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KS4 Chemistry

KS4 Chemistry. Ionic Bonding. Contents. Ionic Bonding. Introducing bonding. Making ions. Ionic bonding. Formulae of ionic compounds. Properties of ionic compounds. Summary activities. Elements. O. K. N. S. C.

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KS4 Chemistry

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  1. KS4 Chemistry Ionic Bonding

  2. Contents Ionic Bonding Introducing bonding Making ions Ionic bonding Formulae of ionic compounds Properties of ionic compounds Summary activities

  3. Elements O K N S C Elements are the simplest substances. There are about 100 different elements. Each element is made up of just one particular type of atom, which is different to the atoms in any other element. Atoms usually join together. This is called bonding. In some elements, atoms bond to form small, simple structures. In other elements, atoms bond into giant structures with millions of atoms.

  4. Compounds H O H Compounds are formed when different elements chemically react with each other. In these reactions different types of atom become chemically bonded. Some compounds, like water, 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.

  5. Properties of compounds + carbon oxygen carbon dioxide + Black solid used as fuel. Colourless gas in which many substances burn. Colourless gas used in fizzy drinks and fire extinguishers. C O O + A compound has different properties to the elements from which it is made because the atoms are joined differently.

  6. Element or compound?

  7. Subatomic particles Atoms consist of three types of subatomic particles: proton exist inthe dense nucleus neutron electron orbit the nucleus in layers called shells

  8. Atoms and electrical charge Total charge = 0 An important feature of subatomic particles is their electrical charge: Atoms have equal numbers of protons and electrons, which means their overall charge is zero. For example, fluorine: 9 protons = +9 9 electrons = -9 10 neutrons = 0

  9. Full electron shells 2nd shell holdsa maximum of8 electrons 1st shell holdsa maximum of2 electrons 3rd shell holdsa maximum of8 electrons Atoms of noble gases have completely full outer shells. This makes them very unreactive or stable. Each shell has a maximum number of electrons that it can hold. Electrons will fill the shells nearest the nucleus first.

  10. Types of bonding Ionic bonding Metal and non-metal atoms Covalent bonding Non-metal atoms only Metallic bonding Metal atoms only Bonding occurs because atoms with incomplete outer electron shells are unstable. By forming bonds, atoms completely fill their outer shells and become stable. Atoms can be bonded in three different ways: All types of bonding involve changes in the number of electrons in the outer shells of atoms.

  11. Contents Ionic Bonding Introducing bonding Making ions Ionic bonding Formulae of ionic compounds Properties of ionic compounds Summary activities

  12. From atoms to ions How can reactive metal atoms become stable positive ions?

  13. Atoms and electron changes Atoms that lose electrons have more protons than electrons and so have a positive charge. They are called positive ions or cations. Atoms that gain electrons have more electrons than protons and so have a negative charge. They are called negative ions or anions. Atoms can obtain completely full outer electron shells by either gaining or losing electrons when they react with other atoms. When this happens, atoms become ions. Unlike atoms, ions have an electrical charge because they contain an unequal number of protons and electrons.

  14. Charges on ions The electron configuration of an atom gives information about how many electrons it must lose or gain to achieve a stable, noble gas configuration. When atoms form ions they obtain an outer electron shell that is either completely full or completely empty. • For atoms with a nearly empty outer shell, it takes less energy to lose electrons to have a full outer shell than it does to gain electrons. • For atoms with a nearly full outer shell, it takes less energy to gain electrons to have a full outer shell than it does to lose electrons.

  15. Positive ions lithium atom = 2.1 ion = Li+ (not Li1+) ion = Mg2+ magnesium atom = 2.8.2 aluminium atom = 2.8.3 ion = Al3+ An atom that loses one or more electrons forms apositive ion. Metal atoms, such as sodium, magnesium and iron,form positive ions. Positive ions have a small ‘+’ symbol and a number by them to indicate how many electrons they have lost. This number is usually the same as the number of electronsin the atom’s outer shell. For example:

  16. The sodium ion Total charge = +1 Total charge = 0 + one electron is lost Na Na Electron arrangement: [2.8]+ (full outer shell) Sodium ion: Sodium atom: 11 protons = +11 11 protons = +11 10 electrons = -10 11 electrons = -11 Electron arrangement: 2.8.1 (partially full outer shell)

  17. The magnesium ion Total charge = +2 Total charge = 0 2+ two electrons are lost Mg Mg Electron arrangement: [2.8]2+ (full outer shell) Magnesium ion: Magnesium atom: 12 protons = +12 12 protons = +12 10 electrons = -10 12 electrons = -12 Electron arrangement: 2.8.2 (partially full outer shell)

  18. Negative ions chlorine atom = 2.8.7 chloride ion = Cl- (not Cl1-) oxide ion = O2- oxygen atom = 2.6 nitrogen atom = 2.5 nitride ion = N3- An atom that gains one or more electrons forms anegative ion. Non-metal atoms, such as chlorine, oxygen and nitrogen,form positive ions. Negative ions have a small ‘-’ symbol and a number by them to indicate how many electrons they have gained to fill their outer shell. For example: The name of the ion is slightly different to that of the atom – it ends with ‘–ide’.

