2.2.7 Dative Covalent Bonding

Question 1

What is the modified octet rule?

Answer 1

1. Unpaired electrons pair up

2. The maximum number of electrons that can pair up is equivalent to the number of electrons in the outer shell

Question 2

Why is SF6 a special exception to ‘8 electrons in outer shell’ rule?

Answer 2

It has 12 electrons in its outer shell, no bonds are dative. S is in G6 and so each e- forms a covelant bond.

Question 3

Which elements are able to expand their ‘octet’?

Answer 3

P, S, Cl, As, Se, Br, Te, I and At

Question 4

What does the dot and cross diagram of BF3 look like?

Answer 4

B is the central atom, with 6 electrons in its outer shell, and three Fs which all have an octet.

Question 5

What is a dative covalent bond? How can it be written?

Answer 5

Once formed, dative covalent bonds are equivalent to any covalent bond. One of the atoms supplied both the shared electrons; written as A arrow B: A is donating a pair of electrons to B
In NH4, this is written with two dots above the central N and an arrow upwards to an H.

Question 6

What is special about NH4+?

Answer 6

Ammonium has one dative cov bond; coming from the lone pair of e- seen in NH3. The extra H has lost an e-, so the ion is positive and H has a noble gas config

Question 7

What ions are responsible for thew reactions of acids?

Answer 7

Oxonium ions: written as H3O+
Eg: HCl(g) + H2O arrow H2O(aq) + Cl-(aq)
In equations, the oxonium ion is often simplified to H+(aq)

Question 8

What does an oxonium ion look like?

Answer 8

H20, with an extra H. The extra H is a dative bond - and so the H looses an electron and the bond is positive. There is also one lone pair of electrons.

Question 9

What is another term for a dative bond?

Answer 9

A coordinate bond.