IMAT Chemistry · Free notes

The Periodic Table: Trends and Groups

Periodic Table has 14 past questions since 2011, and the ministry papers from 2023 on have asked 2 of them. Both ministry questions were about trends: which element has the highest first ionisation energy, and in which directions the atomic radius grows. The older papers also asked students to recognise a group from its chemistry, or to spot a formula that breaks the usual charges. The difficulty is keeping the direction of each trend straight, so learn the two causes behind all of them: a rising nuclear charge across a period and an extra shell at each step down a group.

The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.

IMAT home All formulas on one page

Subtopic notes

Formula & revision sheet

4 formulas · 9 reference tables · 14 gotchas across all subtopics — the exam-eve cheat-sheet

Groups, Periods, Blocks and Typical Charges

Formulas (1)

Typical ion charges from the group, and writing ionic formulas · Charge balance in an ionic formula $\sum (\text{ion charge} \times \text{number of ions}) = 0$

Reference tables (2)

Groups, periods and blocks of the periodic table4 rows

Block	Groups	Subshell being filled	Examples
s-block	Groups 1 and 2 (and helium)	ns	Na, Mg, Ca
p-block	Groups 13 to 18	np	C, O, Cl, Ne
d-block	Groups 3 to 12	(n−1)d	Fe, Cu, Zn
f-block	Lanthanides and actinides, drawn as two rows below	(n−2)f	Ce, U

Metals, non-metals and metalloids3 rows

Class	Where in the table	Typical physical properties	Oxides	Examples
Metals	Left and centre, below the staircase	Shiny, conduct heat and electricity, malleable; mostly solids (mercury is a liquid)	Basic; a few amphoteric	Na, Mg, Fe, Cu
Non-metals	Right, above the staircase, plus hydrogen	Dull, poor conductors (graphite conducts), brittle as solids; many are gases	Acidic ( $\mathrm{CO_2}$ , $\mathrm{SO_2}$ ) or neutral (CO, $\mathrm{H_2O}$ )	C, N, O, S, Cl
Metalloids	Along the staircase	Look metallic but are brittle; semiconductors	Weakly acidic or amphoteric	B, Si, Ge, As

Watch out for (3)

Group 13 to 18 elements have the group number minus 10 valence electrons
→ Groups, periods and blocks of the periodic table
Aluminium is a metal, not a metalloid
→ Metals, non-metals and metalloids
Group 13 metals form 3+ ions
→ Typical ion charges from the group, and writing ionic formulas

Atomic Radius and Ionic Radius

Watch out for (2)

An atom gets smaller across a period even though it gains electrons
→ Atomic radius across a period and down a group
A positive ion is smaller than its atom, never larger
→ Ionic radius compared with atomic radius

Ionisation Energy, Electron Affinity and Electronegativity

Formulas (2)

First and successive ionisation energies · First ionisation energy $\mathrm{X(g)} \rightarrow \mathrm{X^{+}(g)} + e^- \qquad \Delta H > 0$
First and second electron affinity · First and second electron affinity $\mathrm{X(g)} + e^- \rightarrow \mathrm{X^{-}(g)} \qquad \mathrm{X^{-}(g)} + e^- \rightarrow \mathrm{X^{2-}(g)}$

Reference tables (2)

Electronegativity and its values8 rows

Element	Pauling value	Where it sits
Fluorine	3.98	Top of group 17: the highest of all
Oxygen	3.44	Group 16, period 2: second highest
Chlorine	3.16	Group 17, period 3
Nitrogen	3.04	Group 15, period 2
Carbon	2.55	Group 14, period 2
Hydrogen	2.20	Slightly below carbon
Sodium	0.93	Group 1, period 3
Caesium	0.79	Group 1, period 6: among the lowest

Summary of the periodic trends across a period and down a group7 rows

Property	Across a period (left to right)	Down a group	Main reason
Atomic radius	Decreases	Increases	Nuclear charge across; extra shells down
First ionisation energy	Increases (small dips at groups 13 and 16)	Decreases	How tightly the outer electron is held
Electronegativity	Increases	Decreases	Pull of the nucleus on shared electrons
First electron affinity	Generally more exothermic	Less exothermic (from chlorine down)	Pull of the nucleus on an added electron
Metallic character	Decreases	Increases	Ease of losing electrons
Reactivity of metals (groups 1, 2)	Group 1 more reactive than group 2	Increases	Ease of losing electrons
Reactivity of halogens (group 17)	Halogens most reactive in their period	Decreases	Ease of gaining an electron

Watch out for (4)

The noble gas, not the halogen, has the highest ionisation energy in a period
→ First and successive ionisation energies
Second electron affinities are endothermic
→ First and second electron affinity
Oxygen is more electronegative than chlorine
→ Electronegativity and its values
Metal reactivity rises down a group; halogen reactivity falls
→ Summary of the periodic trends across a period and down a group

Alkali Metals, Alkaline Earth Metals, Halogens and Noble Gases

Reference tables (4)

