CHEMICAL BONDING PART 1 IONIC BONDING Boardworks Ltd

CHEMICAL BONDING PART 1 IONIC BONDING © Boardworks Ltd 2003

Elements • Elements are the simplest substances. There 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 N • Even in elements atoms usually join (bond) together. • In some elements atoms bond to form small simple structures. • In other elements atoms bond into giant structures with millions of atoms. N N C N N N © Boardworks Ltd 2003

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 • Other 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 2003

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 2003

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 Na. Cl compound Ni element Cu. SO 4 compound H 2 O compound O 2 element Fe 2 O 3 compound Hg element Si. O 2 compound Rust consists of iron combined with oxygen © Boardworks Ltd 2003

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 2003

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 19 F 9 Fluorine 20 Ne 10 Neon Copy & Fill in the gaps 9 protons 9+ 10 protons ___ 9 electrons 9 - 10 electrons ___ 10 neutrons 0 0 10 ___neutrons ___ Total Charge 0 Total Charge ___0 © Boardworks Ltd 2003

Noble Gases: full shells The electrons around the outside of atoms are arranged in layers called shells 1 st Shell: 2 nd Shell: 8 electrons 2 electrons 3 rd 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 2003

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 2003

IONIC BONDING © Boardworks Ltd 2003

IONIC BONDING Most ionic compounds contain a metal and a non-metal. 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 2003

Opposites attract – lattices The oppositely charged ions are attracted into a lattice that gets bigger and bigger until it consists of millions of ions + + + - - - opposites + - + - + - + attract And ion, and ion! © Boardworks Ltd 2003

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 3 D lattice with millions of ions. -+ +- + - + + -+ -+ -+ +- -+ +- + - + + - +- + -+ +- -+ + -- ++ -+ +- -+ + © Boardworks Ltd 2003

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 2003

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 2003

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 Gains 1 electron (from sodium) Chlorine atom (2. 8. 7) Cl Chlorine I - ion (2. 8. 8) © Boardworks Ltd 2003

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 2003

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 © Boardworks Ltd 2003

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 O 2 - Mg 2+ 2. 8 © Boardworks Ltd 2003

Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide. Mg O Magnesium Oxide Magnesium atom Oxygen atom Mg 2+ O 2 - © Boardworks Ltd 2003

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 © Boardworks Ltd 2003

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 O 2 - Li+ © Boardworks Ltd 2003

Bonding in Lithium Nitride The bonding in lithium nitride similarly involves different numbers of each atom. Li Li N Li Li+ N 3 - © Boardworks Ltd 2003

Bonding in Aluminium Fluoride In aluminium fluoride it is the non-metal atoms that we need more of. F F Al F © Boardworks Ltd 2003

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 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 2003

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 or gain the same number of electrons respectively. Na 1 electron Mg Cl Na+ Cl- O Mg 2+ O 2 - 2 electrons This is not always the case. © Boardworks Ltd 2003

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 1 electron per sodium Na+ O Na Na+ O 2 - The formula will be Na 2 O. © Boardworks Ltd 2003

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 Cl. Mg 2+ 2 electrons Cl Cl- The formula will be Mg. Cl 2 © Boardworks Ltd 2003

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 2003

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. For example, Li 2. 1 Li+ Mg 2. 8. 2 Mg 2+ Al 2. 8. 3 Al 3+ © Boardworks Ltd 2003

Charges and non-metal ions • Outer shells with 5 or more electrons usually gain electrons to fill up the outer shell. For example, • Oxygen (2. 6) gains 2 electrons to form O 2 • Chlorine (2. 8. 7) gains 1 electron to form Cl- O 2. 6 2. 8 O O 2 - Cl 2. 8. 7 2. 8. 8 Cl Cl© Boardworks Ltd 2003

Activity Copy out and fill in the Table below showing what charge ions will be formed from the elements listed. H He B C N O F Ne Al Si P S Cl Ar Li Be Na Mg 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 2003

