C2.1 structure and bonding

1. C2.1 Structure and bonding

2. Key words Atoms Elements Periodic table Compounds Chemical bonding Electrons Ions Electronic structure Alkali metals Ionic compounds Halogens Giant structure Electrostatic forces Lattice Ionic bonding Covalent bonds Macromolecules Giant structures

3. To write formulae for ionic compounds from given symbols and ionic charges to represent the electronic structure of the ions in sodium chloride, magnesium oxide and calcium chloride in the following forms: You should be able to: for sodium ion (Na+)

4. You should be able to: to represent the covalent bonds in molecules such as water, ammonia, hydrogen, hydrogen chloride, chlorine, methane and oxygen and in giant structures such as diamond and silicon dioxide in the following forms:

5. You should be able to: To represent the bonding in metals in the following form:

6. Compounds are substances in which atoms of two or more elements are chemically combined.

7. b) Chemical bonding involves either transferring or sharing electrons in the highest occupied energy levels (shells) of atoms in order to achieve the electronic structure of a noble gas. TOTTERDOWN

8. c) When atoms form chemical bonds by transferring electrons, they form ions . Atoms that lose electrons become positively charged ions. Atoms that gain electrons become negatively charged ions. Ions have the electronic structure of a noble gas (Group 0).

9. Element Symbol Group Charge Potassium K 1 1+ Magnesium     2+ Lithium   1     Ba   2+ Aluminium         Na 1 1+ Chloride Cl -     Bromide Br -   1- Flouride F -     Oxide O 2-     Sulfide S 2-    

10. Element Symbol Group Charge Potassium K 1 1+ Magnesium Mg     2 2+ Lithium   Li 1   1+   Barium Ba   2 2+ Aluminium   Al 3     3+   Sodium Na 1 1+ Chloride Cl - 7     1- Bromide Br - 7   1- Flouride F - 7    1-   Oxide O 2-   6   2- Sulfide S 2-   6   2-

11. d) The elements in Group 1 of the periodic table, the alkali metals , all react with non-metal elements to form ionic compounds in which the metal ion has a single positive charge. Sodium transfers an electron (to chlorine) and so becomes positively charged Chlorine gains an electron so becomes positively charged

12. e) The elements in Group 7 of the periodic table, the halogens, all react with the alkali metals to form ionic compounds in which the halide ions have a single negative charge.

13. Mg + 2F → MgF 2 The ratio of ions is: Mg 2+ : F 1+ 1: 2 So the formula of the compound is MgF 2

14.   Fluoride F - Oxide O 2- Carbonate CO 3 2- Phosphate PO 4 3- Lithium Li +         Barium Ba 2+         Copper Cu 2+         Aluminium Al 3+         Complete the following table with the formula of each compound formed. You do not need to remember the charges on the ions – these are given in the data sheet

15.   Fluoride F - Oxide O 2- Carbonate CO 3 2- Phosphate PO 4 3- Lithium Li +         Barium Ba 2+         Copper Cu 2+         Aluminium Al 3+         Complete the following table with the formula of each compound formed. You do not need to remember the charges on the ions – these are given in the data sheet

16.   Br - OH - NO 3 - SO 4 2- K +         Mg 2+         Fe 3+        

17.   Br - OH - NO 3 - SO 4 2- K +         Mg 2+         Fe 3+        

18. f) An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this is called ionic bonding .

19. g) When atoms share pairs of electrons, they form covalent bonds . These bonds between atoms are strong. Some covalently bonded substances consist of simple molecules such as H 2 , Cl 2 , O 2 , HCl , O, NH 3 and CH 4 .

20. Others have giant covalent structures ( macromolecules ), such as diamond and silicon dioxide. The giant structure of diamond The giant structure of silicon

21. Property Ionic Covalent Melting point High Solubility soluble in water doesn’t usually mix with water Electrical conductivity high low

22. h) Metals consist of giant structures of atoms arranged in a regular pattern. The atoms in metals are closely packed together and arranged in regular layers. This means they can form crystals.

23. i ) The electrons in the highest occupied energy levels (outer shell) of metal atoms are delocalised and so free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions. (HT)

24. Why do atoms bond? They want to have a full outer electron shell . This is why oxygen that we breathe in is O 2 , chlorine gas is Cl 2 etc… METAL NON-METAL METAL NON-METAL What type of bond? metallic ionic ionic covalent

25. What are the properties of the different types of chemical bond? IONIC METALLIC COVALENT COVALENT Type of structure Giant Simple molecules Are ions present? Are delocalised electrons present? How strong is the chemical bond? High/Low melting point? Conductor of electricity?

