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 does a 1s shell contain?

Answer 7

1 orbital, 2 electrons

Question 8

How many orbitals and electrons does a 2p shell contain?

Answer 8

3 orbitals, 6 electrons

Question 9

How many orbitals and electrons does a 3s shell contain?

Answer 9

1 orbital, 2 electrons

Question 10

How many orbitals and electrons does a 3d shell contain?

Answer 10

5 orbitals, 10 electrons

Question 11

How many orbitals and electrons does a 4s shell contain?

Answer 11

1 orbital, 2 electrons

Question 12

Does 3d or 4s have a higher

energy?

Answer 12

3d

Question 13

What is an orbital?

Answer 13

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

Question 14

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

Answer 14

Have opposite spin as repel each other as both negative

Question 15

Explain why chromium does not fit the trend for electronic configuration

Answer 15

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

Question 16

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

Answer 16

It only has one electron in its 4s orbital before
filling 3d
1s² … 3p⁶ 4s¹ 3d¹⁰

Question 17

Explain electron impact ionisation

Answer 17

A sample is vapourised and high energy electrons are fired at it by an electron gun. Knocks off 1 electron to form a 1+ ion.
X(g) -> X+(g) +e-
(these ions fragment).

Question 18

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

Answer 18

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 19

Describe how a time of flight mass spectrometer works

Answer 19

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 20

Define first ionisation energy

Answer 20

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

Question 21

Explain electrospray ionisation

Answer 21

A sample is dissolved in volatile solvent 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)