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Boardworks GCSE Additional Science: Chemistry Covalent Bonding

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Presentation on theme: "Boardworks GCSE Additional Science: Chemistry Covalent Bonding"— Presentation transcript:

1 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

2 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

3 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Why do atoms form bonds? Boardworks GCSE Additional Science: Chemistry Covalent Bonding 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 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Why do atoms form bonds? Boardworks GCSE Additional Science: Chemistry Covalent Bonding 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 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
What is a covalent bond? Boardworks GCSE Additional Science: Chemistry Covalent Bonding Non-metal elements usually just need one or two electrons to fill their outer shells. So how do they form a bond? Cl Cl incomplete outer shells The two non-metal atoms cannot form a bond by transferring electrons from one to another. Instead, they share electrons. Cl Cl Each atom now has a full, stable outer shell. The shared electrons join the atoms together. This is called a covalent bond.

6 How is a covalent bond drawn?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding A covalent bond consists of a shared pair of electrons. Cl Cl covalent bond Only outer shells of electrons are involved in bonding, so the inner shells do not always have to be included in diagrams. Two common ways to represent a covalent bond are: Cl simplified dot and cross diagram solid line Cl

7 Comparing covalent and ionic bonding
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of the differences between covalent and ionic bonding. Appropriately coloured voting cards could be used with this activity to increase class participation.

8 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

9 How are covalent bonds formed?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding How do non-metal atoms form covalent bonds? Teacher notes This illustration contains representations of non-metals forming covalent bonds. It can be used as an introduction to the topic. There are several discussion points relating to the topic: The common room is only for non-metals – no metals allowed Covalent bonding only occurs between non-metals. Ipod sharing Indicating the presence of covalent bonds. The ipods represent shared electrons. All the elements sharing ipods are happy indicating they are stable. Ipod and drink sharing between oxygen atoms Indicating the presence of a double covalent bond. Unstable non-metal atom not bonded to anything else Non-metals need to bond to become stable (apart from the noble gases).

10 Covalent bonding in hydrogen
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Many non-metal elements, such as hydrogen, exist as simple diatomic molecules that contain covalent bonds. How is a covalent bond formed in hydrogen? H H H H Each hydrogen atom needs one more electron in its outer shell and so each atom shares its single unpaired electron. This shared pair of electrons forms a covalent bond and so creates a diatomic molecule of hydrogen. Some molecules contain double or triple covalent bonds. How are these are formed?

11 What are the types of covalent bonds?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This three-stage animation shows how covalent bonds form between atoms of different elements. While showing the animation, the difference between single, double and triple bonds could be pointed out.

12 Can compounds contain covalent bonds?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Covalent bonding can also occur between atoms of different non-metals to create molecules of covalent compounds. These covalent bonds can be single, double or triple. How is a covalent bond formed in hydrogen chloride (HCl, also represented as H–Cl)? Cl Cl H H Teacher notes It should be pointed out that the inner electron shells of chlorine have not been included in the diagrams above because they are not involved with the bonding. By just showing the shells that are involved in bonding, it is clearer to see what is happening. Hydrogen and chlorine both need one more electron to fill outer shells. By sharing one electron each, they both have a stable outer shell and a covalent bond is formed.

13 Covalent bonding in water
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Compounds can contain more than one covalent bond. Oxygen (2.6) needs 2 more electrons, but hydrogen [1] only needs 1 more. How can these three elements be joined by covalent bonding? H O The oxygen atom shares 1 electron with 1 hydrogen atom, and a second electron with another hydrogen atom. What is the name of the molecule that is formed? H2O (or H–O–H) is water.

14 How is the ratio of atoms calculated?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding To calculate the ratio of atoms in a stable covalent compound: 1. Work out how many electrons are needed by each non-metal element to complete its outer electron shell. 2. Work out the ratio of atoms that will provide enough shared electrons to fill all the outer shells. For example, how many nitrogen and hydrogen atoms bond together in an ammonia molecule? element N H electron configuration (2.5) (1) electrons needed 3 1 ratio of atoms 1 3

15 Covalent bonding in ammonia
Boardworks GCSE Additional Science: Chemistry Covalent Bonding How do nitrogen and hydrogen atoms form covalent bonds in a molecule of ammonia? element N H N electron configuration (2.5) (1) H H electrons needed 3 1 ratio of atoms H 1 3 NH3 or H N H H

16 Covalent bonding in methane
Boardworks GCSE Additional Science: Chemistry Covalent Bonding How do carbon and hydrogen atoms form covalent bonds in a molecule of methane? H element C H electron configuration (2.4) (1) C H H electrons needed 4 1 ratio of atoms 1 4 H CH4 or H C H H

17 Covalent bonding in carbon dioxide
Boardworks GCSE Additional Science: Chemistry Covalent Bonding How do carbon and oxygen atoms form covalent bonds in a molecule of carbon dioxide? element C O electron configuration O C O (2.4) (2.6) electrons needed 4 2 ratio of atoms 1 2 double bonds CO2 or O C O A double bond is when two pairs of electrons are shared. In carbon dioxide there are two double bonds – one between each oxygen atom and the carbon atom.

