Reactivity with oxygen, halogens and water

Atomic structure and the periodic table • Properties of transition metals

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How do surface area and temperature affect metal reactivity?

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Greater surface area and higher temperature increase reaction rates and may alter reaction pathways.

Key concepts

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Definition: transition elements

Transition elements occupy the d-block of the periodic table and form ions with partly filled d-subshells. Multiple stable oxidation states appear because electrons from both the s- and d-subshells can participate in bonding. Variable oxidation states cause diverse compound types and frequently produce coloured ions and complex formation.

Definition: Group 1 elements

Group 1 elements (alkali metals) have a single outer s electron. Loss of that electron to form a +1 ion is energetically favourable. Simple ionic compounds form easily and reactions proceed rapidly under mild conditions because ionisation energies are low and electrostatic attractions to non-metals are strong.

Reactivity with oxygen: cause and effect

Cause: Group 1 metals have a low ionisation energy for the outer electron. Effect: Group 1 metals oxidise quickly in air, forming oxides, peroxides or superoxides depending on metal and conditions (for example, sodium forms Na2O2 under some conditions). Cause: Transition metals have higher ionisation energies and multiple oxidation states. Effect: Transition metals oxidise more slowly, often require heat, and frequently form stable metal oxides that may be less reactive. A protective oxide layer on a transition metal surface can slow further oxidation (passivation).

Reactivity with halogens: cause and effect

Cause: Group 1 metals transfer their single outer electron readily to halogen atoms. Effect: Group 1 metals react vigorously with halogens to form ionic halides (e.g., Na + Cl → NaCl). Reaction strength increases down Group 1 as atoms become more reactive. Cause: Transition metals can adopt different positive oxidation states and form halides that display covalent character, variable stoichiometry and different solubilities. Effect: Transition metal-halogen reactions produce a wider variety of compounds (e.g., FeCl2, FeCl3), often requiring controlled conditions.

Reactivity with water: cause and effect

Cause: Group 1 metals have a weakly held outer electron and react exothermically with water. Effect: Group 1 metals react rapidly with cold water to form hydroxides and hydrogen gas; reactivity increases down the group (Li < Na < K etc.). Cause: Transition metals have stronger metallic bonding and variable oxidation states. Effect: Most transition metals do not react with cold water; some react with steam or acids to produce oxides and hydrogen (for example, magnesium reacts slowly with water but reacts with steam).

Limiting factors and exceptions

Cause: Surface area, temperature, oxidation state and protective coatings affect rates and products. Effect: Powdered metals react faster than bulk metals. Elevated temperature increases reaction rates and can change products (e.g., formation of higher oxidation state compounds). Certain transition metals corrode or oxidise only under specific conditions; some become passivated by oxide layers. Group 1 reactivity shows clearer trends but exceptions in oxide types occur for the heavier alkali metals.

Key notes

Important points to keep in mind

Transition elements are d-block metals with variable oxidation states and often slower, condition-dependent reactions.

Group 1 metals have one outer electron, form +1 ions, and react rapidly with oxygen, halogens and water.

Group 1 oxides may be oxide, peroxide or superoxide depending on metal and conditions.

Transition metal oxides can form protective layers that reduce further oxidation (passivation).

Group 1 reactions with water produce hydroxides and hydrogen; reactivity increases down the group.

Transition metals may react with steam or acids rather than cold water; oxidation state controls product.

Surface area, temperature and oxidation state are key limiting factors for observed reactivity.

Halide products differ: Group 1 gives simple ionic halides; transition metals give multiple halides with differing stoichiometry and bonding character.