Bolton Sixth Form College CHEMISTRY DEPARTMENT

Transcription

1 Bolton Sixth Form College CHEMISTRY DEPARTMENT Pre-Enrolment Induction Task Summer 2016 In order to get you fully prepared for A-Level Chemistry, we have set you the following assignment. We will be using the skills and understanding shown in this task in the first few lessons of chemistry and then throughout your chemistry course. Your work must be handed in at your first Chemistry lesson or can be uploaded in advance of the first day of teaching, Monday 5 th September. You can access the pre-induction tasks from the 'New Student Portal' ( and there is a link to the 'New Student Portal' from the College website. The pre-induction tasks are available to download from here and once you have already registered on the portal you can upload any completed tasks via the upload page. If you have any problems registering or logging onto the portal please contact the College on There are 2 parts to this activity. You need to print the pages of the assignment and read the introductions to each part. You should then answer the questions in the spaces provided as fully as you can. Name Structure and bonding Read the following information about structures and bonding and then answer the questions that follow Part A Structure and bonding 1: Ionic structures An ion is a charged particle. Ionic bonds are made between metals and non-metals, e.g. sodium chloride. Metals are elements which form positively charged ions. In ionic compounds, the non-metal will be the negatively charged ion. Non-metals include hydrogen and elements found on the right hand side of the periodic table. The overall charge on the compound is zero. In ionic compounds a lattice (a regular structure) is formed in which each positive ion is surrounded by 6 negative ions and vice versa like this: Sodium ion Chloride ion

2 This lattice is a very strong type of structure because a) ionic bonds are strong b) there are 6 ionic bonds per ion. The force between positive and negative is called electrostatic. To melt an ionic compound, you have to break these strong electrostatic bonds between oppositely charged ions, so the melting point is high. 2: Metallic structures Metallic bonding forms inside metals, e.g. in Sodium. In metallic bonding, the metal atoms lose their outer electrons and become positive these positive ions form a regular structure like this: + Sodium ion Electron The outer electrons form a sea of delocalised electrons which attract and hold the positive ions together. When you melt a metal, you have to overcome the strong attraction between the positive metal ion and the delocalised electrons, so the melting point is high. 3: Covalent structures Covalent structures are made when 2 or more non-metals bond together. There are 2 types of covalent structure: a) macromolecular (giant molecular) which occurs in diamond, graphite, silicon and silicon dioxide (sand). b) simple molecular which happen in most other situations between non-metals. Macromolecular Diamond is made of carbon it forms a giant lattice structure in which each carbon makes covalent bonds to 4 other carbons, like this: Carbon atom This is a very strong structure due to having a large number of strong covalent bonds. To melt diamond, you have to break many strong covalent bonds, so the melting point is high.

3 Graphite is also made of carbon it forms layers in which each carbon is covalently bonded to 3 other carbons like this: Carbon atom The 4 th electron from each carbon is lost and forms a sea of delocalised electrons between the layers. The layers are attracted to each other by weak intermolecular forces, which can be broken if pressure is applied, so layers of graphite in pencils are transferred easily onto your page. However, to melt graphite, you have to break the strong covalent bonds. Simple molecular Simple molecules each have their own individual structures, but inside each of these structures are covalent bonds. An example is water. The molecules in water are H 2O. The molecules attract each other by weak intermolecular forces (Hydrogen Bonding): Intermolecular force Oxygen atom Hydrogen atom When you melt water or any simple molecule, you overcome weak intermolecular forces so the molecules are free to move. You do not break the strong covalent bonds inside each molecule, so the melting point is relatively low. Part A questions Use the periodic table to help you answer these questions and the information you have just read. 1. Which of the types of structure mentioned in the information you have just read, do you expect each of the following substances to form. Substance name Magnesium oxide (MgO) Water (H 2O) Ammonia (NH 3) Lithium fluoride (LiF) Silicon (Si) Chlorine (Cl 2) Iron (Fe) Titanium (Ti) Oxygen (O 2) Diamond (C) Type of structure

