1.1 Atomic Structure

Question 1

What is the relative mass of an electron?

Answer 1

1/1840

Question 2

What is atomic number?

Answer 2

Z

the total number of protons in the nucleus

Question 3

What is mass number?

Answer 3

A

total number of protons and neutrons in the nucleus

Question 4

What is an isotope?

Answer 4

they are atoms of the same element (same number of protons), but have a different number of neutrons

Question 5

Do isotopes have similar chemical/physical properties?

Answer 5

• isotopes have similar chemical properties because they have the same electron structure and the same number of outer electrons
• isotopes have different physical properties because they have different masses

Question 6

What are the 5 main stages of mass spectroscopy?

Answer 6

1. ionisation (electrospray or electron impact)
2. acceleration
3. ion drift
4. deflection
5. detection

Question 7

What is a mass spectrometer used for?

Answer 7

can be used to determine all the isotopes present in a sample of an element and can identify elements
can also measure tha rel. abundance of isotopes

Question 8

What conditions must the chamber be in?

Answer 8

must be in a vacuum so that ions are not absorbed by air particles
and so that air particles do not become ionised (and therefore would register on the detector)

Question 9

What is electron impact ionisation (mass spectrometry)?

Answer 9

-sample is vaporised
-high energy electrons are fired at the sample from an electron gun
-they bombard the sample
- an electron will knock out one outer electron forming a 1+ ion
this method can cause fragmentation

Question 10

What is the formula for electron impact?

Answer 10

X (g) —–> X⁺ (g) +e⁻

remember state symbols

Question 11

What is electrospray ionisation?

Answer 11

-sample is dissolved in a volatile solvent
-it is then injected through a fine, hypodermic needle to produce a fine mist/aerosol
-the tip of the needle has a high voltage
- at the tip of the needle the sample molecule will gain a proton H⁺ from the solvent, will be MH⁺
(solvent evaporates away, while the MH+ ions will move towards a negative plate)

Question 12

What is the formula for electrospray ionisation?

Answer 12

M (g) + H⁺ ——> MH⁺ (g)

Question 13

What type of Mr does electron impact work with?

Answer 13

low Mr

because electron impact can cause larger organic molecules to impact

Question 14

What type of Mr does electrospray ionisation work with?

Answer 14

used for larger Mr molecules

this is a softer technique and fragmentation does not occur

Question 15

What is acceleration?

Answer 15

• 1+ positive ions are accelerated by an electric field
• to a constant kinetic energy
• velocity depends on the mass of the particle