Atomic Structure

Question 1

What is the maximum number of electrons an orbital can contain?

Answer 1

2

Question 2

What happens to the energy level of a 3d shell as soon as an electron enters it?

Answer 2

Before, 3d has higher energy levels than 4s. However as soon as an electron enters 3d, the energy level drops below 4s

Question 3

Why does 4s get filled before 3d?

Answer 3

Because 4s is lower in energy than 3d (until 3d gains an electron and its energy level drops)

Question 4

Why do the orbitals have negative values of energy?

Answer 4

Because that is the amount of energy you must give the electron in order to get rid of an electron from an atom in its gaseous state

Question 5

Define ionisation energy

Answer 5

The energy required to remove 1 mole of electrons from 1 mole of atoms in their gaseous state

Question 6

What are the factors affecting the size of the 1st ionisation energy?

Answer 6

Size of nuclear charge
Distance from the nucleus
Shielding (inner shells block attractive force of nucleus)
Pair repulsion

Question 7

Describe the difference in 1st ionisation energies between Hydrogen and Helium

Answer 7

Helium has a much higher 1st ionisation energy because the nuclear charge has doubled, but the distance from the nucleus and the shielding is the same

Question 8

Describe the difference in 1st ionisation energies between Helium and Lithium

Answer 8

Lithium has a much lower 1st ionisation energy because the electron is coming from a new quantum shell, meaning there is greater shielding and distance from the nucleus

Question 9

Describe the difference in 1st ionisation energies between Lithium and Beryllium

Answer 9

Beryllium has a higher 1st ionisation energy because there is a greater nuclear charge but the shielding and distance from the nucleus is roughly the same

Question 10

Describe the difference in 1st ionisation energies between Beryllium and Boron

Answer 10

Boron has a lower 1st ionisation energy because the electron is coming from a new sub-shell, meaning there is greater shielding and distance from the nucleus

Question 11

Describe the difference in 1st ionisation energies between Boron and Carbon

Answer 11

Carbon has a higher 1st ionisation energy because the nuclear charge is greater but the shielding and distance from the nucleus is roughly the same

Question 12

Describe the difference in 1st ionisation energies between Carbon Nitrogen

Answer 12

Nitrogen has a higher 1st ionisation energy because the nuclear charge is greater but the shielding and distance from the nucleus is roughly the same

Question 13

Describe the difference in 1st ionisation energies between Nitrogen and Oxygen

Answer 13

Oxygen has a lower nuclear charge because there is pair repulsion but the shielding and distance from the nucleus is roughly the same

Question 14

Why do alkali metals appear at the troughs in an atomic number vs ionisation energy graph?

Answer 14

Because they have the minimum nuclear charge for the quantum shell

Question 15

Why do noble gases appear at the peaks in an atomic number vs ionisation energy graph?

Answer 15

Because they have the highest ionisation energy for their quantum shell

Question 16

Why does Helium have the highest 1st ionisation energy?

Answer 16

Because it has the greatest nuclear charge in its quantum shell, and it is the closest to the nucleus

Question 17

Why does 1st ionisation energy decrease as you go down each group?

Answer 17

Because shielding and distance from the nucleus increases

Question 18

What do successive ionisation energies provide evidence for?

Answer 18

Quantum shells

Question 19

What do successive ionisation energies NOT provide evidence for?

Answer 19

Sub-shells

Question 20

What happens to atomic radius as you go across a period and why?

Answer 20

As you go across a period the atomic radius decreases because, as the charge of the nucleus increases, the electrons are more strongly attracted to the nucleus and so they are drawn inwards

Question 21

Why is the 2nd ionisation energy always higher than the 1st?

Answer 21

Because it takes more energy to remove an electron from a positively charged ion than from a neutral atom (because the electrons are attracted to the positively charged nucleus)

Question 22

What is the equation for kinetic energy?

Answer 22

KE = 1/2 mv^2

Question 23

What is the equation for time of flight? (d = length of tube in metres)

Answer 23

t = d/v

Question 24

What is the equation for the mass of an ion?

Answer 24

  1000 x 6.022x10^23

Question 25

What is the expression for time of flight using Ar, d, L and E?

Answer 25

Square root of Ar x d^2
—————-
2000 L E

Question 26

What is an expression for time of flight using Ar?

Answer 26

t1^2 Ar1
——– = ——–
t2^2 Ar2

Question 27

In order to obtain a mass spectrum of a gaseous sample of chromium, the sample must first be ionised. Give two reasons why it is necessary to ionise the chromium atoms in the sample

Answer 27

To allow particles to be accelerated

To generate a current in the detector

Question 28

In a mass spectrometer, what is the difference in velocity between heavy ions and light ions?

Answer 28

The velocity of heavy ions is less than the velocity of light ions (because kE = 1/2 mv^2 and kE is equal for all ions)

Question 29

Define Relative Atomic Mass

Answer 29

The mass of an average atom of an element divided by the mass of one 12C atom, multiplied by 12

Question 30

State how the relative molecular mass of a covalent compound is obtained from its mass spectrum

Answer 30

The Mr is equal to the highest m/z value

Question 31

Describe briefly how positive ions are formed from gaseous atoms in a mass spectrometer

Answer 31

High speed electrons or electrons from an electron gun knock out an (outer-shell) electron

Question 32

What is used in a mass spectrometer to accelerate the positive ions?

Answer 32

A plate of negative voltage

Question 33

Why can’t a mass spectrometer distinguish between a 14N^+ ion and a 14N2^2+ ion?

Answer 33

Because they have the same m/z

Question 34

Why wouldn’t an F- ion reach the detector in a mass spectrometer?

Answer 34

Because it wouldn’t be accelerated (because it is a negative ion)