26. What are the properties of the different types of chemical bond? IONIC METALLIC COVALENT COVALENT Type of structure giant giant Giant Simple molecules Are ions present? yes yes no no Are delocalised electrons present? no yes no (except in graphite) no How strong is the chemical bond? strong strong very strong very strong High/Low melting point? high high very high low Conductor of electricity? when molten/ in solution yes no (except graphite) no

27. Ionic bonds   Make sure you know how to draw the electrons on a diagram to show both atoms and ions Don’t forget to add the charge when drawing diagrams of ions! (Use a square bracket and write the charge top right). Remember – ions have a full outer shell .   What is an ionic bond?

28. Why do ionic substances have high melting points ?             Why can ionic substances conduct electricity when they are molten or in solution, but not when they are solid?

29. Covalent bonds What is this compound?

30. Why do giant covalent substances such as diamond or carbon have very high melting points?           Why do simple covalent bonds have lower melting points?

31. Small molecules Giant covalent structure                     Put these in the correct place: Methane CH 4 Silicon dioxide SiO 2 Diamond C Ammonia NH 3

32. Small molecules Giant covalent structure     Methane CH 4         Ammonia NH 3       Diamond C Silicon dioxide SiO 2 Put these in the correct place:

33. Sodium Chloride   Magnesium oxide   Calcium Chloride   Hydrogen Sulfide   Iron (II) chloride   Iron (III) chloride   Sodium Sulfide   Sodium Sulfate   Calcium Hydroxide   Magnesium Nitrate   Sodium carbonate   Calcium sulfate   Write the correct formula for these compounds

34. Sodium Chloride   NaCl Magnesium oxide   MgO Calcium Chloride Hydrogen Sulfide Iron (II) chloride Iron (III) chloride Sodium Sulfide Sodium Sulfate Na2SO4 Calcium Hydroxide Ca(OH) 2 Magnesium Nitrate   Mg(NO 3 ) 2 Sodium carbonate   Na 2 CO 3 Calcium sulfate   CaSO 4 Write the correct formula for these compounds

35. H 2 gas insoluble no S 8 solid insoluble no H 2 O liquid n/a low CO 2 gas slightly soluble no C 25 H 52 solid insoluble no C 12 H 22 O 11 solid Insoluble no

36. What’s the link?

37. Giant Covalent Structures

38. What is an ionic bond? Li Li What’s missing?

39. Giant Ionic Structures Oppositely charged ions are attracted to each other. This attraction forms a strong ionic bond . The charge on a ion acts in all directions . The ions arrange themselves into a lattice structure , involving huge numbers of ions, which is why they are named giant structures .

40. Because of this, an electric current can be passed through the solution . The same is true when ionic substances are molten. When an ionic substance dissolves, the ions break out of their lattice structure and are free to move about and carry a charge .

41. When atoms share electrons , they are held together very tightly. This is a covalent bond . Example – Hydrogen: H H x H H x Hydrogen atoms Hydrogen molecule H 2

42. You are very likely to get a question about why giant covalent substances (like diamond or silicon dioxide – sand) have very high melting points . Lots (thousands, millions!) of atoms joined together by covalent bonds very strong bonds lots of bonds to be broken need a huge amount of energy/heat to break the bonds therefore a very high melting point

43. Simple covalent substances (molecules) Molecules: a small number of atoms covalently bonded . They have very different properties to giant covalent substances .

44. Simple molecules all have low melting and boiling points. Why? H H x The covalent bonds are very strong, so the atoms are held together tightly. But, the individual molecules are separate from each other. There is a force of attraction between individual molecules (called the intermolecular force ). This is weak, and only a small amount of energy is needed to overcome it. H H H H H H H H H H H H H H H H H H H H

45. Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl STRONG covalent bond WEAK intermolecular force When a molecular substance melts/boils, it is the intermolecular forces that are overcome. The covalent bonds are not broken .

46. Finally, metallic bonds outer shell electrons delocalise (come away from the atom) and are free to move forming a ‘ sea of electrons ’ and leaving positive metal ions the attraction between negative electrons and the positive ions holds the metal together – the electrons act like glue the metal ions are held tightly in neat rows that can slide over each other