Properties of small molecules

Nitrogen, N₂, oxygen, O₂ and fluorine F₂ are all gases.

Nitrogen, oxygen and fluorine are in the same period of the periodic table.

Explain, in terms of electronic configuration, in which period of the periodic table nitrogen, oxygen and fluorine are located.

Fluorine has a boiling point of –188 °C.

Explain why fluorine has a low boiling point.

A mixture of nitrogen and oxygen becomes a liquid when cooled to –200 °C.

Which row shows the changes in energy and movement of the molecules as they are cooled from room temperature to –200 °C?

The mixture of liquid nitrogen and liquid oxygen can be separated.

Which process could be used to separate a mixture of liquid nitrogen and liquid oxygen?

At high temperatures, nitrogen, N₂, can react with oxygen, O₂, to form nitrogen dioxide only.

Write the balanced equation for this reaction.

A student heats a known volume of water by burning propanol.

The student investigates the mass of propanol needed to increase the temperature of the water by 50 °C.

Figure 9 shows the apparatus the student uses.

The student carries out the investigation using the following six steps.

The steps are not shown in the correct order.

step P find the final mass of the spirit burner containing propanol

step Q measure the initial temperature of the water

step R put 100 cm³ water into the beaker

step S find the initial mass of the spirit burner containing propanol

step T when the temperature of the water has increased by 50 °C extinguish the flame

step U place the spirit burner under the beaker of water and light the spirit burner

Write the steps in the correct order.

The first two steps have been completed for you.

State what should be used to find the mass of the spirit burner.

The student finds that 1.40 g of propanol is needed to increase the temperature of the water by 50 °C.

Calculate the mass of propanol needed to increase the temperature of the water by 1 °C.

Alcohols can be oxidised to produce carboxylic acids.

Propanol can be oxidised to propanoic acid.

Complete Figure 10 by giving the names of the missing compounds.

*(c) Compound J is a carboxylic acid and compound K is an alcohol.

Figure 11 gives some information about compounds J and K.

Describe, using Figure 11 and your own knowledge, the similarities and differences between compounds J and K.

Include information about

• the atoms in each molecule

• the structure and bonding

• the properties of each substance.

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.

Figure 11 shows the structure of a molecule of compound S.

Use Figure 11 to deduce the empirical formula of compound S.

The melting points of three samples of S are shown in Figure 12.

State whether each of these samples, A, B and C, is pure or impure and justify your answers using the information in Figure 12.

A scientist uses chromatography in an investigation of compound S.

In the conditions used, compound S has an R_f value of 0.22.

Calculate the distance the spot of compound S moves if the solvent front has moved by 2.4 cm.

*(c) A solution of sodium chloride in water needs to be separated to obtain a sample of pure, dry sodium chloride and a sample of pure water.

Figure 13 shows the boiling points of sodium chloride and water.

Explain this difference in boiling points in terms of the structure and bonding of sodium chloride and water and how this difference is used to choose a method to separate sodium chloride solution into pure, dry sodium chloride and pure water.

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 13 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 5.

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

Part of the structure of potassium chloride is shown in Figure 6.

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 7. 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.

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.

An atom of potassium has atomic number 19 and mass number 39.

Give the electronic configuration of this potassium atom.

This potassium atom forms the ion K⁺.

Which row shows the number of protons and the number of neutrons in this potassium ion, K⁺?

Potassium and caesium are in the same group of the periodic table.

Explain, in terms of electrons, why potassium and caesium are in the same group.

Fluorine boils at –188C. There are forces between fluorine molecules.

Explain, in terms of these forces, why the boiling point of fluorine is low.

Potassium reacts with fluorine to form potassium fluoride. Potassium fluoride is a solid.

Complete the balanced equation for this reaction and add the state symbols.

What are the elements in group 1 of the periodic table called?

Figure 14 shows the melting points and boiling points of elements in group 7 of the periodic table.

Give, using Figure 14, the boiling point of bromine.

State which two elements from Figure 14 are solids at room temperature.

An atom of potassium has atomic number 19 and mass number 39.

Give the electronic configuration of this potassium atom.

This potassium atom forms the ion K⁺.

Which row shows the number of protons and the number of neutrons in this potassium ion, K⁺?

Potassium and caesium are in the same group of the periodic table.

Explain, in terms of electrons, why potassium and caesium are in the same group.

Fluorine boils at –188C. There are forces between fluorine molecules.

Explain, in terms of these forces, why the boiling point of fluorine is low.

Potassium reacts with fluorine to form potassium fluoride. Potassium fluoride is a solid.

Complete the balanced equation for this reaction and add the state symbols.

Carbon dioxide is one of the gases in the Earth’s atmosphere. The percentage of carbon dioxide in the Earth’s atmosphere has changed over time.

Which row of the table shows the approximate percentage of carbon dioxide thought to be in the Earth’s early atmosphere and how this percentage changed to form the Earth’s atmosphere today?

The actual percentage of carbon dioxide in the Earth’s atmosphere today varies.

Explain two factors that cause the percentage of carbon dioxide in today’s atmosphere to vary.

Carbon dioxide is a simple molecular, covalent compound.

It has a low boiling point of –78.5C.

Explain why carbon dioxide has a low boiling point.

Calculate the number of molecules in 0.11 g of carbon dioxide.

Give your answer to two significant figures.

(relative formula mass: CO₂ = 44 Avogadro constant = 6.0210²³)

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.

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.

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.