ScienceVerseLearning path: Molecules
The concepts to learn before Molecules, in order. Each step links to its page and, where one exists, its quiz.
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Your path
- Chemical BondsDirect prerequisite
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.
- MoleculesYour goal
A molecule is a group of atoms held together by covalent bonds that acts as a single particle — such as water, H₂O, or carbon dioxide, CO₂. A molecular formula says which atoms a molecule contains and how many; its three-dimensional shape, which VSEPR theory predicts from repelling electron groups, strongly affects how it behaves. Chemists count molecules in moles: exactly 6.022 140 76 × 10²³ of them.
Where to go next
Concepts that build directly on Molecules:
- Chemical Reactions: A chemical reaction rearranges atoms: bonds in the starting substances (reactants) break and new bonds form, making new substances (products) with different properties. No atoms are created or destroyed, so mass is conserved and a chemical equation must balance. For a reaction to happen at all, particles must collide in the right orientation with at least the activation energy, which is why temperature changes reaction rates.