物质是由不连续的分子或原子构成的。构成原子的微粒有质子、中子和电子，原子中的这三种微粒决定着元素的性质。1．原子核内质子数决定元素的种类。质子数相同的原子（包括由它形成的离子）为同一类原子（总称为某元素），元素的种类与中子数无关。以碳原子为例，有C12、C13、 Substances consist of discrete molecules or atoms. The particles that make up an atom have protons, neutrons, and electrons, and the three particles in the atom determine the nature of the element. 1. The number of protons in the nucleus determines the type of element. The atoms with the same number of protons (including the ions formed by it) are the same type of atoms (collectively referred to as an element), and the type of element is independent of the number of neutrons. Carbon atoms, for example, have C12, C13,