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HIGHER CHEMISTRY > UNIT 1 > Flashcards

UNIT 1 Flashcards

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1
Q

What does measuring the rate of reactions allow chemists to do?

A

Measuring the rate of reaction allows chemists to compare reactions.

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2
Q

How do we calculate the rate of reaction?

A

The rate of reaction can be calculated by change in concentration or mass or volume divided by the time.

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3
Q

How do we calculate the relative rate of a reaction?

A

Rate= 1/time

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4
Q

How do we calculate the time for a reaction?

A

Time = 1/ rate

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5
Q

Successful collisions occur when…

A

The collision geometry is correct and the particles have the right amount of energy.

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6
Q

How does increasing the concentration and pressure increase the rate of reaction?

A
  • More particles are in the same space. As more of theses particles are moving about, you are more likely to have collisions.
  • If the particles colliding have sufficient energy, a successful reaction will occur.
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7
Q

Particle size ( Lumps and powder)

A

Powdered lumps react faster than lumps. Breaking up a solid into smaller pieces exposes more surfaces and hence more particles are available to react.

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8
Q

Temperature

A

Temperature is a measure of the average kinetic energy of the particles in a substance. If the temperature is increased,the particles have more kinetic energy. This means that they will collide with greater force.

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9
Q

Activation energy

A

The activation energy is the minimum amount of energy required by the colliding particles for a chemical reaction to occur. This explains why some chemical reactions do not occur at room temperature. For example methane gas mixed with oxygen gas at room temperature does not react despite particles colliding with one another. The particles do not have enough energy to react. Energy must be applied to allow theses particles to react.

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10
Q

What do energy distribution diagrams show?

A

These diagrams can be used to show the energies of the particles.

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11
Q

How does increasing the temperature lead to an increase in reaction rate?

A

Increasing the temperature leads to an increase in reaction rate because more particles now have energy greater than or equal to the activation energy.

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12
Q

Collision geometry

A

This refers to the position of the reactant when they collide.

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13
Q

Reaction profiles

A

The energy change that occurs when reactant are converted into products is known as the enthalpy change.

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14
Q

Exothermic reactions

A

In an exothermic reaction the products have less energy that the reactant. Heat energy has been released to the surroundings. This has a negative delta H value.

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15
Q

Endothermic reactions

A

The products have more energy that the reactants as energy has been taken in from the surroundings. This causes the temperature to fall. This has a positive delta H value.

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16
Q

What can potential energy diagrams be used to show?

A

They can be used to show the activation energy for a reaction

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17
Q

What is an activated complex and where is it shown?

A

This is an unstable arrangement of atoms which is very high in energy. It is shown at the very top of the activation energy barrier.

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18
Q

What are catalysts and how do they work?

A

They speed up chemical reactions without being used up. They work by forming temporary bonds with reactants,causing the bonds within the reactants to weaken. This lowers the activation energy allowing many more reactions to occur.

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19
Q

What does metallic bonding consist of?

A

Metallic bonding consists of positive metal ions surrounded by a pool of delocalised electrons.

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20
Q

What is metallic bonding?

A

The attraction between the charged metal ions and the electrons is known as metallic bonding.

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21
Q

Why do metals have high boiling points?

A

Metals have high boiling points as there is a lot of energy required to to overcome the strong metallic bonds.

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22
Q

How do metals conduct electricity?

A

As the electrons are free to move, metals conduct electricity.

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23
Q

Give examples of diatomic molecules that contain covalent bonding?

A

Hydrogen,nitrogen,oxygen and the halogens

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24
Q

What bonding and structure does phosphorus have?

A

Phosphorus consists of four phosphorus atoms joined together by covalent bonds

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25
Q

What bonding and structure does sulfur have?

A

Sulfur consists of eight sulfur atoms that join by covalent bonds to form a ‘puckered ring’

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26
Q

Describe the fullerenes

A

They are a form of carbon consisting of five and six membered rings of carbon atoms covalently bonded together

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27
Q

For covalent molecular elements what forces of attraction exist?

A

For covalent molecular elements, the intramolecular forces are covalent. The intermolecular forces are weak London dispersion forces.

