Chapter 3 Chemical Symbols And Formulas Why do we use symbols in chemistry? i. Shorthand less cumbersome than full name ii. Universally understood - better communication across language barriers iii. Flexible can describe ANY chemical compound. A Brief History Of Chemical Symbols 400 BC Democritus suggest concept of atom. 1800s Dalton suggests symbols should be used. Never caught on, too confusing. 1800s Berzelius suggests modern system based on Latin, or first one or two letters of their names. Why Latin? Known to Latin-speaking Romans as well as all those within the very large Holy Roman Empire. Latin was considered the Language of Learning. For several hundred years the Bible was only written in Latin. even new elements are given Latin names 1
Introduction to the Periodic Table and The Families Color PT according to their families Alkali metals Group 1a (green H and ochre Li to Fr) Alkaline earth metals Group 2a (purple Be to Ra) Metalloids pink zigzag. These have both metallic and non-metalic properties. Non-metals light green, ochre and orange on right of table. These include Halogens Group 7a (ochre F to At) Noble Gases Group 8a (orange He to Rn) 2
Properties of metals Shiny Ductile Malleable Conductors Properties of Non-Metals NOT! 3.2 Chemical Formulas chemical formulas combinations of symbols representing a particular compound molecules when two or more atoms are joined together Molecules can be made up of two or more of the same type of atom: Hydrogen H 2 3
Nitrogen - N 2 Oxygen - O 2 Also fluorine - F 2, chlorine - Cl 2, bromine - Br 2, iodine - I 2 4
Sulfur - S 8 but USUALLY they are different atoms water - H 2 O 5
Hydrogen peroxide - H 2 O 2 Carbon monoxide CO, Nitrogen dioxide NO 2, Butane C 4 H 10 6
FORMULAS NAMES Naming Compounds Divide your page into three columns Heading of column I = Metals Heading of Column II = Non-metals Heading of Column III = Leave blank for now When naming a Metal + Non-metal Metal Name : Non-metal root : -ide NaCl KBr Na 2 S Na 3 N MgO 7
When naming a Non metal + non-metal Numerical prefix (if any) : More metallic non metal : Numerical prefix; less metallic non-metal root : - ide Numerical Prefixes Mono -1 Di - 2 Tri 3 Tetra 4 Penta 5 CO CO 2 NO 2 N 2 O 3 CCl 4 Polyatomic -ions Groups of atoms which commonly live together and act as a single ion or atom. Sort of like boys in the hood! 8
Poly Ion Group Formula Combining Capacity carbonate CO 3 2 hydrogen carbonate HCO 3 1 hydroxide OH 1 nitrate NO 3 1 phoshate PO 4 3 sulphate SO 4 2 You can insert these into the Third Column! When naming a Metal + Polyatomic-ion Metal name : Poly-ion name CaCO 3 H 2 SO 4 Be(NO 3 ) 2 9
NAMES FORMULAS Combining Capacity and Writing Formulas The combining capacity is the ability of an atom of that element to combine (form bonds) with other elements. You can think of combining capacity as the number of hooks on an atom. Carbon has a combining capacity of 4. This means an atom of C can join directly with 4 other bonds. Hydrogen has a combining capacity of 1 so one carbon can form bonds with 4 hydrogens. CH 4 So, what are the combining capacities of the atoms in these compounds? Draw it out? What will the formulas be? (Hint: Your Periodic Table lists all the combining capacities of the elements.) Sodium sulfide 10
Magnesium chloride Aluminum bromide Rules of writing formulas: Write the more metallic element first, and the less metallic element second Write combining capacities of both atoms as superscripts. Balance charges (or cross multiply capacities). Simplify if needed. Practice 11
Law of Conservation of Mass matter cannot be created or destroyed during a chemical reaction, you can only change the way it looks. Consider the formation of liquid water from hydrogen gas (H 2 ) and oxygen gas (O 2 ). H 2 + O 2 H 2 O The law of Conservation of matter states that I have to have the same number of hydrogen atoms on each side. Do I? Hint: Say yes, there are 2 on each side! It also says I have to have the same number of oxygen atoms on each side. Do I? Hint: Say No, there are two on the left (reactant side) but only one on the right (product side)! Okay, so what do I do? The only thing I can. Use coefficients to multiply the number of each atom in each molecule until there are equal numbers on each side. How do I learn how to do that? Practice!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Observe: 2H 2 + O 2 2H 2 O Is there equal numbers now? Hint: Say Yup, there are 4 hydrogens on each side and two oxygens on each side! Do you see them? 12
Balancing Equations: + is a road sign that tells you that two chemicals are present together. is a road sign that tells you that the reactants goes to, produces, yields, makes products. Subscripts (little numbers behind an atom) tell how many atoms there are of the element immediately in front of them. Example: In H 2 SO 4 the 2 means there are two hydrogen atoms present and the 4 means there are 4 oxygen atoms present. IF there are brackets around two or more atoms, followed by the subscript, then that subscript multiplies everything within the brackets. Example: In (NH 4 ) 2 SO 4 the first 2 means there are 2 NH4s present. Think! How many N s are present? (2) How many H s? (8) Coefficients (large numbers in front of a molecule) multiply everything between it and the next road sign. Example: In 2H 2 + O 2 2H 2 O 4 H s 4H s 2O s Try these CH 4 + O 2 CO 2 + H 2 O H 2 SO 4 + NaOH Na 2 SO 4 + H 2 O Okay, now try the IFI Handouts 13