Definitions

Question 1

Atomic Number:

Answer 1

Number of protons in the nucleus of an atom.

Question 2

Mass Number:

Answer 2

Sum of number of protons and neutrons in the nucleus of an atom.

Question 3

Nuclear charge:

Answer 3

• Total charge of all the protons in the nucleus.
• It has the same value as the atomic number.
• Increases as you go across the periodic table.

Question 4

Isotopes:

Answer 4

Atoms of the same element with the same number of protons but different number of ​neutrons in the nucleus, e.g. 35Cl and 37Cl.

Question 5

Relative Atomic Mass:

Answer 5

Average mass of an atom of an element, relative to 1/12th of the mass of an atom of carbon-12.

Question 6

Relative Isotopic Mass:

Answer 6

Average mass of an atom of an isotope relative to 1/12th

of the mass of an atom of carbon-12.

Question 7

Relative Molecular Mass:

Answer 7

Average mass of a molecule relative to 1/12th of the mass of an atom of carbon-12.

Question 8

Quantum shells:

Answer 8

Same as electron shells. They specify the energy level of an electron.

Question 9

First Ionisation Energy:

Answer 9

The energy required to remove 1 mole of electrons from each atom in 1 moles of gaseous atoms to from 1 mole of gaseous 1+ ions

Question 10

Second Ionisation Energy: ​

Answer 10

The energy required to remove 1 mole of electrons from each ion in 1 moles of gaseous 1+ ions to form 1 moles of gaseous 2+ ions (could be asked for any successive
ionisation energy)

Question 11

Orbital:

Answer 11

A region in an atom that can hold up to two electrons with opposite spins.

Question 12

Periodicity:

Answer 12

Trends in element properties with increasing atomic number.

Question 13

Hund’s rule:

Answer 13

When electrons fill the orbitals, they occupy them singly before they pair up, e.g. in case of 2p^3 configuration, we would observe the following arrangement of electrons within the 2 p orbitals

Question 14

Pauli Exclusion Principle:

Answer 14

Electrons within the same orbital must have opposite spins.

Question 15

Aufbau Principle: ​

Answer 15

As the atomic number increases, the electrons are added to the orbitals in order of increasing orbital energy until all electrons are accommodated. Notable exceptions: Cr, Cu.

Question 16

Shielding: ​

Answer 16

A decrease in the nuclear charge experienced by an outer shell electron caused by electron-electron repulsion ​between the outer shell electron and electrons from adjacent quantum shells.