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West Lothian Council Lorna C. Webster 1 Atomic numbers Read You already know that elements are made up of tiny particles called atoms. The atoms of different elements are not the same. For example, iron atoms are a different size and weight from gold atoms. Every element has been given a special number called the atomic number. The atomic number can be found on a periodic table for example on pages 1 and 8 of the data book. Look up a data book page 8. You can see from the key what each piece of information means. key Atomic number Name of element symbol 4 Beryllium Be You can see from the key that the element called berylllium has an atomic number of 4. Look up the box for phosphorus and you will see that it has an atomic number of 15. key Atomic number Name of element symbol 15 Phosphorus P Write a heading and try the work below. 1. What are the tiny particles called that elements are made from? Lorna C. Webster 2 2. Are iron atoms the same as gold atoms? Explain your answer. 3. What pages in the data book would you look at to find the atomic number for an element? 4. Copy the boxes above to show how you can work out the atomic number for beryllium. 5. Copy the tables below and fill them in with 20 elements of your choice. Element name atomic number Element name atomic number Ask your teacher if your should do the sheet called “data book exercise”. Lorna C. Webster 3 Molecules and bonds Read Some substances are made up of molecules. A molecule is a group of atoms that are joined together. The join between the atoms is a kind of chemical glue called a bond. A molecule of hydrogen would look like: H atom H bond atom A molecule of water would look like: O H H The bond between the atoms are very strong. Write a heading and try the work below. 1. Explain what a molecule is? 2. Explain what a bond is? 3. Draw a molecule of water and label the atoms and the bonds. 4. Are the bonds between the atoms weak or strong? Lorna C. Webster 4 Read A beaker of water does not only contain one molecule it contains billions of molecules. There is chemical glue holding the different molecules together. This glue is also called bonds but the bonds between molecules are only weak. weak bond O atom H H O H atom H O atom H H Strong bond Continue your work by answering the questions below. 5. A beaker of water contains many molecules of water. What is the chemical glue called that holds them together. 6. Copy the diagram above to show the atoms, strong bonds and weak bonds in a beaker of water. 7. Copy and complete the sentences below. A molecule is a small group of a______ joined together by b_______. The bonds between atoms are s_______ but the bonds between molecules are w______. Lorna C. Webster 5 Substances and ions Read Not all substances are made from molecules. Some substances are made from particles called ions. An ion is a charged particle. An ion can be positively or negatively charged. Substances that are made from ions are called ionic compounds and contain both positive and negative ions joined together by strong bonds. Your teacher may show you a model of the ions in an ionic compound. ions Strong bonds Write a heading and try the work below. 1. What is an ion? 2. What type of charge can an ion have? 3. What type of compounds are made from ions? 4. Are the bonds between ions strong or weak? 5. Collect a copy of the ionic compound diagram and choose two colours to colour in the positive and negative ions before you stick it into your jotter. Lorna C. Webster 6 Read Substances can be solids, liquids or gases at room temperature. In the next experiment you will find out a rule for the state of ionic and molecular compounds. 6. Copy the table below and fill it in using display 4. Substance Molecular or ionic Solid, liquid or gas salt water oxygen polystyrene fertiliser petrol sulphur baking soda methane epsom salts 7. Copy and complete the rule below. Ionic substances are always s________ at room temperature but molecular substances can be s______, l________ or g_____ at room temperature. Lorna C. Webster 7 What about conducting electricity? Read You should already know from S1 and S2 that metals can conduct electricity but what about whether ionic substances or molecular substances conduct electricity. The aim of the next experiment (1.39) is to find out if ionic substances or molecular substances can conduct electricity. The experiment we will use will be set up as shown in the diagram below. power pack 4V AC leads A ammeter carbon electrodes substance being tested Write a heading and try the work below. 1. What is the aim of the experiment (what are you trying to find out? 2. What do you think will happen? 3. Draw a diagram of the experiment before you start. 4. Carry out the experiment by going to each station and connecting up the circuit. Then design a table for your results. 5. Now write a conclusion (what did you find out about the ionic and molecular substances?). Lorna C. Webster 8 What about melting and boiling? Read Ionic and molecular substances are not only different in conduction of electricity, they are also different in how they melt or boil. The stronger the bonds in a substance, the more heat is needed to make the substance melt. Write a heading and try the work below. 1. John has two chemicals labelled A and B. He knows that the bonds in substance A are stronger than the bonds in substance B. Which one will he need to heat up more to make it melt? 2. Copy the table below and complete it using the melting and boiling point chart. Name of substance Phenol molecular or ionic? melting point boiling point in C in C Calcium oxide Naphthalene Sodium bromide 3. Which type of substance always has high melting points and boiling points? 