Boxi Learn › Chemistry › Stage 4 · Systems and Argument
Why the table has rows and columns
CHEM-5 The periodic table is a patternX-2 Evidence outweighs opinion
What many people think
The periodic table is ordered by atomic mass.
The idea
Elements in a column behave alike because they have the same number of outer electrons.
Explain it
Sodium and potassium react fiercely with water, but magnesium barely does, even though magnesium sits between them by mass. Explain why using outer electrons and shells, not mass.
Try at home
Write the first 20 element symbols on 20 cards with their mass. Lay them in a line by mass, then by atomic number. Which two cards change place? Now deal them into rows of 2, 8, 8, 2.