Key terms: Matter and the Atomic Structure

Many marks in this chapter are awarded for a precise definition, so learn each term with the exact wording below. The Malay and Chinese equivalents are given in brackets so you can recognise the term whichever language your paper uses. Cover the definition, say it aloud, then check.

2.1 Matter and the kinetic theory

• Matter (jirim / 物质), anything that has mass and occupies space (has volume).
• Kinetic theory of matter (teori kinetik jirim / 物质动理论), the idea that matter is made of tiny particles in constant, random motion that possess kinetic energy which increases with temperature.
• Particle (zarah / 粒子), the tiny unit of which matter is made; in this chapter an atom, a molecule or an ion.
• Element (unsur / 元素), a substance made up of only one kind of atom, which cannot be broken down into simpler substances by chemical means.
• Molecule (molekul / 分子), a particle made of two or more atoms chemically joined together.
• Ion (ion / 离子), a charged particle formed when an atom gains or loses one or more electrons; in an ion the number of electrons is not equal to the number of protons.
• Diffusion (resapan / 扩散), the movement of particles from a region of higher concentration to a region of lower concentration until they are evenly spread.
• Solid (pepejal / 固体), a state in which particles are closely packed in an orderly arrangement and vibrate about fixed positions, giving a fixed shape and volume.
• Liquid (cecair / 液体), a state in which particles are close but not orderly and can slide past one another, giving a fixed volume but no fixed shape.
• Gas (gas / 气体), a state in which particles are far apart and move freely and randomly, giving neither a fixed shape nor a fixed volume.

2.2 Changes in the state of matter

• Melting point (takat lebur / 熔点), the constant temperature at which a solid changes to a liquid.
• Freezing point (takat beku / 凝固点), the constant temperature at which a liquid changes to a solid.
• Boiling point (takat didih / 沸点), the constant temperature at which a liquid changes to a gas throughout its bulk.
• Condensation (kondensasi / 凝结), the change of a gas into a liquid.
• Sublimation (pemejalwapan / 升华), the change of a solid directly into a gas without passing through the liquid state.
• Heating curve (lengkung pemanasan / 加热曲线), a graph of temperature against time as a substance is heated, showing a plateau at each change of state.
• Cooling curve (lengkung penyejukan / 冷却曲线), a graph of temperature against time as a substance is cooled, with a plateau where heat is released as forces of attraction re-form.

2.3–2.4 The atom and subatomic particles

• Atom (atom / 原子), the smallest particle of an element that has the properties of that element.
• Nucleus (nukleus / 原子核), the small, dense, positively charged centre of an atom, containing the protons and neutrons.
• Proton (proton / 质子), a subatomic particle in the nucleus with a relative mass of 1 and a relative charge of +1.
• Neutron (neutron / 中子), a subatomic particle in the nucleus with a relative mass of 1 and no charge (relative charge 0).
• Electron (elektron / 电子), a subatomic particle in the shells with a relative charge of −1 and a relative mass of about 1/1840 (negligible).
• Subatomic particle (zarah subatom / 亚原子粒子), a particle smaller than an atom; the proton, neutron and electron.
• Relative charge (cas relatif / 相对电荷), the charge of a subatomic particle compared with that of a proton, taken as +1.

2.5 Proton number, nucleon number and isotopes

• Proton number (nombor proton / 质子数), the number of protons in the nucleus of an atom; it defines the element and equals the number of electrons in a neutral atom. Also called the atomic number.
• Nucleon number (nombor nukleon / 核子数), the total number of protons and neutrons in the nucleus. Also called the mass number.
• Isotope (isotop / 同位素), atoms of the same element that have the same proton number but different nucleon numbers (different numbers of neutrons).

2.6 Electron arrangement

• Electron arrangement (susunan elektron / 电子排布), the way the electrons of an atom are distributed among the shells, written as numbers separated by dots, such as 2.8.1.
• Shell (energy level) (petala / 电子层), a region around the nucleus in which electrons move; the first holds a maximum of 2 electrons, the second and third 8 each for the first twenty elements.
• Valence electrons (elektron valens / 价电子), the electrons in the outermost occupied shell of an atom; they determine the element’s chemical properties and its group in the periodic table.

How to use this glossary

Test yourself by writing each definition from memory and comparing it word for word with the version here; the exam often awards the mark only for the precise phrase. Pay special attention to the pairs that students confuse, proton number versus nucleon number, and melting versus boiling, and to the exact wording of isotope, which is one of the most reliably examined definitions in SPM Chemistry. Once the terms are secure, return to the revision notes and practice questions and use these definitions to mark your answers.