4. Collect and complete the types of substances summary sheet and stick it into your jotter. Lorna C. Webster 9 Molecules and formulae Read You have now looked at molecular and ionic substances and the last section of this booklet is about molecules and formula. A formula is just a short way to show how many atoms are present in a molecule. There are two rules that we need to remember about writing formula: Numbers always go after the symbols We do not write the number one Look at the molecule that is shown below. H H H C C H H O H This molecule has two carbon atoms, six hydrogen atoms and one oxygen atom so it will have the formula: C2H6O All that we have done is counted the atoms and put in numbers after the symbols. Lorna C. Webster 10 Write a heading and try the work below 1. What are the two rules for writing formula? 2. Copy the molecule that is show on page 10 and explain why it has the formula C2H6O. 3. Use a data book to copy and complete the table below. Colour of atom Black White Red Green Yellow Blue element name Carbon Hydrogen Oxygen Chlorine Sulphur nitrogen element symbol C 4. Now look at the molecules that your teacher has put around the classroom and for each one: Draw it Colour it in Work out its formula. 5. Which molecules show elements? 6. Explain your answer to question 5. 7. Which molecules have the same formula but a different shape? 8. Collect a model kit and build five of your own molecules. The rules are that you must use the grey bonds and make sure all of the holes on the atoms are full. For each one draw it colour it in and write it’s formula. Your teacher may now ask you to do experiment 1.37. Follow the instructions on the card and present your answers in a table with two headings. Lorna C. Webster 11 Compound names revisited Read You already know that the name of a chemical tells us about the elements that are present. If the name ends in ide the chemical contains two elements. The first part of the name tells us one of the elements. The second part of the name gives us a clue to the name of the second element. eg sodium chloride contains the elements sodium and chlorine (we need to check a data book for the full name of the second element). eg magnesium oxide contains the elements magnesium and oxygen. Write a heading then copy and complete the sentences below to make sure you understand how to do this before you start the next page. Magnesium chloride contains the elements ______________ and __________. Sodium oxide contains the elements ______________ and ______________. Potassium chloride contains the elements ____________ and _____________. Barium oxide contains the elements ___________ and ____________. Nitrogen hydride contains the elements ___________ and _____________. Carbon sulphide contains the elements ____________ and _____________. Lorna C. Webster 12 Names and prefixes Read The name of an object sometimes tells us about the object. For example a tricycle has three wheels; an octopus has eight legs. a triangle has 3 sides a pentagon has 5 sides The little bit that has gone at the beginning of the word is called a prefix. Prefixes have different meanings. prefix meaning mono 1 di 2 tri 3 tetra 4 penta 5 hex 6 hept 7 oct 8 The prefix tells us more about the chemical but does not change the elements that are in it. For example carbon tetrachloride is the same as carbon chloride so it will still contain carbon and chlorine; carbon dioxide will still contain carbon and oxygen. Write a heading and try the work below. 1. How do you know that a tricycle has three wheels? 2. What does the word octopus tell you about the animal? 3. What are the little bits that go infront of words called? 4. Copy the table above that shows the meanings of prefixes 1 to 8. Lorna C. Webster 13 5. Copy and complete the sentences below Sulphur dioxide contains ___________ and __________. Sulphur trioxide contains _________ and ____________. Carbon monoxide contains ____________ and ___________. Nitrogen dioxide contains andoften ____________. If we know the name of a ___________ substance we can work out its Phosphorus pentachloride ___________ and _______. formula even if we cannot contains see the atoms to count them. Silicon tetraflouride contains ____________ and __________. For example you might already have heard the name of a gas Formula and prefixes Read Sometimes we can work out the formula of a molecule even if we cannot see the molecule to count the atoms. We can do this if the name has a prefix in it. Carbon tetrachloride contains carbon and chlorine but tetra means four so this tells us that there are four chlorine atoms. There is not a prefix infront of the carbon part of the name so this means that there is only one carbon atom. The symbol for carbon is C and the symbol for chlorine is chlorine Cl. The carbon The formula for this molecule will be Lorna C. Webster 14 CCl4 You might have heard of a poisonous gas called called carbon monoxide. The diagram below shows you how you can use the name to work out the formula of this gas. Carbon monoxide This tells us the molecule has a carbon atom in it. This tells us there is one oxygen This tells us the molecule has oxygen in it. So the formula will be CO (remember we don’t write one’s in chemistry). Another example is shown below Carbon dioxide This tells us the molecule has a carbon atom in it. So the formula will be This tells us there are two oxygen atoms. This tells us the molecule has oxygen in it. CO2 Write a heading and try the work below. 1. Copy the diagram showing how to work out the formula for the posonous gas called carbon monoxide. Lorna C. Webster 15 2. Copy and complete the table below name carbon dioxide elements present carbon and oxygen formula carbon and chlorine nitrogen and oxygen CCl4 CO2 carbon monoxide sulphur dioxide sulphur monochloride carbon tetrafluoride Phosphorus trihydride Uranium hexafluoride diphosphorus trioxide dinitrogen oxide Diphosphorus pentoxide Lorna C. Webster 16 NO2