  19. The fluoride ion Total charge = - 1 Total charge = 0 - one electron is gained F F Electron arrangement: [2.8]- (full outer shell) Fluoride ion: Fluorine atom: 9 protons = +9 9 protons = +9 10 electrons = -10 9 electrons = -9 Electron arrangement: 2.7 (partially full outer shell)

  20. The sulfide ion Total charge = - 2 Total charge = 0 2- two electrons are gained S S Electron arrangement: [2.8.8]2- (full outer shell) Sulfide ion: Sulfur atom: 16 protons = +16 16 protons = +16 18 electrons = -18 16 electrons = -16 Electron arrangement: 2.8.6 (partially full outer shell)

  21. Building an ion

  22. Calculating ion charges What charges will the ions of these elements have? 1 2.2 2.8.5 2.7 2.8.8.2 2+ + 3- 1- 2+

  23. Transition metal ions Metal Ion Example of compound Some transition metals only make one type of ion.For example: • silver only forms Ag+ ions; • zinc only forms Zn2+ ions. However, most transition metals make more than one type of ion by losing different numbers of electrons. For example: Cu+copper (I) oxide – Cu2O copper Cu2+copper (II) oxide – CuO Fe2+iron (II) chloride – FeCl2 iron Fe3+iron (III) chloride – FeCl3

  24. Comparing electron configurations

  25. Comparing positive and negative ions

  26. Contents Ionic Bonding Introducing bonding Making ions Ionic bonding Formulae of ionic compounds Properties of ionic compounds Summary activities

  27. Ionic compounds Compounds that contain ions are called ionic compounds. These compounds are usually formed by a reaction betweena metal and a non-metal. Why do these substances react? Both the metal and non-metal atoms have incomplete outer electron shells and so are unstable. One or more electrons are transferred from each metal atom to each non-metal atom. The metal and the non-metal atoms end up with completely full outer shells and become very stable. The positive and negative ions are strongly attracted to each other. This electrostatic attraction is called an ionic bond.

  28. Sodium chloride: part 1 sodium Na chlorine Cl sodium chloride NaCl + Sodium chloride is an ionic compound formed by the reaction between the metal sodium and the non-metal chlorine. During the reaction, one electron is transferred from each sodium atom to each chlorine atom.

  29. Cl Sodium chloride: part 2 - + Na Na Cl [2.8]+ [2.8.8]- Sodium has 1 electron in its outer shell. If it loses this electron, it will have no partially-filled shells. Chlorine has 7 electrons in its outer shell. If it gains 1 electron, it will completely fill its outer shell. 2.8.1 2.8.7

  30. Cl Sodium chloride: part 3 - + Na The positive sodium ions and the negative chloride ions are strongly attracted to each other and form an ionic bond.

  31. Magnesium oxide: part 1 magnesium Mg oxygen O magnesium oxide MgO + More than one electron can be transferred during ionic bonding. Magnesium oxide is another ionic compound, formed by the reaction between magnesium and oxygen. During this reaction, two electrons are transferred from each magnesium atom to each oxygen atom.

  32. O Magnesium oxide: part 2 2+ 2- Mg Mg O [2.8]2+ [2.8]2- Magnesium has 2 electrons in its outer shell. If it loses these, it will have no partially-filled shells. Oxygen has 6 electrons in its outer shell. If it gains two electrons, it will completely fill its outer shell. 2.8.2 2.6

  33. O Magnesium oxide: part 3 2+ 2- Mg The positive magnesium ions and the negative oxide ions are strongly attracted to each other and form an ionic bond.

