Chapter 1. Matter, Measurement and Units

Matter is anything that has mass and occupies space. It is classified as pure substances (elements and compounds) or mixtures (homogeneous solutions and heterogeneous mixtures) [1][2]. Physical changes (melting, dissolving) leave composition unchanged; chemical changes (rusting, burning) form new substances.

SI units. The seven base units include the metre (m), kilogram (kg), second (s), kelvin (K) and mole (mol) [11]. Temperature conversion: K = °C + 273.15.

Significant figures. Report a result with only the digits justified by the measurement. In multiplication and division, keep the fewest significant figures of any input; in addition and subtraction, keep the fewest decimal places [2].

Accuracy vs precision. Accuracy is closeness to the true value; precision is the reproducibility of repeated measurements [9].

Dimensional analysis. Treat units as algebraic quantities and cancel them. Example: convert 2.50 L to mL: 2.50 L × (1000 mL / 1 L) = 2500 mL.

Review: (a) Express 0.00450 g in scientific notation. (b) How many significant figures are in 100.0 m?