Atomic structure

What are isotopes?

Atoms of the same element, containing the same number of protons but different numbers of neutrons. They have the same chemical properties as they have the same number of electrons.

How many orbitals and electrons do s shells contain?

1 orbital

2 electrons

How many orbitals and electrons do p shells contain?

3 orbitals

6 electrons

How many orbitals and electrons do d shells contain?

5 orbitals

10 electrons

Does 3D or 4s have a higher energy?

3D

In what order do electrons fill atomic orbitals?

Electrons fill orbitals in order of increasing energy

What would be the relationship between 2 electrons in the same orbital in terms of their spin?

Within an orbital, electrons spin in opposite directions. One spins up while the other spins down.

Explain why chromium does not fit the trend for electron configuration?

It only has 1 electron in its 4s orbital before filling 3d

This gives a half-filled d-subshell (3d5) which makes Cr more stable

Explain why copper does not fit the trend for electron configuration?

It only has1 electron in its 4s orbital before filling 3d

This gives a fully filled d-subshell (3d10) which is more stable than a partially filled one

What are the rules for transition metal configuration?

Fill 4s before 3d

Remove elections from 4s before 3d

Define relative atomic mass

The average mass of an atom of an element compared to 1/12 the mass of an atom of carbon-12

What are the steps of a TOF mass spectrometer?

1. Vaporisation (electron impact)

2. Ionisation

3. Acceleration

4. Flight tube/ion drift

5. Detection

What are the two types of ionisation for a mass spectrometer?

Electron impact and electrospray

How does electron impact ionisation work?

• Sample is vaporised

• High energy electrons are fired at it from an electron gun

• Knocks off 1 electron from each particle, forming 1+ ion

• Molecular ion often breaks down into smaller fragments

• X(g) → X+(g) + e-

How does electrospray ionisation work?

• Sample is dissolved in a volatile solvent (eg water or methanol)

• Then injected through a fine hypodermic needle to give a fine mist

• The tip of the needle is attached to the positive terminal of a high-voltage power supply

• The particles each gain a proton

• X + H+ → XH+

• solvent evaporates to form XH+(g)

Which method of ionisation causes fragmentation?

Electron impact

When would you use the different types of ionisation in mass spec?

• Electron impact used for substances with low formula mass

• Electrospray used for substances with high molecular mass

Describe acceleration in mass spec

+ ions are accelerated using an electric field so that they all have same kinetic energy

Their velocity therefore depends on thejr mass

Describe flight tube in mass spec

+ ions travel through a hole in the negatively charged plate into a tube

TOF depends on its velocity

Describe detection in mass spec

+ ions hit a negatively plate

They’re discharged by gaining an electron from the plate

This generates a movement of electrons and so and electric current is measured

The size of the current gives a measure of the number of ions hitting the plate

Largest current comes from most abundant ions

Define ionisation energy

Energy required to remove 1 mole of electrons from a mole of gaseous atoms (kJmol-1)

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

How does ionisation energy change across period 3?

• IE increases across a period

• Increased nuclear charge

• Decrease in atomic radius

• Electrons is same energy level (same shielding)

• So stronger attraction between nucleus and outer electron

How does ionisation energy change down group 2?

• IE decreases down a group

• Atomic radius increases

• Shielding increases

• So weaker electrostatic attraction between nucleus and outer electron