Prelim 1
(Wks 16)
Significant Figures
– Counting:
1.
All nonzero digits are significant.
2.
Zeroes to the left of the first nonzero digit are not significant.
3.
Zeroes at the end of a number that includes a decimal point are
significant.
Addition and Subtraction:

the answer can contain no more decimal places
than the least accurate
measurement
Multiplication and Division:

the answer can contain no more significant figures
than the least accurate
measurement
Scientific Notation
Addition and Subtraction
– numbers converted to same power of 10,
coefficients added or subtracted and exponent remains
Multiplication
– coefficients multiplied and exponents added
Division
– coefficients divided, exponent of divisor is subtracted from
exponent of number being divided
J.J. Thomson
– cathode ray tubes – discovery of electrons
Bohr’s View
– there are 2n^2 electrons allowed in a level
Modern View
– orbitals that differ in shape and energy
Filling of Orbitals:
1s→2s→2p→3s→3p→4s→3d→4p→5s→
4d→5p→6s→4f
(s=2, p=6, d=10, f=14)
Trends
Size of atoms decreases as you move from left to right
Size of atoms increases as you move down a group
Reactivity for metals increases as you move down a group
Reactivity for nonmetals decreases as you move down a column
Groups:
1A – Alkali, 2A – Alkali Earths – harder, more dense, 7A –
Halogens – diatoms, 8A – Noble Gases – colorless, not reactive
Electromagnetic Radiation:
Λv = C
,
E=hv

Λ
= wavelength, v = frequency, C = speed of light
As Λ decreases, v increases, E increases
As Λ increases, v decreases, E decreases
Troposphere – Tropopause (10 km) – Stratosphere (Ozone) – Mesosphere
(temp decreases as you go higher in the troposphere, and then increases as you
proceed through the stratosphere)

Anthropogenic pollution
– attributable to human activity

Clean Air Act (1990)
– regulates particulates, ozone, CO, nitrogen and
sulfur oxides, ozonedepleting chemicals (freons)

Acid Rain
– H
2SO4 (sulfuric acid) acidifies soil and ground water

Thermal Inversion
–polluted cool air can’t rise above warm air
Photochemical Smog
– formed by action of sunlight on photoreactive
pollutants in the air
Photodissociation
of nitrogen dioxide:
NO
2 → NO + O, O2 + O → O3 (NO and NO2 are both pollutants)
RO
2, NO2 and aldehydes are in smog

Incomplete combustion
– insufficient oxygen – creates CO
Solutions to Smog and Ozone
Scrub sulfur dioxide from coal emissions, cars with better mileage, electric or
hydrogen, fuel cells, catalytic converters (NO
X to N2), minimize volatile
organic compounds

Rainout
– pollutants in air removed by natural precipitation
Because a double bond is stronger than a 1.5 bond and requires more energy
to break, oxygen molecules absorb higherenergy UV radiation (UVC) –
ozone absorbs lower energy (UVB) – therefore, ozone is more reactive
toward UV light than is oxygen.
Steady state – net rate of destruction = net rate of formation