Chapter 3 Molecules & Compounds

3.1 Molecules, Compounds and Formulas  Empirical Formulas  Definition: the simplest whole number ratio for the formula of the elements in a compound  Examples: NaCl, MgCO 3, AlBr 3  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: C 6 H 12 O 6, CO 2, SiO 2

Molecular formulas  Condensed structural formulas – formulas depicting some of the bonding by groupings CH 3 OH, CH 3 CH 2 CH 2 Cl

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 naming The metal goes first always – element name The nonmetal goes second with an –ide at the end MgS – magnesium sulfide Keep 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 3.3 Co (I) and I Ni (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  NaNO 3  NaNO 2  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  Mono1  Di2  Tri3  Tetra4  Penta5  Hexa 6  Hepta7  Octa8  Nona9  Deca10

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  P 2 O 7  SCl 3  CF 4  N 2 O 5  CO  CO 2  H 2 O

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; H 2 O  Formula unit – 1 unit of ionic cmpd; NaCl  Atom – single neutral particle; H  Ion – single charged particle: Na +1

1. How many moles of CaCO 3 can produced starting with 4.22 x 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 CO 2

Determine the percent composition of sodium bicarbonate.

Intensive property  Property that is independent of the size of the sample of a substance  Examples: 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 data Steps: 1. Mass percents are equivalent to masses in grams 2. Convert masses to moles 3. 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 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  CuSO 4. 5H 2 O

 Ex 3.15 A hydrate of magnesium chloride consists of 36.2% water What is the correct formula for this hydrate  Answer :MgCl 2. 3 H 2 O

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

 NiCl g (1 mol/ g) = x10 -4 mol  X H 2 O g (1 mol/ g) = mol  Divide by the smallest to get ratio 6:1  NiCl 2. X H 2 O

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