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Covalent Bonding . Sharing of Electron Pairs: Non-metal with Non-metal Atoms. Covalent Bonding . Compounds that are NOT held together by an electrical attraction, but instead by a sharing of electrons. Occur between nonmetal atoms with electronegativity differences less than 1.67.

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covalent bonding

Covalent Bonding

Sharing of Electron Pairs:

Non-metal with Non-metal Atoms

slide2

Covalent Bonding

  • Compounds that are NOT held together by an electrical attraction, but instead by a sharing of electrons.
  • Occur between nonmetal atoms with electronegativity differences less than 1.67
slide5

Covalent Bonding

A neutral group of atoms joined together by covalent bonds is called a molecule. A compound composed of molecules is called a molecular compound.

The chemical formula for a molecule is called the molecular formula.

slide6

Covalent Bonding

Properties of Molecular Compounds:

  • Composed of two or more nonmetals.
  • Usually gases or liquids at room temperature. But can be found in any physical state at STP.
  • Molecular compounds tend to have lower melting and boiling points than do ionic compounds.
  • Do not conduct electricity. They form nonelectrolytes.in solution.
slide7

Covalent Bonding

Do not conduct electricity. They form nonelectrolytes.

  • Reason: Molecular compounds do not break apart into ions in solutions.
slide8

Covalent Bonding

Molecular compounds tend to have lower melting and boiling points than do ionic compounds.

  • Reason: There are no (or few and weak) bonds holding the molecules together in molecular compounds.

Molecular Compound

(H2O)

Ionic Compound

(NaCl)

slide9

intermolecular bonds

Dispersion forces - caused by motion of electrons (weakest intermolecular force). More electrons = stronger dispersion forces. Diatomic halide molecules are held together by dispersion forces.

gas

gas

liquid

solid

slide10

intermolecular bonds

dipole interactions

slide11

hydrogen bonds

Weak bonds between bonded hydrogen and some electron dense species. (F,O,N)

slide12

polar covalent bonds

Polar bonds have more electrons on one side of the bond than the other. Electrons concentrate around electronegative elements.

slide13

polar covalent molecules

Polar molecules have polar bonds. A molecule with two poles is called a dipole.

slide15

Covalent Bonding

  • Predicting Molecular Geometries & Polarity:
  • Atoms attain an octet (also called noble gas electron configurations) by sharing electrons.
  • The bonds that form from this sharing can be single, double or triple. Triple bonds are shorter and stronger than double bonds, which are shorter and stronger than single bonds.
slide16

Covalent Bonding

  • How Do We Proceed?

Determine total number of valence electrons

Based on usual bond numbers, identify reasonable layout for atoms <VSEPR>

Place bonding electrons between atoms to make usual number of bonds

Place remaining electrons as lone pairs around atoms still lacking an octet

slide19

Covalent Bonding

·

·

·

C

·

Outer e- only shown

H + C

1e-

2e-

1H

6C

4e-

Equivalent to:

slide20

Covalent Bonding

·

·

·

C

·

H + C

Outer e- only shown

slide21

Covalent Bonding

H + C

Positive nuclei

H

2 e- at each H

:

H:

:H

C

:

H

Negative electrons

8 e- at carbon

all atoms closed shell

Outer e- only shown

slide22

Covalent Bonding

H + C Final Structure: Tetrahedral

slide23

Covalent Bonding

:

·

·

N

·

H + N

Outer e- only shown

slide24

Covalent Bonding

H + N

2 e- at each H

:

H:

:H

N

:

H

8 e- at nitrogen

all atoms closed shell

Outer e- only shown

slide25

Covalent Bonding

H + N Final Structure: Trigonal Pyramidal

slide26

Covalent Bonding

:

O :

·

·

H + O

Outer e- only shown

slide27

Covalent Bonding

H + O

2 e- at each H

:

H:

:

O

:

H

8 e- at oxygen

all atoms closed shell

Outer e- only shown

slide28

Covalent Bonding

H + O Final Structure: Bent

slide29

Covalent Bonding

:

: F :

·

H + F

Outer e- only shown

slide30

Covalent Bonding

H + F

8 e- at fluorine

all atoms closed shell

:

:

:

F

:

H

2 e- at H

Outer e- only shown

slide31

Covalent Bonding

H + F Final Structure: Linear

patterns for major elements

Covalent Bonding

Patterns for Major Elements:
  • CH4 C = 4 bonds; all electrons shared
  • NH3 N = 3 bonds; one lone pair
  • H2O O = 2 bonds; two lone pairs
  • HF F = 1 bond; three lone pairs
slide33

Covalent Bonding

Patterns for Major Elements:

4 Bonds

All e-shared

  • Carbon, group IV

3 Bonds

1 Lone Pair

  • Nitrogen, Group V

2 Bonds

2 Lone Pairs

  • Oxygen, Group VI

1 Bond

3 Lone pairs

  • Fluorine, Group VII
other compounds have same pattern

Covalent Bonding

Other Compounds Have Same Pattern:

C = 4 bonds; Cl (like F) = 1 bond

P (like N = 3 bonds; Br (like F) = 1 bond

slide35

Covalent Bonding

Other Compounds Have Same Pattern:

S (like Oxygen) = 2 bonds, 2 lone pairs

C = 4 bonds; O = 2 bonds, 2 lone pairs

multiple bonds

Covalent Bonding

Multiple Bonds
  • Atoms may share more than one pair of electrons
  • a DOUBLE BOND forms when atoms share two pairs of electrons (4 e-)
  • a TRIPLE BOND forms when atoms share three pairs of electrons (6 e-)
  • Total number of bonds per atom unchanged
slide37

Covalent Bonding

4 Bonds, each carbon

Two bonds at oxygen

Multiple Bonds

  • C2H4 Valence e-= 12
  • H2CO Valence e- = 12
slide38

Covalent Bonding

Multiple Bonds

Total valence e-= 16 (Oxygen = 6 e-, each;

Carbon = 4 e-. Four bonds/C; 2 bonds oxygen

Total valence e- = 10 (H = 1, C = 4, N = 5)

Bonds: C = 4, N = 3, H = 1

Total valence e- = 18 (O = 6, Cl = 7, P = 5)

Bonds: Cl = 1, P = 3, O = 2

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