What am I learning? Today I am learning about covalent bonding What am I learning? Today I am learning about covalent bonding How will I know I’ve learnt it?  State simply what a covalent bond is (D)  Draw diagrams to show covalent bonding in molecules (C)  Explain how double covalent bonds occur and draw diagrams (B) How will I know I’ve learnt it?  State simply what a covalent bond is (D)  Draw diagrams to show covalent bonding in molecules (C)  Explain how double covalent bonds occur and draw diagrams (B)

17/12/2015 Topic 3 – Covalent Compounds and Separation Techniques Starter: What is ionic bonding?

Water Methane Carbon dioxide Oxygen Hydrogen chloride EXT: How do you know these? What are the formulae for the following molecules?

17/12/2015 Introduction to Bonding Hi. My name’s Johnny Chlorine. I’m in Group 7, so I have 7 electrons in my outer shell I’d quite like to have a full outer shell. To do this I need to GAIN an electron. Who can help me? Cl

17/12/2015 Covalent Bonding Here comes another one of my friends, Harry Hydrogen Hey Johnny. I’ve only got one electron but it’s really close to my nucleus so I don’t want to lose it. Fancy sharing? Cl H H Now we’re both really stable. We’ve formed a covalent bond.

The “valence” electrons in an atom are the ones on the outer shell. “Co” is a prefix that means joint, with, accompanying. Covalent Bonds are those that involve the sharing of outer electrons. It occurs when non-metals bond with other non-metals only. Oxygen Hydrogen

The “valence” electrons in an atom are the ones on the outer shell. “Co” is a prefix that means joint, with, accompanying. Covalent Bonds are those that involve the sharing of outer electrons. It occurs when non-metals bond with other non-metals only. Oxygen Hydrogen Covalent Bond Hydrogen

H2OH2O

17/12/2015 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 H 2. 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

17/12/2015 Dot and Cross Diagrams H O H Water, H 2 O:

17/12/2015 Dot and Cross Diagrams Oxygen, O 2 : O O

17/12/2015 Dot and cross diagrams Water, H 2 O: Oxygen, O 2 : OH HO O H H 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:

17/12/2015 Dot and cross diagrams Nitrogen, N 2 : Carbon dioxide, CO 2 : Ammonia NH 3 : Methane CH 4 : H H N H H H H H C N N O O C

17/12/2015 Other ways of drawing covalent bonds Consider ammonia (NH 3 ): H H N H H H N H H H N H Bonds formed between non-metals are usually covalent. Common examples are NH 3, CO 2, CH 4, H 2 O etc.

Covalent bonding in methane How do carbon and hydrogen atoms form covalent bonds in a molecule of methane? CH 4 or H C H H H H H H H C

Covalent bonding in carbon dioxide How do carbon and oxygen atoms form covalent bonds in a molecule of carbon dioxide? CO 2 or O C O double bonds 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. O O C

17/12/2015 What am I learning? Today I am learning about the properties of covalent substances What am I learning? Today I am learning about the properties of covalent substances How will I know I’ve learnt it?  State some general properties of covalent substances (D)  Describe the properties of covalent substances (C)  Explain the properties of covalent substances (B) How will I know I’ve learnt it?  State some general properties of covalent substances (D)  Describe the properties of covalent substances (C)  Explain the properties of covalent substances (B)

17/12/2015 Dot and cross diagrams Water, H 2 O: Oxygen, O 2 : OH HO O H H 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:

17/12/2015 Properties of covalent molecules H H Recall our model of a simple covalent compound like hydrogen, H 2 : Hydrogen has a very low melting point and a very low boiling point. Why? 1) The intermolecular forces are very weak so each one of these H 2 molecules doesn’t really care about the others – it’s very easy to pull them apart. 2) When a substance is heated it is the intermolecular forces that are overcome, NOT the covalent bond in each molecule, which is much stronger! Also, the molecules do not carry a charge so covalent compounds usually do not conduct electricity.

Simple molecular covalent compounds These include gases such as hydrogen, methane, oxygen, carbon dioxide and liquids such as water. They have low melting points and low boiling points because there are only weak forces between nearby molecules.

Exam questions Describe the properties of covalent compounds (3 marks) 17/12/2015

Simple molecular covalent compounds They have low melting points and low boiling points because there are only weak forces between nearby molecules meaning less energy is required to break the bonds.

Simple molecular covalent compounds An electric current is a flow of charged particles. The atoms in simple molecular covalent molecules have not lost or gained electrons so there are no charged particles that can move around. Simple molecular covalent compounds are therefore poor conductors of electricity.

