MC test: Covalent structures (2)

Multiple choice test on 4.3 Covalent structures (2)

Use the following 'quiz' to test your knowledge and understanding of this sub-topic. You will need access to a periodic table (Section 6 of the IB data booklet).

If you get an answer wrong, read through the explanation carefully to learn from your mistakes.

Which molecule has a linear shape?

Be only has two pairs of electrons (two electron domains) around the central atom all the rest have more.

 

Which statements are correct about VSEPR theory?

I. Electron domains arrange themselves around the central atom so they are as mutually repulsive as possible.

II. Non-bonded pairs of electrons repel more than bonded pairs of electrons.

III. Single, double and triple bonds all count as one electron domain.

Note that strictly speaking the theory refers to electron domains rather than pairs of electrons even though it is known as Valence Shell Electron Pair Repulsion theory.

 

Which species will have a bond angle less than 109o but more than 100o?

NH4+, CH4 and BF4− all have four bonding pairs of electrons so form regular tetrahedral structures with a bond angle of 109.5o. NH3 possesses three bonding pairs and one non-bonding pair. The non-bonding pairs will repel the bonding pairs more than they repel each other reducing the bond angle to about 107o.

 

Which will contain a bond angle of 120o?

I. NCl3

II. BCl3

III. H2CCH2

BCl3 and H2CCH2 both contain three bonding pairs around the central atom. NCl3 contains four bonding pairs, one of which is a non-bonding pair so its shape will be trigonal pyramid, not trigonal planar.

 

Which molecule contains a bond angle that is not 180o?

Other than H2S all the other molecules contain two electron domains around the central atom.

 

Which has a different shape to the other three species?

 

Ammonia contains four electron domains (three bonding and one non-bonding) so has a trigonal pyramid shape, the other three all contain three domains (three bonding pairs) so have a trigonal planar shape.

 

Which has the smallest bond angle?

Water is the only one of the four that has two non-bonding pairs of electrons and these exert a greater repulsion on the bonding pairs.

 

Which show that a coordinate (dative) bond behaves just like a normal covalent bond when VSEPR theory is applied?

I. BF4−

II. CO32-

III. NH4+

 

Both BF4− and NH4+ contain a coordinate bond but all the bond angles are identical irrespective of the origin of the electrons making up the bonds. The carbonate ion does not contain a coordinate bond.

 

Note this question is for HL only.

Which shapes can be deduced using VSEPR theory for 5 electron domains around the central atom?

I. XeF4

II. SCl4

III. ICl4+

 

XeF4 has six electron domains (four bonding and two non-bonding) giving it a square planar shape. Both SCl4 and ICl4+ have five electron domains (four bonding and one non-bonding) giving them a 'seesaw' shape.

 

Note this question is for HL only.

Which row contains all the correct bond angles for the specified shape?

Row Shape Bond angle(s)
1 trigonal planar 109.5o
2 octahedral 90o and 180o
3 tetrahedral 120o
4 trigonal bipyramidal 90o and 120o

Trigonal planar and tetrahedral have 'swapped' angles and trigonal bipyramidal also has an angle of 180o, which is missing.

 

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