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Types of bonding: OVERVIEW 2 of 43 Boardworks Ltd 2009 There are three types of bond that can occur between atoms: an ionic bond occurs between a metal and non-metal atom (e.g. NaCl) a covalent bond occurs between two non-metal atoms (e.g. I 2, CH 4 ) a metallic bond occurs between atoms in a metal (e.g. Cu)
Ionic bonding 3 of 43 Boardworks Ltd 2009
Charge on the ions 4 of 43 Boardworks Ltd 2009 Metals lose electrons to form positive ions (cations) while non-metals gain electrons to form negative ions (anions). The number of electrons gained or lost by an atom is related to the group in which the element is found. Group 1 2 3 4 5 6 7 8/0 Charge 1+ 2+ 3+ N/A 3-2- 1- N/A Example Na + Mg 2+ Al 3+ N/A N 3- O 2- F - N/A The elements in groups 4 and 8 (also called group 0) do not gain or lose electrons to form ionic compounds.
Representing ionic bonding 5 of 43 Boardworks Ltd 2009
Covalent bonding 6 of 43 Boardworks Ltd 2009
Metallic bonding 10 of 43 Boardworks Ltd 2009
Strength of metallic bonding: ion charge 11 of 43 Boardworks Ltd 2009 The strength of metallic bonding depends on two factors: 1. the charge on the metal ions 2. the size of the metal ions. 1. The charge on the metal ions The greater the charge on the metal ions, the greater the attraction between the ions and the delocalized electrons, and the stronger the metallic bonds. A higher melting point is evidence of stronger bonds in the substance. Element Charge on ion Melting point (K) Na Mg Al 1+ 2+ 3+ 371 923 933
Strength of metallic bonding: ion size 12 of 43 Boardworks Ltd 2009 2. The size of the metal ions The smaller the metal ion, the closer the positive nucleus is to the delocalized electrons. This means there is a greater attraction between the two, which creates a stronger metallic bond. Element Li Na K Rb Cs Ionic radius (nm) Melting point (K) 0.076 0.102 0.138 0.152 0.167 454 371 337 312 302
Types of bonding 13 of 43 Boardworks Ltd 2009
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What are bonds? 16 of 50 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 ). 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.
Why do atoms form bonds? 17 of 50 Bonds involve the electrons in the outer shells of atoms. Each shell has a maximum number of electrons that it can hold. Electrons fill the shells nearest the nucleus first. 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 Filled electron shells are very stable, and unreactive. (do not form bonds)
Why do atoms form bonds? 18 of 50 The atoms of noble gases have completely full outer shells and so are stable. This makes the noble gases very unreactive and so they do not usually form bonds. The atoms of other elements have incomplete outer electron shells and so are unstable. By forming bonds, the atoms of these elements are able to have filled outer shells and become stable.
What are the types of bonding? 19 of 50 Different types of bonds are formed depending on the types of atoms involved: ionic bonding occurs between metal and non-metal atoms. covalent bonding occurs between non-metals atoms only. metallic bonding occurs between metal atoms only. All bonds involve electrons and all bonding involve changes to the number of electrons in the outer shells of atoms. How do you think electrons are involved in ionic bonding?
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From atoms to ions 21 of 50 How can reactive metal atoms become stable positive ions?
How do atoms form ions? 22 of 50 An ion is an atom or group of atoms that has an electrical charge, either positive or 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?
Positive and negative ions? 23 of 50 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. The electron configuration of an atom shows how many electrons it must lose or gain to have a filled outer shell. 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.
How do atoms form positive ions? 24 of 50 An atom that loses one or more electrons forms a positive ion. Metal atoms, such as sodium, magnesium and iron, form positive ions. 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: lithium atom 2.1 lithium ion [ 2 ] magnesium atom 2.8.2 magnesium ion [ 2.8 ] = Mg 2+ aluminium atom 2.8.3 aluminium ion [ 2.8 ] = Li + = Al 3+
How is a sodium ion formed? 25 of 50 Sodium atom: 11 protons = +11 11 electrons = -11 Total charge = 0 Sodium ion: 11 protons = +11 10 electrons = -10 Total charge = +1 + Na loses 1 electron Na 2.8.1 (partially full outer shell) [2.8] (full outer shell)
How is a magnesium ion formed? 26 of 50 Magnesium atom: 12 protons = +12 12 electrons = -12 Total charge = 0 Magnesium ion: 12 protons = +12 10 electrons = -10 Total charge = +2 2+ Mg loses 2 electrons Mg 2.8.2 (partially full outer shell) [2.8] 2+ (full outer shell)
How do atoms form negative ions? 27 of 50 An atom that gains one or more electrons forms a negative ion. Non-metal atoms, such as chlorine, oxygen and nitrogen, 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: chlorine atom 2.8.7 chloride ion [ 2.8.8 ] = Cl - oxygen atom 2.6 oxide ion [ 2 ] = O 2- nitrogen atom 2.5 nitride ion [ 2 ] = N 3- The name of the ion is slightly different to the atom s name.
