Chapter 3Molecules & Compounds

3.1 Molecules, Compounds and FormulasEmpirical Formulas

Definition: the simplest whole number ratio for the formula of the elements in a compound

Examples: NaCl, MgCO3, AlBr3 Ionic Compounds: a compound

consisting of oppositely charged ions held together by electrostatic attractions

Molecular Formulas Definition: a formula consisting of the

exact number of atoms of each element in a molecule of a compound

Examples: C6H12O6, CO2, SiO2

Molecular formulas Condensed structural formulas –

formulas depicting some of the bonding by groupings CH3OH , CH3CH2CH2Cl

Structural formulas

A two dimensional representation of the atoms and bonds

3.3&3.4 Ionic Compounds: formulas, Names and properties Definition: compounds containing a

cation and an anion electrostatically bonded (due to transfer of electrons)

Binary Ionic Formulas – binary means two ion types in the compound

Charges for Main Group Elements+1,+2,+3, skip, -3,-2,-1, NG

Examples

Li and O

Now you try…

Binary compound namingThe metal goes first always – element nameThe nonmetal goes second with an –ide at the end

MgS – magnesium sulfideKeep going

6. Transition Metals+Triangle Stock system – a system of using

Roman Numerals to name transition metal and triangle cations; the Roman Numeral is the charge on the metal ion

Ex 3.3Co (I) and INi (II) and Cl

One more time…keep on going

Transition Metals+Triangle that don’t get R.N.’s Al+3 Zn+2 Cd+2 Ag+1

Polyatomic ions:

Multi-atom ions that are covalently bonded within the ion; keep their names with no ending changes!

Memorize the flash cards provided

Ex 3.4 NaNO3

NaNO2

Your turn …

Properties of ionic compounds Characterized by the electrostatic

attraction between elements Solids at room temperature High melting points Brittle Conduct electricity in the molten state Conduct electricity as solutions

(electrolytes)

Molecular Compounds: formulas, names and properties smaller compounds are gases and

liquids at room temperature Large compounds have low melting

points, are brittle, and characterized by covalent bonding

Writing formulas: prefixes Mono 1 Di 2 Tri 3 Tetra 4 Penta 5

Hexa 6 Hepta 7 Octa 8 Nona9 Deca 10

Naming system: Keep the order of the elements Prefix plus element name for first name Prefix plus element name and –ide ending

for last name Drop mono- prefix from all first names DO NOT REDUCE FORMULAS!

Name the following molecular compounds P2O7

SCl3 CF4

N2O5

CO CO2

H2O

Write the formulas for: Diboron trioxide Tetraphosphorus trisulfide Arsenic pentoxide Phosphorus trichloride Diarsenic heptoxide

3.6 Formulas, Compounds, and the MOLE Representative Particles:

Molecule – 1 unit of covalent cmpd; H2O Formula unit – 1 unit of ionic cmpd; NaCl Atom – single neutral particle; H Ion – single charged particle: Na+1

1. How many moles of CaCO3 can produced starting with 4.22 x 1025 atoms of oxygen and an excess of carbon and calcium atoms?

2. How many atoms of each kind are present in 3.44 moles of dinitrogen heptoxide?

3.7 Determining Compound Formulas Percent composition: The percentage of

the elements in a compound or parts of a mixture; must total = 100%

Determine the percent by mass of each of the elements in CO2

Determine the percent composition of sodium bicarbonate.

Intensive propertyProperty that is independent of the size

of the sample of a substanceExamples: density, solubility, reactivity

with acid, melting point, boiling point

Meaning of subscripts Represent the number of atoms or

ions present in the molecule or ionic compound

NOTE: empirical formula gives the smallest whole number ratio

Empirical and molecular formulas from experimental dataSteps:

1. Mass percents are equivalent to masses in grams2. Convert masses to moles3. Find the mole ratio (divide by smallest)4. These ratios are the subscripts in the empirical formula

Ex3.11Cassiterite is 78.8% tin and 21.2 % oxygen Determine is empirical formula.

Ex3.12 Analysis of 47.25 mg sample of aluminum chloride showed that it contained 9.56 mg of Aluminum. Determine the empirical formula of the compound.

Ex 3.13 A molecular substance is 83.6% carbon and the remaining portion is hydrogen only. Determine its molecular formula if the formula mass is about 86 g/mole.

Ex 3.14 A compound of silicon and fluorine is found to contain 33.01% SILICON AND 66.99% FLUORINE. Its molar mass is 170 +/- 5 g/mole. Determine the empirical and

molecular formulas.

Hydrated compounds An ionic compound that has water

bound within the crystalline structure CuSO4

.5H2O

Ex 3.15 A hydrate of magnesium chloride consists of 36.2% water What is the correct formula for this hydrate

Answer :MgCl2. 3 H2O

Ex 3.16 Determine the number of waters of hydration for nickel (II) chloride from the following lab data.

Initial mass of nickel(II)chloride hydrate 0.235g

Final mass of anhydrous salt 0.128g

NiCl2 0.128 g (1 mol/129.5984g) = 9.8766 x10-4 mol

X H2O0.107 g (1 mol/18.016 g) = 0.005939 mol

Divide by the smallest to get ratio 6:1

NiCl2 . X H2O

HOMEWORK#1 11, 13, 33, 35, 37, 89 Worksheet#2 41, 43, 45, 47, 49, 51, 53#3 55, 57, 77, 83#4 61,63, 85, 87, 93, 97, 99#5 105, 107, 111, 113