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Chemistry A Level > 3.1 The Periodic Table > Flashcards

3.1 The Periodic Table Flashcards

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1
Q

How did Dobereiner arrange the periodic table?

A

He ordered certain groups of three elements (triads) by atomic weight and found the middle element had a weight and properties that were roughly an average of the other two elements

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2
Q

How did Newlands modify the periodic table?

A
  • Newlands arranged the elements in order of their relative atomic weights (relative atomic masses)
  • He suggested that elements show similar properties to the element eight places after it in the table
  • He named this the law of octaves
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3
Q

How did Mendeleev change the period table?

A
  • Elements with similar properties arranged in vertical columns (groups)
  • Gaps were left where no element fitted the repeating pattern and its properties were predicted (these elements were later discovered and matched his predictions)
  • Order of elements rearranged where their properties did not fit
  • The arrangement of the elements in order of their atomic weights corresponded to their so-called valencies and chemical properties
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4
Q

How did Moseley modify Mendeleev’s periodic table?

A

Moseley modified Mendeleev’s periodic table to read that the properties of the elements vary periodically with their atomic numbers rather than atomic weights

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5
Q

What is periodicity?

A

Periodicity is the trend in properties that is repeated across each period

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6
Q

What are the two things all elements in a vertical group have the same?

A
  • Same number of electrons in the outer shell

- The same type of orbital

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7
Q

What is ionisation?

A

Ionisation occurs when atoms lose or gain electrons

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8
Q

What is the ionisation energy?

A

The first ionisation energy of an element is the energy required to remove one electron from one atom in one mole of an element in its gaseous state

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9
Q

What factor affects ionisation energy?

A
  • Electrons are held in their shells by the nuclear attraction to the positive nucleus
  • Electrons in the outer shell are removed first because they experience the smallest nuclear attraction so are most easily removed
  • Therefore the ionisation energy depends on how strong the nuclear attraction is
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10
Q

What three factors affect nuclear attraction?

A
  • Atomic radius
  • Nuclear charge
  • Electron shielding or screening
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11
Q

How does atomic radius affect nuclear attraction?

A

The larger the atomic radius, the smaller the nuclear attraction because the outermost electrons are further away from the nucleus

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12
Q

How does nuclear charge affect nuclear attraction?

A

The bigger the nuclear charge, the larger the attraction force on the outer electrons

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13
Q

How does electron shielding affect nuclear attraction?

A

The more inner shells there are the larger the shielding effect and the smaller the nuclear attraction because this is more electron repulsion and greater distance to the nucleus

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14
Q

What are the successive ionisation energies?

A

A measure of the amount of energy required to remove one electron in turn

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15
Q

What is the trend from one successive ionisation energy to the next? Why?

A

Each successive ionisation energy is higher than the one before.
This is because as each electron is removed, there is less repulsion between the remaining electrons and each shell will be drawn slightly closer to the nucleus. The positive nuclear charge outweighs the negative charge. The nuclear attraction increases with each removed electron so more energy is needed to remove each successive electron

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16
Q

What is the trend in ionisation energy across the period ?

A

Ionisation energy values increase across each period

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17
Q

Why does ionisation energy increase across the period ?

A
  • Across each period, the number of protons in the nucleus increases so there is a greater nuclear attraction
  • Electrons are being added to the same shell so the outer shell is being drawn in
  • There is the same number of inner shells so electron shielding will hardly change

The attraction between the nucleus and outer electrons increases so more energy is needed to remove an electron

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18
Q

Why would there be a small decrease in the first ionisation energies between group 2 and 3 elements?

A
  • Group 3 have their outer electrons in a p-orbital whereas group 2 have theirs in an s-orbital
  • P-orbitals have a slightly higher energy than s-orbitals so are marginally further away from the nucleus
  • Therefore the electrons in these orbitals are slightly easier to remove, hence the lower ionisation energies
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19
Q

Why is there a small decrease between group 5 and 6?

A
  • In group 5, each of the p-orbitals contains only a single electron
  • in group 6, there are two electrons in the p orbital
  • Electrons that are spin-paired experience some repulsion which makes the first outer electron slightly easier to remove so a lower first ionisation energy is observed
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20
Q

What is the trend in atomic radius across a period?

