BONDING

1. BONDING

2. Compounds Compounds are formed when atoms of more than one type chemically join together. The physical and chemical properties of compounds are very different to the original elements. ELEMENTS COMPOUND CARBON DIOXIDE CARBON + OXYGEN (a colourless gas, which supports combustion) (a colourless gas, which extinguishes fire) (a black solid)

3. Atoms can be joined together in 3 possible ways Ionic Bonding Covalent Bonding Metallic Bonding All three ways use the outermost electrons, losing, gaining or sharing these electrons.

4. Ionic Bonding When an ionic bond is formed there is a transfer of electrons from one atom to another. Two oppositely charged ions are formed. The ions clump together, each ion pulling others of the opposite charge around it. A lattice forms, which is a rigid 3D regular arrangement of ions. Ionic bonds result from the attraction between these oppositely charged ions. Ionicbonds form between metals and non-metals Learn this carefully

5. Structure of sodium chloride NaCl All ionic substances have structures similar to this Sodium ions, Na+ A regular giant lattice of ions held together by the attraction between oppositely charged ions Chloride ions, Cl-

6. FORMATION OF IONIC BONDS THINGS TO REMEMBER Metal atoms always lose their outer shell electrons, non-metal atoms receive these electrons. Since this forms ions it is important to write the charge. Metal atoms always form positive ions called cations. Non-metal atoms always form negative ions called anions. click Atoms gain or lose electrons so that they form ions with a complete outer shell. So, an atom with 2 electrons in the outermost shell will lose 2 electrons and form a 2+ ion… and… An atom with 6 electrons in the outermost shell will gain 2 electrons to form a 2- ion. click

7. Two oppositely charged ions are formed, which attract Cl Na Sodium chloride, NaCl Cl Na By losing it’s outer electron the sodium now has a full outer shell. The electron from the sodium completes the outer shell on the chloride ion. Click for bonding diagram This electron transfers to the chlorine

8. Sometimes, you need to draw the outer shell of electrons only Cl Na Cl Na

9. 2 2 Two oppositely charged ions are formed O Mg Magnesium oxide, MgO O Mg Two electrons transfer to the oxygen

10. 2 O Li Li Lithium oxide, Li2O O Li Li Click for bonding diagram

11. 2 Cl Cl Mg Magnesium chloride, MgCl2 Mg Cl Cl Click for bonding diagram

12. Covalent Bonding When two atoms become close, some outer shell electrons become attracted to the nucleus of both atoms. They also contribute to the outer shell of both atoms. A covalent bond is formed by the sharing of electrons between two atoms. A covalent bond is sometimes indicated by a single line linking atoms. X-X Covalentbonds form between non-metals and non-metals

13. Covalent Bonding Covalent bonding can lead to: Small molecules containing a few bonded atoms. These are called simple molecular structures or A molecule Giant structures, where millions of atoms are joined together in a rigid 3-D network called a giant lattice. Compare with ionic compounds where there are oppositely charged ions.

14. SUBSTANCES WITH SIMPLE MOLECULAR STRUCTURES

15. Shared electrons Cl-Cl Cl Cl (2,8,8) (2,8,8) Chlorine, Cl2 Cl Cl Click for bonding diagram (2,8,7) (2,8,7)

16. H-Cl H Cl (2,8,8) (2) Hydrogen chloride, HCl Cl H Click for bonding diagram (2,8,7) (1)

17. H H O Water, H2O H H O (1) (1) (2,6) Click for bonding diagram (2) H H O (2) (2,8)

18. (2) H H (2) H C H C H H H (2) H (2) (2,8) Methane, CH4 H x 4 C (1) (2,4) Click for bonding diagram

19. (2) H N H N H H H (2) H (2) (2,8) Ammonia, NH3 H x 3 N (1) (2,5) Click for bonding diagram

20. O=O O O (2,8) (2,8) Oxygen, O2 x 2 O (2,6) Click for bonding diagram

21. NN N N (2,8) (2,8) Nitrogen, N2 x 2 N (2,5) Click for bonding diagram

22. O O C O=C=O (2,8) (2,8) (2,8) Carbon dioxide, CO2 x 2 O C (2,4) (2,6) Click for bonding diagram

23. GIANT MOLECULAR STRUCTURES

24. CARBON: Diamond and graphite Atoms of carbon can link together in several structures Diamond Graphite Strong covalent bonds Weak attraction carbon atoms

25. Silicon dioxide silicon atoms oxygen atoms

26. Metallic Bonding This is the chemical binding between metal atoms. Metal atoms pack together as closely as possible to form a giant lattice similar to ionic compounds. The outermost electrons on each metal are free to move throughout the structure. Metallic bonding is the attraction of metal ions and free electrons. Positively charged metal ion

27. THE THREE GIANT LATTICES Ionic Oppositely charged ions. Metallic Positive ions in a ‘sea of electrons’ Covalent Atoms A lattice is an ordered arrangement of particles held together by some form of chemical bonding

28. Physical properties of covalent compounds Simple Molecular compounds Strong bonds between atoms Very weak forces of attraction between molecules. Weak intermolecular forces lead to low melting and boiling point. Hence, they are often gases or liquids. These compounds do not conduct electricity because there are no free ions or electrons. They usually do not dissolve in water.

29. Giant molecular compounds Imagine this arrangement of atoms repeated millions of times. All the atoms are held tightly so these compounds have extremely high melting points - always solids. Very strong covalent bonds There are no free ions or electrons (except graphite) so they never conduct electricity. They are insoluble in water.

30. - - - + + + - - - + + + - - - + + - - - - + + + + - + - - - - + + + + - - - - + + + + - - - - + + + Giant ionic compounds High temperatures are needed to provide enough energy to separate the ions. Therefore, ionic compounds have very high melting points. Ionic compounds often dissolve in water. Ionic compounds do not conduct electricity when solid because the ions are not free to move. However, they WILL conduct when molten or dissolved in water.