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A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1
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Page 1: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

A CASE STUDY ON COVALENT BONDING

By: Wong Wei Cong (31) 2A1

Page 2: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

What is Covalent Bonding

Page 3: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

What is Covalent Bonding

Sharing of electrons so as to achieve stable electronic configuration of noble gas

Electrostatic attraction between nuclei of the atoms and the pair(s) of shared electrons

Molecules are formed Generally, covalent bonds are formed between

atoms of non-metals

Page 4: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Exceptions to This Rule

Aluminium Chloride (AlCl3)

Beryllium Chloride (BeCl2)

Page 5: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Electronegativity

Describes tendency of an atom to attract electrons towards itself and thus the tendency to form anions

Affected by both the number of protons and the distance that the valence electrons reside from the nucleus

As you go across a period, electronegativity increases As you go down a group, electronegativity decreases

Page 6: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Polar Bonds

If two atoms of equal electronegativity bond together… Both have same tendency to attract bonding pair of

electrons Electron pair found on average half way between the

atoms Electron pair shared evenly between the atoms “Pure” covalent bonds

If B is a lot more electronegative than A… Electron pair dragged right over to B's end of the bond A has lost control of its electron B has complete control over both electrons Ionic bonds

Page 7: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Polar Bonds (II)

If B is slightly more electronegative than A… B attracts electron pair more than A does B’s end of the bond slightly negative A’s end of the bond slightly positive Polar bond

Water is a polar covalent bond!

Page 8: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Electronegativity of Elements

Page 9: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Electronegativity & Bond Type

Electronegativity Difference

Ionic Character (%)

Covalent Character (%)

Bond Type

0.0 0 100 Covalent

0.5 5 95 Covalent

1.0 20 80 Covalent

1.5 40 60 Polar

2.0 60 40 Polar

2.5 75 25 Ionic

3.0 90 10 Ionic

Page 10: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

So… yes! You guessed it…

Aluminium Chloride is a polar covalent bond!

Electronegativity difference = 1.4

Electronegativity difference = 1.4Beryllium Chloride is a polar

covalent bond!

Page 11: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Formation of Aluminium Chloride

Strongly heated aluminium foil burns in chlorine to form aluminium chloride

Page 12: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Aluminium Chloride

Imagine that aluminum chloride is ionic instead

Contain Al3+ and Cl- ions Aluminium ion: small & packed with

3 positive charges High charge density – polarise

chlorine ions Electron pairs dragged back towards

aluminium to such extent that the bonds become covalent

Chlorine more electronegative than aluminium – electron pairs will not be pulled half way between the atoms

Polar covalent bond formed

Page 13: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Factors Affecting Polarising Ability

In aluminium chloride, aluminium ions polarise chloride ions

Positive ions can polarise nearby negative ions The smaller the positive ion and the larger the number

of charges, the greater the polarising ability The bigger the negative ion, the easier it is to polarise it

Aluminium iodide is covalent as electron pair is easily dragged away from iodide ion

Aluminium fluoride is ionic as aluminium ion cannot polarise small fluoride ion sufficiently to form a covalent bond

Page 14: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

The Mystery of Aluminium Chloride

At room temperature, each aluminium surrounded by 6 chlorines Ionic crystal structure with a lot of covalent

character At ordinary atmospheric pressure, it sublimes at

about 180°C If pressure raised to just over 2 atmospheres, it

melts at 192°C Comparatively weak attractions between

molecules Each aluminium now surrounded by 4 chlorines

rather than 6 Original lattice converted into Al2Cl6 molecules

As temperature increases further, it increasingly breaks up into simple AlCl3 molecules

Page 15: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

The Mystery of Aluminium Chloride (II)

Page 16: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Beryllium Chloride

Imagine that beryllium chloride is ionic instead

Contain Be2+ and Cl- ions Beryllium ion: small & packed with

2 positive charges High charge density – polarise

chlorine ions Electron pairs dragged back

towards beryllium to such extent that the bonds become covalent

Chlorine more electronegative than beryllium – electron pairs will not be pulled half way between the atoms

Polar covalent bond formed

Page 17: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

As a gas, Beryllium Chloride is a linear molecule with all three atoms in a straight line

As a solid, the molecules form long chains (polymers) Coordinate bonds

The Mystery of beryllium Chloride

Gas

Solid

Arrows goes from the atom supplying the pair of electrons to the atom with the empty orbital

Page 18: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Why is Beryllium Chloride not Ionic?

Beryllium has quite a high electronegativity compared with the rest of Group II

Attracts bonding pair of electrons towards itself more strongly

In order for an ionic bond to form, the beryllium has to let go of its electrons, but it is too electronegative to do that

Lewis acid – accepts lone pair of electrons Boils at 520°C – low boiling point, so cannot contain ions Reacts vigorously with water, forming acidic, steamy

hydrogen chloride gas – typical of covalent chlorides

Page 19: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

Chemistry Music Video – Enjoy!

Two atoms met on one fine dayOne asked if he could bondWith the other atom thereOf whom he was really fondThe second atom shrugged and saidWhat’s your pleasure, son?Are you up for electron transferOr electron-sharing fun!

Ionic or covalent?What kind of bonds are these?Involve valence electronsAnd form compounds with ease!

Metal atoms lose electronsAnd become a charge of plusNon-metals gain them happily

Look negative to all of us.The opposite charged ionsAttract to make ionic bondsThe E.N.D. one point seven plusThey dissolve real well in ponds!

Ionic or covalent?What kind of bonds are these?Involve valence electronsAnd form compounds with ease!

If the E.N.D. is point-five or moreAnd two non-metals hadYou have a polar covalent bondOne atoms happy, the others sad!The atom with less E.N.Gets a positive charge that’s slight

Page 20: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

And the other, more greedy atom?Slightly negative to our sight!

Ionic or covalent?What kind of bonds are these?Involve valence electronsAnd form compounds with ease!

If the E.N.D. is point-four or lessTwo non-metal atoms bondWith equal pull on electronsEach atom is equal fondNo charges will developAnd, because of that, no polesThat’s why the bond is called non-polarOn and on and on we roll!

Ionic or covalent?Now its easy for you to tellJust look up the E.N.D.And you will do real well!

Chemistry Music Video – Enjoy!

YouTube Link: http://www.youtube.com/watch?v=oNBzyM6TcK8

Page 22: A CASE STUDY ON COVALENT BONDING By: Wong Wei Cong (31) 2A1.

THANK YOU!

The name’s Bond, Covalent Bond!