Everything from the 5 lessons of this topic on a few pages: the key idea of each lesson, the diagram to remember, the points to learn and the traps examiners set. Read it, cover it, test yourself.
The Periodic Table arranges elements in order of increasing proton number. Vertical columns are groups; horizontal rows are periods. For Groups I to VII the group number equals the number of outer-shell electrons, and the period number equals the number of occupied shells. Elements change from metallic to non-metallic across a period. Extended: elements in the same group have similar chemical properties because they have the same number of outer electrons; the group number predicts the charge on the ion: I +1, II +2, III +3, V −3, VI −2, VII −1.
The Periodic Table is ordered by proton number, not by relative atomic mass. Argon (Ar 40) comes before potassium (Ar 39) because argon has 18 protons and potassium 19. And Group VIII (noble gases) has 8 outer electrons, except helium, which has 2.
The Group I alkali metals are soft, have relatively low melting points and low densities, and are good conductors. They react with cold water to form an alkaline hydroxide and hydrogen: 2Na + 2H2O → 2NaOH + H2. Down the group, the melting point decreases, the density generally increases and the reactivity increases. Their outer electron is further from the nucleus and more easily lost.
Reactivity increases down Group I but decreases down Group VII. Do not carry the Group I trend over to the halogens. And the solution formed with water is alkaline because of the hydroxide, not because of the hydrogen gas.
The Group VII halogens are diatomic non-metals: chlorine (Cl2) is a pale yellow-green gas, bromine (Br2) a red-brown liquid and iodine (I2) a grey-black solid. Down the group the colour gets darker, the density increases and the reactivity decreases. A more reactive halogen displaces a less reactive halogen from a solution of its halide: Cl2 + 2KBr → 2KCl + Br2.
In a displacement reaction the colour change comes from the halogen that is formed, not the one added. Aqueous bromine is orange and iodine solution is brown, so "the solution turns brown" with potassium iodide means iodine has been made.
The transition elements are metals with high densities and high melting points. They form coloured compounds, and the elements and their compounds often act as catalysts. Extended: transition elements have ions with variable oxidation numbers, such as iron(II), Fe2+, and iron(III), Fe3+.
"Coloured compounds" is about the compounds, not the metals: copper metal is pink-brown, but the property that marks a transition element is that its compounds and solutions are coloured. And a catalyst is not used up, so "iron reacts in the Haber process" is wrong.
The noble gases in Group VIII are unreactive, monatomic gases. Their atoms have full outer shells (helium 2, neon 2,8, argon 2,8,8), so they do not need to gain, lose or share electrons to become stable. Because they are unreactive they are used where a non-reactive gas is needed: argon in lamps and as an inert atmosphere, helium in balloons and airships, neon in advertising signs.
Helium replaced hydrogen in airships because it is unreactive (it does not burn), not just because it is light: hydrogen is even less dense but is flammable. And helium has 2 outer electrons, not 8, yet its outer shell is still full.