Chapter 4: The Periodic Table of Elements

4.1 The Development of the Periodic Table

• Key contributors: Lavoisier (grouped gases/non-metals/metals/metal oxides), Dobereiner (triads), Newlands (Law of Octaves), Meyer (atomic volume vs mass graph), Mendeleev (arranged by increasing atomic mass, left gaps for undiscovered elements), Moseley (arranged by increasing proton number, the modern basis). (p.80)
• Basic principle: elements are arranged in ascending order of proton number (1 to 118); elements with similar chemical properties are placed in the same vertical column. (p.81)

4.2 Arrangement in the Periodic Table

• There are 18 groups (vertical columns) and 7 periods (horizontal rows). Group number = number of valence electrons (for 1–2 valence electrons) or valence electrons + 10 (for 3–8 valence electrons). Period number = number of electron shells. (p.82)

4.3 Elements in Group 18

• Group 18 (noble/inert gases): helium, neon, argon, krypton, xenon, radon, oganesson — chemically unreactive due to a full (duplet or octet) valence shell. (p.84)
• Going down Group 18: atomic radius, melting point, boiling point and density all increase. (p.85)

4.4 Elements in Group 1

• Group 1 (alkali metals): lithium, sodium, potassium, rubidium, caesium, francium — have one valence electron and form +1 ions. (p.87)
• Going down Group 1: atomic radius increases; melting and boiling points decrease; reactivity increases (valence electron is further from the nucleus and more easily donated). (p.88)
• Alkali metals react with water to form metal hydroxide + hydrogen gas; with oxygen to form metal oxide; with chlorine to form metal chloride. (p.90)

4.5 Elements in Group 17

• Group 17 (halogens): fluorine, chlorine, bromine, iodine, astatine, tennessine — exist as diatomic molecules, have seven valence electrons and form −1 ions. (p.92)
• Going down Group 17: physical state changes gas → liquid → solid; melting point, boiling point and density increase; reactivity decreases. (p.93)
• Halogens react with water to form acidic solutions; with metals to form metal halides; with alkalis to form metal halide + metal halate + water. (p.94)

4.6 Elements in Period 3

• Period 3: sodium, magnesium, aluminium, silicon, phosphorus, sulphur, chlorine, argon. (p.96)
• Across Period 3 (left to right): atomic size decreases and electronegativity increases; physical state changes from solid to gas. (p.97)
• Oxide properties change from basic oxide (Na₂O, MgO) → amphoteric oxide (Al₂O₃) → acidic oxide (SiO₂, P₄O₁₀, SO₂, Cl₂O₇) across the period. (p.99)

4.7 Transition Elements

• Transition elements are placed between Group 3 and Group 12; all are metals with high melting/boiling points, hardness, and shiny surfaces. (p.101)
• Special characteristics: function as catalysts (e.g. iron in the Haber Process); form coloured ions/compounds; have more than one oxidation number. (p.102)
• Transition elements can also form complex ions (e.g. [Cu(NH₃)₄]²⁺). Industrial catalyst uses: vanadium(V) oxide (Contact Process), iron (Haber Process), platinum (Ostwald Process), nickel/platinum (hydrogenation of vegetable oils). (p.103)