3.1.1 Atomic structure

what is the relative mass and charge of a proton

1, +1

what is the relative mass and charge of a neutron

1, 0

what is the relative mass and charge of an electron

1/1836 , -1

what is the structure of an atom

Nucleus contains protons & neutrons; electrons orbit in shells around the nucleus.

What is the mass number (A) and atomic number (Z)?

• A = protons + neutrons

• Z = number of protons

What are isotopes

Atoms of the same element with same number of protons but different number of neutrons.

What is Ar

relative atomic mass

what is Mr

relative formula / molecular mass

give the definition of relative atomic mass

average mass of 1 atom (of an element) / ½ mass of one atom of 12 C

formula for relative atomic mass

(mass x abundance) + (mass x abundance) / total abundance

what is the function of TOF mass spectrometer

to determine the relative atomic mass of an element

describe the stages of electron spray ionisation

• Sample dissolved in a volatile solvent → usually methanol/water.

• Sprayed through a fine nozzle with high voltage applied.

• Molecules gain a proton (H⁺) → form positive ions (usually M⁺ or [M+H]⁺).

• Solvent evaporates, leaving charged gaseous ions.

• Ions enter the mass spectrometer for acceleration, drift, and detection.

describe the stages of electron impact

• Vaporised sample is bombarded by high-energy electrons from an electron gun.

• One electron is knocked out from each atom/molecule → forms M⁺ ions.

• The ions enter the mass spectrometer for acceleration, drift, and detection.

• At the detector, ions gain electrons, producing a current → size of current gives relative abundance.

Why are molecules ionised in TOF

So they can be accelerated by an electric field and detected

How are ions accelerated

Positive ions are accelerated by an electric field to give all ions the same kinetic energy

How are ions detected

ions hit the detector, gain electrons → produce a current.

How is relative abundance measured

The size of the current is proportional to the number of ions → relative abundance.

why is it carried out in a vacuum

to prevent the ions that are produced from colliding with the molecules in the air

Why can’t electron impact (EI) be used for some molecules?

EI is too harsh for large or fragile molecules (like proteins) because it fragments them. For these, electrospray ionisation (ESI) is used to keep the molecule intact.

How are electrons arranged in shells and sub-shells

s, p, d orbitals:

• s → 1 orbital → 2 electrons

• p → 3 orbitals → 6 electrons

• d → 5 orbitals → 10 electrons

what is the order of the electronic configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶

what is Aufbau’s principle

the lowest energy orbitals get filled first