Chemistry Final Exam Study Guide
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Group 1: alkali metals
Group 2: alkaline earth metals
Group 15: pnictogens
Group 16: chalcogens
Group 17: halogens
Group 18: noble gases
Ionic compounds-composed of oppositely charged ions
o Electrons are either added or subtracted from atoms to form ions
Molecular compounds-composed of molecules, which are made of atoms
Atomic number-number of protons
Mass number-number of protons and neutrons
Metal + nonmetal = ionic
Nonmetal + nonmetal = covalent
Troposphere-lowest region of the atmosphere in which we live
o Contains 75% of our air by mass
Air
o 78% nitrogen
o 21% oxygen
o 1% other gases
Air inversions-cooler air can be trapped beneath warmer air due to weather conditions
o Pollutants often accumulate in the cooler air of an inversion layer
Molecule-fixed number of atoms held together by chemical bonds in a certain spatial
arrangement
Chemical formula-symbolically represents the type and number of each element present
Risk assessment-evaluating scientific data and making predictions in an organized
manner about the probabilities of an occurrence
Toxicity-intrinsic health hazard of a substance
Exposure-the amount of the substance encountered
Chemical reactions-characterized by the rearrangement of atoms when reactants are
transformed into products
Law of Conservation of Mass-number of atoms on each side of the arrow must be equal
Balancing equations
o If an element is present in just one compound on each side, balance it first
o Balance free elements last
o Balance polyatomic ions as a unit
Incomplete combustion-if the amount of oxygen is altered, the hydrocarbon can burn
incompletely
Ozone-a secondary pollutant produced from one or more other pollutants
Green chemistry-reduces pollution through design/redesign of chemical processes
o Use less energy, create less waste, use fewer resources, use renewable resources
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Radiation
o Short-range includes UV, X-rays, and gamma rays
o Causes rupture of molecular bonds
o Visible-ROYGBIV; used for photosynthesis and solar applications
o Infrared-longest of the visible spectrum; causes molecules to bend and stretch
o Microwaves-cause molecules to rotate
Electromagnetic radiation
o Shorter wavelength = higher frequency
o Wavelength-distance traveled between successive peaks
o Frequency-number of waves passing a fixed point in one second
Of the sun’s radiation reaching Earth, approximately 53% is infrared, 39% is visible light,
and 8% is UV
Radiation may be described as having both wave-like and particle-like properties
o The energy of radiation is quantized, with only certain values of energy being
allowed, rather than an energy continuum
Energy of radiation is related to its wavelength and frequency
o Energy is proportional to frequency
o Energy is inversely proportional to wavelength
UV radiation-has sufficient energy to cause certain molecular bonds to break
o UVA-lowest energy
o UVB-medium energy
o UVC-highest energy
o Skin damage by UV
 When UV radiation is absorbed by skin, lower-energy UVA light removes
electrons from molecules such as water, creating free radicals and other
reactive oxygen species
 Higher-energy UVB light causes some chemical bonds to break
 DNA molecules are damaged by free radicals or UVB absorption
 This results in the release of melanin, the compound that gives skin
its color
o Biological effects of UV exposure
 UVC radiation is highly energetic and is absorbed completely by oxygen
molecules (causes O=O double bonds to break)
 UVB is partially absorbed by ozone in the stratosphere (breaks O-O single
bonds in ozone)
 Some UVB reaches Earth’s surface, where it is rapidly absorbed at
the surface of the skin
 UVA is not absorbed by the atmosphere; since it is less energetic than
UVB, it penetrates deeper into skin, causing more damage to underlying
tissue
o Skin cancer
 Most skin cancers are linked to exposure to sunlight
 Can appear at any age, but is more common in older people
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Can develop many years after repeated, excessive exposure has stopped
The UVA in sunlight at Earth’s surface is most strongly linked with skin
cancers; however, UVB may also play a role
 Cancer can arise in different types of skin cells; those in basal or
squamous cells are common, but seldom fatal; cancers in melanocyte cells
(melanoma) are most deadly
 Although some UV exposure is needed for production of vitamin D, too
much exposure leads to cancers and eye disease
o UV index
 Color-coded UV index scale is used to predict the risk of sunburn from
overexposure to UV light from the sun
 Important factors considered by most UV index forecasts:
 The ozone concentration in the upper atmosphere
 Elevation
 Cloud cover
Ozone layer-a region in the stratosphere with maximum ozone concentration
o Concentration of 12,000 ppb in the stratosphere
o Concentration of 20-100 ppb in the troposphere
o The ozone layer provides a natural source of protection against harmful UVB
radiation
o Ozone can be naturally destroyed by dissociation of water molecules into free
radicals
o Data suggests that something beyond natural sources was responsible for
destroying stratospheric ozone
Chlorofluorocarbons (CFCs)-nontoxic, nonflammable, inexpensive, and widely available
o Have revolutionized the air conditioning industry
o These molecules are broken apart by UVC radiation in the upper atmosphere; the
resulting atomic chlorine results in ozone destruction through a series of reactions
o The lower stratosphere over the South Pole is the coldest spot on Earth
o This creates stratospheric clouds (PSCs), which help support the chemical
reactions that produce active chlorine that catalyzes ozone destruction
Montreal Protocol
o 1987
o Caused the production of CFCs to plummet
o Recovery of ozone concentrations is slow, with atmospheric chlorine
concentrations not expected to return to 1980 levels in Antarctica until the year
2070
Alternatives to CFCs
o Hydrofluorocarbons (HFCs) replace chlorine with hydrogen to prevent the release
of atomic chlorine, which catalyzes ozone destruction
o HFCs are greenhouse gases, which play a role in climate change