Patterns in the periodic table

Groups and periods, Group 1 and Group 17 trends, noble gases, transition elements and the reactivity series for G3 Pure and O-Level Chemistry.

SEC G3 Pure Chemistry 2027
9 lessons

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Before you begin

The periodic table lets you predict how an element behaves from where it sits. Its position comes from the element’s electron arrangement, so elements in the same group react alike and properties change steadily along a period. The lessons start with how the table is arranged and how metals and non-metals differ, then look at Group 1, Group 17, the noble gases and the transition elements. The last four lessons rank metals in the reactivity series and use it to explain displacement, extraction and how iron is protected from rusting. Keep the interactive periodic table open as you work.

Be comfortable with: atoms; electron configuration; and ions and ionic bonding.

Learning goals

Describe the Periodic Table as the elements arranged in order of increasing proton number
Relate an element's position in the Periodic Table to its proton number and electronic configuration
Relate the number of outer (valence) electrons to the charge on an ion for the first twenty elements
Explain why elements in the same group are similar using their electronic configurations
Describe the change from metallic to non-metallic character across a period
Relate the number of outer (valence) electrons to metallic or non-metallic character
Predict the properties of Group 1 and Group 17 elements from the Periodic Table
Describe lithium, sodium and potassium as soft, low-density metals with trends in melting point and reaction with water
Describe chlorine, bromine and iodine as diatomic non-metals with trends in colour, state and displacement of other halide ions
Describe the noble gases as unreactive monoatomic elements used to provide an inert environment, such as argon in light bulbs
Explain why the noble gases are unreactive using their electronic configurations
Describe typical transition elements as metals with high melting points and densities, variable oxidation states and coloured compounds
State that transition elements and their compounds often act as catalysts
Place common metals and hydrogen in order of reactivity from their reactions with water, steam and dilute hydrochloric acid
Place common metals and hydrogen in order of reactivity from whether carbon or hydrogen reduces their oxides
Relate the reactivity series to how readily a metal forms its positive ion, using displacement from aqueous ions of other metals
Relate the reactivity series to how readily a metal forms its positive ion, using reactions with oxides of other metals
Deduce an order of reactivity from experimental results
Describe the effect of heat on metal carbonates and relate their thermal stability to the reactivity series
Relate how easily a metal is extracted from its ore to its position in the reactivity series
Describe the conditions needed for iron to rust and how a barrier, such as paint, grease, plastic or galvanising, prevents it
Describe sacrificial protection of iron by a more reactive metal, such as magnesium on underwater pipes

Syllabus statements covered

describe the Periodic Table as an arrangement of the elements in the order of increasing proton (atomic) number
describe how the position of an element in the Periodic Table is related to proton number and electronic configuration
describe the relationship between number of outer (valence) electrons and the ionic charge of an ion for the first twenty elements
explain the similarities between the elements in the same group of the Periodic Table in terms of their electronic configuration
describe the change from metallic to non-metallic character from left to right across a period of the Periodic Table
describe the relationship between number of outer (valence) electrons and metallic/non-metallic character
predict the properties of elements in Group 1 and Group 17 using the Periodic Table.
describe lithium, sodium and potassium in Group 1 (the alkali metals) as a collection of relatively soft, low density metals showing a trend in melting point and in their reaction with water
describe chlorine, bromine and iodine in Group 17 (the halogens) as a collection of diatomic non- metals showing a trend in colour, state and their displacement reactions with solutions of other halide ions
describe the elements in Group 18 (the noble gases) as a collection of monoatomic elements that are chemically unreactive and hence important in providing an inert environment, e.g. argon and neon in light bulbs; helium in balloons; argon in the manufacture of steel
describe the lack of reactivity of the noble gases in terms of their electronic configurations.
describe typical transition elements as metals having high melting point, high density, variable oxidation state and forming coloured compounds
state that the elements and/or their compounds are often able to act as catalysts (see also 10(d)).
place in order of reactivity calcium, copper, (hydrogen), iron, lead, magnesium, potassium, silver, sodium and zinc by reference to — the reactions, if any, of the metals with water, steam and dilute hydrochloric acid
place in order of reactivity calcium, copper, (hydrogen), iron, lead, magnesium, potassium, silver, sodium and zinc by reference to — the reduction, if any, of their oxides by carbon and/or by hydrogen
describe the reactivity series as related to the tendency of a metal to form its positive ion, illustrated by its reaction with — the aqueous ions of the other listed metals
describe the reactivity series as related to the tendency of a metal to form its positive ion, illustrated by its reaction with — the oxides of the other listed metals
deduce the order of reactivity from a given set of experimental results
describe the action of heat on the carbonates of the listed metals and relate thermal stability to the reactivity series
describe the ease of obtaining metals from their ores by relating the elements to their positions in the reactivity series
describe the essential conditions for the corrosion (rusting) of iron as the presence of oxygen and water; prevention of rusting can be achieved by placing a barrier around the metal, e.g. painting; greasing; plastic coating; galvanising
describe the sacrificial protection of iron by a more reactive metal in terms of the reactivity series where the more reactive metal corrodes preferentially, e.g. underwater pipes have a piece of magnesium attached to them.

