3. Periodicity
3. Periodicity
3.1 Periodic table
Nature of science:
Obtain evidence for scientific theories by making and testing predictions based on them - scientists organize subjects based on structure and function; the periodic table is a key example of this. Early models of the periodic table from Mendeleev, and later Moseley, allowed for the prediction of properties of elements that had not yet been discovered.
Understandings:
The periodic table is arranged into four blocks associated with the four sub-levels - s, p, d, and f.
The periodic table consists of groups (vertical columns) and periods (horizontal rows).
The period number (n) is the outer energy level that is occupied by electrons.
The number of the principal energy level and the number of the valence electrons in an atom can be deduced from its position on the periodic table.
The periodic table shows the positions of metals, non-metals and metalloids.
Applications and skills:
Deduction of the electron configuration of an atom from the element’s position on the periodic table, and vice versa.
3.2 Periodic trends
Nature of science:
Looking for patterns - the position of an element in the periodic table allows scientists to make accurate predictions of its physical and chemical properties. This gives scientists the ability to synthesize new substances based on the expected reactivity of elements.
Understandings:
Vertical and horizontal trends in the periodic table exist for atomic radius, ionic radius, ionization energy, electron affinity and electronegativity.
Trends in metallic and non-metallic behaviour are due to the trends above.
Oxides change from basic through amphoteric to acidic across a period.
Applications and skills:
Prediction and explanation of the metallic and non-metallic behaviour of an element based on its position in the periodic table.
Discussion of the similarities and differences in the properties of elements in the same group, with reference to alkali metals (group 1) and halogens (group 17).
Construction of equations to explain the pH changes for reactions of Na₂O, MgO, P₄O₁₀, and the oxides of nitrogen and sulfur with water.
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