COVALENT COVALENT BONDINGBONDING

--formed from the sharing formed from the sharing of pairs of electrons of pairs of electrons between atoms of non-between atoms of non-metallic elementsmetallic elements

- Sharing of electrons - Sharing of electrons occurred to satisfy the occurred to satisfy the octet requirements of the octet requirements of the atomsatoms

In covalent bonds, electrons In covalent bonds, electrons are shared between are shared between

electronegative elements.electronegative elements.

Carbon-carbon covalent Carbon-carbon covalent bondingbonding

PROPERTIES OF PROPERTIES OF COVALENT COMPOUNDSCOVALENT COMPOUNDS

LOW MELTING POINTLOW MELTING POINT – few – few substances have melting substances have melting points which exceeds 300points which exceeds 300ooC.C.

- At room temperature, At room temperature, covalent compounds can exist covalent compounds can exist as a solid, liquid or gas.as a solid, liquid or gas.

- Indicates weak attractive Indicates weak attractive force between the moleculesforce between the molecules

SOFT SOLIDSSOFT SOLIDS – covalent – covalent compound solids are soft at compound solids are soft at room temperatureroom temperature

ELECTRICAL CONDUCTIVITYELECTRICAL CONDUCTIVITY – whether solid, liquid or gas, – whether solid, liquid or gas, covalent compounds are non-covalent compounds are non-conductors of electricityconductors of electricity

MOLECULAR COVALENT MOLECULAR COVALENT ELEMENTSELEMENTS

DIATOMIC MOLECULESDIATOMIC MOLECULES – –

Fluorine – FFluorine – F22 Chlorine – ClChlorine – Cl22

Bromine – BrBromine – Br22 Iodine – IIodine – I22

Hydrogen – HHydrogen – H22 Oxygen – OOxygen – O22

Nitrogen – NNitrogen – N22

OTHERSOTHERS – –

Phosphorus – PPhosphorus – P4 4 Sulfur – SSulfur – S88

NOBLE GASESNOBLE GASES – exists as – exists as neutral atoms neutral atoms NOTNOT molecules molecules

He, Ne, Ar, Kr, Xe and Rn He, Ne, Ar, Kr, Xe and Rn atomsatoms

STEPS IN DRAWING LEWIS DOT STEPS IN DRAWING LEWIS DOT STRUCTURE OF COVALENT STRUCTURE OF COVALENT

COMPOUNDSCOMPOUNDSDraw the Lewis dot structure of HDraw the Lewis dot structure of H22O.O.1. Determine the central atom – The central atom 1. Determine the central atom – The central atom

requires the greatest number of electrons. The requires the greatest number of electrons. The other atoms are called the side atoms.other atoms are called the side atoms.

Number Number of of

valence valence ee--

Number of e- Number of e- needed to needed to satisfy the satisfy the

octetoctet

HH 11 11

OO 66 22

Side atom

Central atom

2. Place the central atom in 2. Place the central atom in the middle and surround it the middle and surround it with the side atoms.with the side atoms.

OH H

3. Determine the total number of 3. Determine the total number of valence electrons needed to satisfy valence electrons needed to satisfy the octet.the octet.

2 2 H atoms x H atoms x 2 e-2 e- / H atoms = / H atoms = 4 e-4 e-

1 1 O atom x O atom x 8 e-8 e- / O atom = + / O atom = + 8 e-8 e-

e- needed for octete- needed for octet 12 12 e-e-

EXCEPTIONS TO OCTET EXCEPTIONS TO OCTET RULERULE

ELEMENTELEMENT VALENCE e- VALENCE e- REQUIREMENREQUIREMEN

TT

HYDROGENHYDROGEN 22BORONBORON 66

PHOSPHORPHOSPHORUSUS

1010

4. Determine the total number of 4. Determine the total number of valence atoms available.valence atoms available.

2 2 HH atoms x atoms x 11 e- / e- / H atoms = H atoms = 22 e-e-

1 1 O atoms x O atoms x 66 e- / O atom = e- / O atom = 6 e-6 e-

e- available 8 e-e- available 8 e-

5. Subtract the total number of 5. Subtract the total number of valence electrons available from valence electrons available from the total number of valence the total number of valence electrons needed to determine electrons needed to determine the number of electrons that the number of electrons that must be shared. must be shared.

e- needed for octet = e- needed for octet = 12 e- 12 e-

e- available e- available = = - - 8 e-8 e-

e- that must be shared 4 e-e- that must be shared 4 e-

6. Place the number of 6. Place the number of shared e-shared e- around the around the central atom. Distribute central atom. Distribute the remaining the remaining electronselectrons..

OH HX X