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 (total number of nucleons)

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 (C¹²)

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. They still have the same chemical properties.

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?

Answer 8

3d

Question 9

What is an orbital?

Answer 9

A region around the nucleus that can hold up to two electrons

Question 10

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

Answer 10

Have opposite spin as repel each other as both negative.

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

1s² … 3p⁶ 4s¹ 3d⁵

Question 12

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

Answer 12

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

1s² … 3p⁶ 4s¹ 3d¹⁰

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 attached to positive terminal of a high-voltage power supply and particles gain a proton from the solvent as they leave the needle, producing XH+ ions (+1 charge and mass of Mr + 1). (ions rarely fragment)

Question 14

When 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 higher 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.