How to use the periodic table in SPM Chemistry

The periodic table is the single most useful reference sheet in SPM Chemistry. You are given a clean copy in the exam, so the skill being tested is not memorising it, it is reading it quickly and pulling the right information out. This guide shows you exactly how to do that, from the numbers printed on each element to predicting how a Group 1 metal or a halogen will behave. It draws on the Form 4 chapter The Periodic Table of Elements, so keep those notes nearby.

How the table is arranged

Every element sits in order of increasing proton number (atomic number), reading left to right, top to bottom. Two things about an element’s position tell you almost everything you need:

• Groups are the vertical columns. In the KSSM syllabus they are labelled Group 1, 2, then 13 to 18, plus the transition elements in the middle block. The group number tells you the number of valence electrons (Group 1 has 1, Group 17 has 7, Group 18 has 8, with helium the exception at 2).
• Periods are the horizontal rows. The period number tells you the number of occupied electron shells.

That single pairing, group gives valence electrons, period gives number of shells, is the core of reading the table, and it links straight back to electron arrangement from Matter and the atomic structure.

Reading the numbers on an element

Each box shows the element’s symbol with two numbers. The larger number is the relative atomic mass (nucleon number) and the smaller is the proton number. For sodium you will see Na with 23 and 11: proton number 11, relative atomic mass 23. Do not mix these up, you need the proton number for electron arrangement, and the relative atomic mass for mole calculations.

Worked example: placing an element from its proton number

Suppose an element has proton number 17.

1. Write its electron arrangement by filling shells 2, 8, 8: 2.8.7.
2. The last shell has 7 valence electrons, so it is in Group 17.
3. There are 3 occupied shells, so it is in Period 3.
4. Seven valence electrons means it is a non-metal that gains one electron to form a 1− ion, this is chlorine, a halogen.

Reverse the logic just as easily: an element in Group 2, Period 4 has 2 valence electrons and 4 shells, so its arrangement is 2.8.8.2 and its proton number is 20 (calcium).

Predicting properties group by group

The table is powerful because elements in the same group behave similarly. The four groups examined most closely are:

• Group 1 (alkali metals): Li, Na, K. Soft, reactive metals with 1 valence electron. Reactivity increases down the group because the outer electron is further from the nucleus and lost more easily. They react vigorously with water to give an alkali and hydrogen gas.
• Group 17 (halogens): F, Cl, Br, I. Non-metals with 7 valence electrons. Reactivity decreases down the group because the atom gains an electron less easily as it gets bigger. Colours deepen down the group, from pale yellow chlorine gas to reddish-brown bromine liquid.
• Group 18 (noble gases): He, Ne, Ar. Chemically inert (unreactive) because they have a stable full valence shell, a duplet for helium, an octet for the rest. This is why they exist as single atoms.
• Transition elements: the middle block. They show variable oxidation states, form coloured compounds and ions, and act as catalysts (iron in the Haber process, for example).

Trends across Period 3

Reading across a period, from sodium to argon, the number of valence electrons rises from 1 to 8 while the number of shells stays the same. Atomic size decreases across the period, and the elements change from metallic (Na, Mg, Al) through metalloid (Si) to non-metallic (P, S, Cl) and finally the noble gas argon. Being able to state this trend clearly earns marks in Paper 2.

Using it well in the exam

• When a question gives you a proton number, immediately write the electron arrangement, it unlocks the group, period and likely ion.
• For an unfamiliar element, find a known element in the same group and reason by analogy: “it is below chlorine, so it behaves like a halogen but is less reactive.”
• Use the relative atomic mass from the table, not from memory, for mole calculations, misreading it is a common careless error.

To build fluency, drill with an interactive periodic table until placing any of the first twenty elements from its proton number takes seconds. If group trends and electron arrangement still feel shaky when they combine in a question, that is a common sticking point our teachers untangle quickly. Our online one-to-one lessons run in English from RM50 an hour, with a paid one-hour trial, so the table becomes a tool you reach for confidently rather than a wall of symbols.