Transcript File
Formulas HOW TO WRITE THEM 1st – Definition A symbolic representation of a compound or molecule Why do they Combine? Atoms Strive to meet two conditions 1. To be neutral - By having the same # of electrons and Protons 2. Have the same # of electrons as a Noble gas - Being nonreactive is the most stable Can they have both at the same time? NO Having the same number of electrons as a Noble gas is more desired They must gain or lose electrons - What would happen to their charge if they gained an electron? Negative - What would happen to their charge if they lost an electron? Positive SOME DEFINITIONS - Ion – an atom that has a charge - Oxidation number – The charge an atom has is called it’s oxidation number. - Valence electrons – The number of electrons on the outside edge of an atom’s outer orbit - Maximum of eight How can there be only eight when some of the orbits can hold more than eight? Well . . . Think of an orbit as having a thickness where: The 1st orbit is only thin enough to hold 2 electrons The 2nd orbit can only hold one thickness of 8 electrons But the 3rd and the 4th orbits are so thick that the electrons are spread out between the inside edge and the out side edge. 1st 2 electrons 2nd 8 electrons 3rd 18 electrons 4th 32 electrons Only eight can be on this outside edge and the rest are inside somewhere Using the periodic table to know what charge an atom takes - Remember that the atoms want the same number of electrons as a Noble gas Examples Cl 17 Protons 17 Electrons Noble Gas 18 Difference -1 O N Na Mg F Br 8 8 10 7 7 10 11 11 10 12 12 10 9 9 10 35 35 36 -2 -3 +1 +2 -1 -1 Subtract the noble gas electrons from the element electrons and that is the charge Bellringer 11/19 *Keep this one in your notes. We will NOT be taking it for a grade! 1. DEFINE AN OXIDATION NUMBER. 1. DEFINE A SUBSCRIPT. 1. WHAT IS THE OXIDATION NUMBER FOR CHLORINE? +1 +2 +3 4 -3 -2 -1 1. SYMBOL: Write the symbol for each element 2. OXIDATION: Add their oxidation numbers 3. PLUS: Put a plus sign between the ions and add an arrow pointing to the right 4. FORMULA: Write the Formula so that the total net charge equals zero 5. BALANCE: Determine how many atoms of each to do this Sally Offered Peter Four Bananas Symbol Oxidation Plus Formula Balance For Example: -Combining Sodium and Chlorine 1. First write their symbols 1. Na 2. +1 3. + 1. Cl 2. -1 3. 4. NaCl (+1) + (-1)= 0 2. Then add the oxidation numbers 3. Put a plus sign and draw an arrow pointing to the right 4. Write the formula (Positive is always 1st) The charges add up to be zero (balanced) Another Example: Magnesium and Fluorine +2 Mg + F - Subscript – The small number below and to the right of the symbol that denotes the number of atoms in a formula. Remember the positive one first! -1 MgF 2 One Mg ion (+2) + Two F Ions (-1) + (-1) = 0 One Mg plus two F charges will add up to be zero. Practice Problems: 1. Potassium and Sulfur K+1 + S-2 K2S 2. Strontium and Bromine Sr+2 + Br-1 SrBr2 3. Lithium and Oxygen Li+1 + O-2 Li2O 4. Calcium and Iodine Ca+2 + I-1 CaI2 5. Aluminum and Chlorine Al+3 + Cl-1 AlCl3 6. Gallium and Oxygen Ga+3 + O-2 Ga2O3 7. Aluminum and Oxygen Al+3 + O-2 Al2O3 8. Boron and Sulfur B+3 + S-2 B2S3 One more rule for the Transition Metals -Transition metals are called that because their ion charge can be one charge in one reaction and a different one in another -Since they are in a state of transition, it is unknown what charge they are for writing formulas - For this reason, a roman Numeral is assigned to represent the charge For example: Iron (III) would be written like this : Fe+3 and Cobalt (IV) would be written like this: Co+4 Here are the Roman numerals up to Fifteen: 1- I 6- VI 11. XI 2- II 7- VII 12. XII 3- III 8- VIII 13. XIII 4- IV 9- IX 14. XIV 5- V 10- X 15. XV -Roman Numerals tell you two things: -It is a Transition metal - It is a Positive Charge that matches the roman numeral Practice Problems: 1. Iron (I) and Sulfur Fe+1 + S-2 Fe2S 2. Lead (IV) and Bromine Pb+4 + Br-1 PbBr4 3. Cobalt (II) and Oxygen Co+2 + O-2 CoO 4. Copper (II) and Iodine Cu+2 + I-1 CuI2 Fe+3 + Cl-1 FeCl3 5. Iron (III) and Chlorine 6. Mercury (I) and Oxygen Hg+1 + O-2 Hg2O 7. Copper (III) and Oxygen Cu+3 + O-2 Cu2O3 8. Silver (II) and Sulfur Ag+2 + S-2 AgS More Problems: Write the symbols with the charges, arrow, and final formula. O and H Li and Cl Na and Po K and Br Mg and I Ca and O Al and S Ca and F Fr and Te Ba and N Na and P Be and At