ScienceVerseLearning path: Periodic Table
The concepts to learn before Periodic Table, in order. Each step links to its page and, where one exists, its quiz.
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Your path
- ElementsDirect prerequisite
A chemical element is a substance made of atoms that all have the same number of protons — the atomic number. Carbon is every atom with 6 protons, oxygen every atom with 8. Atoms of one element can differ in their number of neutrons (isotopes), which is why an element's listed atomic mass is a weighted average rather than a whole number. 118 elements are known; 94 occur naturally on Earth.
- Periodic TableYour goal
The periodic table lists every known element in order of atomic number, in 7 rows (periods) and 18 columns (groups). Elements in the same group have similar outer-electron arrangements and so behave in similar ways, which lets chemists predict properties from position. Mendeleev's 1869 version was so successful that it predicted elements nobody had yet found; the seventh period was completed in 2015.
Where to go next
Concepts that build directly on Periodic Table:
- Chemical Bonds: A chemical bond is the attraction that holds atoms together in a substance. In an ionic bond, oppositely charged ions attract after electrons have moved from one atom to another; in a covalent bond, two atoms share a pair of electrons; in a metal, outer electrons are shared across the whole structure. Bonding lowers a system's energy, so breaking a bond always costs energy and forming one releases it.