introduction to the dative covalent bond

INTRODUCTION TO

THE 

DATIVE COVALENTDATIVE COVALENT 

BONDBOND

FOR 

CAPE UNIT 1CAPE UNIT 1 

CHEMISTRY STUDENTS

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This is a special type of covalent

bond in which both the shared

l b d belectrons are contributed by one

atom onlyatom only.

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It can be defined as

“a covalent bond in which botha covalent bond in which both electrons of the shared pair

b d bare contributed by one of the two atoms”f

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S h b d i l f d tSuch a bond is also referred to

as aas a

co-ordinate bond.

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A co-ordinate or dative covalent bond is established between two atoms where:established between two atoms where:

(a) One of the two atoms has a full outer shell and a non-bonding pair ofshell and a non bonding pair of electrons.

(b) Th th t i i h t f(b) The other atom is one pair short of a full outer shell of electrons.

5

f f

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Examples of such atoms are A and B below:A and B, below:

A. .. .

Bx    x

A x    x. .. . . . B

x x

When A and B combine A contributes both

. . x    x

When A and B combine, A contributes bothelectrons to the covalent bond;

B contributes none6

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The compound AB can be represented as

A B. . x    x

A . . B. .x    x

. . x    x

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AB can also be shown as

A B. . x    x

A→B. .x    x

. . x    x

The covalent bond is represented by an arrow(→) pointing towards the acceptor atom.

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Th t hi h t ib t th l tThe atom which contributes the electron pair is called the donor, while the atom

h h ll d hwhich accepts it is called the acceptor.

The dative covalent bond once formed isThe dative covalent bond, once formed is indistinguishable from a (regular)

covalent bondcovalent bond.

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The compound formed via dativeThe compound formed via dative bonding can be called:

(a) A coordinate compound(a) A coordinate compound.

(b) An addition compound.p

(c) An adduct.

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Examples Of

Coordinate

Bond

Formation

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Combination of ammonia and boron trifluoride

Th it t i i h f ll t h ll i l i fThe nitrogen atom in ammonia has a full outer shell, inclusive of a lone pair which it can donate.

h b b fl d h f lThe boron atom in boron trifluoride is short of two electrons which it accepts to attain a full outer shell.

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Formation of ammonium ion

Th h d i H h l t d tThe hydrogen ion, H+, has no electrons and acceptsa lone pair donated by nitrogen.

After accepting the lone pair, hydrogen has a full outer shellhas a full outer shell.

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Characteristics Of Coordinate CompoundsCompounds

h l d b l h h h l(a) Their melting and boiling points are higher than purely covalent compounds but lower than ionic compounds.

(b) They are sparingly soluble in polar solvents like water but readily soluble in non polar (organic) solventsreadily soluble in non-polar (organic) solvents.

(c) Like covalent compounds they are also poor conductors(c) Like covalent compounds, they are also poor conductors of electricity. Their solutions or fused states also do not conduct.

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