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CHEMICAL BONDING PART 1 IONIC BONDING © Boardworks Ltd 2001 Elements • Elements are the simplest substances. There are about 100 different elements • Each elements has just one particular type of atom that is different to the atoms in any other element S Fe N O K • In some elements atoms bond to form small simple structures. • In other elements atoms bond into giant structures with millions of atoms. N N N • Even in elements atoms usually join (bond) together. N N C N N N © Boardworks Ltd 2001 Compounds • Compounds are formed when different elements chemically react together. • In these reactions different types of atom become chemically bonded. • Like elements some compounds have small simple structures with just a few atoms bonded together • Others compounds have large, complex structures containing thousands or even millions of bonded atoms. H O H Water – a simple structure DNA – a large & complex structure © Boardworks Ltd 2001 Compounds Are Not Just Mixtures • Reacting is different to just mixing. • The physical and chemical properties of compounds are very different to their original elements. ELEMENTS Carbon C (black solid) + oxygen O O (colourless gas, that supports combustion) COMPOUND Carbon dioxide O C O (a colourless gas, that extinguishes fire) © Boardworks Ltd 2001 Activity • Copy the Table and fill in the last column Name Sodium chloride Nickel Copper sulphate Water Oxygen Rust Mercury Sand Formula Element or compound NaCl compound Ni element CuSO4 compound H2O compound O2 element Fe2O3 compound Hg element SiO2 compound Rust consists of iron combined with oxygen © Boardworks Ltd 2001 Bonding and Atoms To understand bonding we must know a little about the atoms from which elements are made. Atoms consist of three types of particles that are even smaller than atoms: –Protons } These exist in –Neutrons } the nucleus. –Electrons } exist in layers (or shells) around the outside of the nucleus © Boardworks Ltd 2001 No charge on element atoms Two of the three particles in atoms have an electrical charge. Protons +1 Neutrons 0 Electrons -1 BUT atoms have equal numbers of protons and electrons. This means their overall charge = zero. For example 9 10 F Ne 19 20 Fluorine Neon Copy & Fill in the gaps 9 protons 9+ 10+ 10 protons ___ ___ 9 electrons 9- 10 electrons ___ 10___ 10 neutrons 0 0 10 ___neutrons ___ Total Charge 0 Total Charge ___0 © Boardworks Ltd 2001 Noble Gases: Full Shells. The electrons around the outside of atoms are arranged in layers called shells st 2nd Shell: 8 electrons 1 Shell: 2 electrons 3rd Shell: 8 electrons Each shell has a maximum number of electrons that it can hold. In noble gases the shells are completely full rather than partially full. During bonding other atoms try to attain the “full electron shell” structure of the noble gases. © Boardworks Ltd 2001 Types of Bonding Atoms can be joined together in 3 possible ways Metal and non-metal Ionic Bonding Non-metals only Metals only Covalent Bonding Metallic Bonding All three types involve changes in the electrons in the outermost electron shells of the atoms © Boardworks Ltd 2001 IONIC BONDING © Boardworks Ltd 2001 IONIC BONDING Most ionic compounds contain a metal and a nonmetal. When metals react they lose outer shell electrons to leave a full electron shell. This produces a charged atom (ion) with a + charge. Lose 1 or more electrons Neutral atom n+ Positive ion When non-metals react with a metal they gain electrons to achieve a full electron shell. Gain 1 or more electrons Neutral atom n- Negative ion © Boardworks Ltd 2001 Opposites Attract – Lattices The oppositely charged ions are attracted into a lattice that gets bigger and bigger until it consists of millions of ions + + + + + - - - + - + - + - + Attract - - Opposites + + - - And ion, and ion, and ion! © Boardworks Ltd 2001 Lattices are 3-Dimensional We have shown ions attracting and building into a 2 dimensional sheet. In fact the whole process will be going on in three dimensions to build up a giant 3-D lattice. And so on to build a giant 3D lattice with millions of ions. -+ +- -+ +- -+ +- + - + - + + -+ + -+ + -+ -+ - -+ - -+ -+ +- -+ +- -+ +- + - + - + + - + - + - + - + + - +- + - + - + + - -- + + -- ++ -+ +- -+ + © Boardworks Ltd 2001 Ions and electron structures Metals lose electrons to form positive(+) ions called cations. Non-metals gain electrons to form negative (–) ions called anions. n+ n- We know that the atoms lose or gain electrons to achieve full electron shells. To understand more about how ionic compounds form we must look at what is happening to the outer shell electrons © Boardworks Ltd 2001 Formation of sodium chloride 1. Formation of