Btec C2 – Chemical Bonding (ACT)

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Lesson 1 – Chemical Bonding

Chemical Bonding Demo… Hydrogen balloon Methane Balloon Carbon dioxide balloon Hydrogen burning in oxygen Questions… What can you tell Mr C about the density of hydrogen and carbon dioxide? What are the boiling points of… Water Hydrogen Carbon dioxide Methane

Experiment… Measure melting point of Salol Solder (tin/lead) Salt Use mercury of IR thermometer Questions… What are the melting points of the compounds above? Which compound has the strongest bonds between atoms? What can you tell Mr C about the strength of bonds between, A pair of CO2 atoms A pair of methane atoms

Task… You will be investigating chemical bonding… Draw a series of diagrams to show how a chlorine atom bonds with a sodium atom, You must include… Atomic structures (showing the electrons) of sodium and chlorine atoms before they bond Atomic structures (showing the electrons) of sodium and chlorine atoms after they bond An indication of where electrons move during the bonding process. Use Longman foundation 2, page 148-149 to help. Use A3 paper as groups, then complete a neat version individually, after Mr. C has checked your work. Extension: Draw diagrams to show how (a) Lithium Fluoride, and, (b) Lithium oxide bonds

Ionic Bonding Sodium has 1 electron in its outer shell Chlorine has 7 electrons in its outer shell, or you could say that it has one space in its outer shell. They both want full outer shells, so, Sodium will loose an electron and gives it to chlorine… So… Sodium has a positive charge Chlorine has a negative charge They are attracted together

Ionic bonding Na Cl + - Na Cl This is where a metal bonds with a non-metal (usually). Instead of sharing the electrons one of the atoms “_____” one or more electrons to the other. For example, consider sodium and chlorine: Sodium has 1 electron on its outer shell and chlorine has 7, so if sodium gives its electron to chlorine they both have a ___ outer shell and are ______. Na Cl + - A _______ charged sodium ion A _________ charged chloride ion Na Cl As opposed to covalent bonds, ionic bonds form strong forces of attraction between different ions due to their opposite ______, causing GIANT IONIC STRUCTURES to form (e.g sodium chloride) with ______ melting and boiling points:

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Lesson 2 – Giant Structures MP ~ 800˚C What is the melting point of sodium chloride? What is the name of the bond between a sodium atom and a chlorine atom? Ionic bonds (transfer of electrons) Strong, This means that the melting point is high as you need a lot of energy to break the strong bonds between atoms.

Task… Make your own sodium chloride structure… MP ~ 800˚C Make your own sodium chloride structure… Colour 8 cubes green, these are the chlorine atoms Colour 8 cubes grey, these are the sodium atoms Using the art straws and sellotape, make a model of the structure of sodium chloride

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Covalent Bonding So far... Ionic Bond Metal and Non-metal NaCl Electron transfer Strong Makes giant structure Covalent Bond Non-metal and Non-metal H2 Sharing electrons Strong bond Individual molecules Metal Bond Metal and Metal Fe Free Electrons Giant random structure

Covalent bonding Consider an atom of hydrogen: Notice that hydrogen has just __ electron in its outer shell. A full (inner) shell would have __ electrons, so two hydrogen atoms get together and “_____” their electrons: Now they both have a ____ outer shell and are more _____. The formula for this molecule is H2. When two or more atoms bond by sharing electrons we call it ____________ BONDING. This type of bonding normally occurs between _______ atoms. It causes the atoms in a molecule to be held together very strongly but there are ____ forces between individual molecules. This is why covalently-bonded molecules have low melting and boiling points (i.e. they are usually ____ or ______). Words – gas, covalent, non-metal, 1, 2, liquid, share, full, weak, stable

The periodic table .5

Covalent Bonding – Sharing Electrons Hydrogen atoms have one electron in their outer shell But they want two..!

