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CHEMICAL COMPOUNDS AND FORMULAS
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An Element is a Pure substance containing only one kind of atom.
eLEMENTS An Element is a Pure substance containing only one kind of atom.
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2 or more elements chemically combined Creates a new substance
Compounds Compounds: 2 or more elements chemically combined Creates a new substance
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substance made of two or more atoms
molecule substance made of two or more atoms Can be the same element or different elements
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Compounds, molecules, and elements
K Au Fe Pb I2 O2 CH4 H2O C6H12O6 CaCO3 Compare and Contrast Molecules and Compounds What do you notice? Compounds are 2 or more different atoms Molecules are 2 or more atoms (can be the same or different)
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Chemical Compounds Two or more elements chemically combined and Formed by chemical bonds between atoms. Ionic bonds: form ions – Covalent bonds: form molecules Compounds Have unique chemical and physical properties. The properties of compounds are very different from the properties of the individual elements.
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Chemical Formulas Chemical formulas describe compounds and list the atoms that are present in the compound. NaCl – Sodium chloride (salt) – Na – Sodium, Cl - Chlorine H2O – Dihydrogen monoxide (water) – H – Hydrogen, O - Oxygen – CO2 – Carbon dioxide – C – Carbon, O - Oxygen
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Subscripts H2O – 2 Hydrogen, 1 Oxygen
Numbers written below and to the right of a chemical symbol in a formula. H2O – 2 Hydrogen, 1 Oxygen Tells how many atoms of an element are in each molecule. Only used if more than one atom is present. CAN Never be changed in a formula
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C9H8O4 C = Carbon – 9 atoms H = Hydrogen – 8 atoms
O = Oxygen – 4 atoms 3 elements total atoms
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H2SO4 H = Hydrogen – 2 atoms S = Sulfur – 1 atom O = Oxygen – 4 atoms
3 elements atoms
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C12H22O11 C = Carbon – 12 atoms H = Hydrogen – 22 atoms O = Oxygen – 11 atoms 3 elements atoms
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Coefficients # placed in front of a chemical symbol or formula
Identifies the # of molecules of a substance 2H2O = 2 molecules of H2O 2FeO3 = 2 molecules of FeO3
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Coefficients X Subscripts
To determine the number of atoms using coefficients you multiply the coefficient with the subscript. 2H2O - 2 molecules of H2O = 4 Hydrogen atoms and 2 Oxygen atoms
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2Fe2O3 2 Molecules of Fe2O3 = 2 X 2 = 4 Fe (iron) atoms
2 X 3 = 6 O (oxygen) atoms
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Coefficient Practice: How many atoms are present?
Carbon: 2 atoms Hydrogen: 8 atoms Hydrogen: 4 atoms Oxygen: 4 atoms Hydrogen: 2 atoms Chlorine: 2 atoms
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Using Parentheses Multiply the subscript with each element in parentheses. Al2(SO4)3 Al = 2 atoms of Aluminum S = 3 X 1 = 3 atoms of Sulfur O = 4 X 3 = 12 atoms of Oxygen
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(CH3)2CHOH C = Carbon = 2x1 = 2+1 = 3 carbon atoms
H = Hydrogen = 3x2 = 6+2 = 8 Hydrogen atoms O = Oxygen = only 1 Oxygen atom
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Parentheses H H Ca O O Calcium: 1 atom Oxygen: 2 atoms
Hydrogen: 2 atoms
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Chemical Formulas KNO3 NH4Cl Check out Potassium Nitrate…
How many atoms of nitrogen are present? How many atoms of oxygen are present? How many atoms of potassium are present? Now Ammonium Chloride… NH4Cl How many atoms of chlorine are present? How many atoms of hydrogen are present? How many atoms of nitrogen are present?
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Chemical Formulas Mg(OH)2 Let’s take it up a notch…
Check out Magnesium Hydroxide… Mg(OH)2 Some formulas involve parenthesis. When this happens, multiply EVERYTHING inside the parenthesis by the subscript that is outside. The subscript outside can NEVER be changed. How many atoms of magnesium are present? How many atoms of hydrogen are present? How many atoms of oxygen are present?
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Chemical Formulas Ca3(PO4)2 Check out Calcium Phosphate…
How many atoms of phosphorous are present? How many atoms of calcium are present? How many atoms of oxygen are present?
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Chemical Formulas 6C9H8O4 Let’s take it up a notch again…
Check out the formula for aspirin… 6C9H8O4 The 6 in front of the formula is a coefficient. It tells how many molecules of a compound are present. You multiply the coefficient by EVERYTHING that comes after it. How many atoms of oxygen are present? How many atoms of hydrogen are present? How many atoms of carbon are present?
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