— mixtures → different substances mixed, not chemically bonded
— needs energy to chemically bond
— the new compound has completely different properties from the original elements (usually)
— unexpected change in colour
— unexpected odour
— a gas is produced unexpectedly
— a precipitate is produced unexpectedly
— temperature change (energy change is more than that supplied)
— usually hard to reverse
— bonds to have a stable outer shell
— loses or gains electron(s) to/from another atom
like a jigsaw puzzle
— lattice structure with alternating negative and positive patterns
— no charge