[Physical Chemistry I] 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

The average mass of all isotopes of an element compared to ¹/₁₂ the mass of an atom of Carbon
12 (C¹²)

Question 6

What is 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 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 fit 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?

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 is used for organic or inorganic molecules with a low formula mass.
Electrospray is 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