C4 (Chemistry): Chemical Patterns

Overview of Module

This module features a central theme of modern chemistry. It shows how theories of atomic structure can be used to explain the properties of elements and their compounds. The module also includes examples to show how spectra and spectroscopy have contributed to the development of chemical knowledge and techniques. This module shows how atomic structure can be used to help explain the behaviour of elements.

The first topic looks at the Periodic Table, the history of its development, and patterns that exist within it, focusing on Group 1 and Group 7. This topic also introduces the use of symbols and equations as a means of describing a chemical reaction.An explanation of the patterns is then developed in the next topic by linking atomic structure with chemical properties.

The third, and final, topic takes this further by introducing ions and showing how ionic theory can account for properties of compounds of Group 1 with Group 7 elements.

Topics (see below for more details description)

C4.1 What are the patterns in the properties of elements?

• The history of the development of the Periodic Table
• Classifying elements by their position in the Periodic Table
• Patterns in Group 1 and patterns in Group 7
• Using symbols and equations to represent chemical reactions

C4.2 How do chemists explain the patterns in the properties of elements?

• Flame tests and spectra and their use for identifying elements and studying atomic structure
• Classifying elements by their atomic structure
• Linking atomic structure to chemical properties

C4.3 How do chemists explain the properties of compounds of Group 1 and Group 7 elements?

• Ions, and linking ion formation to atomic structure
• Properties of ionic compounds of alkali metals and halogens

Detailed Description

C4.1 What are the patterns in the properties of elements?

1. understand that atoms of each element have different proton numbers

2. understand that arranging the elements in order of their proton numbers gives repeating patterns in the properties of elements

3. understand that early attempts to find connections between the chemical properties of the elements and their relative atomic mass were dismissed by the scientific community

4. recall the significant stages in the history of the development of the Periodic Table to include the ideas of Döbereiner, Newlands and Mendeleev

5. understand how Mendeleev used his Periodic Table to predict the existence of unknown elements

6. use the Periodic Table to obtain the names, symbols, relative atomic masses and proton numbers of elements

7. understand that a group of elements is a vertical column in the Periodic Table and that the elements in a group have similar properties

8. recall that a period is a row of elements in the Periodic Table

9. use the Periodic Table to classify an element as a metal or non-metal

10. use patterns in the Periodic Table to interpret data and predict properties of elements. NOTE: Candidates will be given a copy of the Periodic Table (as in Appendix F) with the examination paper

11. recall and recognise the chemical symbols for the Group 1 metals (also known as the alkali metals) lithium, sodium and potassium

12. recall that the alkali metals are shiny when freshly cut but tarnish rapidly in moist air due to reaction with oxygen

13. use qualitative and quantitative data to identify patterns and make predictions about the properties of Group 1 metals (for example, melting point, boiling point, density, formulae of compounds and relative reactivity)

14. describe the reactions of lithium, sodium and potassium with cold water

15. recall that alkali metals react with water to form hydrogen and an alkaline solution of a hydroxide with the formula MOH

16. recall that alkali metals react vigorously with chlorine to form colourless, crystalline salts with the formula MCl

17. understand and give examples to show that the alkali metals become more reactive as the group is descended

18. recall the main hazard symbols and be able to give the safety precautions for handling hazardous chemicals (limited to explosive, toxic, corrosive, oxidizing, and highly flammable). NOTE: See Appendix H for guidance on recent changes to hazard labelling

19. state and explain the precautions necessary when working with Group 1 metals and alkalis

20. recall and recognise the chemical symbols for the atoms of the Group 7 elements (also known as the halogens) chlorine, bromine and iodine

21. recall the states of these halogens at room temperature and pressure

22. recall the colours of these halogens in their normal physical state at room temperature and as gases

23. recall that the halogens consist of diatomic molecules

24. use qualitative and quantitative data to identify patterns and make predictions about the properties of the Group 7 elements (for example melting point, boiling point, formulae of compounds and relative reactivity)

25. understand that the halogens become less reactive as the group is descended and give examples to show this

26. understand how a trend in reactivity for halogens can be shown by their displacement reactions and by their reactions with alkali metals and with iron

27. state and explain the safety precautions necessary when working with the halogens

28. recall the formulae of:

• a. hydrogen, water and halogen (limited to chlorine, bromine and iodine) molecules
• b. the chlorides, bromides and iodides (halides) of Group 1 metals (limited to lithium, sodium and potassium)

29. write word equations for reactions of alkali metals and halogens in this module and for other reactions when given appropriate information

30. interpret symbol equations, including the number of atoms of each element, the number of molecules of each element or covalent compound and the number of ‘formulas’ of ionic compounds, in reactants and products. NOTE: In this context, ‘formula’ is used in the case of ionic compounds as an equivalent to molecules in covalent compounds; the concept of the mole is not covered in the specification

31. balance unbalanced symbol equations

32. write balanced equations, including the state symbols (s), (g), (l ) and (aq), for reactions of alkali metals and halogens in this module and for other reactions when given appropriate information

33. recall the state symbols (s), (l ), (g) and (aq) and understand their use in equations

C4.2 How do chemists explain the patterns in the properties of elements?

1. describe the structure of an atom in terms of protons and neutrons in a very small central nucleus with electrons arranged in shells around the nucleus

2. recall the relative masses and charges of protons, neutrons and electrons

3. understand that in any atom the number of electrons equals the number of protons

4. understand that all the atoms of the same element have the same number of protons

5. understand that the elements in the Periodic Table are arranged in order of proton number

6. recall that some elements emit distinctive flame colours when heated (for example lithium, sodium and potassium). NOTE: Recall of specific flame colours emitted by these elements is not required

7. understand that the light emitted from a particular element gives a characteristic line spectrum

8. understand that the study of spectra has helped chemists to discover new elements

9. understand that the discovery of some elements depended on the development of new practical techniques (for example spectroscopy)

10. use the Periodic Table to work out the number of protons, electrons and neutrons in an atom

11. use simple conventions, such as 2.8.1 and dots in circles, to represent the electron arrangements in the atoms of the first 20 elements in the Periodic Table, when the number of electrons or protons in the atom is given (or can be derived from the Periodic Table)

12. understand that a shell (or energy level) fills with electrons across a period

13. understand that elements in the same group have the same number of electrons in their outer shell and how this relates to group number

14. understand that the chemical properties of an element are determined by its electron arrangement, illustrated by the electron configurations of the atoms of elements in Groups 1 and 7.

C4.3 How do chemists explain the properties of compounds of Group 1 and Group 7 elements?

1. understand that molten compounds of metals with non-metals conduct electricity and that this is evidence that they are made up of charged particles called ions

2. understand that an ion is an atom (or group of atoms) that has gained or lost electrons and so has an overall charge

3. account for the charge on the ions of Group 1 and Group 7 elements by comparing the number and arrangement of the electrons in the atoms and ions of these elements

4. work out the formulae of ionic compounds given the charges on the ions

5. work out the charge on one ion given the formula of a salt and the charge on the other ion

6. recall that compounds of Group 1 metals with Group 7 elements are ionic

7. understand that solid ionic compounds form crystals because the ions are arranged in a regular lattice

8. describe what happens to the ions when an ionic crystal melts or dissolves in water

9. explain that ionic compounds conduct electricity when molten or when dissolved in water because the ions are charged and they are able to move around independently in the liquid.