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7.2 Notes
P 145 Most elements are solid at room
temperature. Of the 92 naturally occurring
elements, 11 are gases. Only 2 (Br and Hg) are
liquid at room temp.
The noble gases and elements to the far right
of the PT have completely filled or nearly filled
energy levels.
When an energy level is completely filled, the
electrons do not interact strongly with other
electrons, reducing intermolecular forces
P146 Periodicity – the repeating pattern of
chemical and physical properties of the
elements
The first element in each row always has a low
melting point (Li, Na, K) The melting and
boiling points rise toward the center of each
row, then decrease again.
IMF are stronger when energy levels are halffull (or half-empty). Elements with half-filled
energy levels have the greatest number of
electrons that can participate in bonding with
other atoms.
P147: Electrical conductor – a material that
allows electricity to flow through easily.
Copper and aluminum are excellent electrical
conductors and used for almost all electrical
wiring.
Thermal conductor – a material that allows
heat to flow easily.
Insulator – a material that slows down or stops
the flow of heat or electricity.
Elements to the far right of PT are NOT good
conductors, as many are a gas.
P148 Metals and metal alloys
Alloy – a solid mixture of one or more
elements
Steel is an alloy of iron and carbon. Ordinary
steel will rust.
Stainless steel and high-strength steel alloys
also contain small percentages of other
elements, such as chromium, manganese, and
vanadium.
Aluminum is light and used when weight is a
factor, such as for airplanes construction.
Titanium combines the strength of steel and
light weight of aluminum. Used for military
aircraft and racing bicycles. Very expensive,
rare, and difficult to use.
Brass – hard, gold-colored metal alloy.
72% copper, 24% zinc, 3%lead, and 1%tin
P149 Carbon – most essential element for life
on our planet.
Virtually all molecules of plants and animals
are constructed with carbon.
Carbon is so important, it has its own branch of
chemistry called “organic chemistry”
Pure carbon is found in nature in 2 very
different forms:
Graphite – a black solid ground up to make a
powder for lubricating locks and keys
Diamond – hardest natural substance known
and has highest thermal conductivity of any
material.
Silicon – is 2nd most abundant element in
Earth’s crust. Used in computer chips. Sand,
rocks, and minerals are mostly made of silicon
and oxygen. Most gemstones, such as rubies
and emeralds, are compounds of silicon and
oxygen, with traces of other elements. Glass
windows are SiO2 (silica)
chromium makes rubies
red and vanadium make emeralds green
Germanium – used for semiconductors
P 150 Nitrogen, Oxygen, and Phosphorus
Nitrogen gas (N2) is 78% of Earth’s atmosphere
Oxygen gas (O2) is 21% of Earth’s atmosphere
Oxygen is most abundant element in Earth’s
crust. 46% of crust is oxygen – all bonded to
other elements in rocks and minerals.
Silicon dioxide SiO2
Calcium oxide CaO
Aluminum oxide Al2O3
Magnesium oxide MgO
Hematite – iron oxide – Fe2O3
Liquid Nitrogen – boiling point -196*C
Rapid freezing, destroys warts
Proteins and DNA both contain nitrogen
Phosphorus – key ingredient of DNA –
molecule responsible for carrying the genetic
code.
Glows in the dark – when phosphorus atoms
absorb light, they store energy and give off a
greenish glow as they re-emit the light.