In the Beginning!
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Early Earth
formed about 4.6 billion years ago (4.6 x 109)
age determined by radiometric means
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Moon rocks 4.3 b.y.o
Oldest meteorites 4.7 b.y.o.
Period of Accretion = Meteoric Bombardment
Nebular cloud began to condense (~ 4.7 b.y.o.); Whirlpools and eddies in cloud
plane condensed into Sun, then the planets by gravitational attraction.
98% of mass became the Sun. As Sun ignited, lighter gases of the inner planets
were blown away by blast wave and solar wind. Outer planets retained these
gases (called Gas giants).
Early Earth was very hot (molten). Lighter elements were pushed toward surface
(H, O, C, N); Heavier elements sank (Fe, Ni, Cu).
Now: ~ 326 million miles3 of H2O on surface : "Water Planet"
Covers 72% of surface:
Ocean (salt) 97%
Fresh
3%
2.2 % Polar ice caps
.8 % Groundwater, Lakes &
Rivers
Composition of Matter
Matter - anything that has mass & takes up space.
Element - a substance that cannot be broken down to simpler substances; has
specific properties. Each has a chemical symbol: O, N, C, Fe, Cu
Atom - the smallest particle of an element that retains the characteristics of that
element.
Nucleus: Neutrons (no charge)
Protons (+ charge)
Electron: move in regions outside nucleus (- charge)
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The number of electrons and protons should be equal in each element.
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Compound - made up of molecules
Molecule - the smallest unit of a compound that retains the characteristics of that
compound.
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Water
The most common compound on Earth's surface
Extremely important to Biological systems; Life could not exist without it. Makes up
55 - 96% of living things;
Adult human: 65 - 72%
Baby: 75%
Steer: 55%
Jellyfish: 96%
Carrot: 88%
Watermelon: 93%
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Molecule: H2O - chemical formula
-two hydrogen atoms covalently bonded to one oxygen atom in a 2:1 ratio.
Covalent bond - the sharing of electrons between two atoms. A very strong
chemical bond!
O
H
oxygen
atom
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+
H
H O H
2 hydrogen
atoms
=
water
Unique Properties of Water
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Water is a Polar molecule with opposite charges on each end.
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Dissolving power - called the "Universal Solvent“
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Cohesion - attraction of "like" molecules. Caused by Hydrogen bonding - unlike
charges of the water molecule attract
Hydrogen bonding - the positive region of one molecule attracts the negative
region of another. Not a true chemical bond! It is a weak attraction water
molecules have for each other; allows water to be a liquid at room temperature;
produces cohesion and high surface tension.
Adhesion - Positive and negative ends can attract other surfaces; called the
"wetting capacity;" due to polarity.
High Heat of Vaporization - water has a large capacity for absorbing heat. Many
hydrogen bonds must be broken for water to vaporize or evaporate.
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Resistance to Temperature Change - Hydrogen bonds absorb heat when they
break and release heat when they form.
Ex: water droplets on cold glass (formation)
evaporative air conditioners; sweating (break)
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Lower Density of Ice - water molecules form an hexagonal matrix when it freezes
due to hydrogen bonding. Takes up more space, therefore is less dense, so it
floats. Prevents lakes and streams from freezing solid; protects life forms during
winter.
Put these notes at bottom of page 4
Question: Why can water dissolve so many things?
Answer - Its Polarity !
Ex: NaCl (common table salt, sodium chloride)
Sodium and chlorine attract one another because they
they have opposite charges
Na+ClWhen this salt dissolves in water,
the sodium and chlorine atoms
separate to form ions. The positive
Na+ is surrounded by the negative
ends of the water molecules.