3.1.1 Atomic Structure PPQs

Question 1

Explain how gaseous atoms of Rubidium are ionised using electron impact ionisation in a mass spectrometer. [2 marks]

Answer 1

• high energy electrons fired at sample from an electron gun
• high energy electrons knock off one electron from each atom, forming a positive ion

Question 2

Write an equation, including state symbols, to show the process that occurs when the first ionisation energy of rubidium is measured using electron impact ionization. [1 marks]

Answer 2

Rb(g) → Rb+(g) + e–

Question 3

State one reason why the first ionisation energy of rubidium is lower than the first ionisation energy of sodium. [1 mark]

Answer 3

• Rb is a bigger atom so electron further from nucleus
• electron lost from a higher energy level
• more shells so More shielding in Rb so less attraction of nucleus in Rb for outer electron

Question 4

By reference to the relevant part of the mass spectrometer, explain how the
abundance of an isotope in a sample of rubidium is determined. [2 makrs]

Answer 4

Relevant part: Detector
Explanation: Current / electrical signal produced proportional to abundance

Question 5

Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer. [3 marks]

Answer 5

• Smaller
• Bigger nuclear charge / more protons in Sr
• Same shielding

Question 6

Predict the element in Period 3 that has the highest 2nd IE [2 markks]

Answer 6

Na - electron removed from the 2p orbital

Question 7

Explain why the IE of every element is endothermic [1 mark]

Answer 7

energy needed to overcome the attraction between the negative electron and positive nucleus

Question 8

define the term relative atomic mass [2 marks]

Answer 8

average mass of one atom of an element / 1/12 mass of one atom of 12C

Question 9

which isotope is deflected most by magnetic field of a mass spectrometer?

Answer 9

the one with lowest m/z

Question 10

complete the electronic configuration of tellurium: [Kr]

Answer 10

[Kr] 5s2 4d10 5p4

Question 11

suggest what might cause the relative atomic mass of an element from a mass spec to be different to the one on the periodic table

Answer 11

• other isotopes present/some isotopes absent
• different abundances of isotopes

Question 12

predict whether the atomic radius of 124Te is larger than, smaller than, or the same as, the atomic radius of 130Te [2 marks]

Answer 12

the same
same no. protons AND same electron configuration

Question 13

Identify the period 3 element that has the highest melting point. Explain your answer. [4 marks]

Answer 13

• silicon
• macromolecular structure
• covalent bonds between atoms
• many strong covalent bonds need lots of energy to break

Question 14

which transition metals have exactly 3 unpaired electrons in their ground state?

Answer 14

Vanadium and Cobalt

Question 15

Name the two methods of ionisation in a mass spectrometer

Answer 15

electrospray and electron impact ionisation

Question 16

which transition metal has only 1 unpaired d electron as an atom?

Answer 16

Scandium

Question 17

An atom has 2 more protons and 3 more neutrons than an atom of 52Cr.
Deduce the symbol, including the mass number and the atomic number, for this atom.

Answer 17

57 26 Fe

Question 18

State two differences between the ‘plum pudding’ model and the model of atomic structure used today.

Answer 18

• central nucleus contains protons and neutrons
• Electrons are now arranged in energy levels/shells/orbitals

Question 19

Magnesium exists as three isotopes: 24Mg, 25Mg and 26Mg. In terms of sub-atomic particles, state the difference between the three isotopes of magnesium. State how, if at all, the chemical properties of these isotopes differ and give a reason for your answer. [3 marks]

Answer 19

• 24Mg has 12n; 25Mg has 13n; 26Mg has 14n OR They have different numbers of neutrons
• No difference in chemical properties Because all have the same electronic structure (configuration)

Question 20

Table 1 shows some data about fundamental particles in an atom. An atom of hydrogen can be represented as 1H. Use data from Table 1 to calculate the mass of this hydrogen atom.

Answer 20

1.6734 × 10^−24 g

Question 21

Which one of the following is a fundamental particle that would not be deflected by an electric field?

A electron

B neutron

C proton

Answer 21

B neutron

Question 22

Deduce the number of protons in 182W

Answer 22

74

Question 23

Deduce the number of neutrons in 186W

Answer 23

112

Question 24

Define the term atomic number.

Answer 24

Number of protons in the nucleus

Question 25

Explain why atoms of an element may have different mass numbers.

Answer 25

They may have different numbers of neutrons

Question 26

When He2+ particles were fired at a thin sheet of gold, most of the particles were detected at point P. What conclusion can be drawn from the detection of He2+ particles at point P?

Answer 26

Gold atoms are mainly empty space.

Question 27

When He2+ particles were fired at a thin sheet of gold, about 1 in 8000 of the particles were detected at point Q. What conclusion can be drawn from the detection of He2+ particles at point Q?

