Topic 3.1.1.1 - Atomic Structure

Question 1

What is the relative atomic mass of a proton?

Answer 1

1

Question 2

What is the relative atomic mass of a neutron?

Answer 2

1

Question 3

What is the relative atomic mass of an electron?

Answer 3

Approximately 0

Question 4

What is the relative atomic charge of a proton?

Answer 4

+1

Question 5

What is the relative atomic charge of a neutron?

Answer 5

0

Question 6

What is the relative atomic charge of an electron?

Answer 6

-1

Question 7

What is the difference between two isotopes?

Answer 7

The number of neutrons, (or the mass number).

Question 8

What are the similarities between two isotopes?

Answer 8

The number of protons and electrons, (or the atomic number).

Question 9

What are the three fundamental particles that make up an atom?

Answer 9

Proton, neutron and electron.

Question 10

Why is are the chemical properties of two different isotopes of the same element identical?

Answer 10

They have the same electron configuration.

Question 11

What are the four stages of a mass spectrometer?

Answer 11

Electrospray Ionisation
Acceleration
Ion Drift
Detection

Question 12

Which two stages of the mass spectrometer require the sample to be ionised?

Answer 12

Acceleration

Detection

Question 13

Describe the process of electrospray ionisation in a TOF Mass Spectrometer

Answer 13

The sample is dissolved in a polar solvent and a high voltage is applied, causing the particles to lose an electron.

Question 14

Describe the process of acceleration in a TOF Mass Spectrometer.

Answer 14

The positive ions are accelerated by an electric field.

Question 15

Describe the relationship between the mass/charge ratio of an ion and it’s time spent during the electron drift phase of a TOF Mass Spectrometer.

Answer 15

The heavier the particle, the lower the speed and the greater the time taken to reach the detector.

Question 16

Describe the process of detection in a TOF Mass Spectrometer.

Answer 16

The ions create a current when they reach the detector. The detector records the time taken to reach it and the current. The greater the abundance of the isotope, the larger the current.

Question 17

What is the definition of relative atomic mass?

Answer 17

The relative atomic mass of an atom is the ratio of the average mass of one atom of that element to 1/12th of the mass of one atom of carbon-12.

Question 18

What is the definition of relative molecular mass?

Answer 18

The relative molecular mass of a molecule is the ratio of the average mass of that molecule to 1/12th of the mass of an atom of carbon-12.

Question 19

What is the charge on any molecule which passes through a mass spectrometer?

Answer 19

Positive

Question 20

The relative atomic mass of a sample of magnesium is 24.46

The isotopes which make up the sample are Mg-24 (75.86%), Mg-25 (13.12%) and one other isotope. Calculate the mass of the missing isotope.

Answer 20

Missing Percentage = 100 - (75.86 + 13.12) = 11.02

24.46 = [ (24 x 75.86) + (25 x 13.12) + ( ? x 11.02) ] / 100

2446 = 1820.64 + 328 + (11.02 x ? )

297.54 = 11.02 x ?

27 = ?

Question 21

Calculate the relative atomic mass of a sample of sodium consisting of the following isotopes: Na-22 (23.14%), Na-23 (59.16%) and Na-25 (17.70%).

Answer 21

RAM = [ (22 x 23.14) + (23 x 59.16) + (25 x 17.70) ]

RAM = [ 509.08 + 1360.68 + 442.5 ] / 100

RAM = 2312.26 / 100

RAM = 23.12

Question 22

Calculate the relative atomic mass of a sample of hydrogen consisting of the following isotopes: H-1 (96.13%), H-2 (2.11%) and H-3 (1.76%).

Answer 22

RAM = [ (1 x 96.13) + (2 x 2.11) + (3 x 1.76) ] / 100

RAM = [ 96.13 + 4.22 + 5.28 ] / 100

RAM = 105.63 / 100

RAM = 1.06

Question 23

What is the electron configuration of carbon?

Answer 23

1s2 2s2 2p2

Question 24

What is the electron configuration of magnesium?

Answer 24

1s2 2s2 2p6 3s2

Question 25

What is the electron configuration of vanadium?

Answer 25

1s2 2s2 2p6 3s2 3p6 4s2 3d3

Question 26

What is the electron configuration of copper?

Answer 26

1s2 2s2 2p6 3s2 3p6 4s1 3d10

Question 27

What is the electron configuration of Na+ ion

Answer 27

1s2 2s2 2p6

Question 28

What is the electron configuration of the Br- ion?

Answer 28

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

Question 29

What is the electron configuration of the Cr3+ ion?

Answer 29

1s2 2s2 2p6 3s2 3p6 4s0 3d3

Question 30

What is the general trend in first ionisation energies across period 2?

Answer 30

Increase

Question 31

What is the reason for the general increase in first ionisation energy across period 3?

Answer 31

The shielding remains constant along the period, but the amount of protons in the nucleus increases. This means the effective nuclear charge increases across the period and so the electrons are held more tightly. Therefore the amount of energy required to remove the electrons increases.

Question 32

Why does lithium have a higher first ionisation energy than sodium?

Answer 32

Sodium has its outer electron in 3s, whereas lithium has its outer electron in 2s. Sodium therefore has more shielding so the electrons are less tightly held and so require less energy to remove.

Question 33

Why does aluminium have a lower first ionisation energy than magnesium?

Answer 33

Aluminium has its outer electron in the 3p orbital, which is slightly more shielded from the nucleus. Therefore the outer electron is less tightly held and so it requires less energy to remove the electron.

Question 34

Why does oxygen have a lower first ionisation energy than nitrogen?

Answer 34

Oxygen has 4 electrons in the 2p orbital, so this is the first time in 2p where spin-pair repulsion occurs. Because the electrons are already being repelled away from the atom, they require less energy to remove.

Question 35

Why is the second ionisation energy of lithium higher than the first ionisation energy of lithium?

Answer 35

After the first ionisation energy, there are more protons in the nucleus than there are electrons in the atom. This means the electrons are more tightly held by the nucleus, and therefore to remove another electron requires even more energy.