Significant Digits
Rules:
- all non zero numbers are significant
- Zeroes at the beginning of a number are not significant.
- Zeroes in the middle are significant
- Zeroes at the end are significant if there is a decimal in the number
Rounding Rules
- if the number being dropped is lower than five, round down
- if the number being dropped is greater than five, round up
- If the number being dropped is five and its followed by zeroes or nothing, if the number before the five is odd round up; if it is even, round down.
- Ex: 12.5-12 10.452-10.5
Unit 1: Matter/Moles
Chemistry- the study of matter
Mole
-6.022x1023 atoms, ions or molecules. A way of expressing a large quantity of something.
Molar Mass
The mass of one mole of an element or a compound.
Unit = g/mol
Symbol = M
Find the molar mass of the following:
NaCl = 58.44 g/mol
NaOH = 40.00 g/mol
Finding moles from mass
n=m/M n=moles m=mass (g) M= molar mass (g/mol)
Ex. How many moles are in 1.2 g of hydrogen chloride?
HCl 1.01+35.45=36.46 n=1.20/36.46 = 0.0329 mol
Finding Atoms, Molecules / Formula Units from Moles:
Avogadros #: 6.022x1023
Ex. Number of atoms in 0.75 mol of Ca:
Atoms=0.75x6.022x1023 atoms / mol = 9.0x1023 atoms
Moles= 1.53x1024 atoms x mol / 6.022x1023 atoms = 2.54 mol
Note: if given number of atoms to find and its an element its just one step; if given the number of atoms to find and its a molecule, multiply your answer by the number of atoms in the molecule. If you are given molecules to find, and it is a molecule, there is only one step.
Ex: how many molecules are in 0.98 mol of SO2?
Molecules = 0.98mol x 6.022x1023 molecules / mol = 5.9x1023 molecules
What is the number of moles in 7.15 x 1024 molecules of HCl?
Moles = 7.15x1024 molecules x mol / 6.022x1023 = 11.9 mol
Conversions
1kg = 1000g
1g = 1000mg
1h = 60 min
1L = 1000 ml
1h = 3600 s
* If bigger than 1000 use scientific notation *
Kg = 850g x 1kg / 1000g = 0.850kg
62g x 1000mg / 1g = 62000 or 6.2x104
· When doing conversions, keep the same number of significant digits that you had in the beginning.
Molar Volume
The volume of 1mol of a gas:
Symbol V
Unit L/mol 22.4 L/mol
(STP standard temperature pressure 101.3KPa 1 atm 760mmHg)
n = v /V n=moles v=volume (L) V=22.4L/mol
How many moles of H2 gas are in 10.5L at STP?
N=v/V n = 10.5L / 22.4L/mol = 0.469 mol
L à molecules
N= 11.2L / 22.4L/mol = 0.5mol
Molecules = 0.5 mol x6.022x1023/ mol = 3.01x1023 molecules
SUMMARY
1) To find moles: n=m/M
2) To find mass m=nM
3) To get atoms from moles: atoms = _____mol x 6.022x1023atoms / mol
4) To get moles from atoms: Mols = ______atoms x mol / 6.022x1023atoms
5) Mass from atoms: mol = ___atoms x mol / 6.022x1023 atoms à m=nM
6) Atoms from mass: n=m/M à atoms=__mol x 6.022x1023atoms/mol
7) Mol from volume n=v/V
8) Volume from mol v=nV
9) Volume from mass: n=m/M v=nV
10) Volume from atoms: mol=___atoms x mol/6.022x1023atoms v=nV
11) Atoms from volume: n=v/V atoms= __mol x 6.022x1023atoms / mol
Isotopes
Protons = +, P+ Electrons = e- Neutrons = neutral (n)
In a neutral atom, the # of P+ and e- are equal.
Isotopes atoms with the same number of P+ but different number of neutrons.
Ex: C12 à 6P+, 6e-, 6n
C13 à 6P+, 6e-, 7n
X = symbol
a=mass number
z = number of protons
Cl35 mass number = 35 protons = 17 electrons= 17 neutrons =18
Radioisotopes
Radioactive isotopes contain too many or too few neutrons so they are not stable. They emit energy, so are radioactive.
Calculating Percent Composition
- the relative mass of each element in a compound
%mass = mass of element / total mass x100
Ex: 8.20g of Mg combines with 5.40g of O to form a compound. What is the percent composition of the compound?
