Dot-and-cross diagrams

i. Draw a dot-and-cross diagram for carbon dioxide.

ii. Describe the shape and explain why the carbon dioxide molecule has this shape

i.

ii.VSEPR (Valence Shell Electron Pair Repulsion) theory can be used to predict the shape of a carbon dioxide (CO₂) molecule. Two oxygen atoms are double-bonded to the carbon atom, which is the core atom in CO2. The carbon atom does not have any lone pairs of electrons. The two double bonds will repel each other and arrange themselves as far apart as possible, resulting in a linear shape.

Complete the dot-and-cross diagram of methanol, CH₃OH.

Five bonding paris of electrons between carbon, oxygen and hydrogen.

Two lone pairs of electron on oxygen.

i. Draw a dot-and-cross diagram for the product of boron trifluoride and ammonia.

ii. Explain how the bond forms between the boron trifluoride and ammonia molecules.

i.

ii. Ammonia has a lone pair of electrons and boron trifluoride has an incomplete outer shell.

Sulfur tetrafluoride is a colourless compound that reacts with water to form toxic products. Draw diagrams to show the arrangement of outer electrons in this compound.

Sulfur is in Group 16 which has 6 valence electrons and Fluorine is in group 17 which has 7 valence electrons.

i. Ammonia, NH₃, is a key chemical in manufacturing certain fertilisers and cleaning products. Write an equation to show the formation of an ammonium ion from ammonia.  

ii. Draw a dot-and-cross diagram to show the bonding in the ammonium ion

i. `NH_3 + H^+ -> NH""_4^+`

ii. 1 central nitrogen atom is surrounded by 5 hydrogen atoms. Simultaneously, 3 shared pairs of electrons and 1 pair of electrons donated from the nitrogen atom

The nitrate(V) ion, `NO""_3^-`, is a polyatomic ion, bonded by covalent bonds. The three oxygen atoms are bonded by one single covalent bond, one double covalent bond and one coordinate bond. 

Draw the dot-and-cross diagram for `NO""_3^-`. 

Around N atom shows that there are double bond, single bond and coordinate bonds.

Draw a dot and cross diagram for HCN

A ‘dot-and-cross’ diagram for nitrogen trichloride, NCl₃, is shown below.

Which shows the correct shape and bond angle in a molecule of NCl₃ ?

A. Pyramidal - 104.5^o

B. Pyramidal - 107^o

C. Tetrahedral - 107^o

D. Trigonal planar - 120^o

The answer is B.

There are three bonding pairs of electrons and one lone pair in NCl₃. That means that there are a total of 4 pairs.

The lone pair of electrons on the N atom repel the bonding pairs slightly and reduce the angle from a normal tetrahedral of 109^o to 107^o.

A is incorrect because the bond angle is too small

C is incorrect because the shape is wrong

D is incorrect because both are wrong.

Ammonia, NH₃, is a small covalent molecule. How many non-bonding, outer-shell electrons are present in one molecule of ammonia?

A. 0

B. 2

C. 5

D. 6

The answer is B.

There are no unbonded electrons in hydrogen and the nitrogen has 5 electrons on the outer shell and shared 3 in total for creating bonds with each hydrogen atoms.

Which of the following molecules obeys the octet rule?

A. BF₃

B. HCN

C. BeCl₂

D. CS₂

The answer is D.

A is incorrect

B is incorrect

C is incorrect

D is correct