+ Chemical Symbols & Formulas
+ Chemical Symbols All elements in the Periodic Table have symbols that are recognized world wide. It does not matter which country you are in or the language you speak. Example: The element Iron is always identified by Fe and Oxygen is O. The names are not always the same but the symbols are. Fe is iron in Canada, fer in France and fier in Romania.
Chemical Symbols A Chemical symbol is an abbreviation of the name of an element. EX: Nitrogen s symbol is N Element Oxygen Nitrogen Hydrogen Sodium Chemical Symbol O N H Na Capital letter if only one letter. Only first letter capital if more than one letter. Second letter of a symbol is never capitalized.
+ Compounds Two or more atoms bonded together with two or more elements To Identify the elements in a compound we must: Look at the periodic table Compare the letters in the compound to the Periodic table Capital letters mean a new element Lowercase letters go with the capital letter before it Na Cl H F Ne Where do we divide the following? NaFNe
+ Making Compounds When two of different elements share electrons they form a bond Na Na Cl Cl We then see Sodium Chloride (NaCl)
+ Molecules Two or more atoms (can be the same or different element) bonded together
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How would you vote? Would you vote to ban the compound Dihydrogen Monoxide from our school? Here are some of the things it does: Can cause excessive sweating and vomiting Is a major component in acid rain Can cause sever burns in gaseous state Accidental inhalation can kill you It contributes to acid rain It decreases the effectiveness of automobile brakes It has been found in tumors of terminal cancer patients
Chemical Formulas A chemical formula is the combination of symbols that represent a particular compound. The chemical formula indicates which elements are present in the compound and how many atoms of that element are present. Ex. 1: Water molecule H 2 O: 2 atoms of hydrogen, 1 atom of oxygen Ex. 2: Sugar molecule C 6 H 12 O 6 : 6 atoms of carbon, 6 atoms of oxygen, 12 molecules of hydrogen
Subscripts: Written at lower right corner behind the symbol of an element Subscripts only refer to the atom that they are BEHIND. Indicates number of atoms for each element in a compound. No subscript means there is only one atom of that element. H 2 O
+ C O 2 Look at your periodic table. What are the two elements we see in the compound above? How many of each element are used to form Carbon Dioxide? How many atoms, how many elements?
+ H O 2 What is this compound called? What elements bond to form it? How many of each element are there? How many atoms, how many elements?
+ HCl Where do we divide the elements in the molecule? What are the elements? What might this be called? How many atoms, how many elements?
+ Mg Cl 2 What are the elements in this molecule? How many of each element are there? What do you think the name of the element might be? How many atoms, how many elements? Pause B4 Next slide
+ Chemical Formulas - Examples How many atoms, how many elements? Calcium Carbonate (chalk) CaCO 3 1 Calcium atom, 1 Carbon atom, and 3 oxygen atoms Sodium Chloride (salt) NaCl 1 Sodium atom, 1 Chlorine atom Acetysalicylic acid (aspirin) C 9 H 4 O 8 9 Carbon atoms, 4 Hydrogen atoms, 8 Oxygen atoms Acetic acid (vinegar) C 2 H 4 O 2 2 Carbon atoms, 4 Hydrogen atoms, and 2 Oxygen atoms
+ Write the following down for reference. Write how many atoms, and how many elements for future reference.
Coefficients A number written in front of a chemical formula that indicates the amount of molecules. 3NaCl = NaCl + NaCl + NaCl = 3 Sodium, 3 Chlorine Coefficients apply to the entire chemical formula. You multiple the coefficient AND subscript. 2Al 2 S 3 = Al 2 S 3 + Al 2 S 3 = 4 Aluminum, 6 Sulfur
+ Write the following down for reference. 3H 2 SO 4
Parentheses If elements or molecules are inside of PARENTHESES, then the SUBSCRIPT behind the parentheses applies to everything inside. Ba(OH) 2 = Ba + OH + OH = 1 Barium, 2 hydroxide molecules = 1 Barium, 2 Oxygen, 2 hydrogen
+ Chemical Reactions & Equations (LT-13) Recognize evidence of a chemical reaction. (LT-14 Recognize that after a chemical reaction takes place, the new substance has new properties different from the original substance. (LT-15) Recognize what a chemical equation is and whether it is balanced or unbalanced. (LT-16) Relate the Law of Conservation of Mass with chemical equations.