Total mass = 13.60g
%Mg = 8.20g / 13.60g x 100 = 60.3 %
%O=5.40g / 13.60g x 100 = 39.7%
Finding the percent composition from a formula (no masses given)
1) find the masses m=nM
2) total mass
3) % mass = mass of element/ mass total x 100
C2H6
C m=nM = (2mol)(12.01g/mol) = 24.02g
H m=nM = (6mol)(1.01g/mol) = 6.06g
%C = 24.02g/ 30.08g = 79.9% %H = 6.06g / 30.08g = 19.1%
Calculating Empirical Formula
à lowest ratio of atoms in a compound N3O9 à NO3
Molecular Formula shows every atom in the compound N3O9
1) find moles of each element n=m/M
2) write each mol as a subscript
3) divide all by the lowest number of moles
4) express as whole numbers *if told % assume 100 g
EF of 25.9% N and 74.1% O
N = n=25.9g / 44.01g/mol = 1.85 mol
O = n=74.1g / 16.00g/mol = 4.63 mol
N1.85 O4.63 à N1O2.5 à N2O5
Hydrate
An ionic compound in its crystal lattice
Anhydrous
An ionic compound with no H2O molecules
% Discrepancy = |A-E| / A x 100
Stoichiometry
- relative amount of reactants and products in a reaction
- 2H2 + O2 à 2H2O
- if you know how much of one you have you can predict how much of another you should get.
Law of Conservation of Mass
- atoms are not created or destroyed in a chemical reaction, they are just rearranged.
- Thats why you have to balance your equations
- Needs the same mass of reactants and products so you need same number of each to do it
- You can have a different number of moles on the reactant and product side
Mole Ratio ratio of one substance in a balanced equation relative to another substance in the equation
4Fe + 3O2 à 2Fe2O3
Calculate the number of moles of Fe2O3 produced when 6.50 mol of Fe react with O2
molFe2O3 = 6.5molFe x 2mol Fe2O3 / 4mol Fe
2Al + 3Br2 à 2AlBr3
?Br = 5AlBr3 x 3 mol Br / 2 mol AlBr3 = 7.5 Br2
There are four types of problems in this:
1) From moles to mass
If given moles and asked to find the mass
- balance equation
- find moles using mole ratio
- find mass using moles m=nM
4Fe + 3O2 à 2FeO3
mol O2 = 0.200mol Fe x 3 mol O2 / 4 mol Fe = 0.150mol O2
m=nM (0.150molO2)(32.00g/mol) = 4.80g
2) Mass to Moles
- if given mass and asked to find moles
- balance
- change mass to moles n=mM
- mole ratio to find moles
4Al + 3O2 à 2Al2O3
Al2O3 n=m/M 6.15/101g/mol = 0.0603mol
Mol Al = 0.0603molAl2O3 x 4mol Al / 2mol Al2O3 = 0.121mol
Unit 2 Structures to Properties
Ionic compound between a metal and a non-metal; solid; high melting point; most are soluble in H2O; conduct electricity when molten or dissolved in H2O
Molecular (covalent) à non metal and a non metal; lacks high mp or bp compared to ionic; solid, liquid and gas; most are not soluble in H2O
Metallic compounds bonds between metals; form alloys; alloys are harder metal compounds than the individual metals; ductile, malleable
Valence Level top level in the energy levels of an atom or ion
Valence Electrons the electrons in the valence level
Octet Rule
All atoms need eight electrons in their valence level to become stable.
|
000
0 00000
000
0 00000
000
0
000
0
0
nucleus |
S orbitals can only hold 2e-
P orbitals can only hold 6e-
D orbitals hold 10 e-
Electrons are filled according to the lowest level possible.
Ex: Cl 17P+ X X \
X
XXX
X
X
Electron Configuration
Ex Cl 17P+ 17Ee-
1s (2) 2s (2) 2p (6) 3s (2) 3p (5)
Lewis Dot Diagrams
Show valence level electrons.
. . .
: CL : Ca
. .
Bonding the formation of covalent bonds is necessary to get a full valence level. Electrons in their orbitals come close enough to other atoms so they can share their electrons but they dont leave their orbital.
. .
H : Cl : 1 bonding electron 3 lone pairs
. .
single bond when atoms share 2 electrons O-Cl
double bond when atoms share 4 elections O=C
Triple Bond when atoms share 6 electrons N=P
Coordinate Covalent Bonding
Bonds formed when both electrons come from the same atoms
- polyatomic ions undergo this type of bonding.
