ch 7: chemical compounds & formulas

What part of a chemical formula indicates how many atoms of each element are present in the compound?

Subscript

The smallest unit of a substance that keeps all of the physical and chemical properties of that substance.

Molecule

The collection of atoms corresponding to an ionic compound's formula such that the molar mass of the compound is the same as the mass of 1 mol of formula units.

Formula Unit

How do cations form?

lose electrons

What is the cation charge?

positive

What is an ion made of two or more atoms?

Polyatomic Ion

How do you write polyatomic ions in compound chemical formulas?

Cation first then anion

How do you write multiple polyatomic ions in a compound chemical formula?

Polyatomic ions in parenthesis

1

mono

2

di

3

tri

4

tetra

5

penta

6

hexa

7

hepta

8

octa

9

nona

10

deca

How are oxyacids named?

Don't name the cation

Acid name comes from the root name of the oxyanion name or its central element

Suffix based on ending of the original name of the oxyanion

Know how to name ionic compounds if given the formula for the compound.

NH4Cl --> Ammonium Chloride

TiBr3 ---> Thalium (II) Bromide

Know how to name a molecular compound if given the formula for the compound.

CO2 ---> Carbon Dioxide

N2O5 ---> Dinitrogen Pentoxide

Know how to write the formula for both molecular and ionic compounds if given the name.

Chromium (VI) Phosphate ---> Cr(PO4)2

Chromium (III) Hydroxide ---> Cr(OH)3

Know what oxidation numbers are and how we use them.

Assigned to atoms composing a compound.

Oxidation Rule 1

A pure elements oxidation number is zero.

Oxidation Rule 2

The more electronegative element in a binary compound is assigned the number equal to the negative charge it would have as an anion. The less electronegative atom is assigned the number equal to the positive charge it would have as a cation.

Oxidation Rule 3

Fluorine is always -1; it is the most electronegative

Oxidation Rule 4

Oxygen is almost always -2, Except in peroxide it is -1, with Fluorine (OF2) it is +2

Oxidation Rule 5

Hydrogen is +1 in all compounds containing more electronegative elements; with metals Hydrogen is -1

Oxidation Rule 6

Sum of oxidation numbers must equal zero.

Oxidation Rule 7

Polyatomic ions must equal charge of the ion

Oxidation Rule 8

Rules 1-7 apply covalently bonded atoms; Oxidation numbers can also be assigned to atoms in ionic compounds.

Oxidation Rule 9

Monoatomic ion oxidation number equal to ion charge Na+, Ca2+, Cl-

Know how to calculate the formula mass of a compound.

Atomic Weight x # of atoms in an element for each element in the compound, and add them together; unit

Know what the molar mass of a compound or element is and how to calculate it.

Atomic weight x # of atoms in an element for each element in the compound; g/mol

If given a mass of a substance, be able to calculate how many moles of that substance are present. If given a number of moles of a substance, be able to calculate how many grams of the substance are present.

amount in moles x molar mass (g/mol) = mass in grams

mass of element in compound x 1/ molar mass of element= amount in moles

Know what precent composition is and how to calculate it for a compound.

(mass of element in sample of compound/ mass of sample in compound) x 100= % of element in compound

(mass of element in 1 mol of compound/ molar mass of compound) x 100= % of element in compound

Know what the empirical formula for a compound is. Assume it is a 100g sample.

1. Calculate the amount of each element in sample

2)Convert the mass composition of each element in moles

%/mass divide smallest number

If given the % of each element in a compound, be able to calculate the empirical formula of the compound.

%/ element mass; divide answers by the smallest number

If given the empirical formula of a compound and the molecular or molar mass of the compound, be able to calculate the molecular formula for the compound.

x(empirical formula)= molecular formula

x=formula mass/ empirical formula mass= rounded answer