Presentation is loading. Please wait.

Presentation is loading. Please wait.

© Boardworks Ltd 20071 of 50. 2 of 50© Boardworks Ltd 2007.

Similar presentations


Presentation on theme: "© Boardworks Ltd 20071 of 50. 2 of 50© Boardworks Ltd 2007."— Presentation transcript:

1 © Boardworks Ltd of 50

2 2 of 50© Boardworks Ltd 2007

3 3 of 50 What are bonds? Compounds are formed when different elements chemically react and form bonds with each other. Some compounds, like water (H 2 0), have small, simple structures with just a few atoms bonded together. Others compounds, like DNA, have large, complex structures containing thousands or even millions of bonded atoms. Elements are the simplest substances that exist on Earth. Each element is made up of just one type of atom, usually joined to other atoms of the same element by bonds. This forms molecules such as chlorine (Cl 2 ).

4 © Boardworks Ltd of 50 Why do atoms form bonds? Bonds involve the electrons in the outer shells of atoms. Filled electron shells are very stable. 1 st shell holds a maximum of 2 electrons 2 nd shell holds a maximum of 8 electrons 3 rd shell holds a maximum of 8 electrons Each shell has a maximum number of electrons that it can hold. Electrons fill the shells nearest the nucleus first.

5 © Boardworks Ltd of 50 Why do atoms form bonds? The atoms of noble gases have completely full outer shells and so are stable. The atoms of other elements have incomplete outer electron shells and so are unstable. This makes the noble gases very unreactive and so they do not usually form bonds. By forming bonds, the atoms of these elements are able to have filled outer shells and become stable.

6 © Boardworks Ltd of 50 What are the types of bonding? Different types of bonds are formed depending on the types of atoms involved: All bonds involve electrons and all bonding involve changes to the number of electrons in the outer shells of atoms. ionic bonding – occurs between metal and non-metal atoms. covalent bonding – occurs between non-metals atoms only. metallic bonding – occurs between metal atoms only. How do you think electrons are involved in ionic bonding?

7 7 of 50© Boardworks Ltd 2007

8 8 of 50 From atoms to ions How can reactive metal atoms become stable positive ions?

9 © Boardworks Ltd of 50 How do atoms form ions? An ion is an atom or group of atoms that has an electrical charge, either positive and negative. Atoms have an equal number of protons and electrons and so do not have an overall charge. Atoms with incomplete outer electron shells are unstable. By either gaining or losing electrons, atoms can obtain full outer electron shells and become stable. When this happens, atoms have an unequal number of protons and electrons and so have an overall charge. This is how atoms become ions. How does an atom become a positive or negative ion?

10 © Boardworks Ltd of 50 Positive and negative ions? The electron configuration of an atom shows how many electrons it must lose or gain to have a filled outer shell. An atom that loses electrons has more protons than electrons and so has a positive overall charge. This is called a positive ion. An atom that gains electrons has more electrons than protons and so has a negative overall charge. This is called a negative ion. Atoms with a nearly empty outer shell, will lose electrons to obtain a full outer shell. Atoms with a nearly full outer shell, will gain electrons to obtain a full outer shell.

11 © Boardworks Ltd of 50 How do atoms form positive ions? An atom that loses one or more electrons forms a positive ion. Positive ions have a small ‘+’ symbol and a number by this to indicate how many electrons have been lost. This number is usually the same as the number of electrons in the atom’s outer shell. For example: Metal atoms, such as sodium, magnesium and iron, form positive ions. lithium ion [ 2 ]lithium atom 2.1 aluminium atom 2.8.3aluminium ion [ 2.8 ] magnesium atom magnesium ion [ 2.8 ] = Mg 2+ = Li + = Al 3+

12 © Boardworks Ltd of 50 How is a sodium ion formed? (partially full outer shell) 11 protons= electrons= -11 Total charge= 0 Sodium atom: 11 protons= electrons= -10 Total charge= +1 Sodium ion: loses 1 electron + [2.8] (full outer shell) Na

13 © Boardworks Ltd of 50 How is a magnesium ion formed? (partially full outer shell) 12 protons= electrons= -12 Total charge= 0 Magnesium atom: 12 protons= electrons= -10 Total charge= +2 Magnesium ion: [2.8] 2+ (full outer shell) 2+ Mg loses 2 electrons

14 © Boardworks Ltd of 50 How do atoms form negative ions? Negative ions have a small ‘-’ symbol and a number by this to indicate how many electrons have been gained to fill their outer shell. For example: An atom that gains one or more electrons forms a negative ion. The name of the ion is slightly different to the atom’s name. Non-metal atoms, such as chlorine, oxygen and nitrogen, form negative ions. chlorine atomchloride ion [ ] = Cl - oxygen atomoxide ion [ 2 ] nitrogen atomnitride ion [ 2 ] = N 3- = O 2-