18 What are simple covalent structures?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Covalent molecules that contain only a few atoms are called simple covalent structures. Most substances that contain simple covalent molecules have low melting and boiling points and are therefore liquids or gases at room temperature, e.g. water, oxygen, carbon dioxide, chlorine and hydrogen. Why? The covalent bonds within these molecules are strong but the bonds between molecules are weak and easy to break. weak bonds between molecules strong bonds within molecules

19 What is the structure of a molecular solid?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding A few substances that contain simple covalent molecules are solid at room temperature. These are molecular solids. Iodine is a molecular solid at room temperature. Two iodine atoms form a single covalent bond to become an iodine molecule. The solid is formed because millions of iodine molecules are held together by weak forces of attraction to create a 3D molecular lattice. Photo credit: Dr John Mileham Image of iodine crystals. weak forces of attraction What properties would you expect molecular solids to have with this type of structure?

20 What are the properties of molecular solids?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding The properties of a molecular solid, such as iodine, are: low melting and boiling points; usually soft and brittle – they shatter when hit. cannot conduct electricity. Why do molecular solids have these properties? The weak forces of attraction between the molecules can be broken by a small amount of energy. This means that the molecular solids are soft and brittle and melt and boil at low temperatures. Photo credit: Dr John Mileham Image of iodine crystals. Molecular solids are also unable to conduct electricity because there are no free electrons or ions to carry a charge.

21 Covalent bonds – true or false?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This true-or-false activity could be used as a plenary or revision exercise on covalent bonds, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.

22 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

23 What are giant covalent structures?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding In some substances, such as sand, diamond and graphite, millions of atoms are joined together by covalent bonds. Photo credit (left): Tijmen van Dobbenburgh Photo credit (middle): Kia Abell Photo credit (right): Dimitris Kritsotakis The covalent bonds in these substances do not form molecules but vast networks of atoms called giant covalent structures. All the bonds are covalent, so giant covalent structures have very high melting and boiling points, and are usually hard.

24 What is the structure of sand?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Sand is mostly made of the mineral quartz, which is silicon dioxide. It has a giant covalent structure made up of silicon and oxygen atoms. Each silicon atom (2.8.4) is bonded to four oxygen atoms, and each oxygen atom (2.6) is bonded to two silicon atoms. Si O

25 What are the allotropes of carbon?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Diamond and graphite appear to be very different substances but what do they have in common? Both diamond and graphite are made up of carbon atoms. Photo credit (left): Christopher Potter Photo credit (right): Dimitris Kritsotakis Different forms of the same element are called allotropes. These allotropes of carbon have different properties because the atoms are bonded in different arrangements which create different giant structures.

26 How does structure affect properties?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding How do the different structures of diamond and graphite influence their properties? Teacher notes This illustration contains discussion points relating to how structure affects properties, including: Graphite as an inappropriate basis of jewellery instead of diamonds because: - Layers of graphite easily break off because bonds between the graphite layers are weak. This means that graphite deposits would be left all over clothes where the jewellery touched/ - The structure of graphite means that it is opaque and dull, and is therefore unattractive for jewellery. - It is very soft so would easily break. - Graphite is much cheaper and more readily available than diamonds and therefore not very exclusive for jewellery! Diamond as an inappropriate basis for pencil lead because: - Diamond, unlike graphite, does not have layers that easily break off. Therefore when writing, no deposit would be left, and therefore no writing would be seen! - Diamond is so hard it would damage anything it was used to write on. - Diamond is a very expensive material. This means it would be far too expensive to use in ever day items like pencils.

27 What is the structure of diamond?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This three-stage animation shows how carbon makes up the structure of diamond, and builds to make a giant covalent lattice.

28 What are the properties of diamond?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding In diamond, all the electrons in the outer shell of each carbon atom (2.4) are involved in forming covalent bonds. This affects the properties of this allotrope of carbon: Diamond is very hard – the hardest natural substance. Diamond has a very high melting and boiling point – a lot of energy is needed to break the covalent bonds. Diamond cannot conduct electricity – there are no free electrons or ions to carry a charge.

29 What is the structure of graphite?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This four-stage animation shows how carbon makes up the structure of graphite, and builds to make a giant covalent lattice. It also shows how graphite is soft and slippery (because the bonds between layers are weak), and can conduct electricity (because there are delocalised electrons between the layers).

