7th Grade Chemistry Quiz

An atom is the smallest unit of matter that retains the properties of an element. Everything around us is made up of atoms.

Burning wood is a chemical change because it forms new substances (ash, smoke, and gases) and cannot be reversed.

Water is made up of two hydrogen atoms (H) and one oxygen atom (O), represented by the chemical formula H2O.

Solids have a definite shape and volume because their particles are tightly packed and only vibrate in place.

An element is a pure substance made up of only one type of atom, like gold (Au) or oxygen (O).

When a substance is heated, its molecules gain energy and move faster. This is why solids can melt and liquids can evaporate when heated.

Air is a mixture because it contains different gases like oxygen, nitrogen, and carbon dioxide that are not chemically bonded together.

A pH of 7 is neutral, meaning the substance is neither acidic nor basic. Pure water is a common example of a neutral substance.

Ionic bonds form when electrons are transferred between atoms, while covalent bonds form when atoms share electrons.

Evaporation is the process where a liquid gains enough energy to change into a gas, usually occurring at the surface of the liquid.