Atomic Structure

Question 1

Give the definition of Atomic Number (Z)

Answer 1

The number of protons in the atom nucleus

Question 2

Give the definition of Mass Number (A)

Answer 2

The number of protons and neutrons in an atom nucleus

Question 3

Give the definition of an a isotope

Answer 3

Atoms of the element with the same number of protons (same atomic number) but different number of neutrons (different mass number).

Question 4

What is the relative mass of an electron?

Answer 4

1/1836

Question 5

What is the relative mass of a neutron?

Answer 5

1

Question 6

What is the relative mass of a proton?

Answer 6

1

Question 7

What are the relative charges of a proton, neutron and electron?

Answer 7

+1, 0, -1 respectively

Question 8

Electrospray ionisation is the first step of mass spectrometry. What does it involve?

Answer 8

A dissolved sample is forced through a fine needle that is connected to the positive terminal of a high voltage supply. The sample loses electrons, forming positive ions. (high voltage knocks electron off sample)

Question 9

What happens in the acceleration area of a mass spectrometer?

Answer 9

Negatively charged plates attracts and accelerates ions to the same kinetic energy. The lighter ions accelerate more as they are lighter.

Question 10

What is the role of an ion detector in a mass spectrometer?

Answer 10

When positive ions his the ion detector, they pick up an electron, causing a current to flow. A flight time can also be detected

Question 11

You are reading a graph giving mass spectrometer readings. There are two vertical lines, one with a m/z of 10, and another with an m/z of 12. What does this mean?

Answer 11

There are two isotope of this element, with the relative isotopic masses of 10 and 12.

Question 12

Give an equation to work out Mr from a mass spectrometer reading.

Answer 12

Mr = Total of (m/z x abundance) / total abundance

Question 13

Why do isotopes have similar chemical properties?

Answer 13

They have the same number of electrons and this is what determines an isotope’s chemical properties.

Question 14

Define 1st ionisation energy

Answer 14

The energy required to remove one mole of electrons from one mole of gaseous atoms and is measured in kj/mol

Question 15

Define 2nd ionisation energy

Answer 15

The energy required to remove one mole of electrons from one mole of gaseous 1+ ions

Question 16

Describe and explain the general trend of 1st ionisation energy among group 2 elements

Answer 16

As you go down the group, the number of electrons an element increases. Therefore the atoms have more electron shells. This means the distance between outer electron and the nucleus increases. Due to this and increased shielding, the electrostatic attraction between them decreases. making the electrons easier to remove.

Question 17

Name the 4 sub levels and the number of orbitals each one has

Answer 17

s - 1, p - 3, d - 5, f - 7 (x2 for no. of electrons)

Question 18

Two elements are anomalous when it comes to their electron structure. Which elements are they?

Answer 18

Cr and Cu

Question 19

What is the correct electron structure for Cu (in terms of orbitals)?

Answer 19

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

Question 20

What is the electron structure of Cr (in terms of orbitals)?

Answer 20

1s2 2s2 2p6 3s2 3p6 4s1 3d5

Question 21

What is the electron structure of 21Se+ (in terms of orbitals)?

Answer 21

1s2 2s2 2p6 3s2 3p6 4s1 3d1

Question 22

Describe and explain the general trend in 1st ionisation energy across a period

Answer 22

There is generally an increase as you go along the period. This is because there is an increased nuclear charge and so the atoms gets smaller. Therefore there isa stronger attraction from nucleus to electron in outer shell.

Question 23

Generally there is an increase in the 1st ionisation energy across a period. However, the energy decreases as you go from group 2 to group 3. Why?

Answer 23

The electron lost from group 3 is from the p orbital, while the one lost from group 2 is from the s orbital. The p orbital is higher energy and better protected by shielding than the s orbital, so it requires less energy to remove

Question 24

What does a mass spectrometer do, and what can you use it for?

Answer 24

Separates atoms and molecules according to their charge and masses
Allows you to identify a sample by measuring its relative atomic mass or molecular mass, or to identify the different isotopes of an element.

Question 25

What happens in the ionisation stage of a Time of Flight (TOF) Mass Spectrometer?

Answer 25

Electrospray - sample dissolved into a volatile solvent. Passed through a hypodermic needle attached to positive terminal at high voltage
Atoms lose an electron and they leave needle as positively charged droplets
They evaporate until they are left as singular positive ions.

Electron gun: Sample vaporised and fired with high energy electrons. An electron is knocked off and positive ions form

Question 26

What is relative atomic mass (Ar)?

Answer 26

Ratio of the mass of one atom of an element relative to 1/12th the mass of one carbon-12 atom

Question 27

Why is an atom’s relative atomic mass measured relative to 1/12th the mass of a carbon-12 atom?

Answer 27

Atoms have a mass that is too small to measure by itself.
Easier to know their masses compared to each other - and the standard atom used is carbon-12 as its Ar is exactly 12 (no other atom has a whole number as their relative Ar).