15 © Boardworks Ltd of 50 How is a fluoride ion formed? 2.7 (partially full outer shell) 9 protons=+9 9 electrons= -9 Total charge= 0 Fluorine atom: 9 protons=+9 10 electrons=-10 Total charge= -1 Fluoride ion: [2.8] - (full outer shell) - FF gains 1 electron

16 © Boardworks Ltd of 50 [2.8.8] 2- (full outer shell) (partially full outer shell) How is a sulfide ion formed? 16 protons= electrons= -16 Total charge= 0 Sulfur atom: 16 protons= electrons= -18 Total charge= -2 Sulfide ion: 2- SS gains 2 electrons

17 © Boardworks Ltd of 50 Building an ion

18 © Boardworks Ltd of 50 Calculating ion charges What is the charge on the ion of each element? calciumhydrogenphosphorusfluorineberyllium Element Electron shells Charge on ion

19 © Boardworks Ltd of 50 Electron configuration of ions The number of protons and neutrons however, remain different for each element. This means that each ion has different properties. For example, oxygen and fluorine both gain electrons to become negative ions. The resulting ions have the same electron configuration: F - 2- O When different elements gain or lose electrons to complete their outer electron shell, they can create ions that have the same electron configuration.

20 © Boardworks Ltd of 50 Comparing electron configurations

21 © Boardworks Ltd of 50 What is a compound ion? Ions can be made up of a single atom or a group of atoms. An ion made up of a group of atoms is called a compound ion. hydroxide sulfate nitrate carbonate ammonium IonFormulaChargeAtoms present NH 4 + CO 3 2- NO 3 - SO 4 2- OH - OOOOOOOOOOO H HHHH C N N S What atoms are present in the following compound ions?

22 © Boardworks Ltd of 50 Comparing positive and negative ions

23 23 of 50© Boardworks Ltd 2007

24 24 of 50 Ions and attraction Why do some ions attract while others repel?

25 © Boardworks Ltd of 50 What is ionic bonding? Compounds that contain ions are called ionic compounds. These compounds are usually formed by a reaction between a metal and a non-metal. Why do these substances react together and form bonds? The metal and non-metal atoms have incomplete outer electron shells and so are unstable. Electrons are transferred from each metal atom to each non-metal atom. The metal and the non-metal atoms form ions with completely full outer shells and become stable. The positive and negative ions are strongly attracted to each other. This electrostatic attraction is called ionic bonding.

26 © Boardworks Ltd of 50 How are ionic bonds formed? Sodium chloride is an ionic compound formed by the reaction between the metal sodium and the non-metal chlorine. Sodium has 1 electron in its outer shell. Chlorine has 7 electrons in its outer shell [2.8.8] - + Cl [2.8] + Na By losing this electron, it has a filled outer shell and forms a positive ion. By gaining an electron from sodium, it has a filled outer shell and forms a negative ion.

27 © Boardworks Ltd of 50 How are ionic bonds formed? The positive sodium ions and the negative chloride ions are strongly attracted to each other. - Cl It is this electrostatic attraction that forms ionic bonds in sodium chloride and other ionic compounds. Na +

28 © Boardworks Ltd of 50 Formation of an ionic bond

29 © Boardworks Ltd of 50 Ions and ionic bonding – summary

30 30 of 50© Boardworks Ltd 2007

31 31 of 50 What is the ratio of ions? Sodium chloride (NaCl) and magnesium oxide (MgO) are simple ionic compounds. Both compounds have a 1:1 ratio of metal ions to non-metal ions, which is shown by the formula of each compound. Na ClNa + Cl - 1 electron Mg Mg 2+ O O 2- 2 electrons In each compound, the metal needs to lose the same number of electrons that the non-metal needs to gain.

32 © Boardworks Ltd of 50 What is the ratio of ions in sodium oxide? What is the ratio of ions needed to make sodium oxide? Sodium (2.8.1) needs to lose 1 electron to form a sodium ion but oxygen (2.6) must gain 2 electrons to form an oxide ion. Na O O 2- Na + 1 electron from each Na atom Two sodium atoms are required for each oxygen atom and so the ratio of sodium ions to oxide ions is 2:1. From this ratio, the formula of sodium oxide is Na 2 O.

33 © Boardworks Ltd of 50 What is the ratio of ions in magnesium chloride? What is the ratio of ions needed for magnesium chloride? Magnesium (2.8.2) needs to lose 2 electrons to form a magnesium ion but chlorine (2.8.7) needs to gain 1 electron to form an chloride ion. Mg Cl Mg 2+ Cl Cl - 1 electron for each Cl atom Two chlorine atoms are required for each magnesium atom and so the ratio of magnesium ions to chloride ions is 1:2. From this ratio, the formula of magnesium chloride is MgCl 2.

