Page 1 of 6. PODCAST 10 29/8/2015 Covalent Structure and Bonding.

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Page 1 of 6 PODCAST 10 29/8/2015 Covalent Structure and Bonding. Hello and welcome to this podcast from allerytutors.com. My name is Chris Harris and I will be running through the varied topic of covalent structure and bonding.

1 Page 1 of 6 PODCAST 10 29/8/2015 Covalent Structure and Bonding. Hello and welcome to this podcast from allerytutors.com. My name is Chris Harris and I will be running through the varied topic of covalent structure and bonding. I will go through what a covalent bond is, the difference between simple molecular and giant covalent and what effect this has on physical properties. You will also find out what a coordinate (dative covalent) bond is. As usual, there will be opportunities for you to practice too. This podcast is designed to go through content required for the new A Level Chemistry specifications and although most content is the same across all exam boards, you should check your specification to make sure you are learning the right content at the right level of detail. All specifications can be fou d o the oa d s e site a d ill list e a tl hat ou eed to k o. Just a quick reminder that I have a set of A Level Chemistry Revision Videos on my YouTube channel just type in Allery Tutors into a search engine or YouTube and you will find them there, please remember to subscribe and join a growing community of fans. Follow me on or like me on Facebook to get all the pre-release info on new videos and podcasts and to ask me questions on all things Chemistry and I will do my best to answer them. It may be a good idea to print off the script for this podcast so you can read and listen at the same time. This way you can scribble all over them with your own notes and thoughts. Visit allerytutors.com to get a hold of them. So, what is a covalent bond? Well in a nut shell it is the sharing of electrons between atoms. The te dates a k to 1 3. The p efi o ea s to sha e (just like i o-operate and co-driver) and valent comes from valence, which in chemistry we refer to the outer electrons. So it is just the sharing of outer electrons. For the purpose of AS Chemistry, covalent bonding mainly occurs between non-metal atoms although covalent features occur in compounds that are generally seen as ionic. Chemistry is never just black and white! So to be more specific, a covalent bond is an electrostatic attraction between a shared pair of electrons and the positively charged nucleus. Covalent bonds are best illustrated using a dot-cross diagram showing how the electron shells overlap in order to obtain a stable configuration (normally an octet / 8 electrons or 2 for Hydrogen). Dot cross diagrams show us how many bond pairing electrons and lone pairs you have which is very useful when you come onto bond angles and shapes. See my video on shapes of molecules on my YouTube channel for more info! The position of the element in the periodic table will tell you how many outer electrons it has, for example Nitrogen is in group 5, so it has 5 electrons in the outer shell. Ammonia contains Nitrogen and has the molecular formula of NH 3, so this means the dot cross will show Nitrogen in the middle with 3 of its electrons being shared with Hydrogen. This leaves 2 electrons left, we pair these up and call these a lone pair of electrons. See the script for this podcast to see a diagram.

2 Page 2 of 6 Ammonia only has single covalent bonds (known as sigma bonds σ bond) but some molecules like Carbon Dioxide has 2 double bonds (CO 2 ). Carbon needs to obtain 4 electrons to become stable and Oxygen needs 2. Carbon shares 2 electrons with each Oxygen in a much stronger double bond. The diagram would show 2 electrons from each element being shared. A double bond contains a σ bond and a π bond. View the script to see this diag a ( oti e ou do t ha e to d a the i les to represent the shells). Triple bonds can exist too which are shorter and stronger than a double bond. E.g. The toxic gas Hydrogen Cyanide contains Hydrogen, Carbon and Nitrogen. Carbon needs 4 electrons, Hydrogen shares 1 and so Nitrogen share 3! See the diagram below by looking at the podcast script. Just e a e that so e ato s do t eed ele t o s to e o e sta le. E.g. Boron Trifluoride (BF 3 ) Boron has 3 electrons in its outer shell and fluorine only needs 1. Each Fluorine atom shares with boron leaving 3 bond pairs and no lone pairs. Boron only has 6 electrons. Some can have more than 8. Sulphur and Phosphorous are examples of elements than can do this so do t e ala ed when you draw a molecule using these elements and it turns out that they have more than 8! E.g. PCl 5 remember Phosphorous must have 5 electrons of its own. Phosphorous has 5 electrons all involved in bonding with 5 Chlorine atoms. Phosphorus has 10 electrons in total!

