General Chemistry Chapter 3

Chemical compounds have _______ chemical properties, _________ to the elements from which they are made

unique, unrelated

Molecular compounds

-held together by covalent bonds

-pairs of electrons are "shared" between atoms

-nonmetals bonded to each other

-exist as discrete molecules

Ionic compounds

-composed of positively and negatively charged ions

-ionic bonds (held together by electrostatic attraction)

-usually a metal cation with a nonmetal anion

-exist as repeating structures called a crystal lattice

Molecular formulas

exact number and type of atoms present in one molecule of a compound

what are molecular formulas used for?

Molecular Compounds Only !!

Empirical formula

simplest whole number ratio of elements in a compound

Formula unit

the smallest electrically neutral unit within the crystal of an ionic compound

example of a formula unit

NaCl = one Na+ and one Cl-

Chemical formulas

Elemental symbols to represent atoms

-subscript (at right) indicates amount of atoms

Diatomic molecular elements (7)

H2 N2 O2 F2 Cl2 Br2 I2

Horses need Oats For Clear Brown I's

Polyatomic

P4, S8, Se*

Naming Binary Ionic compounds

Cation (+) is named first

Anion (-) is second with "ide" ending

Example: NaCl = Sodium chloride

When is a Roman numeral added?

If the metal can form different charges (usually for transition metals), in order to indicate its charge

FeCl2

iron (II) chloride

FeCl3

iron (III) chloride

Formulas of Binary Ionic Compounds

-the net charge on any stable compound is zero

-Figure out the smalls number of ions which will add to zero, and use those values as subscripts

(hint: helpful to write out charges of ions first)

titanium (IV) oxide; write formula

TiO2

Polyatomic ions

- a group of covalently bonded ions with a net charge (+ or -)

-use the ions name in the compound name

-parentheses are used around the ion if more than 1 is present in the chemical formula

Oxyanion

anion containing oxygen and another element (most polyatomics)

More oxygen

-ate (NO3 = nitrate)

Less oxygen

-ite (NO2 = nitrite)

Prefix for more than

per-

Prefix for less than

hypo-

Most oxygen ClO4

More oxygen ClO3

Less oxygen ClO2

Least oxygen ClO

perchlorate

chlorate

chlorite

hypochlorite

Hydrates

ionic compounds which contain a specific number of "water of hydration" in each formula unit

Features of Hydrated ionic Compounds

-waters can usually be removed by heating

-waters separated by a dot in the chemical formula

-Add "prefix then hydrate" to name

prefixes for: half(.5), 1-8

hemi, mono, di, tri, tetra, penta, hexa, hepta, octa

Ex: cobalt (II) chloride

hexahydrate

Naming Binary Molecular Compounds

Made from two nonmetals, the element names are used with the 2nd one ending in "ide"

Prefixes in Binary Molecular Compounds

indicate the # of atoms

Prefix that is only used in front of the the second element

Mono

Acids

compounds that generate H+ when dissolved in water (aq)

Binary acids

contain hydrogen and a nonmetal atom (usually a halogen)

Naming Binary Acids

Named using the nonmetal base name with the prefix "hydro" the suffix "ic" and the word "acid"

Ex: HCL(aq) hydrochloric acid

Oxyacid

acids containing hydrogen and an oxyanion

Naming Oxyacid

use base oxyanion name with a suffix + "acid"

if oxyanion ends in -ate

change to -ic

nitrate = nitric acid

if oxyanion ends in -ite

change to -ous

sulfite = sulfurous acid

Molecular mass

the mass of one molecule of a molecular compound (in amu)

Formula mass

the mass of one formula unit of a compound (in amu)

Molar mass

the mass of one mole of the particles that comprise a substance (in grams)

Calculating molar mass

Count # of each type of atom in a formula and multiply by its atomic mass

ex: 1 mol Co2 = 1 mol C + 2 mol O

Mass Percent Compostion

mass of element in compound

-------------------------- X 100

molar mass of compound

Conversion factos from Chemical Formulas

The subscripts in chemical formulas can be used as conversion factors relating moles of elements or ion per mole of "molecules"

-applies to both molecular or ionic compounds

% composition and Empirical Formulas

1. Assume there is 100 g of the sample, so that the % values will equal the # of grams of each element.

2. Convert grams into moles of each element using its atomic mass.

3. Write a "tentative formula" using these mole values.

4. Divide each mole value by the smallest one found.

5. Convert any fractions to whole numbers by

multiplying all the mole values by the same number.

6. When you have all whole numbers with no common

factor, you have the "empirical formula".

Empirical Formula from Combustion Data

1. Use mass of CO2 to calculate mass and moles of C.

2. Use mass of H2O to calculate mass and moles of H.

3. Subtract masses of C and H from mass of sample to

find mass of "other" element (often O).

4. Convert mass of 3rd element into moles.

5. Write a "tentative formula" using the mole values.

6. Divide each mole value by the smallest one found.

7. Convert any fractions to whole numbers by

multiplying all the mole values by the same number.

8. When you have all whole numbers with no common

factor, you have the "empirical formula".

NOTE: Sig figs don't matter here, but round off errors

will lead to wrong answer. KEEP extra digits!

In Chemical reactions chemical bonds must be_________

broken and/or/ formed

at least _________ substance must be made

one

chemical equations show the

identities and quantities of substances involved in a reaction

Chemical equations describe

the proportions of substances in a chemical reaction

Reactants

initial substances (consumed)

Products

final substances (formed)

Other symbols in Chemical equations (states of matter)

Gas (g)

Liquid (l)

Solid (s)

Aqueous (aq) = dissolved in water

Other symbols in chemical equations (Reaction conditions)

-High temperature (∆)

- Pressure, catalysts, etc. (written with arrow)

• Chemical equations should be ________ to follow the _____________

balanced, law of conservation of mass

Rules of Balancing Equations

An equation can be balanced only by adjusting the coefficients of formulas (#s in front of species)

NEVER CHANGE SUBSCRIPT

Balancing Equation Strategy

• Balance elements that occur in only one compound on each side first.

• Balance free elements last (e.g. O2)

• Balance unchanged polyatomic ions

(or other groups of atoms) as groups.

• Fractional coefficients are acceptable and can be cleared at the end by multiplication.

Combustion Reaction

one that occurs between oxygen and another substance

Hydrocarbons

molecular compounds composed of only hydrogen & carbon

products of complete combustion of a hydrocarbon are ________

carbon dioxide and water