How is a fluoride ion formed? 28 of 50 Fluorine atom: 9 protons = +9 9 electrons = -9 Total charge = 0 Fluoride ion: 9 protons = +9 10 electrons = -10 Total charge = -1 - F gains 1 electron F 2.7 (partially full outer shell) [2.8] - (full outer shell)
How is a sulfide ion formed? 29 of 50 Sulfur atom: 16 protons = +16 16 electrons = -16 Total charge = 0 Sulfide ion: 16 protons = +16 18 electrons = -18 Total charge = -2 2- S gains 2 electrons S 2.8.6 (partially full outer shell) [2.8.8] 2- (full outer shell)
Building an ion 30 of 50
Calculating ion charges 31 of 50 What is the charge on the ion of each element? Element calcium hydrogen phosphorus fluorine beryllium Electron shells 2.8.8.2 1 2.8.5 2.7 2.2 Charge on ion +2 +1-3 -1 +2
Electron configuration of ions 32 of 50 When different elements gain or lose electrons to complete their outer electron shell, they can create ions that have the same electron configuration. For example, oxygen and fluorine both gain electrons to become negative ions. The resulting ions have the same electron configuration: 2- - O F The number of protons and neutrons however, remain different for each element. This means that each ion has different properties.
Comparing electron configurations 33 of 50
What is a Polyatomic ion? 34 of 50 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 Polyatomic ion. What atoms are present in the following compound ions? Ion Formula Charge Atoms present hydroxide OH - -1 O H sulfate SO 4 2- -2 S O O O O nitrate NO 3 - -1 N O O O carbonate CO 3 2- -2 C O O O ammonium NH 4 + +1 N H H H H
35 of 50 Comparing positive and negative ions
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Ions and attraction 37 of 50 Why do some ions attract while others repel?
What is ionic bonding? 38 of 50 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.
How are ionic bonds formed? 39 of 50 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. By losing this electron, it has a filled outer shell and forms a positive ion. Na Na 2.8.1 [2.8] + + Chlorine has 7 electrons in its outer shell. By gaining an electron from sodium, it has a filled outer shell and forms a negative ion. Cl Cl 2.8.7 [2.8.8] - -
How are ionic bonds formed? 40 of 50 The positive sodium ions and the negative chloride ions are strongly attracted to each other. + - Na Cl It is this electrostatic attraction that forms ionic bonds in sodium chloride and other ionic compounds.
Formation of an ionic bond 41 of 50
Ions and ionic bonding summary 42 of 50
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44 of 50 What is the ratio of ions? Sodium chloride (NaCl) and magnesium oxide (MgO) are simple ionic compounds. In each compound, the metal needs to lose the same number of electrons that the non-metal needs to gain. Na Cl Na + Cl - 1 electron Mg 2 electrons O Mg 2+ O 2- Both compounds have a 1:1 ratio of metal ions to non-metal ions, which is shown by the formula of each compound.
What is the ratio of ions in sodium oxide? 45 of 50 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 Na 1 electron from each Na atom Na + O O 2- Na + 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.
46 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 1 electron for each Cl atom Cl Cl Mg 2+ Cl - Cl - 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.
47 of 50 How to write the formula of an ionic compound The formula of a compound uses chemical symbols and numbers to show the ratio of atoms of each element present. 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.
48 of 50 Formula of aluminium bromide What is the formula of aluminium bromide? Symbol Ion charge Balance the number of ions Ratio of ions Formula Al Br +3-1 3 bromide ions are needed for each aluminium ion 1 : 3 AlBr 3 Al 1 electron for each bromine atom Br Br Br Al 3+ Br - Br - Br -
Formula of aluminium oxide 49 of 50 What is the formula of aluminium oxide? Symbol Ion charge Balance the number of ions Ratio of ions Formula Al O +3-2 2 aluminium ions are needed for 3 oxide ions 2 : 3 Al 2 O 3 Al 2 electrons for each oxygen atom Al O O 2- Al 3+ O O 2- Al 3+ O O 2-
More ionic formulae 50 of 50 What are the formulae of all the possible ionic compounds from combinations of these metals and non-metals. metals nonmetals Li Ca Na Mg Al K F LiF CaF 2 NaF MgF 2 AlF 3 KF O Li 2 O CaO Na 2 O MgO Al 2 O 3 K 2 O N Li 3 N Ca 3 N 2 Na 3 N Mg 3 N 2 AlN K 3 N Br LiBr CaBr 2 NaBr MgBr 2 AlBr 3 KBr S Cl Li 2 S CaS Na 2 S MgS Al 2 S 3 K 2 S LiCl CaCl 2 NaCl MgCl 2 AlCl 3 KCl
What is the ionic formula? 51 of 50
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What is an ionic lattice? 53 of 50 In an ionic compound, when any macroscopic sample ions react together, countless atoms will transfer electrons to form countless oppositely charged ions. These oppositely charged species being produced in close proximity are drawn together into an giant, 3D, ordered, solid, three-dimensional array of cations and anions called a crystal lattice The smallest whole number cation-to-anion ratio in this structure represents the chemical formula for the ionic compound The structure of the ionic lattice affects the properties of the ionic compound.