3 Page 3 of 6 Have a go yourself Draw the dot cross diagram for the following molecules Sulphur Dioxide (SO 2 ) and lethal sewer gas, hydrogen sulphide (H 2 S). How many lone pairs of electrons are in each molecule? (Visit allerytutors.com view the script for this podcast to find out the answer) Answer SO 2 Sulphur has 2 electrons left. It has 1 lone pair. Notice Sulphur has more than 8 electrons! Double covalent bond! H 2 S Sulphur has 4 electrons left. It has 2 lone pairs. (Inner electrons not needed) All the molecules that we have looked at so far are classed as simple covalent molecules (simple molecular). That means they exist as small molecules interacting with each other only by weak intermolecular forces. This means a lot of simple molecules have low boiling and melting points due to very little energy required to overcome the weak forces. This explains why simple covalent molecules are mainly gases at room temperature. There are a few covalent structures that have a very high melting and boiling point. We call these giant covalent structures. They are made up mainly non-metals covalently bonded together to form 1 large structure. All the atoms in the structure are connected together by very strong covalent bonds. A covalent bond is significantly stronger than an intermolecular force and hence more energy is required to break the bond, leading to high melting and boiling points. Examples of giant covalent structures are Carbon (in the form of Diamond and Graphite) and Silicon Dioxide (sand). Graphite Graphite is made up Carbon atoms only but its structure gives it unique properties. 1. It is made of carbon layers. Each carbon is bonded 3 times with the spare electron being delocalised and free to move between the layers. 2. The layers can slide over each other which makes graphite useful in pencils and lubricants.

4 Page 4 of 6 3. Due to the delocalised electrons, graphite is a rare example of a non-metal that can conduct electricity. You need free moving electrons or ions for an electric charge to be carried. 4. Graphite is insoluble just like other giant covalent structures as so much energy is needed to break the covalent bonds to allow it to dissolve. 5. The packing of the layers is sparse and so the density of graphite is low which is useful if you want strength and light weight. This is used in Formula 1 cars as carbon fibre. A Diagram of graphite is shown in the podcast script. Download it from allerytutors.com. Strong covalent bonds hold carbon atoms together. Weak intermolecular forces (caused by delocalised electrons) keep layers together. Diamond and Silicon Dioxide Diamond and Silicon Dioxide are also giant covalent but the atoms are structured differently to graphite. The main differences are 1. There are no delocalised electrons so neither can conduct electricity. All electrons are involved in bonding. 2. Diamond is very hard and can be found in jewellery and cutting blades to prevent the blade becoming blunt too quickly. 3. Diamond and Silicon Dioxide (crystal) can be cut into a fixed shape and used in jewellery and ornaments. The specific structure of both allows light to refract well to give a nice sparkly look! Just like graphite, diamond and silicon dioxide have high melting and boiling points, insoluble, and are good conductors of heat. The structure of Silicon Dioxide and Diamond are the same, take a look at the script to see for yourself. Diamond Silicon Dioxide

Page 5 of 6 Have a go yourself Graphene is just one layer of graphite. Can you suggest possible uses for it and explain your answer. (Visit allerytutors.

5 Page 5 of 6 Have a go yourself Graphene is just one layer of graphite. Can you suggest possible uses for it and explain your answer. (Visit allerytutors.com view the script for this podcast to find out the answer) Answer Used in Electronics Used in portable electronics Tissue Engineering Purification Filters Good conductor of electricity due to delocalised electrons. Light weight due to low atomic mass of carbon. Unreactive and insoluble so less likely to be rejected by the body. Nano scale structure allows water to flow through but not larger microbes. Fi all, let s take a ui k look at dative covalent (coordinate) bonds. This is where both electrons come from the same atom to form a bond. In essence a lone pair of electrons comes from one atom to another one. They are weaker than a standard covalent bond and rely on an atom having a lone pair of electrons. In diagrams it represented by an arrow show the direction of electron donation. An example would be ammonia (NH 3 ) accepting a proton (H + ) from an acid to form ammonium (NH 4 + ). Ammonia has a lone pair of electrons on the Nitrogen however the H + ion has no electrons at all. This ea s a t aditio al o ale t o d a t fo. The lo e pair on the Nitrogen is donated to the H + ion and a dative covalent bond is formed. When drawing the displayed formula we draw an arrow going from the Nitrogen to the Hydrogen. A diagram illustrates this on the podcast script. Have a go yourself. Draw the displayed formula of the product when NH 3 (ammonia) reacts with BCl 3 (Boron Trichloride) to form BCl 3 NH 3. (Visit allerytutors.com view the script for this podcast to find out the answer) Answer If you are still a little stuck then watch my videos on these topi s u de the bonding pla list. Worked through examples are available on all these mini tutorials. Well that s the end of this podcast on covalent structure and bonding. I hope this has proved useful and remember to follow me on or like me on Facebook for all the pre-release info on up and coming videos to my YouTube channel and podcasts.

6 Page 6 of 6 That s all folks! Lo e Che ist!

Ionic and Covalent Bonds

Ionic and Covalent Bonds Ionic Bonds Transfer of Electrons When metals bond with nonmetals, electrons are from the metal to the nonmetal The becomes a cation and the becomes an anion. The between the cation