Ionic Bond and Covalent Bond PDF

1 of 50 © Boardworks Ltd 2007 2 of 50 © Boardworks Ltd 2007 What are bonds? 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 (Cl2). Compounds a...

1 of 50 © Boardworks Ltd 2007 2 of 50 © Boardworks Ltd 2007 What are bonds? 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 (Cl2). Compounds are formed when different elements chemically react and form bonds with each other. Some compounds, like water (H20), 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. 3 of 50 © Boardworks Ltd 2007 Why do atoms form bonds? 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. 1st shell holds a maximum of 2 electrons 2nd shell holds a maximum of 8 electrons 3rd shell holds a maximum of 8 electrons Filled electron shells are very stable. 4 of 50 © Boardworks Ltd 2007 Why do atoms form bonds? 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. 5 of 50 © Boardworks Ltd 2007 What are the types of bonding? 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? 6 of 50 © Boardworks Ltd 2007 7 of 50 © Boardworks Ltd 2007 From atoms to ions How can reactive metal atoms become stable positive ions? 8 of 50 © Boardworks Ltd 2007 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? 9 of 50 © Boardworks Ltd 2007 Positive and negative ions? 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. 10 of 50 © Boardworks Ltd 2007 How do atoms form positive ions? 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 ] = Li+ magnesium atom 2.8.2 magnesium ion [ 2.8 ] = Mg2+ aluminium atom 2.8.3 aluminium ion [ 2.8 ] = Al3+ 11 of 50 © Boardworks Ltd 2007 How is a sodium ion formed? Sodium atom: 11 protons = +11 11 electrons = -11 Sodium ion: 11 protons = +11 10 electrons = -10 Total charge = Total charge = 0 +1 + Na loses 1 electron 2.8.1 (partially full outer shell) 12 of 50 Na [2.8] (full outer shell) © Boardworks Ltd 2007 How is a magnesium ion formed? Magnesium atom: 12 protons = +12 12 electrons = -12 Magnesium ion: 12 protons = +12 10 electrons = -10 Total charge = Total charge = 0 +2 2+ Mg loses 2 electrons 2.8.2 (partially full outer shell) 13 of 50 Mg [2.8]2+ (full outer shell) © Boardworks Ltd 2007 How do atoms form negative ions? 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 = O2- nitrogen atom 2.5 nitride ion = N3- The name of the ion is slightly different to the atom’s name. 14 of 50 © Boardworks Ltd 2007 How is a fluoride ion formed? Fluorine atom: 9 protons = +9 9 electrons = -9 Fluoride ion: 9 protons = +9 10 electrons = -10 Total charge = Total charge = -1 0 - F gains 1 electron 2.7 (partially full outer shell) 15 of 50 F [2.8](full outer shell) © Boardworks Ltd 2007 How is a sulfide ion formed? Sulfur atom: 16 protons = +16 16 electrons = -16 Sulfide ion: 16 protons = +16 18 electrons = -18 Total charge = Total charge = -2 0 2- S gains 2 electrons 2.8.6 (partially full outer shell) 16 of 50 S [2.8.8]2(full outer shell) © Boardworks Ltd 2007 Building an ion 17 of 50 © Boardworks Ltd 2007 Calculating ion charges What is the charge on the ion of each element? Element calcium hydrogen phosphorus fluorine beryllium Electron 2.8.8.2 shells 1 2.8.5 2.7 2.2 Charge on ion +1 -3 -1 +2 18 of 50 +2 © Boardworks Ltd 2007 Electron configuration of ions 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: - 2O F The number of protons and neutrons however, remain different for each element. This means that each ion has different properties. 19 of 50 © Boardworks Ltd 2007 Comparing electron configurations 20 of 50 © Boardworks Ltd 2007 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. What atoms are present in the following compound ions? Ion Formula Charge Atoms present hydroxide OH- -1 O H sulfate SO42- -2 S O O O nitrate NO3- -1 N O O O carbonate CO32- -2 C O O O ammonium NH4+ +1 N H H H 21 of 50 O H © Boardworks Ltd 2007 Comparing positive and negative ions 22 of 50 © Boardworks Ltd 2007 23 of 50 © Boardworks Ltd 2007 Ions and attraction Why do some ions attract while others repel? 24 of 50 © Boardworks Ltd 2007 Do ionic compounds conduct electricity? 25 of 50 © Boardworks Ltd 2007 26 of 50 © Boardworks Ltd 2007 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. 27 of 50 © Boardworks Ltd 2007