3.1.1 Atomic Structure

Question 1

Which letter is used to represent the atomic number of an atom?

Answer 1

Z

Question 2

What does the atomic number tell us about an element?

Answer 2

Atomic number = number of protons in an atom

Question 3

What letter represents mass number?

Answer 3

A

Question 4

How is the mass number calculated?

Answer 4

mass number = number of protons + number of neutrons

Question 5

Define relative atomic mass.

Answer 5

Average mass of all isotopes of an element compared to 1/12 the mass of an atom of carbon 12

Question 6

What are isotopes of an element?

Answer 6

Different forms of the same element, containing the same number of protons but different numbers of neutrons.

Question 7

How many orbitals and electrons do these shells contain?
a) 1s b) 2p c) 3s d) 3d e) 4s

Answer 7

a) 1s - 1 orbital, 2 electrons
b) 2p - 3 orbitals, 6 electrons
c) 3s - 1 orbital, 2 electrons
d) 3d - 5 orbitals, 10 electrons
e) 4s - 1 orbital, 2 electrons

Question 8

Does 3d or 4s have a higher energy level?

Answer 8

3d

Question 9

What is an orbital?

Answer 9

A region around the nucleus that can hold us to two electrons.

Question 10

What would be the relationship between 2 electrons in the same orbital in terms of their spin?

Answer 10

Within an orbital, the electrons spin in opposite directions. One electron spins up while the other electron spins down.

Question 11

Explain why chromium does not fit the trend for electronic configuration.

Answer 11

It only has one electron in its 4s orbital before filling 3d

Question 12

Explain why copper does not fit the trend for electronic configuration.

Answer 12

It only has one electron in its 4s orbital before filling 3d

Question 13

What are the two types of ionisation for a mass spectrometer? How do they differ?

Answer 13

1. Electron impact: electron gun (hot wire filament with current through it emitting electrons) knocks off one electron from each particle to form 1+ molecular ions (these ions fragment).
2. Electrospray: sample dissolved in volatile solvent (e.g. water or methanol) and injected through a fine hypodermic needle to give an aerosol. Needle attach to positive terminal of a high-voltage power supple and particles gain a proton from the solvent as they leave the needle, producing XH⁺ ions (+1 charge and mass or Mr + 1). (Ions rarely fragment).

Question 14

What would you use the different types of ionisation in a mass spec?

Answer 14

Electron impact used for organic or inorganic molecules with a low formula mass.
Electrospray used for substances with a high molecular mass including biological molecules (e.g. proteins)

Question 15

Describe how a time of flight mass spectrometer works.

Answer 15

Acceleration - positive ions attracted towards a negatively charged plate.
Ion Drift - ions pass through hole in plate, form a beam with constant kinetic energy, travel along tube to detector. Time of flight is therefore directly proportional to the square root of mass.
Detection - positive ions pick up electrons, current flows, m/z value and time of flight recorded. Largest current from most abundant ions.

Question 16

Define first ionisation energy.

Answer 16

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions.