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Pure Chemistry (Sec 3) > Chapter 05 - Structure and Properties of Materials > Flashcards

Chapter 05 - Structure and Properties of Materials Flashcards

1
Q

What is an element?

A

All substances composed of only one type of atom are elements

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2
Q

Are elements naturally occurring?

A

Most elements are natural (more than 90 out of 118)

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3
Q

Are elements pure?

A

Elements are pure substances that cannot be broken down into simpler substances by chemical methods

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4
Q

What are monoatomic elements?

A

A group of individual atoms of the same element, existing separately and not chemically bonded (E.g. noble gases)

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5
Q

What are molecules of elements?

A

Pure substances made up of 2 or more of the same or different type of atom chemically joined together

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6
Q

What are diatomic elements?

A

Elements that are made up of 2 of the same atom chemically bonded together (E.g. H2,I2)

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7
Q

Do elements have fixed melting and boiling points?

A

Yes, elements are pure substances

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8
Q

Elements can be classified into 2 main categories. What are they?

A

Metals and non-metals

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9
Q

What are compounds?

A

Pure substances made up of atoms of 2 or more different elements chemically combined in a fixed ratio

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10
Q

When do compounds form?

A

Compounds are formed from chemical reactions

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11
Q

Do compounds have similar or different properties from its constituents?

A

Different, a compound has its own chemical and physical properties that are different from its constituent elements (e.g. Iron (II) sulfide (black) formed from iron (gray) and sulfur (yellow))

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12
Q

Do compounds have a fixed ratio of constituents?

A

Yes, a compound is made up of atoms of different elements chemically combined in a fixed ratio (e.g. H2O is made up of 2H and 1O atoms, Ar are 1 and 16. In water, H and O are present in a fixed ratio - 2:8)

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12
Q

When happens to the non metal when a metal and non metal atom combine to form a compound?

A

The last part of the non metal changes to ‘ide’ (e.g. Sodium (Metal) and Chlorine (Non metal) form Sodium ChlorIDE

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13
Q

Do compounds have fixed melting and boiling points?

A

Yes

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14
Q

Each compound has unique physical properties to identify them, what are they?

A

Melting and boiling point (e.g. Pure lead(II) chloride melts at 498°C and boils at 954°C )

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15
Q

How do you represent atoms of different elements in compounds?

A

By different colour or size

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16
Q

What are the 2 ways compounds can be separated?

A

Separating compounds is not easy, and only done by thermal decomposition (compound is heated strongly) and electrolysis (electric current is passed through the compound)

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17
Q

What is a mixture?

A

Mixtures are 2 or more substances (elements/compounds) physically combined

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18
Q

How are mixtures formed?

A

From physical mixing

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19
Q

How are mixtures separated?

A

Mixtures can be separated by physical separation methods (e.g. filtration, distillation)

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20
Q

Do mixtures have foxed melting and boiling points?

A

No, mixtures do not because of the different substances in the mixtures containing different melting and boiling points

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21
Q

Do mixtures have similar or different properties to its constituents?

A

Similar, a mixture retains its physical and chemical properties because the formation of a mixture does not involve a chemical reaction (each substance keeps its original identity)

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22
Q

Do mixtures have a fixed ratio of constituents?

A

No (e.g. 21% of oxygen is inhaled while 16% of oxygen is exhaled)

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23
Q

Do mixtures have fixed ratios of its constituents?

A

No (e.g. air has 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide)

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24
Q

What happens when impurities are added to a pure substance?

A

When impurities are added to a pure substance, the melting point of the substance drops below its normal (pure) melting point.

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25
Q

What is the relationship between the amount of impurities and the melting point of the mixture?

A

The greater the amount of impurities, the lower the impure substance melts below its melting point

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26
Q

What is the relationship between the amount of impurities and the boiling point of the mixture?

A

The greater the amount of impurities, the higher the impure substance boils above its boiling point

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27
Q

Mixtures can come in any ____

A

State (e.g. solid & solid, solid & liquid, gas & gas etc)

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28
Q

What structure do ionic result compounds in?

A

Giant ionic crystal lattice structure

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29
Q

What is the arrangement of the giant ionic crystal lattice structure (GICLS) like?

A

A large number of alternating positive and negative ions held together by electrostatic forces of attraction

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30
Q

Do GICLS have high or low melting/boiling point?

A

The mutual electrostatic attractive force between positive and negative ions is very strong, hence a large amount of energy is needed to overcome it

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31
Q

Do GICLS conduct electricity in the molten/aqueous state?

