Covalent bonding

Figure 1 shows a chemical cell.

The chemical cell contains two metal electrodes placed into an electrolyte and connected in a circuit with a voltmeter.

State what type of compound must be present in the electrolyte.

When the two metal electrodes are placed in the electrolyte, a voltage is produced.

The bigger the difference in reactivity of the metals, the larger the voltage produced.

Which metal, when used for electrode X in Figure 1, would give the largest voltage?

State what happens to the voltage when one of the reactants is used up.

Hydrogen-oxygen fuel cells can also be used to produce a voltage.

Draw the dot and cross diagram for a molecule of oxygen, O₂.

An atom of oxygen has the electronic configuration of 2.6.

Show outer electrons only.

Hydrogen‑oxygen fuel cells are used in spacecraft.

Suggest one advantage of using fuel cells rather than chemical cells in spacecraft.

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

*(d) Crude oil is separated into useful products called fractions using fractional distillation.

Figure 14 shows a fractional distillation column and the fractions kerosene and fuel oil.

Kerosene and fuel oil have different uses depending on their properties.

Describe the properties and uses of kerosene and fuel oil. Include in your answer

• the difference in boiling point

• the difference in viscosity

• the difference in ease of ignition

• their uses and how fuel oil can be converted into kerosene.

Crude oil is a mixture of hydrocarbons.

The majority of hydrocarbons in crude oil belong to one homologous series.

Give the name of this series.

When hydrocarbons undergo combustion, water is produced.

Draw a dot and cross diagram of a molecule of water.

One compound in crude oil contains 0.96 g of carbon atoms combined with 0.32 g of hydrogen atoms.

Calculate the empirical formula of this compound.

(relative atomic masses: C = 12, H = 1.0)

Nitrogen reacts with hydrogen to form ammonia.

The reaction is reversible.

Complete the word equation for the reaction by adding the symbol to show that the reaction is reversible.

nitrogen + hydrogen_........ ammonia

Figure 4 shows the electronic configuration of an atom of hydrogen.

Complete the dot and cross diagram for a molecule of hydrogen, H₂.

H H

Ammonia reacts with sulfuric acid to form ammonium sulfate.

Write the word equation for this reaction.

Ammonium sulfate contains ammonium ions, NH₄⁺, and sulfate ions, SO₄^2–.

What is the formula of ammonium sulfate?

Explain why some farmers spread ammonium sulfate on their fields.

This question is about the properties of different substances.

Silicon tetrachloride is a simple molecular covalent compound.

A molecule of silicon tetrachloride is composed of a silicon atom and four chlorine atoms.

• a silicon atom has 4 outer electrons

• a chlorine atom has 7 outer electrons

Draw a dot and cross diagram of a molecule of silicon tetrachloride, SiCl₄.

Show outer electrons only.

Explain why simple molecular covalent compounds such as silicon tetrachloride have low melting and boiling points.

Part of the structure of rubidium bromide is shown in Figure 7.

Which row shows the most likely melting point and boiling point of rubidium bromide?

*(c) Diamond and graphite are two forms of carbon.

Figure 8 shows how the carbon atoms are arranged in a part of the structure of each of these forms of carbon.

• diamond is one of the hardest known substances on Earth and is used in cutting tools.

• graphite is soft and flaky.

• diamond is a poor electrical conductor, but graphite is a good electrical conductor.

Explain, in terms of structure and bonding, these properties of diamond and graphite.

Magnesium is a metal.

State one physical property of magnesium.

Which element is in the same group of the periodic table as magnesium? Use the periodic table to help you answer this question.

Magnesium atoms have 12 electrons.

Complete the electronic configuration of a magnesium atom.

The electronic configuration of a chlorine atom is 2.8.7

Explain how the electronic configuration of chlorine is linked to its period in the periodic table.

1.20 g of magnesium reacts completely with 3.55 g of chlorine to form magnesium chloride.

Calculate the empirical formula of the magnesium chloride.

(relative atomic masses: Mg = 24.0, C l = 35.5)

You must show your working.

Sodium reacts with chlorine to form sodium chloride, which contains ionic bonds.

Hydrogen reacts with chlorine to form hydrogen chloride, which contains covalent bonds.

Figure 9 shows dot and cross diagrams of these compounds.

Describe the differences between an ionic bond and a covalent bond.

Figure 9 shows the percentage of three gases, X, Y and Z, in the Earth’s early atmosphere.

What is the name of gas Z ?

It is thought that small quantities of hydrogen sulfide, H₂S, were also in the Earth’s early atmosphere.

Draw the dot and cross diagram for a molecule of hydrogen sulfide.

Show outer electrons only.

Acid rain is caused by some pollutant gases present in the atmosphere.

