1.1 Atomic Structure Part 1

Question 1

What is the mass of a proton?

Answer 1

1

Question 2

What is the mass of a neutron?

Answer 2

1

Question 3

What is the mass of an electron?

Answer 3

1/2000

Question 4

What is the charge of a proton?

Answer 4

+1

Question 5

What is the charge of a neutron?

Answer 5

O

Question 6

What is the charge of an electron?

Answer 6

-1

Question 7

What is the atomic number?

Answer 7

The number of protons in the nucleus of an atom

Question 8

What is the mass number?

Answer 8

The number of protons and neutrons in the nucleus of an atom

Question 9

What is an isotope?

Answer 9

Are atoms of the same element (have the same number of protons) with a different number of neutrons

Question 10

Why do isotopes have the same chemical properties?

Answer 10

They have the same number and arrangement of outer shell electrons

Question 11

When are posture ions formed?

Answer 11

When the atom loses electrons

Question 12

When are negative ions formed?

Answer 12

When atoms gain electrons

Question 13

What are the 4 steps in mass spectrometry?

Answer 13

• ionisation
• acceleration
• separation of ions
• detection

Question 14

What are the two ways an atom can be ionised in step one of mass spec.?

Answer 14

Electron impact and electrospray ionisation

Question 15

Describe electron impact ionisation

Answer 15

• Sample is injected into spectrometer and vaporised
• High energy electrons from an electron gun are fired at the sample
• The high energy electrons knock off an electron from each particle to form positive ions

Question 16

Write the equation for the electron impact ionisation of magnesium

Answer 16

Na (g) -> Na+ (g) + e-

g

Question 17

Explain electrospray ionisation

Answer 17

• sample is dissolved in polar solvent
• 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 supply
• particles gain a proton (H+ ion) from the solvent to form positive ions

Question 18

What is the general equation for electrospray ionisation?

Answer 18

M(g) + H+ -> MH+ (g)

Question 19

What is important about the mass of the result of electrospray ionisation?

Answer 19

Mass is one more than the sample

Question 20

Why is a volatile solvent used in electrospray ionisation?

Answer 20

So it can be easily evaporated

Question 21

What does the mass of the ion at the end of mass spec. depend on?

Answer 21

The type of ionisation

Question 22

What is the mass of ion in electron impact ionisation?

Answer 22

Mass of element / compound

Question 23

What is the mass of the ion at the end of electrospray ionisation?

Answer 23

(Mass of element / compound) + 1

Question 24

How are positive ions accelerated in mass spec.?

Answer 24

An electric field is applied

Question 25

What does applying an electric field do to the ions in mass spec.?

Answer 25

- accelerates them | - gives them the same kinetic energy

Question 26

What does the velocity that an ion travels in mass spec. Depend on?

Answer 26

The mass

Question 27

Which type of ions reach the detector first in mass spec.?

Answer 27

Lighter ions

Question 28

Why is the whole spectrometer kept under vacuum?

Answer 28

- to stop unwanted reactions | - only analyse our sample

Question 29

What is the detection part of mass spec.?

Answer 29

The detector records the different ions as they arrive

Question 30

How can ions be detected in mass spec.?

Answer 30

The positive ion accepts an e-

Question 31

A graph of the results from mass spec has been drawn. The relative atomic mass of Mg is 24.3. Why is there no peak at 24.3?

Answer 31

Because isotopes have whole mass numbers, 24.3 is the average

Question 32

Why must the sample be ionised in mass spec.?

Answer 32

So it can be accelerated So it can be detected

Question 33

What is the isotopic mass?

Answer 33

The mass of an isotope relative to 1/12th the mass of an atom of carbon-12

Question 34

What is relative atomic mass (Ar)?

Answer 34

The weighted average mass of all the isotopes relative to 1/12th the mass of an atom of carbon-12

Question 35

How do you calculate relative atomic mass?

Answer 35

(Mass x abundance of each isotope) / total abundance

Question 36

Why is there only two peaks on the graph of mass spectra obtained from electrospray ionisation?

Answer 36

It doesn't cause fragmentation

Question 37

What is electron impact ionisation used for?

Answer 37

Identifying unknowns

Question 38

What is electrospray ionisation used for?

Answer 38

Finding the Mr of large, delicate molecules such as DNA