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Regents Chemistry Review By Topic: FORMULAS, EQUATIONS AND CHEMICAL REACTIONS

Types Of Formulas


Ionic: ionic compounds contain metal + nonmetal, or metal + polyatomic ion or two polyatomic ions. Metals can be found to the left of the staircase on the Periodic Table. Polyatomic ions can be found in Table E on the Reference Table. Examples: NaCl, KNO3


Molecular: consist of nonmetals only. Nonmetals can be found to the right of the staircase on the Periodic Table. Example: NH3, CO


Empirical: elements will be in their smallest whole number ratios. The subscripts can not be divided further. Example: CH4, NO2


Structural : shows the bonding between atoms in a molecule. Example: O=C=O


Naming And Writing Formulas For Ionic Compounds


Metal + Nonmetal

Name of Metal + Name of Nonmetal ending in "ide"

Example: NaCl = sodium chloride


Metal + Polyatomic Ion

Name of Metal + Name of Polyatomic Ion

Example: Li2SO4 = lithium sulfate


Polyatomic ion + Nonmetal

Name of Polyatomic Ion + Name of Nonmetal ending in "ide"

Example: NH4Cl = ammonium chloride


Polyatomic ion + Polyatomic Ion

Name of the First Polyatomic Ion + Name of the Second Polyatomic Ion

Example: NH4OH = ammonium hydroxide


Ionic compounds with TRANSITION METALS


For metals that can have more than one possible charge, the name of the metal must be followed by a Roman numeral in parenthesis, indicating the charge.


Transition metals are located in the middle of the Periodic Table with atomic numbers 21 through 80.

Trick: The charge of the transition metal is usually (but not always) the subscript of its partner. For example CuI2 is copper (II) oxide


Writing Formula for Ionic Compounds

  1. Separate your compound into two parts and write their formulas.

  2. Identify the charges(oxidation numbers) of the two parts. If you have a Roman numeral, that's the charge of the metal. Group 1= +1 Group 2 = +2 Group 16 = -2, Group 17= -1 Al= +3. If something has a 1, we do not need to write the number 1. If both parts have the same charges/oxidation numbers, they will cancel and we do not have to write them.

Example: Iron (II) oxide

Fe^2+ O^2- = Fe2O2 = FeO


Naming Molecular Compounds


Molecular compounds consists of nonmetals only (usually).


We use prefixes to signify the number of atoms of each element


mono = 1

di = 2

tri = 3

tetra = 4

penta = 5

hexa = 6

hepta = 7

octa = 8

nona = 9

deca = 10


Name of nonmetal with prefix + name of nonmetal ending in "ide" with prefix


Note: We do NOT use prefix mono for the first element.


For example:

N2O4 = dinitrogen tetroxide

CO = carbon monoxide


Balancing chemical equations:

We balance chemical equations by putting coefficients in front of molecules. The coefficient gets distributed to all atom in the molecule. For example 2NH3 means two nitrogen atoms and 2*3=6 hydrogen atoms.

In a balanced equation, the number of atoms of each element on the left of the arrow will be equal to the number of atoms of each element to the right of the arrow.


Types of Chemical Reactions:

Synthesis = two or more reactants come together to form one product A+B--> AB

Decomposition = opposite of synthesis, one reactant breaks into multiple products.

AB --> A+B

Single Replacement= one element replaces another element that is a part of a compound A +BC --> AC +B

Double Replacement = two elements in two compounds replace one another. Think of two dancing couples switching partners. AB +CD --> AD +CB


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