The Periodic Table organises elements by proton number and electron configuration. Group and period trends explain reactivity patterns for metals and non-metals.
Arranged by increasing proton number. Periods: horizontal rows (number of electron shells). Groups: vertical columns (number of outer electrons). Elements in the same group have similar chemical properties (same number of outer electrons). Metals on the left, non-metals on the right. Metallic character increases down a group and from right to left across a period.
Group I (alkali metals: Li, Na, K): soft, low density, react with water → metal hydroxide + H₂. Reactivity increases down the group (outer electron further from nucleus, easier to lose). Group VII (halogens: F, Cl, Br, I): diatomic molecules, coloured. Reactivity decreases down the group (harder to gain electron as atom gets larger). Halogen displacement: more reactive halogen displaces less reactive from its salt solution.
Properties of metals: strong, malleable, ductile, conduct heat and electricity, high melting points (usually). Transition metals: coloured compounds, catalysts, multiple oxidation states, form complex ions. Iron rusts: Fe + O₂ + H₂O → hydrated iron(III) oxide. Prevention: painting, oiling, galvanising (zinc coating), sacrificial protection, stainless steel. Alloys: brass (Cu+Zn), steel (Fe+C), stainless steel (Fe+Cr+Ni).
Group I metals react by losing their outer electron. Going down the group, the outer electron is further from the nucleus with more shielding, so it is easier to lose → more reactive. Group VII non-metals react by gaining an electron. Going down the group, atoms are larger, the incoming electron is further from the nucleus, so it is harder to attract → less reactive. The key principle: losing electrons gets easier with size, gaining electrons gets harder with size.
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