Exam questions Describe the electrical conductivity of covalent compounds (3 marks) 17/12/2015

Simple molecular covalent compounds An electric current is a flow of charged particles. The atoms in simple molecular covalent molecules have not lost or gained electrons so there are no charged particles that can move around. Simple molecular covalent compounds are therefore poor conductors of electricity.

17/12/2015 Giant Covalent structures (“lattices”) 1. Diamond – a giant covalent structure with a very ____ melting point due to ______ bonds between carbon atoms 2. Graphite – carbon atoms arranged in a layered structure, with free _______ in between each layer enabling carbon to conduct _________ (like metals) Words – melting, high, electrons, bonds, strong, electricity 3. Silicon dioxide (sand) – a giant covalent structure of silicon and oxygen atoms with strong _____ causing a high ______ point and it’s a good insulator as it has no free electrons O O O O Si O O O O O O Notice that giant covalent structures have very different properties to individual covalent molecules:

Giant molecular covalent compounds These consist of billion of atoms all joined together by covalent bonds. These have high melting points and high boiling points because all the atoms are joined together by these strong covalent bonds and so a lot of energy is needed to break these bonds.

Giant molecular covalent compounds Carbon can form two different types of giant molecular covalent compounds. 1)Diamond which is very hard and so is used in cutting tools. 2)Graphite which is very soft and is used to make electrodes or used as a lubricant.

Giant molecular covalent compounds Diamond All atoms are joined with strong covalent bonds.

Giant molecular covalent compounds Graphite Easily rubs away in layers because although the covalent bonds within the layers are strong, there are only weak forces between the layers.

17/12/2015 Using Covalent Structures Form of carbon PropertyUsesWhy? Carbon – diamond Very hardDrill tipsExtremely strong covalent structure GraphiteSoft, conducts electricity Lubricants and making electrodes Graphite is arranged in layers that can slide over each other and it contains free electrons.

17/12/2015 What am I learning? Today I am learning about separation techniques What am I learning? Today I am learning about separation techniques How will I know I’ve learnt it?  Describe some techniques for separating miscible and immiscible liquids (C)  Explain the science behind the separation techniques (B) How will I know I’ve learnt it?  Describe some techniques for separating miscible and immiscible liquids (C)  Explain the science behind the separation techniques (B)

How do you separate oil and water?Immiscible

17/12/2015 Separating Immiscible Liquids “Immiscible” means “two liquids that can’t be dissolved”, e.g. oil and water: Separating these liquids is fairly easy – you simply allow them to settle and then “tap off” the heavier liquid at the bottom using a separating funnel.

17/12/2015 Separating miscible liquids Miscible liquids are liquids that have dissolved together, so separating them is much harder. Here’s an example – distillation: This apparatus can be used to separate water and ethanol because they have different _____ ______. The ______ will evaporate first, turn back into a _______ in the condenser and collect in the _______. The water remains in the round flask, as long as the _______ does not exceed 100 O C. Words – temperature, boiling points, ethanol, beaker, liquid

Fractional distillation Remember from core…

17/12/2015 Fractional Distillation of Air Air can be distilled in the same way – you simply have to get it cold enough first: Liquefied air at -200 O C Gaseous nitrogen out at -190 O C Liquid oxygen out at -185 O C

17/12/2015 What am I learning? I am learning about chromatography as a separation technique What am I learning? I am learning about chromatography as a separation technique How will I know I’ve learnt it?  Describe the method of chromatography as a separation technique (C)  Carry out the method for producing a chromatogram (C)  Calculate the Rf values using a chromatogram (B) How will I know I’ve learnt it?  Describe the method of chromatography as a separation technique (C)  Carry out the method for producing a chromatogram (C)  Calculate the Rf values using a chromatogram (B)

17/12/2015 R G B XChromatography Chromatography can be used to separate a mixture of different inks. Some example questions… Z 1) Ink X contains two different colours. What are they? 2) Which ink is ink Z made out of?

17/12/2015 R f value The Rf value is a way of measuring how far a substance has moved: R G B This line marks the distance travelled by the solvent R f value = Distance travelled by substance Distance travelled by solvent

17/12/2015 Example questions Calculate the R f values of the following: R G B 10cm 2cm 8cm 5cm

359 Foods Containing Colouring Sudan 1 Recalled he Food Standards Agency has announced the recall of another 100 foods, bringing the total to 359, found to contain the illegal colouring Sudan 1, which is linked to cancer. Sudan 1 (bright red dye), also used in shoe and floor polish, has been banned in foods since 1995 in the UK. In this recent scare, Sudan 1 inadvertently got into the foods th May 2006 T How could we test this ?

17/12/2015 Using Chromatography Chromatography can be used to test which foods contain which ingredients. For example, consider the dye Sudan 1, which was found in 450 foods in Which dye contains Sudan 1? Sudan 1 Dye 1 Dye 2 Dye 3