1.01 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 at element ?

Answer 2

The number of protons.

Question 3

What letter represents the mass number of an atom ?

Answer 3

A.

Question 4

How is mass number calculated ?

Answer 4

It is number of protons + number of neutrons.

Question 5

Define relative atomic mass.

Answer 5

Average mass of all naturally occurring isotopes of an element compared to 1/12th 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 number 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 ? What does this mean ?

Answer 8

3d is higher energy. This means that the 4s orbital fills before the 3d orbitals.

Question 9

What is an orbital ?

Answer 9

A region around the nucleus that can hold up to 2 electrons.

Question 10

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

Answer 10

Have opposite spin as repel each other as both negative.

Question 11

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

Answer 11

It only has one electron in its 4s orbital before filling 3d
Cr : 3p6 4s1 3d5.

Question 12

Explain why copper does not fit the trend of electron configuration.

Answer 12

It only has one electron in its 4s orbital before filling 3d
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 knocks off one electron from each particle’s higher energy electrons to form 1+ molecular ions
2. Electrospray: sample is dissolved in volatile solvent and is injected through a fine hypodermic needle. A high voltage is run through the solvent and particles gain a proton, producing HX+ ions

Electron impact samples fragment and Electrospray 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 samples with a low formula mass
Electrospray is used for substances with higher molecular mass including biological molecules.

Question 15

Describe how a time of flight mass spectrometer works.

Answer 15

4 stages; Ionisation, acceleration, ion drift, detection

Ionisation - Electron impact / electrospray
Acceleration - Positive ions are attracted to a negative plate in the apparatus
Ion drift - Ions pass through a whole in plate, form a beam with constant kE and travel to the detector. TOF is proportional to the sq. root of the mass.
Detection - positive ions pick up electrons, creates current, m/z value and TOF recorded. Largest current is produced by the 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.