666771104-Mce-Igcse-Chemistry-Ppt-c02.pptx

Mole Cambridge chemistry IGCSEc04.pptxc06.pptx

1. ELEMENTS, COMPOUNDS AND MIXTURES CHAPTER 2 1 The following content has not been through the Cambridge Assessment International Education endorsement process.

2. 2 Questions Why do you think hydrogen is used in airships? What are other examples of elements around you? Hydrogen combines with oxygen to form water. Do you know of other substances that are formed when hydrogen combines with other elements? How do we tell if a substance is an element, a compound or a mixture?

3. 3 In this section, you will learn the following: Describe the differences between elements, molecules and compounds. 2.1 Elements and C ompounds

4. When sugar is heated, it breaks down into carbon and water vapour . 4 An element is a pure substance that cannot be broken down into two or more simpler substances by chemical processes. 2.1 Elements and Compounds What are elements? Sugar and water can be broken down into simpler substances. Thus, they are not elements.

5. 5 Chemical symbols of elements Chemical symbols are used represent elements. A chemical symbol consists of one or two letters. If the symbol contains two letters, the first letter of the chemical symbol is always in upper case and the second letter is in lower case. Names and symbols of some common elements

6. 6 Atoms Atoms are the smallest particles of an element that have the chemical properties of that element. Each element contains only one type of atoms. Monatomic elements Monatomic elements Elements that exist as individual atoms are called monoatomic elements . Examples: Noble gases, such as helium, neon, argon, krypton, xenon and radon.

7. 7 Molecules A molecule is a group of two or more atoms that are chemically combined . H 2 represents a molecule of hydrogen. 2H represents two atoms of hydrogen. Hydrogen molecule (H 2 ) Two hydrogen atoms (2H)

8. 8 Diatomic molecules are those that are formed by the combination of two atoms. There are also molecules that contain three or more atoms. Diatomic molecules Diatomic molecules Molecules with three or more atoms

9. 9 For example: Water (H 2 O) Ratio Hydrogen atoms : Oxygen atoms 2 : 1 Hydrogen atoms : Oxygen atoms 2 : 2 A compound is a pure substance containing two or more elements that are chemically combined in a fixed ratio. What are compounds? Hydrogen peroxide (H 2 O 2 ) Ratio The ratio of hydrogen to oxygen in water is always 2 : 1.

10. 10 A compound may be made up of molecules or another type of particles called ions. Ions are electrically charged particles. An ion carries either positive or negative charge(s). Composition of a compound Water is made up of molecules. Sodium chloride is made up of ions.

11. 11 Compound has different properties from its constituent elements. For example, magnesium burns in oxygen to form a compound called magnesium oxide. Magnesium and oxygen are its constituent elements. Magnesium oxide has properties different from magnesium and oxygen. When magnesium burns in air, a white solid called magnesium oxide is formed. Properties of a compound

12. 12 Can you write down the constituent elements of each compound in the table? Naming of compounds Every compound has a chemical name that indicates the elements it contains. ? ? ? ? ? ?

13. 13 The chemical formula tells us the types of atoms (i.e., elements) present in the compound; the ratio of the different atoms present in the compound. Chemical formula of water Chemical formula of a compound A compound can be represented by a chemical formula.

14. 14 To find the ratio of atoms in the chemical formula of lead(II) nitrate The ratio of atoms in lead(II) nitrate is lead : nitrogen : oxygen = 1: 2 : 6.

15. 15 Chemical formulae of some compounds Can you write down the ratio of atoms of each compound in the table? ? ? ? ?

16. 16 Chemical processes such as thermal decomposition and electrolysis can be used to decompose compounds. These processes break down compounds into elements or simpler compounds. Decomposition of compounds

17. 17 Thermal decomposition of copper(II) carbonate Thermal decomposition of copper(II) carbonate

18. 18 What are the differences between elements and compounds? Comparing elements and compounds

19. 19 In this section, you will learn the following: Describe the differences between mixtures and compounds. 2.2 Mixtures

20. 20 A mixture is made up of two or more substances that are not chemically combined. hydrogen neon water ammonia 2.2 Mixtures Different types of mixtures

21. 21 Alloys as examples of mixtures Most wind instruments such as the trumpet are made of brass, which is an alloy of copper and zinc.

22. 22 What are the differences between mixtures and compounds? The following slides features a table showing the differences between mixtures and compounds.

23. Comparing mixtures and compounds Iron is magnetic but sulfur is not. The iron can be separated with a magnet. Unlike the elements that form it, iron(II) sulfide does not have any magnetic properties. 23

24. How can we determine if a substance is an element, a compound or a mixture? We can conduct an experiment to determine if a substance is an element, a compound or a mixture. Let’s Investigate 2A Reactions of substances A to E with water or when heated 24

25. What have you learnt? ? ? ? ? ? ? ? ? ? 25

26. What have you learnt? 26

27. Acknowledgements