Lessons

Work through them in order.

Periodic foundations

Groups

Transition elements and reactivity

Practise and check

Or choose

Topic reference

Quick reference

Idea	What to remember
arrangement	in order of increasing proton number
group	Groups 1 and 2: 1 and 2 outer electrons; Groups 13–17: 3–7 outer electrons; Group 18: full outer shell (helium has 2)
period	period number = number of occupied electron shells
common ions	Li⁺, Na⁺, K⁺; Mg²⁺, Ca²⁺; Al³⁺; N³⁻ (in nitrides); O²⁻, S²⁻; F⁻, Cl⁻; carbon and silicon do not form simple ions
across a period	metals on the left, non-metals on the right
Group 1 (Li, Na, K)	down the group: melting point falls and reactivity rises; react with cold water to give an alkaline hydroxide and hydrogen
Group 17 (Cl, Br, I)	down the group: colour darkens, gas → liquid → solid, reactivity falls; a more reactive halogen displaces a less reactive one from its halide
halogens in water	chlorine pale yellow-green; bromine orange; iodine brown
Group 18	monatomic and unreactive; argon in light bulbs and steel-making, neon in advertising lamps, helium in balloons
transition elements	high melting point and density, variable oxidation states, coloured compounds, catalysts
reactivity series	K > Na > Ca > Mg > Zn > Fe > Pb > (H) > Cu > Ag
metal displacement	a more reactive metal displaces a less reactive metal from a solution of its salt
carbonates on heating	the more reactive the metal, the more stable its carbonate
extraction	above zinc: electrolysis; zinc to copper: reduction with carbon; silver and gold: can be found uncombined
rusting	needs oxygen and water; prevented by barriers, galvanising or an attached block of magnesium

Core knowledge to remember

A group is a vertical column. Elements in the same group have the same number of outer electrons, so they have similar chemical properties.
A period is a horizontal row. Its elements have the same number of occupied electron shells.
Across a period, elements change from metals to non-metals: metals tend to lose electrons, non-metals tend to gain or share them.
Group 1 metals are soft, with low densities. Down the group they lose their single outer electron more easily, because it is further from the nucleus, so they become more reactive.
Group 17 elements are diatomic non-metals. Down the group they gain an electron less easily, so they become less reactive.
Group 18 elements are monatomic and unreactive, because their atoms already have full outer shells.
Transition elements have high melting points and densities, form ions with different charges, form coloured compounds and are often catalysts.
The reactivity series ranks metals by how readily they form positive ions. A metal higher in the series reacts more vigorously with water and acids, displaces lower metals, forms a more stable carbonate and is harder to extract.

Common mistakes

Arranging the table by relative atomic mass instead of proton number.
Getting a trend backwards: Group 1 reactivity increases down the group, but Group 17 reactivity decreases.
Writing halogens as single atoms; they are Cl₂, Br₂ and I₂.
Expecting a less reactive element to displace a more reactive one, for metals or halogens.
Using the group number as the ion charge for every element: Group 17 forms 1- ions, and transition elements form ions with different charges.
Thinking helium is not a noble gas because it has only 2 outer electrons; its only shell is full.
Saying that heating a carbonate extracts the metal; it gives the oxide, which must then be reduced.
Saying rusting needs only water, or only oxygen; it needs both.