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28
Q

Why do covalent molecular elements have relatively low melting and boiling points?

A

Because only the weak London dispersion forces have to be broken to melt and boil them.

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29
Q

Why do some covalent molecular elements have high melting and boiling points?…give examples in answer.

A

Sulfur, phosphorus and the fullerenes , have many more electrons than the lighter molecules, therefore there are stronger London dispersion forces between the molecules,resulting in the higher melting points of these elements .

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30
Q

What do covalent network structures consist of?

A

Covalent network structures consist of many thousands of atoms joined together by covalent bonds.

31
Q

Why do covalent network structures have high melting and boiling points?

A

Covalent network structures have high melting and boiling points as strong covalent bonds must be broken for the solid to melt.

32
Q

Give examples of covalent network structures and describe each of them.

A

Carbon diamond:
Each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement. It is very hard and strong. All the four outer electrons are used to form covalent bonds to other carbon atoms so it does not conduct electricity.

Carbon graphite:
Each carbon atom forms three covalent bonds to neighboring carbon atoms forming layers of hexagonal rings. The fourth outer electron becomes delocalised between the layers allowing carbon graphite to conduct electricity. These layer are held together by weak London dispersion forces. Graphite is an effective lubricant.

Boron and silicon:
Boron forms a rigid covalent network structure with a similar tetrahedral structure to carbon diamond.

33
Q

What are monatomic elements? and give an example

A

The noble gases a mono atomic element and they consists of single atoms which are not bonded to neighboring atoms.

34
Q

What happens when monoatomic elements are cooled?

A

When they are cooled they move closer to form a liquid and then they form a solid with weak London dispersion forces.

35
Q

Why do monoatomic elements have low melting points?

A

The monoatomic element shave low melting points as only weak London dispersion forces have to be overcome.

36
Q

Why does the melting points increase as you decent the noble gas group?

A

The melting points increase as you descend the noble gas group because the London dispersion forces become stronger. This is because there are more electrons.

37
Q

what is the covalent radius?

A

The covalent radius is a measure of the size of an atom. It is half the distance between the nuclei of two covalently bonded atoms of an element.

38
Q

Going across the period,covalent radius…..

A

decreases

39
Q

Going down a group,covalent radius….

A

increases.

40
Q

What two facts help explain trends in the periodic table?

A

Nuclear charge of the atom and the number of filled electron shells.

41
Q

What happens to the nuclear charge and the number of filled electron shells going across the period?

A

Going across the period,the nuclear charge increases but the number of filled electron shells remains the same.

42
Q

Why does the covalent radius decrease?

A

An increase in the nuclear charge results in electrons being more strongly attracted to the nucleus which means that the covalent radius decreases.

43
Q

Going down the group the number of filled electron shells….

A

…increases!

44
Q

Explain what happens when the number of filled electron shells increases. ( hint: think of the screening effect)

A

As the number of filled electron shells increases, the extra layer of electrons ‘shields’ the outer electrons from the positive nucleus so that the outer electrons are less strongly attracted to the nucleus. The ‘shielding’ is also known as ‘screening’

45
Q

Electronegativity: what is it?

A

Is a measure of attraction for electrons in a covalent bond.

46
Q

Going down the group electronegativity……

Going across the period electronegativity…

A

decreases

increases.

47
Q

Explain what happens to the electronegativity as the nuclear charge increases going across the period.

A

As the nuclear charge increases the atom attracts bonded electrons more strongly therefore the nuclear charge increases going across the period.

48
Q

Explain what happens to electronegativity as the number of filled electron shells increases going down the group

A

As the number of filled electron shells increases the extra shells shield the bonded electrons from the nuclear charge which means that electrons are less strongly attracted to the atom therefore electronegativity decreases going down the group.

49
Q

Ionisation energy: What is it?.

A

’ the energy required to remove one mole of electrons from one mole of gaseous atoms’

50
Q

Going down a group, the ionisation energy….

Going across a period, the ionisation energy…

A

decreases

increases

51
Q

Explain why the ionisation energy increases going across the period.

