Periodic Table: Organisation and Predicting Properties
The periodic table at IGCSE goes beyond simple group trends to cover the properties of transition elements, the metals found in the central block of the periodic table, and how the acidic or basic character of the oxides of Period 3 elements changes systematically across the period, from the strongly basic oxide of sodium to the strongly acidic oxides of sulfur. Edexcel 4CH1 and Cambridge 0620/0971 expect students to use these trends to predict the properties of elements and compounds not taught directly.
Before you start
Make sure you're comfortable with these topics first:
Method
- Learn the key properties of transition elements that make them different from Group 1 metals: high density, high melting points, hardness and strength, and that many can show more than one (variable) oxidation state in their compounds, such as iron as Fe2+ (iron(II)) or Fe3+ (iron(III)), and copper as Cu+ (copper(I)) or Cu2+ (copper(II)).
- Learn that transition metal compounds are often coloured (for example, copper(II) compounds are typically blue, and iron(III) compounds are typically orange or brown), and that transition metals and their compounds are frequently used as catalysts, for example iron in the Haber process, or manganese(IV) oxide to speed up the decomposition of hydrogen peroxide.
- Across Period 3, from sodium to argon, learn that the elements change from metals (sodium, magnesium, aluminium) through a metalloid (silicon) to non-metals (phosphorus, sulfur, chlorine, argon), and that this metallic-to-non-metallic trend explains the acid-base trend of their oxides.
- Learn the Period 3 oxide trend: metal oxides are basic (sodium oxide, Na2O, and magnesium oxide, MgO, react with acids to form a salt and water), aluminium oxide (Al2O3) is amphoteric (it reacts with both acids and bases), and non-metal oxides are acidic (sulfur dioxide, SO2, and sulfur trioxide, SO3, form acidic solutions and react with bases).
- To predict a property of an untaught element, locate its group and period, then reason from the properties of the nearest elements you do know: properties change gradually down a group and across a period, so an element between two known elements should have intermediate properties.
- When explaining why a trend occurs, always refer back to electron structure: reactivity trends depend on the distance of the outer shell from the nucleus and the shielding provided by inner shells, not simply on the group number itself.
Worked example
Aluminium oxide, Al2O3, is described as amphoteric. Predict and explain what would be observed if aluminium oxide powder is added separately to (a) dilute hydrochloric acid and (b) dilute sodium hydroxide solution.
- Recall that 'amphoteric' means a substance can react as both a base (with acids) and an acid (with alkalis/bases).
- With dilute hydrochloric acid, aluminium oxide reacts as a base: it dissolves, forming a colourless solution of aluminium chloride and water: Al2O3(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2O(l).
- With dilute sodium hydroxide, aluminium oxide reacts as an acid: it also dissolves, forming a colourless solution containing sodium aluminate.
- In both cases the white solid aluminium oxide powder disappears/dissolves into a colourless solution, unlike a purely basic oxide (such as magnesium oxide), which would react with the acid but not dissolve in the alkali.
- Final answer: aluminium oxide dissolves in both the acid and the alkali, showing that it is amphoteric.
Practice questions
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Q1State one physical property of a typical transition element that is different from a Group 1 metal such as sodium.Show answer
Answer: Any one of: much higher density, much higher melting point, or much harder/stronger (Group 1 metals are soft and have low density and low melting points by comparison).
Q2Give the two ion charges (oxidation states) commonly formed by copper.Show answer
Answer: Cu+ (copper(I)) and Cu2+ (copper(II)).
Q3Name a transition metal compound commonly used as a catalyst to decompose hydrogen peroxide.Show answer
Answer: Manganese(IV) oxide, MnO2.
Q4State whether magnesium oxide (MgO) is acidic, basic or amphoteric.Show answer
Answer: Basic.
Q5Sulfur trioxide (SO3) dissolves in water to form sulfuric acid. State whether sulfur trioxide is a basic, acidic or amphoteric oxide, and give a reason.Show answer
Answer: Acidic; it is the oxide of a non-metal, and non-metal oxides form acidic solutions when dissolved in water.
Q6Explain why aluminium oxide is described as amphoteric.Show answer
Answer: Because it reacts with both acids (behaving as a base) and alkalis/bases (behaving as an acid), unlike most metal oxides, which are only basic.
Q7Predict whether phosphorus(V) oxide (P4O10), the oxide of a Period 3 non-metal, is likely to be acidic or basic. Give a reason.Show answer
Answer: Acidic; phosphorus is a non-metal, and non-metal oxides in Period 3 (like sulfur dioxide and sulfur trioxide) are acidic.
Exam-style questions
Written in the style of a IGCSE Science exam paper, with a full mark scheme.
Give two properties, other than colour, that are typical of transition elements but not of Group 1 metals.
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Sodium oxide (Na2O) and sulfur dioxide (SO2) are both oxides of Period 3 elements. (a) State whether each oxide is acidic or basic. (b) Explain, in terms of metallic and non-metallic character, why they have different acid-base behaviour.
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A student is given three unlabelled white powders from Period 3: sodium oxide, aluminium oxide and sulfur trioxide. She adds a spatula of each powder to a test tube of dilute hydrochloric acid, and a spatula of each to a separate test tube of dilute sodium hydroxide solution. Predict what she would observe with each powder in each solution, and use your predictions to identify which powder is which.
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Free printable worksheet
Want more practice on paper? Download the periodic table: organisation and predicting properties worksheet pack - 6 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 13 of IGCSE Science Workbook, the whole course as one free printable PDF.
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