Topic 3: Periodicity

Question 1

Period

Answer 1

A horizontal row of elements

Period number is the same number of shells in the atom

Question 2

Metals + non-metals on the periodic table

Answer 2

Metals are on the left and non metals are on the right

Metalloids seperate metals from non metals

Question 3

Which group are the alkali metals?

Answer 3

Group 1

Question 4

Which group are the alkali earth metals?

Answer 4

Group 2

Question 5

Which group are the halogens?

Answer 5

Group 17

Question 6

Which group are the noble gases?

Answer 6

Group 18

Question 7

Define: Atomic radius

Answer 7

The distance from the nucleus to the outermost electron

Question 8

Define: Ionic radius

Answer 8

The distance from the nucleus to the outermost electrons in an ion

Question 9

Define: First ionization energy

Answer 9

The energy required to remove one mole of electrons from one mole of gaseous atoms

Question 10

Define: Electron affinity

Answer 10

The energy released when one mole of an electron is added to one mole of gaseous atoms

Question 11

Define: Electronegativity

Answer 11

A measure of the attraction an atom has for a shared pair of electrons in a covalent bond

Question 12

Atomic radius trends

Answer 12

Increases down a group (as the number of electron shells increases)

Decreases across a period (as electrons are added the nuclear charge increases. this causes more attraction between the nucleus and the electrons resulting in a smaller radius)

Question 13

Ionic radius trends

Answer 13

Ionic radii increase down a group (more shells)

Ionic radii decreases across a period (become more electronegative)

Ionic radii of cations are smaller than their parent atoms (because there are more protons than electrons so valence electrons are more strongly attracted to the nucleus)

Ionic radii of anions are larger than their parent atoms (because there are more electrons, increasing the inter-electron repulsion)

Question 14

Ionization energy trends

Answer 14

Ionization energy increases across a period (increase in nuclear charge causes an increase in the attraction between electrons and nucleus making it harder to remove electrons)

Ionization energy decreases down a group (valence electrons are further from the nucleus since there are more shells so it is easier to remove electrons)

Question 15

Electron affinity trends

Answer 15

Generally metals have a low EA and non metals have a higher EA

The greater the distance between the nucleus and the outer energy level, the weaker the electrostatic attraction is and the less energy is released when an electron is added to the atom

Question 16

Electronegativity trends

Answer 16

Electronegativity increases across a period and decreases down a group

Metals have low electronegativities because they lose electrons easily

Non-metals have high electronegativities because they gain electrons to complete their outer shells

Question 17

Trends across group 1

Answer 17

• Atomic/ionic radius increases (more shells)
• First ionization energy decreases (more shells)
• Electronegativity decreases (increased distance and more electron shielding)
• Melting points decrease (atoms become larger and so bonds become weaker)
• Reactivity increases down the group (shielding makes it easier for loss of electron)

Question 18

Trends across group 17

Answer 18

• Atomic/ionic radius increases (more shells)
• First ionization energy decreases (more shells)
• Electronegativity decreases (increased distance and more electron shielding)
• Melting points increase (van der waal forces become greater with more electrons)
• Reactivity decreases down the group (outer shell becomes further from nucleus so electrons are less easily gained)

Question 19

Oxides

Answer 19

When elements bond with oxygen, oxides are formed

Oxides of Na, Mg & Al are ionic and have high melting points (as they are metals)
Oxides of P,S,Cl are covalent and have low melting points (as they are non-metals)

Silicon oxide has a giant covalent structure so high melting point

Question 20

Oxides acid-base characteristics

Answer 20

Change from basic (Na,Mg) to amphoteric (Al,Si) to acidic (P,S,Cl) across period 3

Question 21

Amphoterric

Answer 21

Elements that show both acidic and basic properties (e.g Al and Si)

Question 22

The reactions of oxides

Answer 22

Basic oxides dissolve in water to form alkaline solutions (because of hydroxide ions)

Acidic oxides react with water to form acidic solutions

Aluminium oxides partake in neutralisation reactions whilst silicon dioxide does not react with water but does react with alkalis to form silicates.