4 2. What type of bonds do you break, or what type of forces do you overcome, when you melt the following Ammonia (NH 3 molecules) Paraffin wax (a hydrocarbon) Diamond Sodium oxide (Na 2O) Copper 3. Explain why water has a lower melting point than diamond. (3) 4. Explain why diamond is a very hard substance. (3) 5. Draw a picture in the style shown in Part A to show the structure of potassium bromide (2) 6. Draw a picture in the style shown in Part A to show the structure of potassium. (2)

5 Extension 7. What are intermolecular forces? Give examples. (Research) (include information below or on a separate sheet) Part B formulae of simple ionic compounds (Stretch and challenge) Use the periodic table: You will notice that the groups of the periodic table are labelled either 1,2,3,4,5,6,7,0 or (1)-(18). the first of these two numbering systems for the following. It is easier to use Formation of ions An ion is a charged particle. Ions of opposite charge can bond together. (forming ionic bonds) Ions are formed when an atoms gains or loses electrons to get a complete outer shell Group 1 elements have 1 electron in their outer shell. They lose this electron, which means they lose a negative charge, hence end up with a charge of +1. A sodium ion is written as Na + Group 6 elements have six electrons in their outer shell; they pick up two electrons from their surroundings to complete their outer shell. They now have two extra negative charges: they carry a -2 charge. An oxide ion is written as O 2- Q1. Work out the charge on the ions formed by Group 2, 3, 5(15) and 7 (17) explaining your answer in each case. Group of periodic table Charge on ion Explain why this is the charge:

6 Q2. Give the symbols of the following ions. The first metal ion and the first non-metal ion are done for you as examples. You will need to think which group of the periodic table the element is in. Transition metals can have different charges, so they are given as roman numerals in the name: eg copper(i) is Cu + but copper(ii) is Cu 2+. Metal ion name Symbol of ion Non-metal ion name Symbol of ion Sodium Na + Oxide O 2- Lithium Fluoride Aluminium Sulfide Copper(II) Cu 2+ Chloride Cobalt(II) Nitride Iron(III) Bromide Formula You can use the charge of 2 ions to work out the formula of the resultant compound. This uses the 'crossover' or 'swap-and-drop' method. The total charges now add to 0. e.g. The formula of Sodium oxide: Sodium = group 1= charge of 1+ Na + O 2- Oxygen = group 6 = charge of 2- Na + O 2- Na 2 O 1 Therefore Na 2 O In the above example, the charge numbers are swapped to the other element and written as a subscript. Note that 1 is not written and that the ratio should be simplified, e.g. Mg 2O 2 would be simplified to MgO.

7 Q3. Write the formulae of the following compounds (Show your working): Sodium fluoride, Aluminium oxide, Lithium sulfide, Aluminium nitride, Cobalt(II) chloride, Iron (III) oxide. Name of compound Formula of compound Sodium fluoride Aluminium oxide Lithium sulfide Aluminium nitride Cobalt(II) chloride Iron(III) oxide Balancing Equations Q4. Balancing a Chemical Equation is very important in order to work out the mass of substances or concentrations needed for the production of products. It is important that you practice these and are confident with them before the start of the course. There are different methods for balancing equations. The number of atoms must be the same on both sides of the equation. By only putting numbers in front of the formulas, write out the balanced equation for the reactions below. (a) N 2 + H 2 NH 3 (b) H 2 + O 2 H 2O (c) SO 2 + O 2 SO 3 (d) Na + Cl 2 NaCl

8 (e) H 2 + Cl 2 HCl (f) Fe + Cl 2 FeCl 3 (g) Na + H 2O NaOH + H 2 (h) K + H 2O KOH + H 2 (i) HCl + Ca(OH) 2 CaCl 2 + H 2O (j) HCl + Ba(OH) 2 BaCl 2 + H 2O