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Periodicity 2

Periodicity 2. Trends Across Period 3. Atomic radii decreases from left to right across period 3 due to the increasing attraction experienced by the outer-shell electrons. The first ionization energy and electronegativity increases from left to right across period 3.

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Periodicity 2

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  1. Periodicity 2

  2. Trends Across Period 3 • Atomic radii decreases from left to right across period 3 due to the increasing attraction experienced by the outer-shell electrons. • The first ionization energy and electronegativity increases from left to right across period 3.

  3. Chemical Properties of Elements and Their Oxides • Just as the physical properties exhibit a periodicity within groups and periods, so do the chemical properties of the elements and some of their compounds.

  4. Trends Within a Group • The alkali metals are known for their reactive nature. • Their tendency to react, sometimes violently, with water means that they must be stored under oil. • The reactivity of the alkali metals with water increases down group 1. 2Li(s) + H2O(l) Li2O(aq) + H2(g)

  5. Trends Within a Group • Lithium, sodium and potassium all produce alkaline solutions when they react with water. Li2O(s) + H2O(l ) 2LiOH(aq) • The increase in the reactivity can be explained by the decrease in the electrostatic attraction between the outer-shell electron and the positive nucleus of the alkali metal.

  6. Trends Within a Group • The increasing reactivity of the alkali metals can also be seen in their reaction with halogens. • As Li, Na and K all lose electrons easily (are good reducing agents) and the halogens gain electrons easily (are good oxidizing agents), these reactions are predictably violent. 2Na(s) + Cl2(g) 2NaCl(s)

  7. Trends Within a Group • The smaller the halogen atom, the greater is its ability to gain electrons. • This can be explained by the closeness of the outer shell to its nucleus.

  8. The Oxides of Period 3 Elements • Each of the period 3 elements reacts with oxygen. • The large difference in electronegativity between the metals and oxygen produces an ionic compound, whereas the non-metals form a covalent compound with oxygen.

  9. The Oxides of Period 3 Elements • Na burns in air to produce Na2O, which reacts easily with water to produce a strongly alkaline solution of NaOH. • To the right of Na is Mg, which reacts the same. • The decrease in metallic nature from left to right across period 3 can be seen from the very different behaviour of Al. • Al2O3 can behave as an acid or a base. • Al2O3 does not dissolve in water, but will react with acids or bases.

  10. The Oxides of Period 3 Elements • Further to the right in period 3, P burns violently in air to make P4O10, which then reacts violently with water to make a weakly acidic solution. • We generalize this trend: • Non-metals form acidic oxides • Metals form basic oxides • Al forms an amphoteric oxide

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