Notes

ch 4 molecules & compounds

molecule - 2 or elements combined; elements can be the same or different (compound)

chemicals bonds - hold atoms together in a compound; result from attractions between charged particles that compose atoms

types of chemical bonds:
a) ionic - occur between a metal & non-metal; oppositely charged ions attract one another
b) covalent - occur between 2 or more non-metals; atoms share electrons
c) metallic

cation ex
anion ex

ionic compounds - composed of cations & anions; ions are arranged in a repeating 3D pattern forming a crystal; formula gives the smallest possible integer # of ions in substance (w/o writing charges) so the combination is electrically neutral
ex: ionic compound formula of Mg2+ & N3- = common multiple of charges is 6, so 3 Mg2+ & 2 N3- = Mg3N2
ex: Ca2+ & PO4(3-) = common multiple of charges is 6, so 3 Ca2+ & 2 PO4(3-) = Ca3(PO4)2


naming ionic compounds:
categorized into 2 types depending on the metal in the compound:
type 1: binary ionic compounds - metal forms only 1 type of ion (charge is invariant)
name of cation (metal) & base name of anion (nonmetal) + -ide
type 2. metal forms more than 1 type of ion (charge varies in different compounds); charge cannot be predicted & must be noted in name
name of cation (metal) & (charge of cation in roman numerals in parantheses) & base name of anion (nonmetal) +-ide
(insert slide 19 type 2 cation chart)

Naming inorganic (no carbon) compounds:
1. cation is always named first /w name of cation w/o the word ion
2. anion is named second /w name of anion w/o the word ion
ex: cation anion name chart
Na+ & Br- = Sodium bromide
Mg2- & O2- = Magnesium oxide
Al3+ & Cl- = Aluminum chloride

monatomic ions - ions formed from a single atom
insert chart (slide 11)

rules for predicting charge on a monatomic ion:
1. most main-group metals: 1 monatomic /w charge = group #
2. some main-group metals /w high atomic #s have more thsan 1 cation: 1 cation will have the charge of the group #, the other will have the charge of the group #-2
3. most transition metals form more than 1 cation, one of which is +2
4. main-group non-metals: 1 monatomic anion /w charge group #-8

naming monatomic ions:
a) metal forms only 1 cation = named after metal
b) metal forms more than 1 cation = stock system: charge written using a roman numeral (old system = add suffix -ic for high-charge cations & -ous for low charge cations)

polyatomic ions: ions formed from 2 or more atoms
(insert polyatomic ions slide 20)

acids & corresponding anions:
-oxoacids contain hydrogen, oxygen, & a 3rd central atom
to name an acid from its anion name:
1. change an -ate to -ic
2. change an -ite to -ous
3. add word "acid"
(insert slide 26)
highlight: HCl, HNO3, H2SO4, H3PO4, H2CO3 (slide 26)


molecular compounds - composed of 2 or more nonmetals

naming molecular compounds:
1. write name of element /w the smallest group # first
2. if the 2 elements are in the same group, write the element /w the greatest row # first

3. the prefixes of each element indicate the # of atoms present

prefix + name of 1st element + prefix + base name of 2nd element + -ide

(insert prefixes chart slide 28)

hydrate - a compound containing water molecules weakly bound in crystals; formula of a hydrate is written /w a dot before the water molecule(s) included
ex: (slide 31)

hydrates are named using the anhydrous (w/o water) compound name followed by the prefix for the # of water molecules included & the word "hydrate"
ex slide 32

chemical formula - represents compound; indicates the type & # of each element present in the compound
catagorized into 3 different types:
1. empirical formula
2. molecular formula
3. structural formula

molecular model - more accurate & complete way to specify a compound
ball&stick molecular model - represents atoms as balls & chemical bonds as sticks; how the 2 connect reflects a molecule's shape

space-filling molecular model - atoms fill the space between e/o to more closely represent the best estimate for how a molecule might appear if scaled to visible size
(pictures slide 37)

lewis structure model: depict the structural formula by representing a substance's valence electrons as dots; focus on valence electrons b/c chemical bonding involves the transfer or sharing of valence electrons btwn 2 or more atoms
(picture slide 38)

lewis theory - predicts the # of electorns a metal atom should lose or a nonmetal atom should gain in order to attain a stable electorn arrangement
octet rule: each atom has 8 electrons in its valence shell; allows prediction of formulas of ionic compounds that result & relative strengths of the resulting ionic bonds based on coulomb's law

covalent bonding:
bonding pairs - electrons shared by atoms
lone pairs - electrons not shared by atoms but belong to a particular atom (nonbonding pairs)
(insert ex slide 45)

types of covalent bonds:
a) single covalent - 2 atoms share 1 pair of electrons
B) double covalent - 2 atoms share 2 pairs of electrons; elements that can double-bond /w e/o & themselves are C, N, O, S, & P
c) triple covalent - 2 aotms share 3 pairs of electrons; elements that can triple-bond /w e/o & themselves are C, N, O, & S

formula mass/molecular mass of a compound
molecular mass (weight) - mass of an indivudal molecule or formula unit; mass of 1 mole of the compound

determining a compound's molecular mass: sum of the masses of the aatom in a isngle molecule or formula unit
mass compound -> mol of compound -> # of molecules
molar mass avogadro's #
(ex 48-51)

composition of compounds: % of each element in a compound can be dtermined form
1. the formula of the compound &
2. the experimental mass anlaysis of the compound

% mass of element Z = (molecular mass of element Z/mass of 1 mol of compound) * 100%

-chemical formula or mass percent can be used as a conversion facotr

percentage composition/elementaal analysis - mass % of each element in the compound; composition is determiend by the experiment (often by combustion)
-when a compound is burned, it component elements form oxides
ex: CO2 & H2O are weighed to determine the amount of C & H in the original compound

empirica formula - formula of a substance written /w the smallest integer subscripts; simplest whole-# ratio of the aotms of elements in a compound
-can be detemriend form elemental analysis:
a. masses of elements formed when a compound is decomposed or that rect together to form a compound
b. percent composition (empirical formula represents ratio of atoms or moles of atoms, not masses)

finding an empirical formula, molecular formula:
1. convert the percentages to grams (if not given, assume 110 g of compound)
2. convert mass (grams) to moles
3. divide all by the smallest # of moles to obtain the aotm-to-atom ratio for each of the elements in the compound (if the results is within .1 of a whole #, round)
4. multiply all mole ratios by a # to make all whole #s (if ratio is .5, multiply all by 2; if ratio is .33 or .67, multiply all by 3, etc)
5. empricial formula: molecular formula = (empirical formula) x n