S2 Chemistry

1. S2 Chemistry Covalent Bonding

2. Word Equations Learning Intention • We are learning about covalent bonding

3. Success Criteria • I can describe a covalent bond in terms of atoms sharing electrons • I can explain how a covalent bond holds two atoms together. • I can explain what is meant by a discrete molecule • I can explain what is meant by a covalent network substance • I can state that covalent bonds within a molecule are strong and that the forces of attraction between molecules are weak

4. The Covalent Bond • The covalent bond is a shared pair of electrons between non metal atoms. H2 gas - + + -

5. The Covalent Bond • The two atom are held together by the electrostatic attraction of the protons to the shared pair of electrons.

6. The Covalent Bond • A molecule is 2 or more atoms joined by covalent bonds

7. The Covalent Bond • The atoms share electrons so that they achieve the stable arrangement of the noble gasses.

8. The Covalent Bond • The first electron energy level can only hold 2 electrons then it is full. • Hydrogen achieves this stable arrangement by sharing an electron with another atom

9. The Covalent Bond • When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x o F x o F o x x o o

10. The Covalent Bond • When 2 fluorine atoms come close enough they overlap their electron clouds to share a pair of electrons x x o o x x o F F o x o x x o o F F

11. The Covalent Bond • Each atom would now appear to have the same electron arrangement as the noble gas neon. • We can write the fluorine molecule as F-F or F2

12. The Covalent Bond Oxygen x x o x o o x o o x o x

13. The Covalent Bond Oxygen o x o x o x x o x o x o

14. The Covalent Bond Oxygen o x o x o x x o x o x o The oxygen molecule has two shared pairs of electrons It can be written as O O of O2

15. Conduction • Covalent compounds never conduct electricity. • Demo

16. Molecular Models • Black = carbon • White = hydrogen • Red = oxygen • Green = fluorine/chlorine/iodine • Blue = nitrogen

17. Molecular Models • It is very difficult to draw molecular models so chemists use a short version.

18. Molecular Models • Use the molecular models to make up a model of – • Fluorine • Oxygen • nitrogen

19. Molecules • Molecules are described as discrete.

20. Molecules • Molecules are described as discrete. • This means that each molecule is separate from the next.

21. Molecules • Molecules are described as discrete. • This means that each molecule is separate from the next. • Between the molecule there is very little holding them together

22. Molecules • Molecules are described as discrete. • This means that each molecule is separate from the next. • Between the molecule there is very little holding them together • Within the molecules they are held together by strong covalent bonds.

23. Molecular Explanations H O H O Strong covalent bond Within molecules H H Weak attraction between molecules

24. Electron Clouds • The electrons in an atom are not actually arranged in the structured form shown in the target diagram.

25. Electron Clouds • The electrons in an atom are not actually arranged in the structured form shown in the target diagram. x x x x x x F x x x

26. Electron Clouds • The first level is spherical in shape while the second and third are tetrahedral. x x x x x x F x x x

27. Electron Clouds • The first level is spherical in shape while the second and third are tetrahedral. x x x x x x F x x x

28. Electron Clouds • The electrons fill each of the ‘petals’ singly at first and then they pair up. x x x x x x x x F x x x x x x x x

29. Electron Clouds • The electrons fill each of the ‘petals’ singly at first and then they pair up. Single electrons x x x x x x x x F x x x x x x x x

30. Electron Clouds • The tetrahedral shape of the clouds give an indication of the shape of the molecules.

31. Eg methane

32. Covalent Network Structures • A covalent network structure is a vast 3-dimensional arrangement of atoms strongly bonded together by covalent bonds.

33. Covalent Network Structures • Unlike molecules which have a definite formula, there is no fixed number of atoms in a covalent network.

34. Covalent Network Structures • Each line in the diagram represents a covalent bond – a shared pair of electrons. In this way each carbon atom achieves the stable octet of electrons. • The diamond structure can be described as a lattice because of its regular repeating pattern.

35. Covalent Network Structures • There are only carbon atoms in diamond so the formula is just C. • The formula for silicon dioxide, SiO2 indicates that the proportion of silicon atoms to oxygen atoms is 1:2

36. Covalent Network Properties

37. Covalent Network Properties

38. Covalent Network Properties • Compared to molecular substances, covalent networks are very hard and have a very high melting point. • Compared to ionic substances, covalent networks are not soluble in water and do not conduct when liquid (no charged particles).

39. Covalent Network Properties • Covalent network substances are very hard solids because the strong covalent bonds extend throughout the structure • To melt these substances the strong covalent bonds must be broken and this takes a considerable amount of energy.

40. Bonding Learning Intention We are learning about the 4 different types of bonding

41. Bonding Success Criteria I can describe the 4 types of bonding I can describe the properties of the different types of compounds I can give examples