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. (3.1)

• 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.

Guidance:

• Only examples of general trends across periods and down groups are required. For ionization energy the discontinuities in the increase across a period should be covered.
• Group trends should include the treatment of the reactions of alkali metals with water, alkali metals with halogens and halogens with halide ions.

• Industrialization has led to the production of many products that cause global problems when released into the environment.

Theory of knowledge:

• The predictive power of Mendeleev’s Periodic Table illustrates the “risk-taking” nature of science. What is the demarcation between scientific and pseudoscientific claims?
• The Periodic Table is an excellent example of classification in science. How does classification and categorization help and hinder the pursuit of knowledge?

Utilization:

• Syllabus and cross-curricular links:
• Topic 2.2—anomalies in first ionization energy values can be connected to stability in electron configuration
• Topic 8.5—production of acid rain

Aims:

• Aims 1 and 8: What is the global impact of acid deposition?
• Aim 6: Experiment with chemical trends directly in the laboratory or through the use of teacher demonstrations.
• Aim 6: The use of transition metal ions as catalysts could be investigated.
• Aim 7: Periodic trends can be studied with the use of computer databases.