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 isotope

Answer 3

Atoms of the element with the same atomic number but a different mass number

Question 4

What is the relative mass of a neutron?

Answer 4

1

Question 5

What is the relative mass of a proton?

Answer 5

1

Question 6

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

Answer 6

+1, 0, -1 respectively

Question 7

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

Answer 7

A volatile sample (X) is dissolved in a solvent and then is forced through a fine needle that is positively charged and connected to a high voltage supply. The sample gains a H+ ion, forming XH+

Question 8

What happens in the acceleration area of a mass spectrometer?

Answer 8

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

Question 9

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

Answer 9

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

Question 10

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 10

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

Question 11

Give an equation to work out relative atomic mass in mass spectrometry.

Answer 11

RAM = Σ(isotopic mass x relative abundance)/total abundance

Question 12

Why do isotopes have similar chemical properties?

Answer 12

They have similar chemical properties as only the number of neutrons is different. The number of electrons is the same, and it’s the electrons which are involved in chemical reactions and so determine the properties

Question 13

Define 1st ionisation energy

Answer 13

The energy required to remove one mole of electrons from one mole of gaseous atoms, under standard conditions

Question 14

Define 2nd ionisation energy

Answer 14

The energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions

Question 15

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

Answer 15

There is a general decrease down the group. This is because as you go down the group, the number of electrons an element has increases. This means they have more shells and so there is more shielding, thus the nuclear charge holding the electrons in place is weakened, making the electrons easier to remove.

Question 16

Name the 4 sub levels (we’ve been taught) and the number of orbitals each one has

Answer 16

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

Question 17

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

Answer 17

Chromium and Copper

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

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 21

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 21

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 22

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

Answer 22

Separates atoms and molecules according to their charge and masses
Allows you to identify a sample by measuring its atomic mass or molecular weight