A

The ions can move about in the molten/aqueous solution because the GICLS has broken down and there are mobile electrons that can conduct electricity

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32
Q

Do GICLS conduct electricity in the solid state?

A

In the solid state, ions are not mobile so they cannot move around because they are held strongly at fixed positions by the ionic bonds in the GICLS

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33
Q

Is GICLS soluble in water?

A

Most GICLS are soluble in water to form aqueous compounds

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34
Q

Is GICLS soluble in organic solvents?

A

No

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35
Q

Are GICLS hard or soft?

A

GICLS are hard as the electrostatic attractive forces between oppositely charge ions hold them together strongly allowing ionic compounds to be hard and resist deforming because the ions resist motion

36
Q

What happens when a lot of force is applied on a GICLS?

A

Strong force applied on GICLS can cause the ions of different charge to move away from their lattice positions while ions of the same charge approach each other and repel one another. These repulsive forces become greater than the attractive forces causing the lattice structure to shatter

37
Q

What are the 2 structures of covalent substances?

A

Simple covalent molecules (SCM) and giant covalent substances (GCM)

38
Q

What are the 2 structural properties that covalent molecules have?

A

1) Strong covalent bonds
2) Weak intermolecular forces of attraction

39
Q

Do SCM have high or low melting/boiling points?

A

Low melting/boiling points. The intermolecular forces of attraction are weak, so lesser energy is needed to overcome it

40
Q

Some SCM are volatile. Why?

A

They can evaporate easily which is why they exist as gases/liquids at room temperature

41
Q

What happens as molecules in SCM get larger?

A

As molecules get larger, the intermolecular forces of attraction get stronger, so more energy is needed to overcome them causing the melting/boiling points to increase

42
Q

Are SCM soluble in water?

A

No, SCM are insoluble in water

43
Q

Are SCM soluble in organic solvents?

A

Yes

44
Q

Can SCM conduct electricity at any state?

A

SCM are neutral molecules as they do not have mobile charged carriers like ions or delocalised electrons that can move about to conduct electricity. However, certain SCM can dissociate (break into ions) in water to produce mobile ions to conduct electricity

45
Q

How are GCM formed?

A

A large number of atoms covalently bonded to one another

46
Q

What structural property exists in all GCM?

A

A network of strong covalent bonds in solid state

47
Q

How do strong covalent bonds differ between GCM and SCM?

A

The strong covalent bonds only exist within the molecule in SCM while the strong covalent bonds extend throughout the entire structure, forming a continuous network

48
Q

What is carbon’s role in GCM?

A

Carbon is a non metallic element that can produce two GCM: diamond and graphite

49
Q

Diamond and graphite are ____ of the carbon element

A

Allotropes - different structures formed by the same element

50
Q

What is the structure of diamond?

A

Each carbon atoms forms covalent bonds with 4 other carbon atoms forming a 3D networks structure in tetrahedral arrangement

51
Q

What is the structure of graphite?

A

Each carbon atom forms covalent bonds with 3 other carbon atoms forming a layered structure of hexagonal rings of carbon atoms

52
Q

Do GCM have high melting/boiling points?

A

Due to the network of strong covalent bonds, a large amount of energy is required to break these strong bonds

53
Q

Why are diamonds and graphite heat resistant?

A

Both have covalent bonds that are incredibly strong. Heat energy needs to be very high to break these bonds. Additionally, GCS are made up of a rigid lattice that doesn’t allow for much movement of atoms. Heat energy causes atoms to vibrate. In a GCS, the lattice holds the atoms tightly in place, so the vibrations are less likely to disrupt the structure.

54
Q

Can diamonds conduct electricity?

A

No, diamonds do not have delocalised electrons or mobile ions to conduct electricity

55
Q

Can graphite conduct electricity?

A

Yes. There is 1 unbonded electron from each carbon atom which are delocalised. These delocalised electrons can move about freely.
Fun fact: Graphite is cheaper than copper to be used as the conducting material in machinery

56
Q

Are diamonds hard?

A

Yes diamonds are very hard as they have many strong covalent bonds that require a large amount of energy to break apart. Hence, diamond is used for cutting tools or coating drill bits

57
Q

Is graphite hard?

A

No, graphite is soft and slippery. As each layer is held by weak intermolecular forces of attraction that can be overcome easily by a small amount of energy, Therefore, the layers slide over each other easily. This makes it suitable for lubricants or pencil lead

58
Q

Are GCM soluble in water?

A

Most GCM are insoluble in water

59
Q

Are GCM soluble in organic solvents?

