Key terms: The Periodic Table of Elements

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.

4.1–4.2 The table, groups and periods

• Element (unsur / 元素), a substance made of only one kind of atom, which cannot be broken down into simpler substances by chemical means.
• Periodic table (jadual berkala / 周期表), the arrangement of all elements in order of increasing proton number, in rows and columns that group elements with similar properties.
• Group number (nombor kumpulan / 族数), the number that gives the count of valence electrons for a main-group element; the halogens, for example, are Group 17.
• Period number (nombor kala / 周期数), the number that gives the count of occupied electron shells in an atom.
• Proton number / atomic number (nombor proton / 质子数), the number of protons in the nucleus of an atom; it fixes the identity of the element and its position in the table.
• Group (kumpulan / 族), a vertical column of the periodic table; elements in the same group have the same number of valence electrons and therefore similar chemical properties.
• Period (kala / 周期), a horizontal row of the periodic table; the period number equals the number of occupied electron shells in the atom.
• Valence electron (elektron valens / 价电子), an electron in the outermost occupied shell of an atom; the number of valence electrons determines the group and much of the element’s chemistry.
• Electron arrangement (susunan elektron / 电子排布), the way electrons are distributed among the shells of an atom, written for example as 2.8.1.
• Atomic radius / atomic size (jejari atom / 原子半径), a measure of the size of an atom; it decreases across a period and increases down a group.
• Metal (logam / 金属), an element that tends to lose electrons to form positive ions; metals are on the left and centre of the table.
• Non-metal (bukan logam / 非金属), an element that tends to gain or share electrons; non-metals are on the right of the table.
• Metalloid / semi-metal (metaloid / 准金属), an element with properties between those of metals and non-metals, such as silicon.
• Ion (ion / 离子), a charged particle formed when an atom loses electrons (a positive ion) or gains electrons (a negative ion).
• Reactivity (kereaktifan / 反应活性), how readily an element takes part in a chemical reaction; in this chapter it is explained by how easily an electron is lost or gained.
• Electron shell (petala / 电子层), a region around the nucleus in which electrons are found; the number of occupied shells gives the period number.
• Nuclear charge (cas nukleus / 核电荷), the positive charge of the nucleus due to its protons; a greater nuclear charge attracts the electrons more strongly and reduces the atomic size across a period.

4.1 Development of the periodic table

• Law of octaves (hukum oktaf / 八音律), Newlands’ observation that, arranged by atomic mass, every eighth element had similar properties.
• Triad (triad / 三元组), Döbereiner’s group of three elements with similar properties, where the middle element’s relative atomic mass is about the average of the other two.
• Relative atomic mass (jisim atom relatif / 相对原子质量), the average mass of the atoms of an element compared with a standard; the basis Mendeleev used to order his table.

4.3 Group 1: alkali metals

• Alkali metal (logam alkali / 碱金属), an element in Group 1, with one valence electron; soft, reactive metals that form alkaline hydroxides with water.
• Metal hydroxide (hidroksida logam / 金属氢氧化物), the alkaline compound formed when a Group 1 metal reacts with water, for example sodium hydroxide.

4.4 Group 17: halogens

• Halogen (halogen / 卤素), an element in Group 17, with seven valence electrons; reactive non-metals that exist as diatomic molecules.
• Diatomic molecule (molekul dwiatom / 双原子分子), a molecule made of two atoms joined together, as in chlorine, bromine and iodine.
• Displacement reaction (tindak balas penyesaran / 置换反应), a reaction in which a more reactive halogen takes the place of a less reactive one in its salt solution, releasing the less reactive halogen.
• Halide (halida / 卤化物), the salt formed when a halogen combines with a metal, for example potassium bromide.

4.5 Group 18: noble gases

• Noble gas (gas adi / 稀有气体), an element in Group 18 with a stable, full valence shell, so it is chemically inert.
• Monatomic (monoatom / 单原子), existing as single, separate atoms, as the noble gases do.
• Octet (oktet / 八隅体), a stable arrangement of eight electrons in the outermost shell; a duplet is the stable arrangement of two electrons in helium.
• Inert (lengai / 惰性), chemically unreactive; used to describe the noble gases, which have no tendency to lose, gain or share electrons.

4.6 Period 3 and transition elements

• Transition element (unsur peralihan / 过渡元素), a metal in the central block of the table (such as iron, copper and zinc) with characteristic special properties.
• Variable oxidation number (nombor pengoksidaan berubah-ubah / 可变氧化数), the ability of a transition element to show more than one oxidation number, such as iron as Fe²⁺ and Fe³⁺.
• Catalyst (mangkin / 催化剂), a substance that speeds up a reaction without being used up; many transition elements and their compounds act as catalysts.
• Complex ion (ion kompleks / 络离子), an ion in which a central metal ion is bonded to surrounding molecules or ions; transition elements readily form them.
• Amphoteric oxide (oksida amfoterik / 两性氧化物), an oxide that reacts with both acids and alkalis, such as aluminium oxide.

How to use this glossary

Learn each term with the exact wording, because in this chapter the definition itself is often the mark. Notice how the terms connect: the group fixes the valence electrons, which set the reactivity, which you explain through atomic size and whether an electron is lost or gained. A one-to-one teacher can test your definitions and check that you use the precise word, “displacement” rather than “swap”, “inert” rather than “does not like reacting”, which is exactly the precision the SPM Chemistry marking scheme expects. Once the definitions are secure, move on to the practice questions and use them in full sentences.