3. Periodicity

Question 1

What is the nuclear charge of an atom?

Answer 1

The atomic number.

Question 2

What is the effective nuclear charge of an atom?

Answer 2

The attractive positive charge of protons acting on valence electrons.

(The effective nuclear charge is always less than the total number of protons present in a nucleus due to the shielding effect).

Question 3

Periodic Trends: Effective Nuclear Charge

Answer 3

Across a period: increases.
(electron shielding remains constant).

Down a group: constant.
(increase in additional shells balanced by the increase in the number of protons).

Question 4

What is atomic radius?

Answer 4

Distance from the centre of the nucleus to outermost electron of an atom.

Question 5

Periodic Trends: Atomic Radius?

Answer 5

Across the period: decreases.
(greater attraction to the nucleus)

Down a group: increases.
(increased number of shells).

Question 6

Periodic Trends: Ionic Radius?

Answer 6

Across the period: decreases.
(greater attraction to the nucleus as more protons are added but the valence shell number remains constant).

Down a group: increases.
(increased number of shells).

Question 7

What is the difference between ionic radius and atomic radius?

Answer 7

The ionic radius is the distance from the nucleus to the outermost electrons in an ion.

The atomic radius is the distance from the center of the nucleus to the outermost shell of an atom.

Question 8

What is a cation?

Answer 8

A positively charged ion.

Question 9

What is an anion?

Answer 9

A negatively charged ion.

Question 10

What is ionisation energy?

Answer 10

The energy required to remove one mole of electrons from one mole of gaseous atoms in their ground state.

Question 11

Periodic Trends: Ionisation Energy?

Answer 11

Across a period: increases.
(closer to a full shell configuration).

Down a group: decreases.
(greater shielding effect, less attraction).

Question 12

Why are groups 2 and 3 as well as 15 and 16 exceptions to the increasing IE trend?

Answer 12

Ex: Its easier to remove from group 3/16 than from group 2/15 because group 2/15 would have a filled sub-shell.

Question 13

What is electron affinity?

Answer 13

The energy charge when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions.

Question 14

Periodic Trends: Electron Affinity?

Answer 14

Across a period: increases.
(the electrons added to energy levels become closer to the nucleus).

Down a group: decreases.
(increased shielding effect, weaker bonds).

Question 15

What groups are an exception to the EA trends and why?

Answer 15

Group 2: elements already have a full valence s shell and the addition of a new electron would move to the higher energy p shell that is otherwise left empty in the neutral atom.

Group 15: Due to increased electron-electron repulsion when adding electrons into a half-full orbital.

Question 16

What is electronegativity?

Answer 16

The measure of the ability of an element’s atoms to attract electrons in a covalent bond.

Question 17

Periodic Trends: Electronegativity?

Answer 17

Across a period: increases.
(nuclear charge increases, attracting bonding pairs of electrons strongly).

Down a group: decreases.
(the radius of the atom increases and the number of protons increases + shielding).

Question 18

What are some trends in chemical and physical properties of metals?

Answer 18

Chemical:
- easily donates electrons
- reactivity increases down a group

Physical:
- good conductors of electricity
- low density
- grey shiny surface (when cut)

Question 19

Periodic Trends: Oxides?

Answer 19

Across the period:
basic - amphoteric - acidic

Question 20

What group 3 oxides are ionic?

Answer 20

Ionic compounds are formed between a metal and a nonmetal so the oxides of Na, Mg, and Al have giant ionic structures.

Question 21

What group 3 oxides are covalent?

Answer 21

Covalent compounds are formed between non-metals so the oxides of P, S, and Cl are molecular covalent.

Question 22

What is electrical conductivity?

Answer 22

A measure of ionic character and can only be measured in the molten state when electrons are free to move.

Question 23

Of the period 3 oxides, which elements are basic?

Answer 23

Na -> Na2O
Mg -> MgO

Question 24

Of the period 3 oxides, which elements are amphoteric?

Answer 24

Al -> Al2O3
Si -> SiO2

Question 25

What does it mean for an oxide to be amphoteric?

Answer 25

It can react to neutralise base or acid - they show acidic and basic properties.

Question 26

Of the period 3 oxides, which elements are acidic?

Answer 26

P -> P4O6 and P4O10
S -> SO3 and SO2
Cl -> Cl2O7 and Cl2O

Question 27

What is the reaction of a metallic oxide (basic)?

Answer 27

Basic oxides dissolve in water to form a basic or alkaline solution due to the presence of hydroxide ions.

The solution produced has pH>7.

ex: Na2O+H2O⟶2NaOH
MgO+H2O⟶Mg(OH)2
​

Question 28

What is the reaction of a non-metallic oxide (acidic)?

Answer 28

Non-metallic oxides react readily with water to produce acidic solutions with pH<7.

ex: P4O10+6H2O⟶4H3(PO4)
​ P4O6+6H2O⟶4H3(PO3)

​ex.2: SO3+H2O⟶H2(SO4)
SO2+H2O⟶H2(SO3)

Question 29

What is a exception to amphoteric oxides?

Answer 29

Silicon dioxide does not react with water, but reacts with concentrated alkalis to for silicates:

ex: SiO2 + 2OH(-) -> SiO3 (2-) + H20

Question 30

What is a mettalloid?

Answer 30

A chemical element whose physical and chemical properties fall in between the metal and non-metal categories.