How to read the periodic table
The periodic table is a map, not just a list. A cell identifies an element; its row, column and region then give clues about electron structure and chemical behaviour.
Start with the atomic number
The atomic number Z is the number of protons in the nucleus. It uniquely identifies the element. Sodium has Z = 11, so every sodium nucleus contains 11 protons.
Na is the chemical symbol. The decimal value is an atomic-mass value, not the atomic number and not the mass number of one isotope.
A group is a column; a period is a row
Modern groups are numbered 1 to 18. Elements in the same group often share features of their outer electron structure. Periods run horizontally; sodium is in period 3 and group 1.
Group
Useful for comparing chemical families and, especially for main-group elements, valence-electron patterns.
Period
Gives a useful reference for the highest occupied principal electron shell in the ground state.
s, p, d and f connect the table to electron configuration
The four blocks correspond to the type of subshell associated with electron filling. Their letters come historically from the spectroscopic terms sharp, principal, diffuse and fundamental.
Read sodium step by step
Its electron configuration is 1s² 2s² 2p⁶ 3s¹. The final 3s¹ electron helps explain both its s-block position and its relationship with the alkali metals.
What can you infer from Cl?
Chlorine has Z = 17, lies in period 3 and group 17, and its ground-state configuration ends in 3s² 3p⁵. It therefore has seven valence electrons and commonly forms chloride, Cl⁻.
Position gives clues, not the whole chemistry
The table helps predict families, electron patterns and broad periodic trends. It does not by itself give exact reactivity, toxicity, melting point or the behaviour of a real compound. Use it as a starting map, then check data and chemical models.
Common questions
Why is the atomic mass often a decimal?
Because the displayed value usually reflects isotope masses and their natural abundances. It is not the proton count.
Are group and block the same thing?
No. A group is a column; a block describes an electronic region. Helium shows the distinction clearly.