Unit 1 - Atomic structure and electrons in atoms

Question 1

Define element

Answer 1

A substance containing only one type of atom. All atoms in an element have the same proton number

Question 2

Define atom

Answer 2

The smallest part of an element that can take part in a chemical change

Question 3

Define atomic number

Answer 3

The number of protons in the nucleus of an atom

Question 4

Define isotope

Answer 4

Atoms of the same element with a different number of neutrons

Question 5

Define mass number

Answer 5

The number of protons + the number of neutrons

Question 6

Describe energy levels (quantum shells)

Answer 6

Each electron in an atom has its particular average amount of energy. The further from the nucleus the more energy the electron has

Question 7

Describe sub-shells (subsidary quantam shells)

Answer 7

Regions of the principal quantum shells where electrons exist in defined areas associated with particular amounts of energy (s,p,d etc.)

Question 8

Define first ionisation energy

Answer 8

The energy needed to remove 1 mole of electrons from 1 mole of atoms of an element in the gaseous state to form 1 mole of gaseous ions

Question 9

Write the equation for the 2nd ionisation energy of Lithium

Answer 9

Li⁺(g) → Li²⁺(g) +e⁻

Question 10

Describe the relationship between orbitals and the periodic table

Answer 10

Elements in groups 1 and 2 have outer electrons in an s sub-shell (s-block elements). Elements in groups 13 to 18 have outer electrons in a p sub-shell (p-block elements). Elements that add electrons to the d sub-shells are called the d-block elements (most of these are transition elements)

Question 11

Describe spin-pair repulsion

Answer 11

A pair of electrons in the same orbital repel each other because they have the same charge. Pairing the spinning electrons so they spin in opposite directions reduced the repulsion. Electrons in the p and d orbitals go into separate orbitals before being paired up.

Question 12

Define a free radical

Answer 12

A species with an unpaired electron

Question 13

Explain why there is a general increase in IE across a period

Answer 13

Nuclear charge increases, distance between the nucleus and outer electron remains resonably constant, shielding by inner shells remains reasonably constant

Question 14

Explain why there is a rapid decrease in ionisation energy between the last element in one period and the first element in the next period

Answer 14

The distance between the nucleus and outer electron increases, they shielding by inner shells increases, these two factors outweigh the increased nuclear charge

Question 15

Explain why there is a slight decrease in IE between Be and B

Answer 15

Be 1s²,2s² B 1s²,2s²,2p¹ - The distance between the nucleus and outer electron increases slightly, the shielding by inner shells increases slightly, these two factors outweigh the increased nuclear charge

Question 16

Explain why there is a slight decrease in IE between nitrogen and oxygen. Explain why there is a slight decrease in IE between nitrogen and oxygen

Answer 16

N 1s²,2s²,2p³ O 1s²,2s²,2p⁴ - The electron removed from the oxygen is from the orbital that contains a pair of electrons. The IE for oxygen is lower because of spin-pair repulsion