A

There is a decrease in atomic radius across a period because the increased nuclear charge pulls the electrons in towards it

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21
Q

Why is there a sharp decrease in first ionisation energy between the end of one period and start of the next ?

A

A new shell is being added further away from the nucleus which leads to:

  • an increase in the distance of the outermost shell in the nucleus
  • an increase in electron shielding of the outermost shell by inner shells
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22
Q

What is the trend in ionisation energy down the group?

A

It decreases. This is because the number of shells increases so the distance of the outer electrons from the nucleus increases so there is a weaker nuclear attraction
There are also more inner shells so the shielding effect on the outer electrons increases so there is a weaker attraction

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23
Q

What is trend in number of protons down a group?

A

The number of protons in the nucleus increases moving down a a group

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24
Q

What is the trend in ionisation energy down the group?

A

First ionisation energy decreases down a group because the attraction between the nucleus and the outer electrons decreases moving down a group so less energy is needed to remove an electron

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25
Q

What is metallic bonding ?

A

The electrostatic attraction between positive metal ions (cations) and delocalised electrons

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26
Q

What is a giant metallic lattice structure ?

A
  • The delocalised electrons are spread throughout the structure
  • These electrons can move within the structure
  • it is impossible to tell which electron originated from which positive ion
  • the charges must balance over the whole structure
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27
Q

What is a giant metallic lattice often described as?

A

A lattice of positive ions fixed in position and surrounded by a sea of delocalised electrons

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28
Q

Why do giant metallic lattices have high melting and boiling points?

A
  • The electrons are free to move throughout the structure but the positive ions remain where they are
  • the attraction between the positive ion and negative delocalised electrons is very strong
  • A high temperature is needed to overcome the metallic bonds and dislodge the ions from their rigid position
29
Q

Why are giant metallic lattices good electrical conductors?

A
  • Metals are good conductors of electricity
  • The delocalised electrons can move freely anywhere within the lattice
  • This allows the lattice to conduct electricity even in a solid state
30
Q

Why is a giant metal lattices malleable and ductile? (Can be hammered into different shapes and can be drawn out or stretched)

A

Delocalised electrons can move so the atoms or layers can slide past each other

31
Q

What is the metal to non-metal trend across periods 2 and 3?

A

Metal elements to non-metal elements

32
Q

Why is Silicon classified as a semi-metal/metalloid?

A

It has the shiny appearance of a metal but is brittle. It can also conduct electricity, but very poorly

33
Q

What is the trend in melting point between group 1 and 4?

A

Melting points increase steadily because the elements have giant structures. The nuclear charge increases as does the number of electrons which causes a stronger attraction

34
Q

What is the trend in melting point between group 4 and 5?

A

Sharp decrease in melting point because the elements have simple, molecular structures so the molecules are only attracted by weak intermolecular forces

35
Q

What is the trend in melting point between group 5 and 8?

A

Remains relatively low because the elements have simple molecular structures

36
Q

Compare the structure and bonding of diamond and GRAPHENE

A

Diamond forms a lattice where each carbon atom is bonded to four other carbon atoms.

Graphene forms a two-dimensional giant lattice one carbon atom thick

37
Q

What are three properties of group 2 elements?

A
  • Reasonably high melting points and boiling points
  • Light metals with low densities
  • Form colourless compounds
38
Q

What do group 2 elements need to do to achieve noble gas configuration?

A

Lose two electrons

39
Q

What is the trend of reactivity down group 2 and why?

A

Reactivity increases going down the group. This is because each successive element has its outer electrons in a higher energy level, has a larger atomic radius and feels more shielding.

40
Q

Are group 2 elements reducing or oxidising agents?

A

They are reducing agents because they are oxidised to form 2+ ions

41
Q

What is the product of a reaction of a group 2 element and oxygen?

A

Group 2 elements react with oxygen to form an ionic oxide. This is a redox reaction.

42
Q

What are the products of a reaction in which a group 2 element reacts with water?

A

The products are hydroxide and water. Moving down the group, the metals react more vigorously. This is also a redox reaction

43
Q

What are the products of a reaction where a group 2 element reacts with a dilute acid?

