chapter 4 chemical bonding

Topics: Chemical bond, Chemical bonding, Ion Pages: 9 (790 words) Published: August 23, 2014
1.1

INTRODUCTION



Chemical bonding – the force of attraction between the two atoms



Valence electron – the outer most shell electrons



There are three types of chemical bonding
i.

Ionic bond: ________________________________________

ii.

Covalent bond: _____________________________________

iii.

Dative Covalent bond: _______________________________

1.1.1 LEWIS DOT SYMBOL




A shorthand to represent the valence electron of an atom.
The element symbol surrounded by dots that represent the valence electrons. The Lewis structures for the certain elements in the second periods of the periodic table are shown below.



Lewis structures can also be used to show bonding between atoms. o The bonding electrons are placed between the atoms and can be represented by a pair of dots or a dash (each dash represents one pair of electrons, or one bond).

Eg: Lewis structures for H2 and O2.

1

FGS 0064 Chemistry I
Center for Foundation Studies (CFS)

1.1.2 THE OCTET RULE
The atoms of the representative elements form bonds to obtain 8 valence electrons. Atoms achieve noble configuration by transferring of electrons or sharing electrons.

1.2







IONIC BONDING
Exist between Metal + Non metal
Formed by the transferring of electrons from metal atom to non metal atom Formation of oppositely charged cation and anion → the two ions held together by strong electrostatic force (ionic bond)
Metal loses its valence e → cation
Non – metal gains e → anion
Eg : Formation of NaCl, MgBr2

1.2.1 PROPERTIES OF IONIC COMPOUNDS






The ions occupy fixed positions in the ionic lattice
They can conduct electricity (in melting state or in a solution phase) High melting and boiling points
Rarely soluble in organic solvents
Water-soluble

2

FGS 0064 Chemistry I
Center for Foundation Studies (CFS)

Exercise
Use Lewis dot symbols to show the formation of the following ionic compounds. i)
ii)
iii)
iv)
v)
vi)

Lithium Chloride
Potassium Oxide
Sodium Oxide
Aluminium Chloride
Calcium Bromide
Magnesium Oxide

3

FGS 0064 Chemistry I
Center for Foundation Studies (CFS)

1.3





COVALENT BONDING
Two atoms share a pair of electrons
Exists between Non – metal and non - metal
Atoms that are bonded through covalent bond produce molecule Eg : Formation of F2

1.3.1 PROPERTIES OF COVALENT COMPOUNDS
 Usually gases, liquids or low melting solids
 Insoluble in water
 Do not conduct electricity

1.3.2 TYPE OF COVALENT BONDING
 Single bond
 Double bond
 Triple bond
 Bond energy Triple > Double > Single
 Bond length

Single > Double >Triple

4

FGS 0064 Chemistry I
Center for Foundation Studies (CFS)

1.3.3 FORMAL CHARGE
Formal charge= no. of valence e- in free atom – [ no. of non-bonding e- + ½ no. of bonding e-]  Formal charge is utilized to find the most plausible Lewis structure. In general, a Lewis structure with formal charges of zero is preferable.

1.3.4 RESONANCE
“The situation in which two or more possible Lewis structures can be written but no structure can accurately reflects the actual one.”

5

FGS 0064 Chemistry I
Center for Foundation Studies (CFS)

1.3.5 DRAWING LEWIS STRUCTURE OF MOLECULES AND
POLYATOMIC IONS.
Steps in writing Lewis structure:
1. Draw the skeletal structure, joining atoms by single bonds. - the least electronegative element is normally the central atom. 2. Determine the no. of valence e associated with each atom. Combine them to determine the total no. of e.

3. Link the central atom to each of the surrounding atoms with a single bond. - Substract the no of e involved in bonding from the total valence e. 4. Use the balance valence e in pairs to fill the octets of the terminal atom. 5. If there are not sufficient the e available to complete the octet of the atoms, move lone pairs of the terminal atoms to form double or triple bond with central atom.

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