Covalent bonding
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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

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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


Covalent Bonding

H••H


Covalent Bonding


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.


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.


Covalent Bonding

Do not conduct electricity. They form nonelectrolytes.

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


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)


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


intermolecular bonds

dipole interactions


hydrogen bonds

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


polar covalent bonds

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


polar covalent molecules

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


non-polar covalent bonds


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.


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


hybrid orbital geometries


hybrid orbital geometries


Covalent Bonding

·

·

·

C

·

Outer e- only shown

H + C

1e-

2e-

1H

6C

4e-

Equivalent to:


Covalent Bonding

·

·

·

C

·

H + C

Outer e- only shown


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


Covalent Bonding

H + C Final Structure: Tetrahedral


Covalent Bonding

:

·

·

N

·

H + N

Outer e- only shown


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


Covalent Bonding

H + N Final Structure: Trigonal Pyramidal


Covalent Bonding

:

O :

·

·

H + O

Outer e- only shown


Covalent Bonding

H + O

2 e- at each H

:

H:

:

O

:

H

8 e- at oxygen

all atoms closed shell

Outer e- only shown


Covalent Bonding

H + O Final Structure: Bent


Covalent Bonding

:

: F :

·

H + F

Outer e- only shown


Covalent Bonding

H + F

8 e- at fluorine

all atoms closed shell

:

:

:

F

:

H

2 e- at H

Outer e- only shown


Covalent Bonding

H + F Final Structure: Linear


Covalent Bonding

Patterns for Major Elements:

  • CH4C = 4 bonds; all electrons shared

  • NH3 N = 3 bonds; one lone pair

  • H2OO = 2 bonds; two lone pairs

  • HFF = 1 bond; three lone pairs


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


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


Covalent Bonding

Other Compounds Have Same Pattern:

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

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


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


Covalent Bonding

4 Bonds, each carbon

Two bonds at oxygen

Multiple Bonds

  • C2H4 Valence e-= 12

  • H2CO Valence e- = 12


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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