The formulae of ionic compounds This is most quickly done in 5 stages. Remember the total + and – charges must =zero For example, the formula of calcium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Br Ca 2+ Br 1 Br 2 1 Ca. Br 2 Br. Ca 2+ Br- 2 electrons © Boardworks Ltd 2003

The formulae of ionic compounds For example, the formula of aluminium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Al 3+ Br 1 Br 3 1 Al. Br 3 Br- Br Al Br 3 electrons Br Al 3+ Br. Br- © Boardworks Ltd 2003

The formulae of ionic compounds For example, the formula of aluminium oxide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula 2 e- Al Al 3+ O 2 O 3 (to give 6 e-) 2 Al 2 O 3 O 2 - O Al 3+ 2 e- Al 2 e- O O O 2 Al 3+ O 2 - © Boardworks Ltd 2003

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 2003

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 nitrate sulphate NO 3 SO 42 - 12 - ammonium NH 4+ hydroxide carbonate Atoms present N O O O S O O 1+ N H H OH- 1 - O H CO 32 - 2 - C O O O © Boardworks Ltd 2003

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. For example, what is the formula of lithium nitrate? 1. Symbols: Li NO 3 - 2. Charge on ions 1+ 1 - 3. Need more of 4. Ratio of ions 5. Formula neither 1 1 Li. NO 3 © Boardworks Ltd 2003

More Complicated Formulae • What is the formula of magnesium nitrate? 1. Symbols: Mg NO 3 - 2. Charge on ions 2+ 1 - 3. Need more of 4. Ratio of ions 5. Formula NO 3 - 1 2 Mg(NO 3)2 • The brackets around the NO 3 - ion show that the 2 refers to two complete NO 3 - ions. • It represents a total of 2 nitrogens and 6 oxygens with each magnesium ion. © Boardworks Ltd 2003

More Complicated Formulae • What is the formula of sodium sulphate? 1. Symbols: Na+ SO 42 - 2. Charge on ions 1+ 2 - 3. Need more of 4. Ratio of ions 5. Formula Na+ 2 1 Na 2 SO 4 • No brackets here as only one SO 42 - ion needed. • Note although Na contains 2 letters it only represents a single atom – so no brackets! © Boardworks Ltd 2003

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 Al 3+ OH- 3+ 1 OH- 1 3 Al(OH)3 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 2003

Write down how to work out the formula of ammonium sulphate. 1. Symbols: NH 4+ 2. Charge on ions 1+ 3. Need more of NH 4+ 4. Ratio of ions 5. Formula 2 SO 422 - 1 (NH 4)2 SO 4 Again we need brackets as 2 complete NH 4+ ions are needed meaning that for each sulphate ion there are 2 nitrogen and 8 hydrogens. © Boardworks Ltd 2003

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 Al 3+ SO 42 - 3+ 2 - 3 Al 2(SO 4)3 No brackets for Al as only one atom even though it’s 2 letters. We do need brackets around the SO 4 to show it is 3 complete sulphate ions. © Boardworks Ltd 2003

Copy this choosing words from below to fill the gaps. lose electrons • • • lattices gain 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 2003

Which of the following will have ionic bonding? A. Copper chloride B. Iron C. Brass D. Sulphur dioxide © Boardworks Ltd 2003

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 2003

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 16 O 8 © Boardworks Ltd 2003

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 23 Na 11 © Boardworks Ltd 2003

What formula compound will be formed from Mn 4+ and O 2 - ions? A. B. C. D. Mn 2 O 4 Mn. O 2 Mn 2 O Mn. O 4 © Boardworks Ltd 2003

What formula compound will be formed from Ga 3+ and SO 42 - ions? A. B. C. D. Ga 2(SO 4)3 Ga 3(SO 4)2 Ga 2 S 3 O 12 Ga (SO 4)3 © Boardworks Ltd 2003