A

A salt and hydrogen gas is formed. The reaction becomes more vigorous moving down the group

44
Q

What is the result of a reaction of group 2 oxides + water?

A

A metal hydroxide is formed

45
Q

What is the trend of solubility of hydroxides down the group?

A

The solubility of hydroxides in water increases down the group. When a hydroxide is more soluble than another it will release more OH- ions which will make a more alkaline solution

46
Q

What is the overarching use of group 2 metal compounds?

A

Neutralising acids

47
Q

What is calcium hydroxide used for?

A

Used as ‘lime’ to reduce the acidity levels of soil

48
Q

What is magnesium hydroxide used for?

A

Used in indigestion medicines to neutralise a build-up of too much hydrochloric acid

49
Q

What is calcium carbonate used for?

A

Useful building material- used in the building trade and in the manufacture of glass and steel.

50
Q

What is a drawback of using group 2 carbonates as building materials?

A

They react readily with acids and seeing as most rainwater has an acidic pH, it leads to gradual erosion of buildings made of limestone or marble

51
Q

What are two properties of group 7 elements?

A
  • have low melting and boiling points

- exist as diatomic molecules

52
Q

What is the trend in boiling point down the halogen group?

A

Moving down the group the boiling point increases because the physical state changes from gas to solid. This is because each successive element has an extra shell which leads to a higher level of London forces between the molecules

53
Q

What is the trend in reactivity down the halogen group?

A

The reactivity decreases down the group because the atomic radius increases and shielding increases so the ability to gain an electron decreases because there is less nuclear pull from the nucleus.

54
Q

What happens when a more reactive halogen is in the same reaction as a less reactive halogen? What is this called?

A

The more reactive halogen will oxidise and displace a halide of the less reactive halogen.
This is called a displacement reaction

55
Q

What indicates that redox reaction has occurred?

A

Halogens form different-coloured solutions so colour changes indicate that redox reactions have occurred

56
Q

What is commonly added to help distinguish between the two halogens in solution?

A

An organic solvent like cyclohexane

57
Q

Name the colour of the halogens in water and the colour in cyclohexane:

  • Cl2
  • Br2
  • I2
A

pale green —– pale green
orange —— orange
brown —— violet

58
Q

What is disproportionation?

A

Disproportionation is a reaction in which the same element is both reduced and oxidised.

59
Q

What are two examples of disproportionation reaction?

A
  • Reaction of chlorine with water to form hydrochloric acid and chloric (I) acid
  • Reaction of chlorine with cold dilute aqueous sodium hydroxide
60
Q

How can you test unknown samples?

A

Using qualitative tests- which can tell you which ions are present. Many of these tests involve a precipitation reaction.

61
Q

What is the method for identifying carbonate ions?

A
  • Add a dilute strong acid to the suspected carbonate

- Collect any gas formed and pass it through limewater

62
Q

What is a positive result for carbonate ions?

A
  • Fizzing/colourless gas is produced

- The gas turns limewater cloudy

63
Q

What is the method for identifying sulfate ions?

A

-Add dilute hydrochloric acid and barium chloride to the suspected sulfate

64
Q

What is the positive result for sulfate ions?

A

-A white precipitate of barium sulfate is produced

65
Q

What is the method for identifying halide ions?

A
  • Dissolve suspected halide in water
  • Add an aqueous solution of silver nitrate
  • Note the colour of the precipitate formed
  • If the colour is hard to distinguish add aqueous ammonia (dilute then concentrated)
  • Note the solubility of the precipitate in aqueous ammonia
66
Q

What is the positive result for halide ions?

A
  • Silver chloride: white precipitate, soluble in dilute ammonia
  • Silver bromide: cream precipitate, soluble in concentrated ammonia
  • Silver iodide: yellow precipitate, insoluble in dilute and concentrated ammonia
67
Q

What is the method for identifying ammonium ions?

A
  • Add sodium hydroxide solution to the suspected ammonium compound and warm very gently
  • Test any gas evolved with red litmus paper
68
Q

What is the positive result for ammonium ions?

A
  • Ammonia gas will turn red litmus paper blue

- Ammonia gas has a distinctive smell

Chemistry A Level (6 decks)

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