.. . . 2-
OCl : O . : O :
. . . . . .
: O : S : O :
: O :
Electronegativity
- the ability of an atom to attract electrons to itself
- the higher the electronegativity, the stronger the attraction
.. 3 2.1
H N H N : H
| 8- 8+
H
Bond Dipole
ß
N-H
Valence Shell Electron Pair Repulsion Theory
- used to predict the shapes of molecules
- lone pairs influence the shape of molecules
1) Linear
central atom has 2 atoms attached to it and no lone pairs
Ex. ClF .. ..
: Cl F :
.. ..
2) Bent
central atom has 2 atoms attached and has lone pairs
HNO .. ..
N = O :
|
H
3) Pyramidal
central atom has 3 atoms attached and 1 lone pair
..
N
/ | \
H H H
4) Tetrahedral
central atom has 4 atoms attached and no lone pair
H
H C H
H
5) Trigonal Planar
3 atoms on the central atom and no lone pairs, double bond present.
H
\ ..
C = O :
/
H
Polar Bond à unequal sharing of electrons between 2 atoms
Non-polar bond à the electrons are shared equally because there is no difference in the electronegativity.
Polar molecule à there is a molecular dipole present in the molecule; there is a net movement of es in one direction.
.. ß
H2S : S - H Polar
^ |
H
Non polar there is no molecular dipole since there is no net movement of electrons in one direction.
Ex. CO2
.. ..
: O=C=O:
ß à
Like dissolves like: polar structures only dissolve in polar solvents and likewise for non polar.
Intramolecular forces: forces if attraction that exist within a molecule or compound. (holds the atom together)
Intermolecular forces: forces of attraction between one molecule and another. (only for molecular compounds)
Three types: 1) London dispersion forces 2) dipole-dipole forces
3) hydrogen bonding
LDF all molecules have London dispersion forces because they have electrons.
-a force attracted between the electron in one molecule to the proton of another
-the higher the number of electrons, the stronger the bond so the higher the boiling point
Ex. Cl2 or Br2
LDF 34e- LDF 70e-
Bromine had higher boiling point
Note: if LDF are the same, the bulkier compound has the higher boiling point.
D-D forces
- only polar molecules have D-D forces
-this is a weak force and it does not compare to a lot of electrons in LDF
Ex. H Cl or I2
LDF 18 LDF 106e- I2 has higher BP
D-D
Hydrogen Bonding a very strong force of attraction
-only occurs between N-H O-H and F-H
Order for BP trends (weakest to strongest)
Molecular, metallic, ionic, network covalent
Network covalentA 3-D arrangement of continuous branches which make it very strong. SiO2
The larger the electronegativity difference between 2 atoms, the more polar the bond.
Ex. OF2 or SBr OF2 has more polar bonds
Exothermic reactions A net release of energy during a chemical reaction or phase change.
Form bonds releases energy
Break bonds needs energy
The energy needed to break the bonds in the reactants is less than the energy released when the bonds in the products were formed.
Endothermic reaction - a new absorption of energy during a chemical reaction of phase change.
The energy needed to break the bonds in the reactants is more than the energy released when the bonds in the products were formed.
Ionic Bonding
Between a metal and a non metal (NaC
- transfer of electrons
Cation positive ion
Anion negative ion
Naming write full name of first ion
- second ion ends in Ide (unless polyatomic ion)
- no prefixes
- multivalent ions say which charge is on the ion by using brackets and roman numerals.
- if you are not told the charge to use, use the charge that forms the most common/stable ion.
Fe(OH)3 à iron (III) hydroxide
Crystal Lattice a 3-D arrangement of alternating positive and negative ions
* The greater the difference in electronegativity between the metal and non metal, the more ionic the bond.
Ex. Which is more ionic?
Na O Al O
2.6 2.0
Lewis Structures cation has empty orbital around the symbol
Anion has 8 electrons around the symbol
. .
{ Na }+ { : Cl : }
. .
Metallic Bonding
Metals have low electronegativity so they lose electrons easily
Sea of Electrons
-when metals lose electrons they become positive
- the positive charge of an atom attracts the negative electron of another
- electrons are moving throughout the metal and they move in and out of orbitals.
Density
D=m/V D = density m = mass V=volume
g/ml g ml
the mass of a given volume of liquid
D H2O = 1g/ml
If an objects density is less than that of water, it will float and vice versa.