Answer 27

Gold atoms have a small, positive nucleus

Question 28

Define the term relative atomic mass.

Answer 28

average mass of an atom or isotopes divided by the mass of 1 atom of 12C, multiplied by 12

Question 29

Explain, in detail, how the relative atomic mass of an element can be calculated from data obtained from the mass spectrum of the element.

Answer 29

- Spectrum gives (relative) abundance and m/z - Multiply m/z by relative abundance for each isotope - Sum these values - Divide by the sum of the relative abundances

Question 30

Define the term mass number of an atom.

Answer 30

Mass number = number of protons + neutrons

Question 31

write an equation to represent the second ionisation of strontium

Answer 31

Sr+(g) -> Sr2+ + e-

Question 32

define the term 'first ionisation energy'

Answer 32

the amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state

Question 33

write an equation for the second ionisation energy of oxygen

Answer 33

O+(g) -> O2+(g) + e-

Question 34

On 2 axes, add crosses to estimate the successive ionisation energies of oxygen.

Answer 34

Question 35

Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron.

Answer 35

Outer electron is being removed from a positive ion and therefore requires more energy

Question 36

Identify the diagram in the figure below that shows the correct relative sizes of the ions in sodium fluoride. Justify your answer.

Answer 36

B: Both Na+ and F– same electron arrangement (isoelectronic). Na+ has more protons so stronger attractions for outer electrons

Question 37

Explain why the second ionisation energy of calcium is lower than the second ionisation energy of potassium. [2 marks]

Answer 37

- In Ca+ outer electron is further from nucleus - More shielding in Ca+

Question 38

Identify the s-block metal that has the highest first ionisation energy.

Answer 38

Be

Question 39

Deduce which of Na+ and Mg2+ is the smaller ion. Explain your answer.

Answer 39

Mg2+ because Mg2+ has more protons and has the same shielding

Question 40

State and explain the general trend in the values of the first ionisation energies of the elements Na to Ar. [3 marks]

Answer 40

- Trend : Increases (1) - Increased nuclear charge or proton number AND the shielding remains the same (1) - Stronger attraction between nucleus and outer e– (1)

Question 41

Explain why the value of the first ionisation energy of magnesium is higher than that of sodium.

Answer 41

- Increased nuclear charge - Same shielding

Question 42

Explain why the value of the first ionisation energy of neon is higher than that of sodium.

Answer 42

- Electron removed from a shell of lower energy - Less shielding

Question 43

Predict whether an atom of 88Sr will have an atomic radius that is larger than, smaller than or the same as the atomic radius of 87Rb. Explain your answer. [3 marks]

Answer 43

- Smaller - Bigger nuclear charge / more protons in Sr - Similar/same shielding

Question 44

The Ne atom and the Mg2+ ion have the same number of electrons. Give two reasons why the first ionisation energy of neon is lower than the third ionisation energy of magnesium.

Answer 44

- Mg2+ ion smaller than Ne atom so Mg2+ e– closer to nucleus - Mg2+ has more protons than Ne / e– is removed from a charged Mg2+ion vs neutral Ne atom

Question 45

A student studying GCSE science is puzzled by data which indicate that a sodium atom is larger than a chlorine atom and that a sodium ion is smaller than a chloride ion. How should an A–level Chemistry student explain this apparently conflicting information. [6 marks]

Answer 45

- A Cl atom has more protons in its nucleus than a Na atom has - Both have 3 shells of electrons - Electrons more strongly attracted by Cl nucleus so size smaller than Na - An electron shell is lost when a Na ion is formed from a Na atom - Inner electrons more strongly attracted so ion smaller than atom - An electron is added to the outer shell when a Cl ion is formed - Greater repulsion between shells so size of chloride ion greater than Cl atom

Question 46

Element Q forms a sulfate with formula QSO4. Which of these could represent the electronic configuration of an atom of Q?

Answer 46

B

Question 47

Tellurium is the element with atomic number of 52. Complete the electron configuration of tellurium.

Answer 47

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p4

Question 48

Explain why the first ionisation energy of sulfur is different from that of phosphorus.

Answer 48

- e− paired in 3p orbital in S - Paired e− repel so less energy needed to remove

Question 49

Draw a cross on the diagram to show the first ionisation energy of aluminium.

Answer 49

Al between 500 – 700 (between Na and Mg)

Question 50

State which of the first, second or third ionisations of aluminium would produce an ion with the electron configuration 1s2 2s2 2p6 3s1

Answer 50

Second

Question 51

State the trend in first ionisation energies in Group 2 from beryllium to barium.

Answer 51

- Decreases - Atomic radius increases - As group is descended there is more shielding - Less attraction between the nucleus and the outer electron

Question 52

What is the maximum number of electrons that can be accommodated in an s sub-level?

