Topic 1.1 - Atomic Structure

Which letter is used to

represent the atomic

number of an atom?

Z

What does the atomic

number tell us about an

element?

Atomic number = number of protons in an atom

What letter represents mass

number?

A

How is the mass number

calculated?

mass number = number of protons + number of

neutrons (total number of nucleons)

Define relative atomic mass

Average mass of all isotopes of an element

compared to ¹/₁₂ the mass of an atom of Carbon

12 (C¹²)

What are isotopes of an

element?

Different forms of the same element, containing

the same number of protons but different

numbers of neutrons. They still have the same

chemical properties

How many orbitals and

electrons do these shells

contain?

a) 1s b) 2p c) 3s d) 3d d) 4s

a) 1s- 1 orbital, 2 electrons

b) 2p- 3 orbitals, 6 electrons

c) 3s- 1 orbital, 2 electrons

d) 3d- 5 orbitals, 10 electrons

e) 4s- 1 orbital, 2 electrons

Does 3d or 4s have a higher

energy?

3d

What is an orbital?

A region around the nucleus that can hold up to

two electrons

What would be the

relationship between 2

electrons in the same orbital

in terms of their spin?

Within an orbital, the electrons spin in opposite

directions. One electron spins up while the other

electron spins down

Explain why chromium does

not fit the trend for

electronic configuration

It only has one electron in its 4s orbital before

filling 3d

1s² … 3p⁶ 4s¹ 3d⁵

Explain why copper does

not for the trend for

electronic configuration.

It only has one electron in its 4s orbital before

filling 3d

1s² … 3p⁶ 4s¹ 3d¹⁰

What are the two types of

ionisation for a mass

spectrometer? How do they

differ?

1. Electron impact: electron gun (hot wire filament with current through it emitting

electrons) knocks off one electron from each particle to form 1+ MOLECULAR

IONS (these ions fragment).

2. Electrospray: sample dissolved in volatile solvent (e.g. water or methanol) and

injected through a fine hypodermic needle to give an aerosol. Needle

attached to positive terminal of a high-voltage power supply and particles gain

a proton from the solvent as they leave the needle, producing XH + ions (+1

charge and mass of Mr + 1). (ions rarely fragment)

When would you use the

different types of ionisation

in a mass spec?

Electron impact used for organic or inorganic molecules with

a low formula mass.

Electrospray used for substances with a higher molecular

mass including biological molecules, e.g. proteins.

Describe how a time of flight

mass spectrometer works

Acceleration - positive ions attracted towards a negatively charged plate.

Ion Drift - ions pass through hole in plate, form a beam with constant kinetic

energy, travel along tube to detector. Time of flight is therefore directly

proportional to the square root of mass.

Detection - positive ions pick up electrons, current flows, m/z value and time of

flight recorded. Largest current from most abundant ions

Define first ionisation energy

The energy required to remove one mole of

electrons from one mole of gaseous atoms to

form one mole of gaseous 1+ ions