2.4 Electrons, Bonding & Structure

This question is about ionic bonding and structure.

The strength of ionic bonding in different compounds can be compared by using the amount of energy required to separate the ions, as shown in Table 1.

Table 1

Using the data in Table 1, explain how changing the cation affects the bond strength in an ionic compound.

Coal often contains traces of iron(II) disulfide, FeS₂, also known as pyrite or 'fool's gold'.

FeS₂ is an ionic compound made of Fe²⁺ and S₂^2- ions.

[1]

[2]

Silver chloride, AgCl, is a chloride compound that has uses in photography films as well as having antiseptic properties. Silver chloride also has a high melting point. 

[2]

[3]

Aluminium chloride, $\text{A}{\text{l}}_{\text{2}}\text{C}{\text{l}}_{\text{6}}$, does not conduct electricity when molten but aluminium oxide, $\text{A}{\text{l}}_{\text{2}}{\text{O}}_{\text{3}}$, does. Explain this in terms of the structure and bonding of the two compounds.

The nitrate (V) ion, NO₃^-, 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 dative covalent bond.

Draw the Lewis structure for NO₃^-. 

An ionic compound has the empirical formula H₄N₂O₃. 

Suggest the formulae of the ions present in this compound.

Cyanide is a fast-acting chemical, which can be found in various forms and can have toxic effects on the body.

Draw the dot-and-cross structure for a CN^- ion. 

Show the outer electrons only.

Compare the average bond enthalpy in the cyanide ion to the average bond enthalpy of the C-N bond in methylamine, CH₃NH₂. Explain your answer.

Ethyne, C₂H₂, is a hydrocarbon which can be used in the artificial ripening of fruits. It can be synthesised by a two-step process.

Firstly, calcium oxide and coal react together to form calcium carbide (CaC₂) and carbon monoxide. The second step involves calcium carbide reacting with water to form calcium hydroxide and ethyne, C₂H₂.

Write two equations to represent the two-step process forming ethyne, C₂H₂. State symbols are not required.

Draw a dot-and-cross diagram of the ethyne molecule, C₂H₂.

Describe the bonding in calcium carbide, CaC₂.

Compare and contrast the expected physical properties of calcium oxide and calcium carbide.

Oxides of elements in the same period of the Periodic Table can have significantly different properties. 

The compounds SO₂ and MgO are both oxides but with different melting points as shown below.

Describe the bonding in, and the structure of, SO₂ and MgO and explain the difference in their melting points.

Predict how the melting point of sodium chloride will compare the that of magnesium oxide and justify your answer.

SO₂ can be represented by more than one valid dot-and-cross diagram. One way of drawing it involves a single dative bond between the sulfur and one of the oxygens.

Draw this dot-and-cross diagram of SO₂ and identify the types of bonds present.

The melting and boiling points of lithium and some lithium halides are shown below:

Identify the pattern, if any, in the melting and boiling points of the lithium halides. 

Two students, A and B, are comparing the properties of lithium and lithium chloride.

Student A states that both lithium and lithium chloride will conduct electricity, but Student B states that only lithium will conduct electricity. 

State whether Student A, Student B, or neither student is correct. Explain your answer.

Students A and B went on to discuss the solubility of lithium and the lithium halides in water.

Student A states that both lithium and all of the lithium halides will be soluble in water, but Student B states that only lithium bromide and lithium iodide will be soluble in water.

State which student, if any, is correct. Explain your answer. 

Describe the bonding process that forms lithium halides, with respect to electrons.

Phosphorous trichloride, PCl₃, bonds covalently.

Draw a dot-and-cross diagram to show the bonding in PCl₃. Show the outer electrons only.

Compare the bonding in phosphorous trichloride and ammonia.

Boron trifluoride reacts with ammonia to form the trifluoroborane-ammonia complex.

Describe the type of bond that forms between the boron trifluoride and ammonia molecules.

Draw a displayed formula showing the bonding for the trifluoroborane-ammonia complex, F₃BNH₃.

Combustion of carbon compounds is responsible for global warming, breathing and respiratory problems.

Write balanced symbol equations to show the complete and incomplete combustion of propane, C₃H₈.

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

Draw a dot-and-cross diagram for carbon monoxide.

State the number of lone pairs and different types of bond in a carbon monoxide molecule.

The average bond enthalpy for the carbon-oxygen bond is shown.

Explain why the average bond enthalpy value for the carbon-oxygen bond found in carbon monoxide is higher than the carbon dioxide value.

The displayed formula of a carbonate ion, CO₃^2-, is shown below.

Draw the dot-and-cross diagram for the carbonate ion.

The nitrate, NO₃^-, ion is a polyatomic ion containing one single covalent bond, one double covalent bond and one dative covalent bond.

Draw the displayed formula of the nitrate ion.

When magnesium oxide is added to warm dilute nitric acid, a reaction takes place forming a solution containing ions.

Write an equation for this reaction, including state symbols.

Solid magnesium oxide does not conduct electricity. When magnesium oxide reacts with dilute nitric acid, the solution formed does conduct electricity.

Explain the difference in the electrical conductivity of the magnesium oxide and the solution formed.