A

Most GCM are insoluble in organic solvents

60
Q

What are macromolecules?

A

A macromolecule is a very large molecule composed of thousands (or even millions) of atoms

61
Q

What kind of substances are macromolecules?

A

Macromolecules are covalent substances

62
Q

What are polymers?

A

A polymer is a type of macromolecule made by joining many covalent molecules into chains of much larger molecules. The difference between a polymer and a macromolecule, is that polymers are always made up of repeating units while macromolecules are not necessarily

63
Q

Name 2 natural polymers

A

Silk, wool, starch, rubber

64
Q

Name 2 man-made polymers

A

Nylon, polystyrene, polyester, other plastics

65
Q

Are macromolecles hard?

A

Polymers vary in flexibility and hardness due to many different combinations of atoms (e.g. safety helmets, clothing)

66
Q

Why are macromolecules solid at room temperature?

A

Due their large size. However, macromolecules can be formed by molecules over a range of sizes

67
Q

Do polymers have high melting/boiling point?

A

There is no fixed melting/boiling point because macromolecules can be formed by molecules over a range of sizes

68
Q

Why do macromolecules tend to soften over a range of temperatures?

A

The molecular vibrations with a higher kinetic energy overcomes the weak intermolecular forces of attraction (e.g. poly(ethene) is a polymer with low mp/bp due to weak intermolecular forces of attraction between molecules)

69
Q

Can macromolecules conduct electricity in any state?

A

No, they do not have delocalised electrons or mobile ions to conduct electricity

70
Q

Are macromolecules soluble in water?

A

Nope, insoluble

71
Q

Are macromolecules soluble in organic solvents?

A

Yes

72
Q

How are atoms arranged in a giant metallic lattice structure?

A

The same sized atoms occupy fixed positions, arranged in a regular pattern and evenly distributed throughout the solid

73
Q

Are GMLS hard?

A

The layers of atoms can slide over each other easily when a force is applied causing a metal to be soft, malleable and ductile

74
Q

What do the terms malleable and ductile mean?

A

Malleable = A solid that can be beaten or hammered into shapes or thin sheets without breaking
Ductile = A solid that can be pulled or stretched into wires without breaking

75
Q

Do GMLS have high melting/boiling points?

A

Yes, because the metallic bonds hold the atoms strongly so a large amount of energy is needed to overcome them

76
Q

Can GMLS conduct electricity?

A

GMLS are good conductors of electricity and heat because the ‘sea of delocalised electrons’ are free to move within the GMLS. They act as charge carriers to conduct electricity and heat

77
Q

Are GMLS soluble in water?

A

No, insoluble

78
Q

Are GMLS soluble in organic solvents?

A

No, insoluble

79
Q

Metals are pure. To make metals stronger, they are mixed with other elements to form ____

A

Alloys which are a mixture of a metal with one or more other elements in an irregular lattice arrangement

80
Q

Why does mixing a metal with other elements make it stronger and harder?

A

Different elements have different sized atoms disrupting the regular lattice arrangement of atoms in a metal causing alloys to have a irregular lattice arrangement. Hence, a larger force is needed to make the layers of atoms slide over each other causing an alloy to be stronger, harder and less malleable and ductile than the pure metal

81
Q

Are alloys pure?

A

No alloys are mixtures because the elements that make it up are physically mixed together

82
Q

Do alloys have a high melting/boiling point?

A

Alloys are mixtures so they melt/boil over a range of temperatures

83
Q

Can alloys conduct electricity?

A

Alloys are good conductors of electricity and heat like metals because they also have a ‘sea of delocalised electrons’ that are free to move within the GMLS. They act as charge carriers to conduct electricity and heat

84
Q

Are alloys soluble in water?

A

No, insoluble

85
Q

Are alloys soluble in organic solvents?

A

No, insoluble

86
Q

Name 2 alloys, the main elements in the alloy, it’s purpose and examples

A

1) Steel, iron and carbon, is to increase strength and hardness in cutlery or buildings and bridges
2) Bronze, copper and tin, is to increase strength and hardness in bells or medals
3) Brass, copper and zinc, is to increase strength and hardness in plumbing or musical instruments
4) Stainless steel, iron, carbon, nickel and chromium, is to resist corrosion in utensils or surgical instruments
5) Solder, tin and lead, is used to lower the melting point in electrical wires or circuit boards
6) Rose gold, copper and gold, is used to improve appearance or produce new colours in jewellery

87
Q

Why are pure metals not widely used?

A

1) They are soft
2) They react with air and water

Pure Chemistry (Sec 3) (8 decks)

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