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Chemical Formulas and Equations

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Presentation on theme: "Chemical Formulas and Equations"— Presentation transcript:

1 Chemical Formulas and Equations
Mrs. Brostrom Integrated Science

2 Chemical Formulas A chemical formula is a shorthand way to use chemical symbols and numbers to represent a substance Shows how many atoms of each kind are present in a molecule methane (CH4), water (H2O), carbon dioxide (CO2) Atom # C 1 H 4 Atom # H 2 O 1 Atom # C 1 O 2

3 A subscript is the number written below and to the right of the chemical symbol in a formula
If there is no subscript than only one atom of the element is present Salt (NaCl), Magnesium chloride (MgCl2) Atom # Na 1 Cl Atom # Mg 1 Cl 2

4 Writing Formulas for Covalent Compounds
Composed of two nonmetals The prefix tells you how many atoms of each element are in the formula Prefix # of Atoms Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10

5 Writing Formulas for Ionic Compounds
Sodium chloride NaCl Na has a charge of 1+ Cl has a charge of 1- (1+) + (1-) = 0 Magnesium chloride MgCl2 Mg has a charge of 2+ (2+) + 2(1-) = 0 Contains a metal and a nonmetal Make sure the compounds charge is 0 or the ion’s charges have cancelled out. Add the suffix -ide to the nonmetal

6 Describing Reactions by Using Chemical Equations
A chemical equation uses symbols and formulas as a shortcut to describe a chemical reaction. The starting materials in a chemical reaction are reactants. The substances that are formed from the reaction are products. C + O2CO2

7 Equations Must Be Balanced
Atoms are never lost or gained in a chemical reaction, they are just rearranged. When writing a chemical equation, the number of atoms in the product must equal the atoms in the reactants. The law of conservation of mass states that mass is neither created or destroyed in ordinary chemical and physical changes.

8 How to Balance an Equation
H2 + O2 H2O To balance equations, you must use coefficients (a number that is placed in front of a chemical symbol or formula). Count the atoms Balance the O atoms Balance the H atoms 2H2 + O2 2H2O Atom Reactant Product H 2 O 1 Atom Reactant Product H 4 O 2

9 Balance the following equations
Na + Cl2NaCl Mg + N2Mg3N2 Na + Cl NaCl Atom Reactant Product Na Cl Atom Reactant Product Mg N Mg N2 Mg3N2 Atom Reactant Product Na Cl Atom Reactant Product Mg N

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