Atomic Structure

Question 1

What is the plum pudding model?

Answer 1

An initial idea is that the atom consists of a sphere of small positive charge with a small negative charge distributed within it.

Question 2

What is the electron shell model?

Answer 2

A model that which the atom consists of a small dense, central nucleus surrounded by orbiting electrons in shells.

Question 3

What is the relative mass and charge of protons, electrons and neutrons respectively?

Answer 3

Proton - 1, +1
Electron - 1/1840, -1
Neutron - 1, 0

Question 4

What is represented by the number A.

Answer 4

Mass number/ sum of protons and neutrons in an atom.

Question 5

What is represented by the number Z.

Answer 5

Atomic Number/ equal number of protons

Question 6

Define Isotopes

Answer 6

Isotopes

? Atoms of the same element with the same atomic number but different number of neutrons.

Question 7

Define orbitals

Answer 7

Orbitals

? Regions of space that electrons are most likely to be in which can hold up to two electrons.

Question 8

How are ions formed?

Answer 8

When an atom loses or gains electrons meaning it is no longer neutral and have an overall charge.

Question 9

What is Mass Spectrometry

Answer 9

It is an analytical technique used to identify the different isotopes and find the overall atomic mass of an element.

Question 10

What are the 4 steps in mass spectrometry?

Answer 10

Ionisation, Acceleration, Ion Drift, Detection.

Question 11

Describe electron impact ionisation.

Answer 11

1. The sample is vapourised and injected into the mass spectrometer where a high voltage is passed through.
2. This causes electrons to be removed from the atoms leaving with a +1 charge.

Better for species of small molecules

Question 12

Describe the acceleration step.

Answer 12

The positively charged ions are accelerated towards a negative charged detection plate.

Question 13

Describe Ion drift.

Answer 13

The ions are deflected by a magnetic field into a curved path. The radius of the path is dependent on the charge and mass of the ion.

Question 14

Describe the detection step.

Answer 14

When the positive ions hit the negatively charged detection plate, they gain an electron producing a flow of charge.

The greater the abundance the greater the current produced.

Question 15

Calculating Ar from mass spectrometry

Answer 15

=m/z * abundance divided by total abundance

Question 16

What is an electron spin?

Answer 16

Within an orbital, electron pair up with opposite spin, so that the atom is as stable as possible. Electron in the same orbit must have the opposite spin (represented by arrows).

Question 17

What are the 3 rules for writing out electronic configurations?

Answer 17

1. The lowest energy orbital is filled first
2. Electron with the same spin fill up an orbital first before pairing begins
3. No single orbital holds more than 2 electrons.

Question 18

Define ionisation energy

Answer 18

? The minimum energy required to remove one mole of electrons from one mole of atoms in gaseous state.

Question 19

When do successive energies happen?

Answer 19

When further electrons are removed. This requires more energy as the electrostatic attraction increases.

Question 20

Trends in ionisation energy, along a period and down a group.

Answer 20

Along a period - increases, due to decreasing atomic radius and greater electrostatic forces of attraction

Down a group - decreases, due to an increasing atomic radius and shielding which reduces the effect of the electrostatic forces of attraction.

Question 21

Describe electrospray ionisation

Answer 21

Good for high Mr compounds

1. Sample molecules are dissolved in a volatile solvent
2. Sample is injected through a hypodermic needle to give fine aerosol
3. The tip of the needle is attached to the (+) terminal of a high voltage power supply
4. The sample is ionised by gaining a proton from the solvent as they leave the needle

X + H+ –> XH+

Question 22

What are the advantages and disadvantages of electron impact ionisation

Answer 22

Sometimes part of the molecules are knocked off by high energy electrons - fragmentation
Parts of methyl groups or side chains are removed.

Detects the exact Mr

Question 23

What are the advantages and disadvantages of electrospray ionsiation

Answer 23

Soft ionisation technique - limited fragmentaion

Data would be given in Mr+1 You need to remember to subtract the mass of the proton to find the correct Mr

Question 24

Why are there multiple peaks?

Answer 24

Different isotpoes

Question 25

Give a reason why the second ionisation energy of silicon is lower than the second ionisation energy of aluminum.

Answer 25

Electron in Si is removed from a higher energy orbital

Question 26

Predict the element in period 3 that has the highest second highest energy and give a reason.

Answer 26

Na, electron is removed from the 2p subshell nearest to the nucleus.

Question 27

Explain why the ionisation energy of every element is endothermic.

Answer 27

Heat energy is needed to overcome the attraction between the electrons and nucleus.

Question 28

Explain the general increase in the values of first ionisation energies of the elements Na-Ar

Answer 28

Increased in nuclear charge, thus the atom gets smaller with the same shielding. Strong attraction between nucleus and the outer electrons.

Question 29

Explain why aluminum and sulfur does not follow the general increasing trend of ionisation energy ?

Answer 29

Al - electron is removed from the 3p subshell which is further away from the nucleus
S - Electron pair in the 3p subshell, repulsion between the electrons