34 © Boardworks Ltd of 50 How to write the formula of an ionic compound To work out the formula of an ionic compound: 1.Write down the symbol for each element – the metal is always written first. 2.Calculate the charge for each type of ion. 3.Balance the number of ions so that the positive and negative charges are balanced and equal zero. This gives the ratio of ions. 4.Use the ratio to write down the formula of the ionic compound. The formula of a compound uses chemical symbols and numbers to show the ratio of atoms of each element present.

35 © Boardworks Ltd of 50 Formula of aluminium bromide What is the formula of aluminium bromide? AlBr +3 AlBr 3 3 bromide ions are needed for each aluminium ion 1 : 3 Symbol Balance the number of ions Ion charge Ratio of ions Formula Al Br Al 3+ Br Br - 1 electron for each bromine atom

36 © Boardworks Ltd of 50 Formula of aluminium oxide What is the formula of aluminium oxide? AlO +3-2 Al 2 O 3 2 aluminium ions are needed for 3 oxide ions 2 : 3 Symbol Balance the number of ions Ion charge Ratio of ions Formula AlAl 3+ AlAl 3+ O O 2- O O 2 electrons for each oxygen atom

37 © Boardworks Ltd of 50 More ionic formulae What are the formulae of all the possible ionic compounds from combinations of these metals and non-metals. metals non- metals LiCaNaMgAlK F O N Br S Cl LiFCaF 2 NaFMgF 2 AlF 3 KF Li 2 OCaONa 2 OMgOAl 2 O 3 K2OK2O Li 3 NCa 3 N 2 Na 3 NMg 3 N 2 AlNK3NK3N LiBr CaBr 2 NaBrMgBr 2 AlBr 3 KBr Li 2 SCaSNa 2 SMgSAl 2 S 3 K2SK2S LiClCaCl 2 NaClMgCl 2 AlCl 3 KCl

38 © Boardworks Ltd of 50 What is the ionic formula?

39 39 of 50© Boardworks Ltd 2007

40 40 of 50 What is an ionic lattice? In an ionic compound, millions and millions of ions are packed together in a regular cubic arrangement, joined by ionic bonds. The structure of the ionic lattice affects the properties of the ionic compound. The ionic lattice will continue to build in this way until there are no more ions left to add. This forms a giant 3D structure called an ionic lattice.

41 © Boardworks Ltd of 50 Why do ionic compounds form crystals? Ionic compounds such as sodium chloride, form crystals, with a cubic shape. This is due to the structure of the ionic lattice. All ionic compounds form lattices and crystals when solid.

42 © Boardworks Ltd of 50 Heating ionic compounds Why are ionic compounds solid at room temperature and have high melting points and boiling points? Larger ionic charges produce stronger ionic bonds and so much more heat is required to break the ionic bonds in magnesium oxide than in sodium chloride. sodium chloride magnesium oxide Compound Ion charges Melting point ( o C) Boiling point ( o C) 1 + and and ,413 2,8523,600 strong ionic bonds hold ions together Ionic bonds are strong and a lot of heat is needed to break them.

43 © Boardworks Ltd of 50 Do ionic compounds conduct electricity?

44 © Boardworks Ltd of 50 How can ionic compounds conduct electricity? When liquid (molten), the ions can break free of the lattice and are able to move. The ions are charged particles and so can carry an electric current. As solids, ionic compounds cannot conduct electricity because their ions are bonded together in the lattice. ions in solid state cannot move ions in molten state can move and conduct electricity Ionic compounds are usually soluble in water because water molecules have a slight electrical charge and so can attract the ions away from the lattice. When dissolved, the ions are free to move and can carry an electric current.

45 © Boardworks Ltd of 50 Why are ionic compounds brittle? Ionic compounds are brittle – they shatter when they are hit. When the lattice is hit, a layer of ions is shifted so that ions with the same charges are lined up together. These like charges repel each other and so split the ionic lattice causing it to shatter. repulsion force Ionic bonds are strong, so why does this happen?

46 © Boardworks Ltd of 50 True or false?

47 47 of 50© Boardworks Ltd 2007

48 48 of 50 Glossary  bond – A strong force that joins atoms or ions together in molecules and giant lattices.  compound ion – An ion made up of a group of atoms, rather than one single atom.  ionic bond – The electrostatic force of attraction between oppositely charged ions.  ionic compound – A compound made up of ions.  ionic lattice – A giant 3D structure of closely packed, oppositely-charged ions.  negative ion – An atom or group of atoms that has gained electrons and so has a negative charge.  noble gas – An element that has a full outer electron shell and so is very stable and unreactive.  positive ion – An atom or group of atoms that has lost electrons and so has a positive charge.

49 © Boardworks Ltd of 50 Anagrams

50 © Boardworks Ltd of 50 Multiple-choice quiz


Download ppt "© Boardworks Ltd 20071 of 50. 2 of 50© Boardworks Ltd 2007."

Similar presentations


Ads by Google