Answer 52

2

Question 53

What evidence from the diagram supports the fact that 2 electrons max can be in an s sub-level?

Answer 53

Two elements before the drop in energy to Al

Question 54

What evidence from the diagram supports the fact that the 3p sub-level is higher in energy than the 3s?

Answer 54

ionisation energy of Al < that for Mg

Question 55

What evidence from the diagram supports the fact that no more than three unpaired electrons can be accommodated in the 3p sub-level?

Answer 55

- fall in energy from P to S - From Al to P there are 3 additional electrons

Question 56

Describe how the molecules are ionised using electrospray ionisation. [3 MARKS]

Answer 56

- Sample is dissolved in a volatile solvent - Injected through hypodermic needle at high voltage - Each molecule/particle gains a proton/H+

Question 57

Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer. [2 marks]

Answer 57

- ion hits the detector and gains an electron - relative abundance is proportional to the size of the current

Question 58

Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass spectrometer [2 marks]

Answer 58

- Ions, not molecules, will interact with and be accelerated by an electric field - Only ions will create a current when hitting the detector

Question 59

A sample of ethanedioic acid was treated with an excess of an unknown alcohol in the presence of a strong acid catalyst. The products of the reaction were separated and analysed in a time of flight (TOF) mass spectrometer. Two peaks were observed at m / z = 104 and 118. Outline how the TOF mass spectrometer is able to separate these two species to give two peaks. [4 marks]

Answer 59

- Positive ions are accelerated by an electric field to a constant kinetic energy - The positive ions with m / z of 104 have the same kinetic energy as those with m / z of 118 and move faster - Therefore, ions with m / z of 104 arrive at the detector first

Question 60

Calculate the mass, in kg, of one atom of 46Ti

Answer 60

Question 61

A molecule Q is ionised by electron impact in a TOF mass spectrometer. The Q+ ion has a kinetic energy of 2.09 x 10^–15 J. This ion takes 1.23 x 10^–5s to reach the detector. The length of the flight tube is 1.50 m Calculate the relative molecular mass of Q.

Answer 61

169

Question 62

A naturally occurring sample of the element boron has a relative atomic mass of 10.8. In this sample, boron exists as two isotopes, 10B and 11B. Calculate the percentage abundance of 10B in this naturally occurring sample of boron.

Answer 62

20%

Question 63

A sample of strontium has a relative atomic mass of 87.7 and consists of three isotopes, 86Sr, 87Sr and 88Sr. In this sample, the ratio of abundances of the isotopes 86Sr :87Sr is 1:1. Calculate the percentage abundance of the 88Sr isotope in this sample.

Answer 63

80%

Question 64

A TOF mass spectrum was obtained for a sample of barium that contains the isotopes 136Ba, 137Ba and 138Ba. The sample of barium was ionised by electron impact. Identify the ion with the longest time of flight.

Answer 64

138Ba+

Question 65

A sample contains two isotopes of Copper, 63B and 65B. 63B has an abundance 2.33 times greater than 65Cu. Calculate the relative atomic mass of the sample to one decimal place.

Answer 65

63.6

Question 66

In a time of flight mass spectrometer, molecule X is ionised using electrospray ionisation. What is the equation for this ionisation?

Answer 66

X(g) + H+ → XH+(g)

Question 67

Define the term relative molecular mass (Mr).

Answer 67

average mass of one molecule / 1/12th atom of C12

Question 68

Which shows the electron configuration of an atom of a transition metal? A [Ar] 4s2 3d0 B [Ar] 4s2 3d8 C [Ar] 4s2 3d10 D [Ar] 4s2 3d10 4p1

Answer 68

B - Nickel

Question 69

A sample of the element Q consists of several isotopes. All of the Q+ ions in the sample of Q that has been ionised in a TOF mass spectrometer have the same kinetic energy. The time of flight of a 82Q+ion is 1.243 × 10−5 s. Calculate the time of flight of the 86Q+ion.

Answer 69

Question 70

The mass spectrum of tellurium also has a small peak at m/z = 64 despite the Ar being 128. Explain the existence of this peak.

Answer 70

2+ ion formed / 2 electrons removed From 128 (Te)

Question 71

Sodium reacts with aluminium and hydrogen to form solid NaAlH4. Suggest why NaAlH4 has a high melting point.

Answer 71

- contains oppositely charged ions - strong attraction between ions

Question 72

Which statement is not correct about the P3 elements sodium to chlorine? A. Sodium has the largest atomic radius. B. Sodium has the lowest melting point. C. Silicon has the highest melting point. D. Chlorine has the highest first IE.

Answer 72

B - Sodium has the lowest melting point