Covalent Bonding – Sharing Electrons Hydrogen atoms have one electron in their outer shell But they want two..! If they go round as a pair they can share electrons, so they both have a full outer shell This sharing of electrons is known as Covalent bonding

Covalent Bonding 2 In a water molecule the hydrogen and oxygen atoms are covalently bonded e.g. electrons from the oxygen atom x electrons from the hydrogen atom

Dot and cross diagrams Water, H2O: H O H O H H Oxygen, O2: O O O O Step 1: Draw the atoms with their outer shell: Step 2: Put the atoms together and check they all have a full outer shell: H O H O H H Oxygen, O2: O O O O

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Metallic Bonding Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points. Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are flexible. Longman FND 2, page 146-147

Questions – Summary of Chemical Bonding Match the correct type of bonding to the elements that are joined... Draw a diagram to show how the atoms are bonded in each type of bond. Show the electron arrangement. Summary Q from Longman 2... (pages...146, 148 & 154) Element 1 Element 2 Type of bonding Magnesium Chlorine Metal Carbon Hydrogen Ionic Iron Covalent

Experiment... Investigate the solubility of group 1 salts, covalent and metallic compounds in water and alcohol. Worksheet: ‘Solubility’ Watch animation, complete task sheet on different types of bonding

Questions to summarise Covalent / ionic and metallic bonds

Sodium Chloride…. Na+ or H+ ion Cl- or OH- ion Dissolved in water, sodium chloride will split up and form the following ions… Na+ Cl- From salt H+ OH- From water Na+ or H+ ion Cl- or OH- ion The positive ions (Na+ and H+) will, be attracted to the negative electrode (metal ions are usually positive) The negative ions (Cl- and OH-) will be attracted to the positive electrode (non- metal ions are usually negative)

Questions on Electrolysis Foundation Science 1 Draw a series of diagram to show what happens to the atoms when sodium chloride dissolves in water, then undergoes electrolysis

Assessment Grading criteria P2 Investigate and describe ionic, covalent and metallic bonds. Grading criteria M2 Investigate and explain the properties of substance with ionic, covalent and metallic bonds. Grading criteria D2 Explain bonding in terms of stability… a means to achieving a full outer shell either by transferring or sharing electrons.

What you need to do… Scenario…. You work in a research laboratory at the University of Plymouth. The Environment Agency has approached you with four chemical samples that have been found near the play area at ‘Freedom Field Park’. They have asked you to identify the type of substance as either ionic, covalent or metallic and given them an outline of the type of properties these substance will have. You will carry out a practical assignment to identify the four unknown samples and you will produce a letter from the University to the Environment Agency in London. This letter will include your identification of the four samples and justify your reasons (P2) an explanation of the properties of the samples (M2) and detailed explanation of the structure of any covalent or ionic substances found (D2)

Numbers in black – Longman FND book 2 Exp Test the four samples and identify them as either ionic, covalent or metallic. Show you results in a table. Diagram. Justify your identification of each sample with data from your tests. 146,148 154, 135, 139, 143 Write you letter from the University to the Environment Agency Describe what your results tell you about the four samples. Include your results and what you results show, with justification. Use diagrams to explain how the atoms bond together in ionic, covalent and metallic bonding. 150, 142 Explain, with a diagram, in the letter, how ionic substances dissolve in solution. 148, 139 Explain, in the letter, why ionic substances have a higher melting and boiling point compared to simple covalent. 146, 143 Explain, in the letter, why metals and dissolved ionic substances conduct electricity. Int, 138 Explain, in the letter, why graphite is an unusual giant covalent and how it is able to conduct electricity. Use dot and cross diagrams in the letter to explain how the ionic substances achieve stability through transferring electrons. 154, 136 Use dot and cross diagrams in the letter to explain how the covalent substances achieve stability through sharing electrons. Numbers in black – Longman FND book 2 Numbers in Blue – AQA Science book

Exp Test the four samples and identify them as either ionic, covalent or metallic. Show you results in a table. Diagram. Justify your identification of each sample with data from your tests. 146,148 154, 135, 139, 143 Write you letter from the University to the Environment Agency Describe what your results tell you about the four samples. Include your results and what you results show, with justification. Use diagrams to explain how the atoms bond together in ionic, covalent and metallic bonding. 150, 142 Explain, with a diagram, in the letter, how ionic substances dissolve in solution. 148, 139 Explain, in the letter, why ionic substances have a higher melting and boiling point compared to simple covalent. 146, 143 Explain, in the letter, why metals and dissolved ionic substances conduct electricity. Int, 138 Explain, in the letter, why graphite is an unusual giant covalent and how it is able to conduct electricity. Use dot and cross diagrams in the letter to explain how the ionic substances achieve stability through transferring electrons. 154, 136 Use dot and cross diagrams in the letter to explain how the covalent substances achieve stability through sharing electrons.