Explain how impurities in fossil fuels can result in acid rain.

A student investigates the effect of acid rain on cress plants.

The student uses this method.

step 1 grow 20 cress plants in each of two dishes, A and B

step 2 water the cress plants in dish A with 10 cm³ of dilute hydrochloric acid with a pH of 2

step 3water the cress plants in dish B with 10 cm³ of pure water with a pH of 7

step 4 repeat steps 2 and 3 every day for one week

step 5 count how many plants are still alive after one week.

State what piece of equipment the student could use to measure the pH of each liquid.

Explain one improvement that the student could make to the method to make the results more valid.

Figure 1 shows a bag of NPK fertiliser.

N, P and K are the symbols of three elements that are essential for plant growth.

N is the symbol for nitrogen.

Name the other two elements, P and K, that are essential for plant growth.

You may want to refer to the periodic table.

Many fertilisers are produced using ammonia.

Ammonia is produced on an industrial scale from the reaction of nitrogen with hydrogen.

The equation for the reaction is

nitrogen + hydrogen ammonia

State the name of this industrial process.

State the meaning of the symbol in the equation.

Figure 2 shows the electronic configurations for an atom of nitrogen and an atom of hydrogen.

Which dot and cross diagram for ammonia, NH₃, is correct?

Ammonia reacts with nitric acid to produce ammonium nitrate.

Write the word equation for this reaction.

Figure 9 shows a sample of hydrogen peroxide solution decomposing to form water and oxygen gas.

Write the word equation for hydrogen peroxide solution decomposing.

In this reaction hydrogen peroxide is a solution, water is a liquid and oxygen is a gas.

Draw one straight line from each substance to its correct state symbol.

Describe the test to show the gas produced is oxygen.

Figure 10 shows the electron arrangement for an atom of hydrogen and an atom of oxygen.

Complete the dot and cross diagram in Figure 11 for a molecule of water, H₂O.

Draw outer shell electrons only.

Liver contains the enzyme catalase.

A piece of liver was added to another sample of hydrogen peroxide solution.

Figure 12 shows the results.

Figure 13 shows a graph of the volume of oxygen produced from the hydrogen peroxide with and without liver.

Figure 13

Complete the missing label on the axis of the graph.

Describe what the graph shows about the difference in decomposition of hydrogen peroxide with and without liver.

Describe how the apparatus in Figure 12 could be modified to find the volume of gas produced when the liver is added to the hydrogen peroxide.

When solid sodium chloride is mixed with water, sodium chloride solution forms.

What name is given to the process of mixing a solid with water to form a solution?

Sodium reacts with hydrochloric acid to form sodium chloride and hydrogen.

Write the word equation for this reaction.

The hazard symbol shown in Figure 1 is used on containers of sodium.

What is the meaning of this hazard symbol?

Hydrogen has one electron in its electron shell. Figure 2 shows the incomplete dot and cross diagram of a hydrogen molecule.

Complete Figure 2 to show the electrons in the covalent bond between the two atoms of hydrogen.

The pH of a sodium chloride solution was measured.

State what could be used to measure the pH of a solution.

Sodium chloride solution is neutral.

Give the pH of this solution.

The word equation for the reaction between copper carbonate and dilute sulfuric acid is

copper sulfuric copper carbon

Complete the balanced equation for this reaction.

Calculate the relative formula mass of copper carbonate, CuCO₃. (relative atomic masses: C = 12.0, O = 16.0, Cu = 63.5)

relative formula mass of CuCO₃ =_........

What is the chemical test to show that a gas is carbon dioxide?

Figure 4 shows a conical flask containing dilute sulfuric acid. Copper carbonate is added to the acid in the flask. The copper carbonate is added one spatula measure at a time until the reaction has finished.

State two observations that would show the reaction has finished.

The electronic configuration of carbon is 2.4 The electronic configuration of oxygen is 2.6

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

Show outer electrons only.

Chlorine, bromine and iodine are elements in group 7 of the periodic table.

Chlorine is toxic.

State one safety precaution that should be taken when using chlorine in the laboratory.

Chlorine reacts with hydrogen to form hydrogen chloride.

Write the word equation for this reaction.

Hydrogen chloride dissolves in water to form an acidic solution.

State what is seen when blue litmus paper is placed into this solution.

A chlorine atom has seven electrons in its outer shell. A hydrogen atom has one electron in its outer shell.

Complete the dot and cross diagram of a molecule of hydrogen chloride. Show outer shell electrons only.

Name the type of bonding in a molecule of hydrogen chloride.

If chlorine solution is added to sodium bromide solution a reaction occurs.

chlorine + sodium bromide sodium chloride + bromine

Give a reason why this reaction occurs.

Figure 8 shows apparatus used to find out if a solution conducts electricity.

