Chemical bonds

Ammonia can be produced from the reaction of hydrogen with nitrogen.

What is the percentage by mass of nitrogen in ammonia, NH₃?

(relative atomic masses: H = 1.0, N = 14)

The reaction between hydrogen and nitrogen is exothermic.

Figure 8 shows the reaction profile of this exothermic reaction.

Which arrow represents the activation energy for the reaction?

Describe what the reaction profile shows about the energy involved in bond breaking and bond making in this reaction.

Ammonia, NH₃, and silicon dioxide, SiO₂, are both compounds that are made of two non-metallic elements.

Ammonia has a boiling point of –33 °C. Silicon dioxide has a boiling point of 2230 °C.

Explain why the boiling points of ammonia and silicon dioxide are so different.

Bromine is a liquid at room temperature and vaporises readily. Bromine has a simple molecular structure.

Which row of the table shows the most likely melting and boiling points of bromine?

Part of the structure of graphene is shown in Figure 3.

Explain why graphene will be a good conductor of an electric current.

Part of the structure of potassium chloride is shown in Figure 4.

Potassium chloride has a melting point of 770 °C.

Explain why potassium chloride has a high melting point.

*(d) A molecule of methane can be represented in several different ways as shown in Figure 5. These representations have been labelled A – E to assist you in your answer.

Describe what information can be obtained from each representation including the limitations of these representations of methane.

An ion of element X can be represented as

This ion of element X has 54 electrons.

Calculate the number of protons and the number of neutrons in this ion.

number of protons_........

number of neutrons_........

A sample of silicon contains isotopes.

State, in terms of subatomic particles, how atoms of these isotopes are the same.

This sample of silicon contains three isotopes.

92% of the atoms are silicon-28 5% of the atoms are silicon-29 3% of the atoms are silicon-30

Calculate the relative atomic mass of silicon in this sample.

relative atomic mass =_........

*(c) Figure 4 shows some properties of three substances, A, B and C.

Deduce, using the information in Figure 4, the structure and bonding of substances A, B and C, explaining their properties in terms of their structure and bonding.

In the 19th century, Mendeleev arranged the elements known at the time to form his periodic table. Mendeleev’s periodic table is different from the modern periodic table.

State one difference between Mendeleev’s periodic table and the modern periodic table.

Aluminium oxide reacts with hydrochloric acid to form a salt and water.

State the name of the salt formed.

In this reaction aluminium oxide is a base.

State the type of reaction that takes place when an acid reacts with a base.

Gallium, Ga, is in the same group of the modern periodic table as aluminium.

The formula of aluminium oxide is Al₂O₃.

Predict the formula of gallium oxide.

Gallium oxide has a very high melting point. Gallium oxide does not conduct electricity when solid but does conduct electricity when molten.

What type of substance is gallium oxide?

Figure 5 shows the changes of state for gallium and the arrangement of particles in liquid gallium.

Complete the boxes for solid gallium and gaseous gallium by drawing the arrangement of the particles in each of these physical states.

Give the name of the change of state labelled Y in Figure 5.

Gallium metal is a conductor of electricity.

Explain how metals conduct electricity.

The molecular formula of butene is C₄H₈.

Which of the following is the empirical formula of butene?

Calculate the relative formula mass of butene, C₄H₈.

(relative atomic masses: H = 1, C = 12)

relative formula mass_........

When burnt completely in air, butene forms carbon dioxide and water.

Balance the equation for this reaction by putting numbers in the spaces provided.

C₄H₈ + 6O_{2 ........} CO₂ +_........ H₂O

Describe the test to show that a gas is carbon dioxide.

Substance X is a gas at room temperature. It is a simple molecular, covalent substance.

Which row of the table shows the properties that substance X is most likely to have?

Diamond has a giant covalent structure.

State one property of diamond that is the result of its giant covalent structure.