C3- Structure and Bonding

Question 1

1. State the three types of strong chemical bonds.

Answer 1

Ionic, covalent and metallic.

Question 2

2. In ionic bonds, what are the bonds formed between?

Answer 2

For ionic bonding the particles are oppositely charged ions.

Question 3

3. In covalent bonding, what are the bonds formed between?

Answer 3

For covalent bonding the particles are atoms which share pairs of electrons.

Question 4

4. In metallic bonding, what are the bonds formed between?

Answer 4

For metallic bonding the particles are atoms which share delocalised electrons

Question 5

5. Between which classes of elements do ionic bonds form?

Answer 5

Ionic bonding occurs in compounds formed from metals combined with non-metals.

Question 6

6. Between which classes of elements do covalent bonds form?

Answer 6

Covalent bonding occurs in non-metallic elements and in compounds of non-metals.

Question 7

7. Between which classes of elements do metallic bonds form?

Answer 7

Metallic bonding occurs in metallic elements and alloys.

Question 8

8. How does an ionic bond form?

Answer 8

• When a metal atom reacts with a non-metal atom electrons in the outer shell of the metal atom are transferred.
• Metal atoms lose electrons to become positively charged ions.
• Non-metal atoms gain electrons to become negatively charged ions.
• The ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 have the electronic structure of a noble gas (Group 0).
• The ionic bond is the result of the strong electrostatic attraction between the oppositely charged ions.

Question 9

9. Describe the characteristics of an ionic structure.

Answer 9

• An ionic compound is a giant structure of ions.
• Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions.
• The forces act in all directions in the lattice and this is called ionic bonding.

Question 10

10. Describe the characteristics of a covalent molecule or structure.

Answer 10

• When atoms share pairs of electrons, they form covalent bonds.
• These bonds between atoms are strong.
• Covalently bonded substances may consist of small molecules, such as H2, Cl2, O2, N2, HCl, H2O, NH3 and CH4.
• Some covalently bonded substances have very large molecules, such as polymers.
• Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.

Question 11

11. Describe the characteristics of a metallic structure.

Answer 11

• Metals consist of giant structures of atoms arranged in a regular pattern.
• The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure.
• The sharing of delocalised electrons gives rise to strong metallic bonds.

Question 12

12. State the three states of matter

Answer 12

The three states of matter are solid, liquid and gas.

Question 13

13. What are the transitions between states and where do they occur?

Answer 13

Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point.

Question 14

14. What is the model that represents the three states of matter?

Answer 14

The particle model

Question 15

15. How does the particle model represent the three states of matter?

Answer 15

• In this model, particles are represented by small solid spheres.
• In solids, they are in a close packed, regular arrangement
• In liquids they are in a close packed, random arrangement.
• In gases, the particles are separate from each other.

Question 16

16. How is particle theory used to explain melting, boiling, freezing and condensing?

Answer 16

• The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance.
• The nature of the particles involved depends on the type of bonding and the structure of the substance.
• The stronger the forces between the particles the higher the melting point and boiling point of the substance.

Question 17

17. What are the limitations of the particle model?

Answer 17

Limitations of the simple model include that there are no forces between the spheres, that all particles are represented as spheres and that the spheres are solid.

Question 18

18. How are the states of matter represented in a chemical equation?

Answer 18

In chemical equations, the three states of matter are shown as (s), (l) and (g), with (aq) for aqueous solutions.

Question 19

19. Why do ionic structures have high melting and boiling points?

Answer 19

These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds.

Question 20

20. Why do ionic compounds conduct electricity when molten or in aqueous solution?

Answer 20

When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow.

Question 21

21. Why do simple covalent structures have low melting and boiling points?

Answer 21

• Substances that consist of small molecules are usually gases or liquids.
• These substances have only weak forces between the molecules (intermolecular forces).
• It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.
• The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points.

Question 22

22. Why do simple covalent compounds not conduct electricity?

Answer 22

These substances do not conduct electricity because the molecules do not have an overall electric charge.

Question 23

23. What is a polymer?

Answer 23

Polymers are very large molecules where the atoms in the polymer are linked to other atoms by strong covalent bonds.

Question 24

24. Why are polymers solid at room temperature?

Answer 24

The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.

Question 25

25. Why do giant covalent structures have high melting and boiling points?

Answer 25

All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures.

Question 26

26. Why do most metals have high melting and boiling points?

Answer 26

Metals have giant structures of atoms with strong metallic bonding. The strong forces are difficult to overcome, so the melting and boiling points are high.

Question 27

27. Why are metals malleable (bendable) and ductile (can be drawn into wires)?

Answer 27

In metals, the layers of atoms are able to slide over each other. This means metals can be bent and shaped.

Question 28

28. What is an alloy?

Answer 28

An alloy is a mixture of two or more metals.

Question 29

29. Why are most metals in everyday use alloyed?

Answer 29

Metals such as pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with other metals to make alloys.

Question 30

30. How does mixing two metals in an alloy make them harder?

Answer 30

The different sizes of atoms in an alloy distort the layers in the structure, making it more difficult for them to slide over each other, so alloys are harder than pure metals.

Question 31

31. Why are metals good conductors of electricity?

Answer 31

Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal.

Question 32

32. Why are metals good thermal (heat) conductors?

Answer 32

Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons.

Question 33

33. Describe the structure of diamond.

Answer 33

In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity.

Question 34

34. Describe the structure of graphite.

Answer 34

* In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings and so graphite has a high melting point. * The layers are free to slide over each other because there are no covalent bonds between the layers and so graphite is soft and slippery. * In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct thermal energy and electricity

Question 35

35. What is graphene?

Answer 35

Graphene is a single layer of graphite and so is one atom thick.

Question 36

36. What are Fullerenes?

Answer 36

Fullerenes are molecules of carbon atoms with hollow shapes.

Question 37

37. Describe the structure of Fullerenes.

Answer 37

The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms.

Question 38

38. What was the first Fullerene to be discovered?

Answer 38

The first fullerene to be discovered was Buckminsterfullerene (C60) which has a spherical shape.

Question 39

39. What are carbon nanotubes?

Answer 39

Carbon nanotubes are cylindrical fullerenes. They have high tensile strength, high electrical conductivity and high thermal conductivity.

Question 40

40. What are the uses of Fullerenes?

Answer 40

Fullerenes can be used for drug delivery into the body, as lubricants, as catalysts and carbon nanotubes can be used for reinforcing materials, e.g. in tennis rackets.

Question 41

41. What is nanoscience?

Answer 41

Nanoscience refers to structures that are 1–100 nm in size, of the order of a few hundred atoms.

Question 42

42. Describe a nanoparticle.

Answer 42

* Nanoparticles, are smaller than fine particles, which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m). * In comparison, coarse particles have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust.

Question 43

43. Why do nanoparticles have different properties to the same material that is present as a coarse particle?

Answer 43

* Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. * It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes.

Question 44

44. Describe uses for nanoparticles.

Answer 44

* Nanoparticles have many applications in medicine for controlled drug delivery and in synthetic skin. * They have uses in electronics; in cosmetics and sun creams; in the development of new catalysts for fuel cells materials; in deodorants and in fabrics to prevent the growth of bacteria.

Question 45

45. Describe the use of nanoparticles in sun creams.

Answer 45

* Nanoparticles are being used in sun creams. Some of the benefits of nanoparticles in sun creams include better skin coverage and more effective protection from the sun's ultraviolet rays. * Disadvantages include potential cell damage in the body and harmful effects on the environment.