sodium ions Sodium has 1 electron in its outer shell If it loses this it will have no partially filled shells. Na Sodium atom (2.8.1) Loses 1 electron Na+ Sodium 1+ ion (2.8.0) This only happens if there is another atom able to accommodate the lost electron. © Boardworks Ltd 2001 Formation of sodium chloride 2.Formation of Chloride ions Chlorine has 7 electrons in its outer shell. If it gains 1 electron it can achieve a full outer electron shell. It is, therefore, going to be able to accept the electron that the sodium wants to lose. Cl Cl Gains 1 electron (from sodium) Chlorine atom (2.8.7) Chlorine I - ion (2.8.8) © Boardworks Ltd 2001 Formation of Sodium Chloride The overall process. Sodium loses its outer electron. Chlorine gains it. The result is both end up with full shells Two oppositely charged ions are formed, which attract. Millions of such pairs form a giant lattice Na Na Cl Cl © Boardworks Ltd 2001 Simpler electron diagrams • We can assume full inner electron shells. We can therefore sometimes shorten bonding diagrams by omitting to draw the inner electron shells. Na Cl Na Cl © Boardworks Ltd 2001 Bonding in Magnesium Oxide More than one electron may be transferred between atoms in ionic bonding. Mg 2.8.2. Magnesium atom O Magnesium Oxide 2.6 Oxygen atom O2- Mg2+ 2.8 2.8 © Boardworks Ltd 2001 Activity Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide. Mg O Magnesium Oxide Magnesium atom Oxygen atom Mg2+ O2- © Boardworks Ltd 2001 Activity Copy the diagram and draw another box showing the electron configuration in sodium fluoride. Na 2.8.1. Sodium atom F Sodium Fluoride 2.7 Fluorine atom F- Na+ 2.8 2.8 © Boardworks Ltd 2001 Bonding in Lithium Oxide • The bonding in lithium oxide is more complicated in that there are different numbers of each atom. Li O Li+ Li O2- Li+ © Boardworks Ltd 2001 Bonding in Lithium Nitride • The bonding in lithium nitride similarly involves different numbers of each atom. Li Li N Li Li+ Li Li+ N3- © Boardworks Ltd 2001 Bonding in Aluminium Fluoride • In aluminium fluoride it is the non-metal atoms that we need more of F F F F Al F Al F © Boardworks Ltd 2001 Activity 1. 2. 3. 4. 5. Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms: Lithium (2.1) and fluorine (2.7) Sodium (2.8.1) and sulphur (2.8.6) Magnesium (2.8.2) and sulphur (2.8.6) Magnesium (2.8.2) and fluorine (2.7) Aluminium (2.8.3) and nitrogen (2.5) Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by the non-metal © Boardworks Ltd 2001 Electrons Lost = Electrons Gained • Both sodium chloride and magnesium oxide are simple ionic compounds. • In both cases the metal and non-metal need to lose the same number of electrons. Na 1 electron Mg Cl Na+ Cl- O Mg2+ O2- 2 electrons •This is not always the case. © Boardworks Ltd 2001 Different numbers of electrons Consider the reaction of sodium with oxygen. – Sodium (2.8.1) needs to lose 1 electron. – Oxygen (2.6) needs to gain 2 electrons • This can only happen if there are two sodium ions formed for every one oxygen ion formed Na Na+ 1 electron per sodium O2- O Na Na+ The formula will be Na2O © Boardworks Ltd 2001 Different numbers of electrons Consider the reaction of magnesium with chlorine. – Magnesium (2.8.2) needs to lose 2 electron. – Chlorine (2.8.7) needs to gain 1 electrons •We need 2 chlorines for every one magnesium Cl Mg ClMg2+ 2 electrons Cl Cl- The formula will be MgCl2 © Boardworks Ltd 2001 Charges on ions • When atoms form ions they aim to attain electron shells that are either completely full or completely empty. • If we know the electron configuration of an atom we can usually work out how many electrons it must lose or gain to achieve a noble gas configuration. • This will tell us the charge on its ion. © Boardworks Ltd 2001 Charges and Metal ions • Metals usually lose electrons to empty this outer shell. • The number of electrons in the outer shell is usually equal to the group number in the Periodic Table. Eg. Li 2.1 Li+ Mg 2.8.2 Mg2+ Al 2.8.3 Al3+ © Boardworks Ltd 2001 Charges and non-metal ions • Outer shells with 5 or more electrons usually gain electrons to fill up the outer shell. E.g. • Oxygen (2.6) gains 2 electrons to form O2• Chlorine (2.8.7) gains 1 electron to form Cl- O 2.6 O2- Cl 2.8.7 Cl© Boardworks Ltd 2001 Activity • Copy out and fill in the Table below showing what charge ions will be formed from the elements listed. