Cambridge Science States of Matter Practice Test 2026 – Complete Exam Prep

Chemical formulas are the way we show what a particle is made of and how many atoms of each element it contains. The symbols for the elements are written with subscripts indicating the number of atoms of each element; for example, H2O has two hydrogens and one oxygen, and NaCl has one of each. This directly encodes the exact counts in the particle. The atomic number tells how many protons an atom has, not how many atoms are in a molecule; isotopes refer to variants of an element with different neutron numbers; and bonding describes how atoms connect, not the exact counts.