By Chantelle Dickie, Produced in 2003 As you go through this self-paced tutorial, follow the instructions carefully. You will need your periodic table as you work through the tutorial. Click on the left mouse button to move to the next screen or to reveal answers. Make sure that you try to figure out the answers for yourself before revealing the correct ones. There’s no need to hand in anything for this. It’s entirely for your benefit! In this tutorial, you will review atomic structure and Bohr models. You will also learn how to use your knowledge of atomic structure to predict what happens… If you already remember the basics of atomic structure, click on the icon below to skip the review. Atoms are made up of three types of subatomic particles. Before clicking to see the answers, see if you can fill in the table below on your own: Name 1. Protons 2. Neutrons 3. Electrons Location Type of charge In the nucleus Positive In the nucleus No charge Spinning around the nucleus Negative Protons and neutrons in nucleus Electrons 7 p+ 7n 12 p+ 12 n Nitrogen Magnesium Do you need review of Bohr models? Try to predict what the Bohr models above will look like when completed. Once you think you know, click once to reveal the answer. If you’re already a pro, you may find this review “Bohr”-ing so click the icon to skip it. Remember, Bohr’s theory has three main ideas: Electrons move around the nucleus of the atom in orbits (sometimes called shells). Orbits or shells Electron travels around the nucleus (like a runner around a track) Nucleus It may help to think of these orbits as layers of an onion! Each orbital is a certain distance away from the nucleus of the atom and can hold a specific number of electrons. 1st orbit 2nd orbit Nucleus 3rd orbit Maximum number of electrons 1st orbit 2nd orbit 3rd orbit 2 8 8 After the orbital closest to the nucleus is full, electrons start filling the next orbit, and the next. First, count how many electrons you have in total (equal to the atomic number). Let’s say 11 for this example. Then you can start filling the orbitals. Two electrons can fit in the first orbital. Next, count how many electrons you still need a “home” for. We have 9 left, so not all of them will fit into the second orbital. Put in the eight that do fit and… That leaves one to fit into the third orbital. Here are more practice questions. Make sure you figure out the answer by yourself before clicking to see if you got it correct. 8 p+ 8n 14 p+ 14 n 3 p+ 4n Oxygen Silicon Lithium (Atomic Number = 8, Atomic Weight = 16) (Atomic Number = 14, Atomic Weight = 28) (Atomic Number = 3, Atomic Weight = 7) Still need more help? Go back to your class notes and review before continuing. When atoms come towards each other, which of the subatomic particles do you think will determine how the atoms will react? Click on the answer you think is correct. Protons Neutrons Electrons Remember, protons and neutrons are “hidden” away in the nucleus so they won’t come into contact with the other atoms. Since they don’t “touch” the other atoms, the protons and neutrons don’t have a say in how the atoms will react. Click here to try again. You’re right! Since the electrons are spinning around outside the nucleus, they are the subatomic particles that would “touch” the other atom’s electrons first. Now we can use what we know about our Bohr models to predict just how the atoms will react with each other. Atoms want to be happy. Do you know what makes atoms happy? They’re pretty easy to please… All they want is a full outer orbital. It doesn’t matter to them whether it’s the 1st, 2nd, 3rd or 7th orbital. They just don’t want to have any orbitals with any space for electrons. 8 p+ 8n Full = 3 p+ 4n 14 p+ 14 n Empty = To get a complete outer orbital, atoms depend on other atoms. This is why atoms form compounds. A compound is a combination of 2 or more atoms. For example, CO2 and H2O O C O Carbon dioxide Water There are two ways that atoms can combine to get a complete outer shell. To see if you can figure out the two ways, consider these situations: 1) You have 20 candies, but only want 18 of them. Your friend has 8 candies and would like 10. Is there any way you could you solve this problem? You could give your friend 2 candies. 2) You have a car (and a license) but your little brother doesn’t. How can he get to school? You could give him a ride and SHARE the car. Atoms use the same ideas that you came up with to get a full outer shell. Ionic bonding is the the type of bonding that happens when atoms decide to give or take electrons from another atom. It happens between a metal and a non-metal. For example, when sodium and chlorine react, sodium gives one electron to chlorine. To figure out whether atoms will gain or lose electrons when they form compounds, we look at their combining number. The combining number is usually found on the periodic table in the box for each element above and to the right of the symbol. Atomic number Symbol Atomic mass Name 9 F -1 Combining number 19.00 Fluorine If the combining number is positive (+), the atom will lose electrons. If it’s negative (-), the atom gains electrons. See if you can fill in this table before clicking to reveal the correct answers. Element Gains or loses? How many? Magnesium Combining Number +2 Loses 2 Phosphorus -3 Gains 3 Oxygen -2 Gains 2 Boron +3 Loses 3 Zinc +2 Gains 2 Back to our candy story. How might you solve the problem if you want 2 pieces of candy but your friend only has 1 to give away? I’d find another friend who wants to give away one candy and take one from each of them. Atoms do the same thing. For example, oxygen wants 2 electrons and magnesium can only give 1 electron. How many magnesium atoms do you think would combine with one oxygen? 2 magnesium Mg2O 1 oxygen There’s an easy way to figure out how many of each atom will be in the compound. I’ll tell it to you (‘cause that’s just the kind of person I am!) 1)Put down the symbols of the ions, add brackets around any complex ion. Write the positive (metallic) ion first. e.g. Ca Cl 2) Put combining numbers above each symbol. e.g. Ca+2Cl-1 3) Cross out the positive and negative, criss-cross the combining numbers and use them as subscripts. e.g. Ca+2 Cl-1 Ca1Cl2 = CaCl2 It’s almost that easy! There are just a few more rules you need to know… * If an element has a subscript of one, you don’t need to use it. i.e. Na1Cl1 = NaCl * If there are subscripts that can be reduced, you must reduce them. Remember, they can be reduced if there’s a smaller number that can divide into both numbers equally. i.e. Mg2O2 = MgO C2O4 = CO2 Here are some for you to try. Remember to figure them out for yourself before you click on the mouse! Element #1 Element #2 Formula Calcium Fluorine CaF2 Bromine Strontium SrBr2 Magnesium Sulfur MgS Phosphorus Calcium Ca3P2 Scandium Oxygen Sc2O3 Did you have trouble with any of these? Yes No •Did you remember to write the metallic element first? Remember that the metallic elements are found on the left hand side of the periodic table. •Did you remember to cross out the positive and negative signs of the combining numbers? The subscripts shouldn’t have any (+) or (-) in front of them. •Did you remember to cross over the subscripts? •Did you remember to reduce the subscripts? You are now finished this tutorial. By now, you should know: •The structure of atoms •How to draw Bohr models of atoms •What an ionic bond is •How to predict the chemical formulas of compounds If you have any questions about the information in this tutorial, please come and see me!!