Chemical Reactions The process by which one or more substances change to produce one or more new and different substances. Bonds in compounds get broken or form together in a chemical reaction.
Chemical Equations Chemical equations are used as a shorthand description of a chemical reaction. A Chemical Equation MUST: Have the same number and type of atoms on each side of the yield sign. Have bonds that are broken and/or new bonds which are formed. Charcoal is used to cook food on a barbecue. When the carbon in charcoal reacts with oxygen in the air, the primary product is carbon dioxide Write the following example down of what a chemical equation looks like. C + O2 CO2 Reactants Yields Products
+ Vocabulary Reactants = Everything on the left side of the arrow Yields = The arrow means a reaction has occurred (to produce, produces, to form, forms, yields, gives) Plus Sign = Use a +sign to represent and, plus, reacts with, added to, combines, mixes Products = Everything on the right side of the arrow REACTANTS + REACTANTS PRODUCTS + PRODUCTS
Different types of Reactions (and their equations) Yes you need to write this down. Type What is happening Example A+B AB (Synthesis) AB A+B (Decomposition) A+BC AC + B or (Displacement) AB+CD AC+ BD Two or more elements combine to form a new compound A compound breaks down into elements or smaller compounds Elements/compounds rearrange to form new compounds Fe+ S FeS 2 H 2 O 2 H 2 + O 2 HBr + NaOH ---> NaBr + H 2 O
+ Balancing Chemical Equations Coefficients used to balance chemical equations. # placed in front of a chemical symbol or formula in an equation to balance the equation and follow the law of conservation of mass. SUBSCRIPTS ARE NEVER CHANGED!!!! Chemical Equations show how many atoms or molecules are reacting or formed in the equation. Ex: 4 sodium atoms combine with 2 oxygen atoms to form 2 molecules of sodium oxide. Write the following equation down and count the atoms on the reactants side and the product side. 4Na + O 2 2Na 2 O
+ Balanced or unbalanced? To determine whether or not an equation is balanced, count the atoms for each element on the product and reactant sides of the equation. They must be equal Balanced Unbalanced Cu + O2 ----> Cu2O 2Mg + O 2 2MgO Elements Reactants Products Elements Reactants Products Mg 2 2 O 2 2 Cu 1 2 O 2 1
+ Law of Conservation of Mass (COM) The mass of atoms and molecules is neither created or destroyed in chemical reactions. The # of atoms in the reactants must equal the # of atoms in the products in a chemical reaction.
Law of Conservation of Energy Law of Conservation of Energy -states that energy can be neither created or destroyed in a chemical reaction. Chemical Reactions can be: Exothermic-energy is released (feels warm) exo -out of therm - heat OR Endothermic-energy is absorbed (feels cold) endo -into
+ Law of Conservation of Energy / Mass Chemical Equations must be balanced to represent no new element was created or an element destroyed. 6CO 2 + 6H 2 O + Light Energy = C 6 H 12 O 6 + 6O 2
+ Rates of Reactions How quickly chemical reactions take place. 4 factors affect the rate of reaction. Temperature Concentration Surface area Catalysts and Inhibitors
+ Temperature Higher temperatures produce faster rates of reaction. Particles of the reactants are moving faster and collide more often with more energy.
+ Concentration Concentration - a measure of the amount of one substance dissolved in another. Higher concentrations of reactants = faster rate of reactions
+ Catalysts and Inhibitors Catalyst - substance that speeds up a reaction. Lowers the activation energy of a reaction allowing the reaction to happen more quickly. Example - Enzymes in the body Inhibitor - substance that slows down or stops a chemical reaction. Example - Preservatives added to foods
+ Surface Area Surface area - the amount of exposed surface of a substance. Greater surface area of reactants = faster rate of reaction.
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