Group 1: the alkali metals5 rows

Metal	Melting point (°C, approx.)	Reaction with cold water	Flame colour
Lithium	181	Fizzes steadily	Crimson red
Sodium	98	Melts into a ball and darts across the surface	Yellow-orange
Potassium	63	Melts and the hydrogen catches fire	Lilac
Rubidium	39	Violent	Red-violet
Caesium	28	Explosive	Blue-violet

Group 2: the alkaline earth metals4 rows

Metal	Reaction with water	Hydroxide	Note
Beryllium	No reaction, even with steam	$\mathrm{Be(OH)_2}$ , amphoteric	Its oxide is amphoteric, unlike the rest
Magnesium	Very slow with cold water; fast with steam, giving MgO	$\mathrm{Mg(OH)_2}$ , barely soluble	Burns with a bright white flame
Calcium	Steady fizzing with cold water	$\mathrm{Ca(OH)_2}$ , slightly soluble (limewater)	Limewater turns milky with $\mathrm{CO_2}$
Barium	Vigorous with cold water	$\mathrm{Ba(OH)_2}$ , quite soluble	$\mathrm{BaSO_4}$ is insoluble (used in X-ray imaging)

Group 17: the halogens4 rows

Halogen	State at room temperature	Colour	Oxidising power
Fluorine, $\mathrm{F_2}$	Gas	Pale yellow	Strongest
Chlorine, $\mathrm{Cl_2}$	Gas	Yellow-green	Strong
Bromine, $\mathrm{Br_2}$	Liquid	Red-brown	Moderate
Iodine, $\mathrm{I_2}$	Solid	Shiny grey-black solid; violet vapour when heated	Weakest of the four

Group 18: the noble gases4 rows

Gas	Outer-shell electrons	Typical use
Helium	2	Balloons (light and non-flammable); cooling the magnets in MRI scanners
Neon	8	Advertising signs that glow red
Argon	8	Inert atmosphere for welding; filling light bulbs
Xenon	8	Bright lamps; forms compounds such as $\mathrm{XeF_4}$

Watch out for (3)

In a metal hydride, hydrogen is negative
→ Group 1: the alkali metals
The oxide formula gives the group away
→ Group 2: the alkaline earth metals
Halogen reactivity falls down the group
→ Group 17: the halogens

Transition Metals and Their Oxidation States

Formulas (1)

Finding the oxidation state of a metal in a compound or ion · Sum of oxidation states $\sum \text{oxidation states of all atoms} = \text{overall charge}$

Reference tables (1)

Properties of the transition metals6 rows

Ion	Electron configuration	Colour in water
$\mathrm{Cr^{3+}}$	$[\mathrm{Ar}]\,3d^3$	Green
$\mathrm{Mn^{2+}}$	$[\mathrm{Ar}]\,3d^5$	Very pale pink
$\mathrm{Fe^{2+}}$	$[\mathrm{Ar}]\,3d^6$	Pale green
$\mathrm{Fe^{3+}}$	$[\mathrm{Ar}]\,3d^5$	Yellow to orange-brown
$\mathrm{Cu^{2+}}$	$[\mathrm{Ar}]\,3d^9$	Blue
$\mathrm{Zn^{2+}}$	$[\mathrm{Ar}]\,3d^{10}$	Colourless

The configurations follow the rule from Atomic Structure: the 4s electrons leave first.

Watch out for (2)

Not every transition metal is reactive
→ Properties of the transition metals
Share the total between the metal atoms
→ Finding the oxidation state of a metal in a compound or ion

PYQ weightage by concept

15 concepts · 0 PYQs — where the marks actually sit, so you know what to drill first

Groups, Periods, Blocks and Typical Charges0 PYQs · 0%

Concept	PYQs	Share
Groups, periods and blocks of the periodic tablefoundation	—	—
Metals, non-metals and metalloidsfoundation	—	—
Typical ion charges from the group, and writing ionic formulasfoundation	—	—

Atomic Radius and Ionic Radius0 PYQs · 0%

Concept	PYQs	Share
Atomic radius across a period and down a groupfoundation	—	—
Ionic radius compared with atomic radiusfoundation	—	—

Ionisation Energy, Electron Affinity and Electronegativity0 PYQs · 0%

Concept	PYQs	Share
First and successive ionisation energiesfoundation	—	—
First and second electron affinityfoundation	—	—
Electronegativity and its valuesfoundation	—	—
Summary of the periodic trends across a period and down a groupfoundation	—	—

Alkali Metals, Alkaline Earth Metals, Halogens and Noble Gases0 PYQs · 0%

Concept	PYQs	Share
Group 1: the alkali metalsfoundation	—	—
Group 2: the alkaline earth metalsfoundation	—	—
Group 17: the halogensfoundation	—	—
Group 18: the noble gasesfoundation	—	—

Transition Metals and Their Oxidation States0 PYQs · 0%

Concept	PYQs	Share
Properties of the transition metalsfoundation	—	—
Finding the oxidation state of a metal in a compound or ionfoundation	—	—