covalent bonding covalent bond: a chemical bond formed when two atoms share electrons

Covalent bondingCovalent bond: A chemical bond formed when two atoms share electrons.


Co means “together, joint, jointly.”



Double bond: When two pairs of electrons are shared between atoms.



Double bond: When two pairs of electrons are shared between atoms.

Molecular compounds: Molecules formed through covalent bonding.

Electron dot diagram

C O H NF


C O H NF

Review: What number of valence electrons do atoms want in order to be stable?


C O H NF

Review: What number of valence electrons do atoms want in order to be stable?

Answer: 0 or 8


C O H N F

Atoms want 0 or 8 valence electrons to be stable.

However, there are two exceptions: hydrogen and helium. They are stable when their inner shell of 2 is filled.

Atoms want 0 or 8 valence electrons to be stable. However, there are two exceptions: hydrogen and helium. They are stable when their inner shell of 2 is filled.

Helium

Helium

Thus hydrogen only needs one more valence electron to be stable. Helium is already stable.

F

Examples of covalent bonds/molecular compounds


F F

F2


F F O

F2


F F O HHF2


F F O HH

Water moleculeH20

F2


O


O O


O OOxygen molecule O2

(double bond)


O OOxygen molecule H20(double bond)

H3N



NH3N



N HH3N

H

H


C02


C02 C


OC02 C


OC02 C O


OC02 C O

double bond


NN2


NN2 N


NN2

triple bond(this is the maximum numberof bonds possible)

N

More aboutmolecular compounds

• Atoms in molecular compounds do not have strong plus-minus charges.

• Thus less heat is needed to melt or boil molecular solids.

• Salt (an ionic compound) melts at 801° C. Sugar (a molecular compound) melts at 185° C.

• Because electrons do not move between the atoms, molecular compounds do not conduct electricity well.

• Because electrons do not move between the atoms, molecular compounds do not conduct electricity well.

• This includes compounds such as rubber and water, which do not conduct electricity.

Polar molecular compounds• Some atoms pull more strongly on the shared electrons than other atoms do.


• As a result, the valence electrons move closer to the stronger atoms.


• As a result, the valence electrons move closer to the stronger atoms.

• Since electrons have a negative charge, the strong atom will now have a slightly negative charge, and the weaker atom a slightly positive charge.

Nonpolar bond

F F

Equal pull

Polar bond

H F

Unequal pull

+ -

Water is a polar bond

Electrons are

pulled toward

the oxygen

atom.

Water is a polar bond

Electrons are

pulled toward

the oxygen

atom.

This causes cohesion: The attraction that occurs between particles of the same substance.

Can you think of examples of water’s cohesion (holding together)?


Water droplets


Surface tension


Water transport in plants

http://www.youtube.com/watch?v=CT4pURpXkbY




Why don’t oil and water mix?

Why don’t oil and water mix?• The polar water molecules are attracted more

strongly to each other than they are to the nonpolar oil molecules.

Why don’t oil and water mix?• The polar water molecules are attracted more

strongly to each other than they are to the nonpolar oil molecules.

• Soap molecules are polar on one end and nonpolar on the other.

covalent bonding covalent bond: a chemical bond formed when two atoms share electrons

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