  34. Formation of an ionic bond

  35. Simplified electron diagrams + + Na Na - - Cl Cl The inner electron shells can sometimes be left out of electron diagrams because they are not involved in bonding. can also be drawn as can also be drawn as

  36. Drawing simplified electron diagrams 2- 2+ S Mg Mg S [2.8.8]2- [2.8]2+ Draw a simplified electron diagram for magnesium sulfide. 2.8.6 2.8.2

  37. More complicated ionic bonding Na Cl Na+ Cl- 1 electron Mg O Mg2+ O2- 2 electrons Sodium chloride and magnesium oxide are simple ionic compounds. In each case, the metal and non-metal need to lose and gain the same number of electrons. This is not always the case.

  38. Sodium oxide Na Na+ O2- O 1 electron per atom Na Na+ What happens in the reaction between sodium and oxygen? Sodium (2.8.1) needs to lose 1 electron but oxygen (2.6) needs to gain 2 electrons. Therefore, two sodium atoms are required for each oxygen atom.

  39. Magnesium chloride Cl Cl- Mg 1 electron for each atom Mg2+ Cl Cl- What happens in the reaction between magnesium and chlorine? Magnesium (2.8.2) needs to lose 2 electrons but chlorine (2.8.7) needs to gain 1 electron. Therefore, two chlorine atoms are required for each magnesium atom.

  40. Bonding in lithium oxide Li Li + + O Li 2- O [2]+ Li [2.8]2- Draw a simplified electron diagram for lithium oxide. 2.1 2.6

  41. Bonding in magnesium fluoride F F 2+ - - Mg Mg F F [2.8]2+ [2.8]- Draw a simplified electron diagram for magnesium fluoride. 2.7 2.8.2

  42. Further ionic bonding total number of electrons lostby the metal total number of electrons gained by the non-metal = Draw simplified electron diagrams for the following atoms: 1. Lithium (2.1) and fluorine (2.7) 2. Sodium (2.8.1) and sulfur (2.8.6) 3. Magnesium (2.8.2) and sulfur (2.8.6) 4. Magnesium (2.8.2) and fluorine (2.7) 5. Aluminium (2.8.3) and nitrogen (2.5)

  43. Contents Ionic Bonding Introducing bonding Making ions Ionic bonding Formulae of ionic compounds Properties of ionic compounds Summary activities

  44. Formulae of ionic compounds A formula uses chemical symbols and numbers to show the ratio of atoms of each element present in the compound. To work out the formula of an ionic compound, follow this procedure: 1. Write down the symbol for each atom. 2. Calculate the charge for each ion. 3 Balance the number of ions so the positive and negative charges equal zero. This gives a ratio of ions. 4. Write down the formula without the ion charges – the metal is always written first.

  45. Formula of sodium fluoride Na F Na+ F- 1 electron What is the formula of sodium fluoride? Na F 1- 1+ 1 sodium ion is needed for each fluoride ion 1 : 1 NaF

  46. Formula of aluminium bromide Br Br- 1 electron for each atom Al Br Al3+ Br- Br Br- What is the formula of aluminium bromide? Al Br 1- 3+ 3 bromide ions are needed for each aluminium ion 1 : 3 AlBr3

  47. Formula of aluminium oxide O O2- Al Al3+ 2 electrons for each atom O O2- Al3+ Al O O2- What is the formula of aluminium oxide? Al O 2- 3+ 2 aluminium ions are needed for 3 oxide ions 2 : 3 Al2O3

  48. More ionic formulae metals non-metals Work out the formulae of all the possible ionic compounds from combinations of these metals and non-metals. LiF CaF2 NaF MgF2 AlF3 KF Li2O CaO Na2O MgO Al2O3 K2O Li3N Ca3N2 Na3N Mg3N2 AlN K3N LiBr CaBr2 NaBr MgBr2 AlBr3 KBr Li2S CaS Na2S MgS Al2S3 K2S LiCl CaCl2 NaCl MgCl2 AlCl3 KCl

  49. Compound ions Ion Formula Charge Atoms present hydrogen-carbonate HCO3- Ionic compounds can contain ions consisting of groups of atoms rather than a single atom. These are compound ions. O H hydroxide OH- 1- S O O O O sulfate SO42- 2- N O O O nitrate NO3- 1- C O O O carbonate CO32- 2- N H H H H ammonium NH4+ 1+ H C O O O 1-

  50. More complicated formulae Working out the formulae for compounds containing compound ions is the same as for simple ionic compounds. The compound ion is treated as a single particle, not individual particles. 1. Write down the symbol for each atom. 2. Calculate the charge for each ion. 3 Balance the number of ions so the positive and negative charges equal zero. This gives a ratio of ions. 4. Write down the formula without the ion charges. If more than one compound ion is required, brackets must be put around the ion, before the number.

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