30 What are the properties of graphite?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding In graphite, only three of the four electrons in the outer shell of each carbon atom (2.4) are involved in covalent bonds. This affects the properties of this allotrope of carbon: Graphite is soft and slippery – layers can easily slide over each other because the weak forces of attraction are easily broken. This is why graphite is used as a lubricant. Graphite conducts electricity – the only non-metal to do so. The free electron from each carbon means that each layer has delocalized electrons, which can carry charge.

31 Are there other allotropes of carbon?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding A third class of carbon compounds have been discovered in recent years. These are called fullerenes. Buckminsterfullerene is one type of fullerene. It contains 60 carbon atoms, each of which is bonded to three others by two single bonds and one double bond. C The atoms in this allotrope of carbon form a sphere, like the shape of a football. The molecules can be called ‘bucky balls’. They are large but are not classified as giant structures.

32 Complete the sentences
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This completing sentences activity provides the opportunity for some informal assessment of students’ understanding of covalent bonding.

33 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

34 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Bonding and structure Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This matching activity could be used as a plenary exercise to check students’ ability to understand the structure of different covalent substances. Coloured traffic light cards could be used with this activity to increase class participation.

35 Simple or giant covalent structure?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This drag and drop activity could be used as a plenary exercise to check students’ ability to identify which structures are simple covalent and which are giant covalent. Class voting or the use of coloured traffic light cards could be make this a whole-class exercise.

36 How does bonding affect properties?
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Does the type of bonding in a substance affect its properties? Teacher notes This illustration contains representations of the different properties of different types of structures with different types of bonding. It can be used as a discussion point about the differences between ionic, covalent and metallic bonding. There are several discussion points relating to the topic: Iodine – a simple molecular structure Because it has weak bonds, it has a low melting and boiling point and is therefore starting to melt and evaporate in the sun Sodium chloride – an ionic compound Because it is an ionic compound, it is soluble in water. This is because the slightly charged water molecules can attract the ions of sodium chloride away from the lattice. Diamond – a giant covalent structure Hard and strong and unaffected by the water of the heat of the sun. He is using sodium chloride as salt on his chips. Copper – metallic structure Copper, as a metal, is ductile (able to be drawn out into wires). It is also unaffected by the water and the heat from the sun. See also the GCSE Science chemistry ‘Metals and Alloys’ presentation for more information on metallic bonding. See the GCSE Additional Science chemistry ‘Ionic Bonding’ presentation for more information about ionic bonding.

37 Bonding and structures
Boardworks GCSE Additional Science: Chemistry Covalent Bonding The type of bonding in a substance affects the properties of that substance. Can you fill in the gaps in the table below? Type of structure Particles in structure State at room temperature Bonding millions of metal and non-metal ions giant ionic lattice solid ionic simple molecular few non-metal atoms usually liquid or solid covalent giant covalent lattice millions of non-metal atoms solid giant metallic lattice millions of metal ions solid (except mercury – liquid) metallic

38 Melting and boiling point: giant structures
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Substances with giant structures generally have high melting and boiling points because all the atoms are strongly bonded together to form a continuous 3D lattice. A large amount of energy is needed to break these bonds. strong covalent bonds holds atoms together strong metallic bonds holds ions together strong ionic bonds holds ions together

39 Effect of structure on properties
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This matching activity could be used as a plenary exercise to check students’ ability to understand the properties of different structures. Coloured traffic light cards could be used with this activity to increase class participation.

40 The effect of bonding on properties
Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of the properties of differently bonded structures.

41 Boardworks GCSE Additional Science: Chemistry Covalent Bonding

42 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Glossary (1/2) Boardworks GCSE Additional Science: Chemistry Covalent Bonding allotrope – A structurally different form of an element with different physical properties. covalent bond – A strong bond between two atoms in which each atom shares one or more electrons with the other. covalent compound – A compound containing atoms joined by covalent bonds. double bond – A covalent bond in which each atom shares two of its electrons. giant structure – A structure containing millions of atoms or ions bonded together. The structure extends in three dimensions until all available atoms are used up.

43 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Glossary (2/2) Boardworks GCSE Additional Science: Chemistry Covalent Bonding molecule – A small group of atoms which are held together by covalent bonds.  molecular solid – A solid substance made up of molecules held together by weak forces of attraction, forming a lattice. single bond – A covalent bond in which each atom shares one of its electrons. triple bond – A covalent bond in which each atom shares three of its electrons.

44 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Anagrams Boardworks GCSE Additional Science: Chemistry Covalent Bonding

45 Boardworks GCSE Additional Science: Chemistry Covalent Bonding
Multiple-choice quiz Boardworks GCSE Additional Science: Chemistry Covalent Bonding Teacher notes This multiple-choice quiz could be used as a plenary activity to assess students’ understanding of covalent bonding. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.


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