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Symbol Li N Cl Ca K Al O Br Outer electrons 1 5 7 2 1 3 6 7 1 8 Charge 1+ 3- 1- 2+ 1+ 3+ 2- 1- 1+ 0 Na Ne © Boardworks Ltd 2001 The formulae of ionic compounds This is most quickly done in 5 stages. Remember the total + and – charges must =zero • Eg. The formula of calcium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Ca Br 2+ 1Br 2 1 CaBr2 Br- Br Ca2+ Ca Br Br- 2 electrons © Boardworks Ltd 2001 The formulae of ionic compounds • Eg. The formula of aluminium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Al Br 3+ 1Br 3 1 AlBr3 Br- Br Al Br 3 electrons Br Al3+ BrBr© Boardworks Ltd 2001 The formulae of ionic compounds • Eg. The formula of aluminium oxide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula 2e- Al Al 3+ O 2O 3 (to give 6 e-) 2 Al2O3 O2- O Al3+ 2e- Al O2- O Al3+ 2e- O O2© Boardworks Ltd 2001 Activity • Using the method shown on the last few slides, work out the formula of all the ionic compounds that you can make from combinations of the metals and non-metals shown below: •Metals: Li Ca Na Mg Al K •Non-Metals: F O N Br S Cl © Boardworks Ltd 2001 More Complicated Formulae • • Ionic compounds may contain ions consisting of groups of atoms rather than a single atom. Here are some more complicated ions you may come across. Ion Formula Charge Atoms present nitrate sulphate NO3SO42- 12- N O O O S O O O O ammonium NH4+ 1+ N H H H H hydroxide OH- 1- O H carbonate CO32- 2- C O O O © Boardworks Ltd 2001 More Complicated Formulae • • • When working out formula you simply treat the entire group of atoms as though it were a single atom. The only difficulty is to do with how we write down the final answer. E.g.1 What is the formula of lithium nitrate? 1. Symbols: Li NO3- 2. Charge on ions 1+ 1- 3. Need more of 4. Ratio of ions 5. Formula neither 1 1 LiNO3 © Boardworks Ltd 2001 More Complicated Formulae • What is the formula of magnesium nitrate? 1. Symbols: Mg NO3- 2. Charge on ions 2+ 1- 3. Need more of 4. Ratio of ions 5. Formula NO3- 1 2 Mg(NO3)2 • The brackets around the NO3- ion show that the 2 refers to two complete NO3- ions. • It represents a total of 2 nitrogens and 6 oxygens with each magnesium ion. © Boardworks Ltd 2001 More Complicated Formulae • What is the formula of sodium sulphate? 1. Symbols: Na+ SO42- 2. Charge on ions 1+ 2- 3. Need more of 4. Ratio of ions 5. Formula Na+ 2 1 Na2SO4 • No brackets here as only one SO42- ion needed. • Note although Na contains 2 letters it only represents a single atom – so no brackets! © Boardworks Ltd 2001 Activity • Write down how to work out the formula of aluminium hydroxide. 1. Symbols: 2. Charge on ions 3. Need more of 4. Ratio of ions 5. Formula Al3+ OH- 3+ 1OH- 1 3 Al(OH)3 Note: Again we need brackets as 3 complete OH- ions are needed meaning that for each aluminium there are 3 oxygens and 3 hydrogens. © Boardworks Ltd 2001 Activity • Write down how to work out the formula of ammonium sulphate. 1. Symbols: NH4+ 2. Charge on ions 1+ 3. Need more of NH4+ 4. Ratio of ions 5. Formula SO42- 2 2- 1 (NH4)2SO4 Note: Again we need brackets as 2 complete NH4+ ions are needed meaning that for each sulphate ion there are 2 nitrogen and 8 hydrogens. © Boardworks Ltd 2001 Activity • Write down how to work out the formula of aluminium sulphate. 1. Symbols: 2. Charge on ions 3. Need more of Need to get total charge =6 4. Ratio of ions 2 5. Formula Al3+ SO42- 3+ 2- 3 Al2(SO4)3 Note: No brackets for Al as only one atom even though it’s 2 letters. We do need brackets around the SO4 to show it is 3 complete sulphate ions. © Boardworks Ltd 2001 Activity Copy this choosing words from below to fill the gaps. lose electrons • • • • • lattices gain metal metal and non-metal react. Formed when a _____ lose electrons to empty their outer Metals ___ electron shell. gain electrons to fill their outer Non-metals _____ electron shell. The ratio of metal ions to non-metal ions will electrons lost depend upon the number of ________ and gained. Lattices. The ions formed join up into giant _____. © Boardworks Ltd 2001 Which of the following will have ionic bonding? A. Copper chloride B. Iron C. Brass D. Sulphur dioxide © Boardworks Ltd 2001 Which of the following is NOT true of ionic bonding? A. B. C. D. Metal ions have a + charge Non-metal ions have a - charge They form a 2 dimensional lattice They have giant structures © Boardworks Ltd 2001 Which of the following is true about the oxide ion? A. B. C. D. Formed by oxygen atoms losing 2 electrons. Oxygen ions have an empty second shell Exist in pairs Have a 2- charge 8 O 16 © Boardworks Ltd 2001 Which of the following is true about the sodium ion? A. B. C. D. Has a 2,8,1 electron arrangement Formed by sodium atoms gaining 1 electron. Sodium ions have an empty second shell Have a 1+ charge 11 Na 23 © Boardworks Ltd 2001 What formula compound will be formed from Mn4+ and O2- ions? A. B. C. D. Mn2O4 MnO2 Mn2O MnO4 © Boardworks Ltd 2001 What formula compound will be formed from Ga3+ and SO42- ions? A. B. C. D. Ga2(SO4)3 Ga3(SO4)2 Ga2S3O12 Ga (SO4)3 © Boardworks Ltd 2001