Why do ionic compounds form crystals? 54 of 50 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.
Heating ionic compounds 55 of 50 Why are ionic compounds solid at room temperature and have high melting points and boiling points? Compound sodium chloride magnesium oxide Ion charges Ionic bonds are strong and a lot of heat is needed to break them. Melting point ( o C) Boiling point ( o C) 1 + and 1-801 1,413 2 + and 2-2,852 3,600 strong ionic bonds hold ions together 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.
56 of 50 Do ionic compounds conduct electricity?
57 of 50 How can ionic compounds conduct electricity? As solids, ionic compounds cannot conduct electricity because their ions are bonded together in the lattice. 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. 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.
58 of 50 Why are ionic compounds brittle? Ionic compounds are brittle they shatter when they are hit. Ionic bonds are strong, so why does this happen? force repulsion 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.
Electronegativity 59 of 50 Electronegativity is defined as the ability of an atom in a molecule to attract electrons to itself. Electronegativity is a function of two properties of isolated atoms: The atom s ionization energy (how strongly an atom holds onto its own electrons) The atom s electron affinity (how strongly the atom attracts other electrons) For example, an element which has a large (negative) electron affinity and a high ionization (always endothermic, or positive for neutral atoms) Will attract electrons from other atoms and resist having electrons attracted away We say these atoms are highly electronegative
Electronegativity trends: across a period 60 of 43 Boardworks Ltd 2009 Electronegativity increases across a period because: 1. The atomic radius decreases. 2. The charge on the nucleus increases without significant extra shielding. New electrons do not contribute much to shielding because they are added to the same principal energy level across the period.
Electronegativity trends: down a group 61 of 43 Boardworks Ltd 2009 Electronegativity decreases down a group because: 1. The atomic radius increases. 2. Although the charge on the nucleus increases, shielding also increases significantly. This is because electrons added down the group fill new principal energy levels.
Electronegativity is dictated by: 62 of 43 Boardworks Ltd 2009 The number of protons in the nucleus across a period you are increasing the number of protons, but filling electrons in the same Bohr quantized energy level. You are only filling sub-shells, so electronegativity increases from left to right The distance from the nucleus down groups, you are placing electrons into new quantized energy levels, so moving further away from the attractive power of the nucleus. Outer shell becomes further away from the nucleus. The amount of shielding by the inner electrons level of shielding upon bonding electrons increases down groups, and adds to the reduction in electronegativity. Shielding is caused by repulsion of electrons for each other.
63 of 43 Boardworks Ltd 2009 Ions & Atomic Radius Negative Ions As extra electrons are added to a neutral atom (eg O to make O -2 ) the ion has the same positive nuclear charge (due to protons), and an increased number of electrons surrounding the nucleus. The electrostatic repulsion increases The volume occupied by the electrons increases NEGATIVE IONS are LARGER than the corresponding neutral atom
64 of 43 Boardworks Ltd 2009 Ions & Atomic Radius Positive Ions As electrons are removed from a neutral atom (eg Mg to make Mg +2 ) the ion has the same positive nuclear charge (due to protons), and a decreased number of negative electrons surrounding the nucleus. The electrostatic repulsion decreases The volume occupied by the electrons decreases POSITIVE IONS are SMALLER than the corresponding neutral atom
65 of 50 Electronegativity & Ionic Bonds Formed between two atoms with large differences in their ionization energies and electronegativity's An electronegativity difference of greater than 1.6 can be classified as an ionic bond In this case we can essentially say electrons are transferred from one atom to another
Summary of Ionic Bonding 66 of 50
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Worksheet KEY 69 of 50
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True or false? 71 of 50
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Glossary 73 of 50 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.
74 of 50 Complete Assignment #2