Atomic Structure

Question 1

Define Relative Atomic Mass (Ar)

Answer 1

Relative atomic mass is the average mass of one atom compared to one twelfth of the mass of one atom of carbon-12

Question 2

John Dalton discovery in 1803

Answer 2

Atoms are spheres and each element is made from different spheres

Question 3

J.J Thomson Discovery in 1897

Answer 3

Discovered the electron. Developed the plum pudding model.

Question 4

1909 Ernest Rutherford ( gold leaf experiment)

Answer 4

Discovered the nucleus. Also discovered that the nucleus was very small and positively charged. He also concluded the atom was mainly empty space made up a negative cloud

Question 5

1913 Niels Bohr discovery

Answer 5

Discovered a problem with Rutherford’s model. He proposed electrons were in fixed energy shells.

Question 6

Define Ionisation

Answer 6

Ionisation energy is the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in the gaseous state

Question 7

Define Successive Ionisation

Answer 7

The removal of more than 1 electron from the same atom is called successive ionisation

Question 8

The equation to work out the number of moles in a specific volume of a gas

Answer 8

pV=nRT
p= pressure (pa)
V= Volume (m^3)
n=Moles (mol)
R= Gas Constant (8.31 JK-1 mol-1)
T= Temperature (K)

Question 9

Explain how ions are detected and relative abundance is measured in a TOF mass spectrometer?

Answer 9

Ion hits the detector and gains an electron. Relative abundance of each isotope is proportional to the current.

Question 10

Explain why is it necessary to ionise molecules when measuring their mass in a TOF mass spectrometer

Answer 10

Ions, not molecules, will interact with and be accelerated by an electric field.
Only ions will create a current when hitting the detector.

Question 11

Explain why the second ionisation energy of boron is higher than the first ionisation energy of boron.

Answer 11

Electron being removed is closer to the nucleus

Question 12

The processes of the Time Of Flight Mass Spectrometer

Answer 12

1. Vaporisation- The sample is vaporised so it can travel through the TOF mass spectrometer.
2. IONISATION- the sample is used through a nozzle making a high-pressure jet. A high voltage passes through causing the loss of an electron. A gaseous positively charged sample is produced. we call this electrospray ionisation.
3. ACCELERATION- the positive ions are passed through an electric field. Particles with a lower mass/ charge (m/2) ratio will accelerate quicker.
4. ION DRIFT- particles travel through with a constant speed and kinetic energy. They drift through and particles with lower mass/charge (m/z) ratios travel faster.
5. DETECTION- ions are detected as an electrical current is made when a particle hits that pate. Particles with lower m/z reach the detector first as they travel faster.

Question 13

Relative Molecular Mass (Mr)

Answer 13

Relative molecular mass is the average mass of a molecule compared to one twelfth of the mass of one atom of carbon-12

Question 14

Relative Isotopic Mass

Answer 14

The mass of an atom of an isotope of an element is measured on the scale on which the mass of an atom of 12C is exactly 12.

Question 15

Describe how ions are formed in a time of flight (TOF) mass spectrometer ( electron impact ionisation)

Answer 15

The sample is bombarded by high energy electrons. The sample loses an electron.

Question 16

Describe how ions are formed in a time of flight (TOF) mass spectrometer (electrospray ionisation)

Answer 16

The sample is dissolved in a volatile solvent. Injected with needle at high voltage. Each molecule gains an electron

Question 17

What is a mole

Answer 17

The mole is the amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12.

Question 18

Empirical formula

Answer 18

An empirical formula is the simplest ratio of atoms of each element in compound