6.2.1 Elements on Planet Earth
The Science of Elements…..
• Has progressed from the “earth, air, water,
fire” theory proposed by the ancient Greeks
to the current idea that elements are
composed of atoms.
• Here we will put the early theory into a
modern context as we look at the elements
found in air (the atmosphere), water (the
hydrosphere) and Earth (the crust or
lithosphere).
Air: Elements in the Atmosphere
The Atmosphere usually refers to a gaseous envelope
surrounding a planet.
The earth's atmosphere is a very thin layer wrapped
around a very large planet.
Two gases make up the bulk of the earth's atmosphere:
nitrogen (N2 ), which comprises 78% of the
atmosphere, and oxygen (O2 ), which accounts for
21%. Various trace gases make up the remainder.
Air: Elements in the Atmosphere
Earth has a radius of some
6400 km. Ninety-nine
percent of the earth's
atmosphere is contained
within a layer approximately
50 km thick. Life on earth
inhabits a layer no more than
9 km thick, extending from a
bare few kilometers above
sea level (airborne
organisms and life on
mountains) to a few
kilometers below (deep
ocean basin creatures and
subterranean microbial
communities).
Air: Elements in the Atmosphere
The biosphere is the portion of
earth in which all known life
forms exist. It occupies a thin
layer of air (atmosphere), water
(hydrosphere), and land
(lithosphere).
Air: Elements in the Atmosphere
The thin envelope of air that
surrounds our planet is a
mixture of gases, each with its
own physical properties. The
mixture is far from evenly
divided. Two elements,
nitrogen and oxygen, make up
99% of the volume of air. The
other 1% is composed of "trace"
gases, the most prevalent of
which is the inert gaseous
element argon. The rest of the
trace gases, although present in
only minute amounts, are very
important to life on earth. Two in
particular, carbon dioxide and
ozone, can have a large impact
on atmospheric processes.
Air: Elements in the Atmosphere
Photosynthesis and Respiration make use of the
elements, hydrogen, oxygen, and carbon, cycling
them through the atmosphere.
Respiration:
glucose + oxygen
carbon dioxide + water + energy
Photosynthesis:
sunlight + carbon dioxide + water
glucose + oxygen
Water: Elements in the Hydrosphere
Hydrosphere refers to all the water that occurs
at the Earth’s surface.
Water, in its different forms, cycles continuously through the
lithosphere, hydrosphere, atmosphere, and biosphere. Water
evaporates into the atmosphere from the land and the sea.
Plants and animals use and reuse water and release water
vapour into the air. Once in the air, water vapour circulates and
can condense to form clouds and precipitation, which fall back
to earth. At one time or another, all of the water molecules on
earth have been in an ocean, a river, a plant, an animal, a cloud,
a raindrop, a snowflake, or a glacier!
Water: Elements in the Hydrosphere
The water cycle
Water is essential for life on
earth. It is recycled through
the water or hydrologic cycle,
which involves the following
processes:
Evaporation, Condensation,
Sublimation, Precipitation,
Transpiration, Surface runoff,
Infiltration, and Percolation.
Earth: Elements in the Crust
Lithosphere:
• The outermost layer of the Earth's crust consisting of
a mosaic of rigid plates of granite type rock. These
plates float upon a solid, but plastic layer of rock
called the asthenosphere.
• The Lithosphere varies in depth from approximately
10 km under the oceans to 30 km under the
continents.
• The Lithosphere includes all land surface and soil,
but not the organisms. Also includes the ocean
bottom, but not organisms.
Earth: Elements in the Crust
The lithosphere contains all
of the cold, hard solid land of
the planet's crust (surface),
the semi-solid land
underneath the crust, and
the liquid land near the
centre of the planet.
Elements found in the earth’s
crust are O, Si, H, Cl, P, C,
S, Ar, N, and F
Different Kinds of Elements
• Metals, most of the elements in the periodic
table.
E.g., C,O,N, F,S,….
• Non-metals, over half of the non-metals are
gases at room temperature.
E.g., Al, Fe, Ca, Na, K, Mg, Ti, Mn,….
• Metalloids, the transition from metal to nonmetal on the periodic table is not sharp. Some
of the elements along the border have
properties that are intermediate between metals
and non-metals.
E.g., B, Si, Ge, As, Sb, Te,…..
State
Appearance
Metals
• solids at
room
temperature,
except for
mercury (a
liquid)
• shiny lustre
NonMetals
• some gases • not very
at room
shiny
temperature
• some solids
• only one
liquid
(bromine)
Metalloids • solids at
room
temperature
• can be
shiny or dull
Conductivity
Malleabiility and
Ductility
• good
conductors of
heat and
electricity
• malleable
• ductile
• poor
conductors of
heat and
electricity
• brittle
• not ductile
• may conduct
electricity
• poor
conductors of
heat
• brittle
• not ductile