4.1 Ionic & Covalent Bonding

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.

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.

Ammonia, NH₃, has the same crystalline structure as SO₂ and yet its melting point is 2℃. Explain the difference in melting point between SO₂ and NH₃.

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

Silver chloride has a high melting point and a structure similar to sodium fluoride.

Explain why, with reference to structure and bonding, why silver chloride has such a high melting point.

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

Draw the Lewis structure for a CN^- ion. 

Show the outer electrons only.

Ammonia, NH₃, and boron trifluoride, BF₃, react together to form NH₃BF₃. Each of the molecules NH₃ and BF₃ have different features of its electronic structure which allows them to bond together. Explain how the two molecules bond together and what type of bond is formed between NH₃ and BF₃.

You may use a labelled diagram to help you.

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.

State why magnesium and oxygen form an ionic compound while carbon and oxygen form a covalent compound.

Explain why the melting point of phosphorus(V) oxide is lower than that of sodium oxide in terms of their bonding and structure.

N, N–dinitronitramide N(NO₂)₃, also known as trinitramide, has been identified as a potentially more environmentally friendly rocket fuel oxidant.

Using section 10 of the data booklet, outline how the length of the bond between nitrogen atoms in trinitramide compares with the bond between nitrogen atoms in nitrogen gas, N₂.

Describe the bonding within the carbon monoxide molecule.

Ammonia, NH₃, is a chemical that is key in the manufacture of certain fertilisers and cleaning products.

An ammonia molecule will react with an H⁺ ion, to form the ammonium ion, NH₄⁺.

Draw a Lewis (electron dot) diagram to show the bonding in the ammonium ion and name the type of bond formed between the ammonia molecule and the hydrogen ion. 

Lewis (electron dot diagrams) are used to show the electron arrangement in the valence shells of covalently bonded molecules.

            Draw Lewis diagrams for the following molecules:

(i)         Hydrogen cyanide.

(ii)        Carbon dioxide.

(iii)        Boron trifluoride.

Using your answer to part (b), identify and explain the species that is likely to form a coordinate covalent bond.

Using your answer to part (c), Explain, with the help of a diagram, the covalent bond formed between the species in part (c) and ammonia.

For each of the molecules below, draw the Lewis (electron dot) structure and use the valence shell electron pair repulsion theory (VSEPR) to predict the shape of each molecule.

Oxygen difluoride (OF₂), phosphorus trifluoride, (PF₃) and boron trichloride, (BCl₃).

Crystalline ionic compounds do not conduct electricity. 

State and explain in which states ionic compounds conduct electricity.

The melting point of sodium chloride, NaCl, is 801° C. 

Explain, with reference to structure and bonding, why sodium chloride melts at such a high temperature.

We can use electronegativity values to deduce whether a compound is likely to be ionic or covalent.

Use Table 7 of the Data Booklet to state and explain whether each of the following compounds are ionic or covalent:

   ICl

   SrCl₂

   RbI

   HI

Diimide, N₂H₂, is a useful reagent in organic synthesis and can be made by the thermal decomposition of azodicarboxylic acid 

         (NCOOH)₂ (g) → N₂H₂ (g) + 2CO₂ (g) 

Another useful compound of nitrogen is hydrazine, N₂H₄. 

Draw Lewis (electron dot) structures for diimide and hydrazine.

Deduce the molecular geometry of diimide and estimate its H-N-N bond angle.

List, with an explanation, the three compounds in order of increasing carbon to oxygen bond length (shortest first). 

               H₃COCH₃              CO              CO₂       

Use Table 8 of the Data Booklet to predict which bond in each of the following pairs is more polar:

   (i)         C–H or C–Cl

   (ii)        Si–Li or Si–Cl

Three types of covalent bonds are present in the molecules in the following equation. 

            2C₂H₂ (g) + 5O₂ (g) → 4CO₂ (g) + 2H₂O (l) 

Identify one bond in these molecules that is correctly described by the following: 

 (i)       A polar single bond. 

(ii)       A non-polar double bond. 

(iii)      A non-polar triple bond.

Explain which of the bonds in part (a) is the shortest.

Table 1 shows the carbon-carbon bond enthalpy values for three different hydrocarbons. 

Table 1 

Explain the difference in carbon-carbon bond enthalpy values for the three hydrocarbons.

We can use electronegativity values to deduce whether a compound is likely to be pure covalent(non-polar) or polar covalent. 

Use Table 8 of the Data Booklet to state and explain whether each of the following covalent compounds are polar or non-polar:

      H₂

      HCl

      CO