent Bonds Unevenly matched, but
willing to share.
44
- water is a polar molecule because oxygen is
more electronegative than hydrogen, and therefore
electrons are pulled closer to oxygen.
45
Bond Polarity

• HCl is POLAR because it has a positive end and a
  negative end.

Cl has a greater share in bonding electrons than
does H.
Cl has slight negative charge (-d) and H has
slight positive charge ( d)
46
Electronegativity, ?

• ? is a measure of the ability of an atom in a
  molecule to attract electrons to itself.

Concept proposed by Linus Pauling 1901-1994
47
Linus Pauling, 1901-1994

• The only person to receive two unshared Nobel
  prizes (for Peace and Chemistry).
• Chemistry areas bonding, electronegativity,
  protein structure

48
ElectronegativityFigure 9.9
49
Molecular Polarity

• Molecules will be polar if
• a) bonds are polar
• AND
• b) the molecule is NOT symmetric

All above are NOT polar
50
Consequences of H2O Polarity
51
Molecular Polarity, BF3
B atom is positive and F atoms are negative.
BF bonds in BF3 are polar.
But molecule is symmetrical and NOT polar
52
Molecular Polarity, HBF2
B atom is positive but H F atoms are negative.
BF and BH bonds in HBF2 are polar. But molecule
is NOT symmetrical and is polar.
53
Is Methane, CH4, Polar?

• Methane is symmetrical and is NOT polar.

54
Is CH3F Polar?
CF bond is very polar. Molecule is not
symmetrical and so is polar.
55
Substituted Ethylene

• CF bonds are MUCH more polar than CH bonds.
• Because both CF bonds are on same side of
  molecule, molecule is POLAR.

56
Substituted Ethylene

• CF bonds are MUCH more polar than CH bonds.
• Because both CF bonds are on opposing ends of
  molecule, molecule is NOT POLAR.

57
Metallic Bond
- Bonds found in metals, which hold metal atoms
together very strongly.
58
Metallic Bond

• Formed between atoms of metallic elements
• Electron cloud around atoms
• Good conductors at all states, lustrous, very
  high melting points
• Examples Na, Fe, Al, Au, Co

59
Metallic Bonds Mellow dogs with plenty of bones
to go around.
60
Ionic Bond, A Sea of Electrons
61
Metals Form Alloys

• Metals do not combine with metals.
• They form Alloys which is a solution of a metal
  in a metal.
• Examples are steel, brass, bronze and pewter.