Chemical Elements and the Periodic Table
A map that organizes every kind of atom by atomic number and repeating chemical patterns
Big idea
A chemical element is a pure substance whose atoms all have the same number of protons. The periodic table puts the elements in order of increasing atomic number, so it is both a catalogue and a pattern-finding map. A cell tells us an element's identity; its row and column help us make careful predictions.
By the end, you can: define element and atomic number; read a symbol and element cell; locate periods and groups; distinguish broad metal, nonmetal, and metalloid regions; and use table position to make a limited, evidence-based prediction.
1. What makes an element an element?
All matter is made from atoms. At the centre of an atom is a nucleus containing protons. The number of protons is the atom's atomic number, written as Z. Every hydrogen atom has Z = 1, every carbon atom has Z = 6, and every oxygen atom has Z = 8. If the proton number changes, the element's identity changes.
Macroscopic level
We observe substances: copper wire conducts electricity, oxygen supports respiration, and sulfur is a yellow solid under ordinary classroom conditions.
Particle level
A piece of elemental copper contains copper atoms. Each copper atom has 29 protons. Models simplify atoms; they are not tiny coloured balls in reality.