Glucose solution and sodium chloride solution are tested. Glucose is a typical simple molecular covalent compound. Sodium chloride is an ionic compound.

State what would happen to the lamp when glucose solution is tested.

State what would happen to the lamp when sodium chloride solution is tested.

Figure 9 shows how the conductivity of one solution changes as its concentration increases.

Figure 9

Describe how the conductivity of this solution changes as its concentration increases from 0 to 500 g dm^–3.

Propene can be produced by the cracking of some hydrocarbons obtained from crude oil.

The equation shows the cracking of one molecule of decane to produce one molecule of butene and one molecule of another product.

decane butene

Calculate the values of x and y in C_xH_y.

State the total mass of products formed if 25 g of decane is cracked in this way.

The structure of a molecule of ethene is shown in Figure 8.

Figure 9 shows the incomplete dot and cross diagram for a molecule of ethene.

Complete Figure 9 to show the electrons of the C C double bond.

The incomplete combustion of ethene in air produces water as one of the products.

Give the name of another product of the incomplete combustion of ethene.

Substance X is an unsaturated hydrocarbon. The structure of a molecule of substance X is shown in Figure 10.

Explain how the structure of substance X shows that it is an unsaturated hydrocarbon.

Two liquid hydrocarbons, A and B, were tested with bromine water. One hydrocarbon was known to be an alkane. The other hydrocarbon was known to be an alkene.

Each hydrocarbon was shaken with a few drops of bromine water.

The results of the tests were hydrocarbon A + bromine water: the mixture turned from orange to colourless. hydrocarbon B + bromine water: the orange colour remained.

Explain these results.

Figure 1 shows the dot and cross diagram for a molecule of ammonia.

What do the dots and crosses represent in the diagram?

Give the formula for the molecule of ammonia.

Ammonia can be manufactured by the Haber process.

The word equation for the reaction is

nitrogen + hydrogen ammonia

State the meaning of the symbol.

In the Haber process, the percentage yield of ammonia at equilibrium changes with temperature.

Figure 2 shows how the percentage yield of ammonia at equilibrium changes with temperature.

State what happens to the percentage yield of ammonia at equilibrium as the temperature increases.

Use the graph to find the percentage yield of ammonia at equilibrium at 450°C.

Ammonia reacts with nitric acid to form ammonium nitrate.

Complete the word equation for this reaction.

An ammonium ion has the formula NH₄⁺.

A nitrate ion has the formula NO₃^–.

Which of the following is the formula for ammonium nitrate?

Explain why farmers spread ammonium nitrate on their fields.

Covalent substances can be simple molecular covalent or giant covalent.

Ammonia is a simple molecular, covalent substance.

Which is the most likely set of properties for ammonia?

Ammonia, NH₃, is made by reacting nitrogen with hydrogen.

Write the balanced equation for this reaction.

Oxygen, O₂, is also a simple molecular, covalent substance.

Draw a dot and cross diagram for the molecule of oxygen.

*(c) Figure 8 shows the arrangement of carbon atoms in diamond, graphene and a fullerene (C₆₀).

Consider these three substances.

Explain, in terms of their structures and bonding, their relative melting points, strengths and abilities to conduct electricity.

(a) A chlorine atom contains 17 electrons, 18 neutrons and 17 protons.

State the mass number of this chlorine atom.

Give the electronic configuration of this chlorine atom.

Describe what you would see if damp, blue litmus paper is placed into chlorine gas.

Chlorine exists as diatomic molecules.

In a molecule, two chlorine atoms are joined by a covalent bond.

Describe what is meant by a covalent bond.

Explain why chlorine is a gas, rather than a liquid, at room temperature.

When the gas hydrogen chloride, HC l, is dissolved in water, a solution forms. Blue litmus paper dipped in this solution turns red.

State why the litmus paper turns red.

Figure 13 lists the halogens in the order in which they appear in group 7 of the periodic table.

The melting points of four of the halogens are given.

Estimate the melting point of iodine.

Bromine reacts with heated iron.

Give the name of one halogen that would react with iron more vigorously than bromine.

(a) A chlorine atom contains 17 electrons, 18 neutrons and 17 protons.

State the mass number of this chlorine atom.

Give the electronic configuration of this chlorine atom.

Describe what you would see if damp, blue litmus paper is placed into chlorine gas.

Chlorine exists as diatomic molecules.

In a molecule, two chlorine atoms are joined by a covalent bond.

Describe what is meant by a covalent bond.

Explain why chlorine is a gas, rather than a liquid, at room temperature.

When the gas hydrogen chloride, HC l, is dissolved in water, a solution forms. Blue litmus paper dipped in this solution turns red.

State why the litmus paper turns red.