A

The outermost electrons are more strongly held because of an increase in nuclear charge so the energy needed to remove them increases going across the period.

52
Q

Explain why the ionisation energy as the number of filled electrons shells increases

A

An electron is being removed from the outer most shell. This shells is very distant from the nucleus and therefore although the nuclear charge is increasing ,less energy is needed to remove the electron. Also an additional factor is the screening effect of the inner electrons. These inner electrons reduce the attraction of the nucleus for the outermost electrons therefore reducing the ionisation energy.

53
Q

What is pure covalent/non polar covalent bonding?

A

This when a covalent bond is formed between two atoms with the same electronegativity. The atoms have an equal attraction for electrons in the covalent bond.

54
Q

What is a polar covalent bond?

A

This is when two atoms with different electronegativity values form a covalent bond. The atom with the higher elecronegativity value is assigned the delta minus symbol and the atom with the lower value is assigned the delta plus symbol

55
Q

What is an ionic bond?

A

An ionic bond is when electrons are transferred from one atom to another causing one atom to loose electrons and the other atom to gain electrons. The attraction between the positive ions of one element and the negative ions of the other element is know as an ionic bond.

56
Q

What kinds of metals form an ionic bond?

A

When a metal bonds with a non metal, an ionic bond forms as the metal has a low electronegativity value and the non metal has a much higher electronegativity value.

57
Q

What can the bonding continuum help us do?

A

It can be used to help us appreciate the differences in bonding, where pure ionic bonding and pure covalent bonding are at opposite ends and polar covalent bonding is in the middle.

58
Q

What are the three main characteristics of compounds that can be used to help decide whether a compounds is ionic or covalent?

A

1) Ionic compounds will conduct electricity when molten or when they are dissolved in water, covalent compounds will not conduct
2) Ionic compounds tend to have high melting points as a lot of energy is required to break the strong ionic bonds that exist in the ionic lattice.
3) Ionic compounds are usually soluble in water.

59
Q

What are the three main types of wan der waals forces?

A

1) London dispersion forces
2) Permanent dipole-permanent dipole interactions
3) Hydrogen bonding

60
Q

What are LDF forces?

A

LDF forces are the weakest force of attraction and can operate between atoms and molecules.

61
Q

What are LDF forces caused by?

A

They are caused by the uneven distribution of electrons

62
Q

Describe induced dipoles.

A

This is when one side of the atom has an excess of electrons which causes it to become delta negative and the other side becomes delta positive. The electrons in the neighboring atom will shift away from an approaching delta negative causing delta positive to appear. This is called induced dipoles as one atom has caused this to happen to its neighbor.

63
Q

What is the main force of attraction between polar molecules?

A

London dispersion forces.

64
Q

How to pdp-pdp interactions occur?

A

These occur between polar molecules.

65
Q

What interactions do polar molecules have?

A

The molecules that make up the compounds have a permanent dipole where one side of the molecule is delta positive and the other side of the molecules is delta negative.

66
Q

How does polarity cancel?

A

It cancels when molecules have a symmetrical arrangement of polar bonds.

67
Q

How does hydrogen bonding occur?

A

occurs between molecules where there is an atom of H joined to an atom of N,O or F.

68
Q

Which is the strongest of the three intermolecular forces?

A

Hydrogen bonding.

69
Q

What does the differences in intermolecular forces give rise to?

A

They give rise to compounds having different melting and boiling points.

70
Q

Solubility can be predicted using the rule ‘like dissolves like’. What does this mean?

A

This means that polar molecules and ionic substances will dissolve in polar solvents and non polar compounds will dissolve in non-polar solvents.

71
Q

Do viscous liquids have strong intermolecular forces?

A

Yes

72
Q

What happens to the viscosity if you increase the number of hydroxyl groups.

A

Increasing the number of hydroxyl groups in a molecule increases the viscosity.

73
Q

Describe why ice is less dense than water

A

The water molecules adopt an efficient hydrogen bonding whereby the water the water molecules adopt an ‘open lattice’ structure which results in lots of spaces between water molecules.

HIGHER CHEMISTRY (3 decks)

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