1. Atomic Structure

Question 1

Relative mass and charge of proton,neutron,electron

Answer 1

proton - mass= 1, charge= +1
neutron - mass = 1, charge = 0
electron - mass = 1/1840, charge =-1

Question 2

What is relative atomic mass, Ar ?

Answer 2

the average mass of an atom of an element on a scale where an atom of carbon-12 is 12

Question 3

What is relative isotopic mass ?

Answer 3

The mass of an atom of an isotope of an element on a scale where an atom of carbon-12 is 12.

Question 4

what is the relative molecular ( formula ) mass, Mr ?

Answer 4

sum of all relative atomic masses of the atom in one formula unit

Question 5

What does a mass spectrometer do ?

Answer 5

tells you
- relative atomic mass
- relative molecular mass
- relative isotopic abundance
- and used to identify elements

Question 6

What are the 4 key stages in time of flight mass spectrometry?

Answer 6

• ionisation
• acceleration
• Ion drift
• detection

Question 7

What are the two key ways a sample can be ionised?

Answer 7

• electron impact ( or electromagnetic ionisation )
• electrospray ionisation

Question 8

When is electron impact ionisation used instead of electrospray ionisation ?

Answer 8

It’s used for elements and substances which have a lower molecular mass

Question 9

what happens during electron impact ionisation?

Answer 9

• sample is vaporised to a gaseous state
• electron gun is fired with high energy electrons
• this knocks electrons off the sample to form 1+ ions as they lose an electron
  X (g) ——> X+ (g) + e-

Question 10

what happens in electrospray ionisation?

Answer 10

• sample dissolved and in a volatile state
• sample goes into a fine hypodermic needle with a positive terminal at high voltage
• sample gains a proton as it leaves terminal
  X (g) + H+ ——> XH+ (g)

Question 11

Why is electrospray ionisation used instead of electron impact ionisation?

Answer 11

It’s used for substances which have a higher molecular mass
- called a soft ionisation technique as fragmentation is unlikely

Question 12

What happens during stage 2, acceleration ?

Answer 12

• the 1+ ions formed from either method are accelerated through by an electric field
• they are all accelerated to have the same kinetic energy

Question 13

What happens in stage 3, ion drift/flight tube?

Answer 13

• the ions enter a region with no electric field so they just drift through it
• lighter ions will travel faster so have a shorter time of flight

Question 14

what happens in stage 4, detection ?

Answer 14

• once passed through the positive 1+ ions will hit a negatively charged detector plate
• as they hit this they gain an electron
• this gaining of electron discharges ion and a current is produced
• the size of the current is proportional to the abundance of the ions hitting the plate
• detector is connected to computer that produces mass spectrum

Question 15

Key equation in time of flight mass spectrometry?

Answer 15

KE = 1/2 mv^2

Question 16

Key equation for finding time of flight

Answer 16

t = d/v
t= time of flight (s)
d= length of flight tube (m)
v= velocity (m s-1)

Question 17

What’s an isotope?

Answer 17

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

Question 18

How many electrons can each shell hold?

Answer 18

Shell 1 - 2 electrons
Shell 2 - 8 electrons
Shell 3 - 18 electrons
Shell 4 - 32 electrons

Question 19

In shell 1 what sub-shells are there?

Answer 19

Shell 1 = 2 electrons - S

Question 20

In shell 2 what sub-shells are there?

Answer 20

Shell 2 = 8 electrons
S - 2 electrons
P - 6 electrons

Question 21

In Shell 3 what sub-shells are there?

Answer 21

Shell 3 = 18 electrons
s - 2 electrons
p - 8 electrons
d - 10 electrons

Question 22

In shell 4 how many sub-shells are there?

Answer 22

Shell 4 = 32 electrons
s - 2 electrons
p - 6 electrons
d - 10 electrons
f - 14 electrons

Question 23

When is 4s added into electron configuration?

Answer 23

Always after 3p and before 3d
e.g. 1s2s2p3s3p4s3d4p

Question 24

electron configuration for Mg

Answer 24

Mg = 12 electrons
1s^2 2s^2 2p^6 3s^2

Question 25

Shapes of orbitals?

Answer 25

s - orbital is a sphere
p - orbital is a dumbbell
d - orbital is two dumbbells on top of each other

Question 26

What is ionisation energy ?

Answer 26

The minimum energy required to remove one mole of electrons from one mole of atoms in a gaseous state - measured in kJmol^-1

Question 27

Example of ionisation equation

Answer 27

Na (g) ———> Na+ (g) + e-

Question 28

When do successive ionisation energies occur?

Answer 28

When further electrons are removed.
- usually requires more energy because as electrons removed the electrostatic forces of attraction between positive nucleus and negative outer electron increases.
- more energy is needed to overcome this attraction so ionisation energy increases

Question 29

What trends do the first ionisation energy follow across the periodic table?

Answer 29

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

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

Question 30

What group has the highest ionisation energy?

Answer 30

Group 0

Question 31

What group has the lowest ionisation energy?

Answer 31

Group 1 (easiest to remove e -)

Question 32

On a successive ionisation energy graph what does a sudden large increase indicate ?

Answer 32

It indicated a change in energy level
- this is because the electron is being removed from an orbital closer to the nucleus so more energy is required to do so

Question 33

Definition of orbital?

Answer 33

A regional within an atom that can hold up to two electrons with opposite spin

Question 34

Definition of sub-shell

Answer 34

A group of brutales of the same type within a shell