Chapter 2 Chemistry of Life

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21- Atoms, Ions and Molecules

An Atom is the smallest basic unit of

matter.

All atoms share the same basic structure.

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Atoms consist of three types of particles:

Protons, Neutrons and Electrons.

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Protons and Neutrons form the center of

the atom- the nucleus.The electrons (e-)

Move around the outside of the nucleus.

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Protons are positive (+), neutrons are

neutral, and electrons are negative (-).

Atoms have an equal number of protons

and electrons, so they are electrically

neutral.

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An element is one particular type of

atom, and it cannot be broken down into

a simpler substance.

Ex. Hydrogen, calcium, helium, oxygen…

All atoms of the same element have the

same number of protons. Ex. Oxygen has

8 protons, Hydrogen has 1 proton.

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Electrons move in clouds called energy

levels around the nucleus.

The first energy level holds 2 electrons,

the second energy level holds 8

electrons, and the third energy level

holds 8 electrons.

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Chlorine has 17 e-

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Atoms are considered stable when they

have a full energy level. Atoms are

considered unstable (reactive) when they

do not have a full energy level.

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Four Elements make up over 90% of

organisms:

Carbon

Oxygen

Nitrogen and

Hydrogen!

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A compound is a substance made of

two or more different atoms bonded

together.

Ex. H2O, CO2

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An Ion is an atom that has gained or lost

an electron. The ion has a charge, positive

or negative.

ex. H+, or Cl-

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An atom will gain or lose electrons to

have a full energy level. If they gain e- ,

they become more negative. If they lose

e-, they become more positive.

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Electrons can be transfered from one

atom to another atom

Ex. Na to Cl Na+ and Cl-

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Then a Ionic Bond can form. It is an

attraction between two oppositely

charged ions.

Ex. Na+ and Cl- NaCl

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A Covalent bond is the sharing of a

pair or e- between atoms.

Ex. H2O Oxygen needs two more e-, each

H needs one more e-, so oxygen shared

with two Hydrogen.

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A molecule is two or more atoms held

together by covalent bonds.

Ex. H2O, O2

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O2 molecule

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2-2 Properties of Water

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Cells of all organisms are mostly water.

Water gives cells structure, and

transports materials within organisms.

All the process necessary for life take

place in a watery (aqueous) environment.

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Water is a polar molecule. One end in

slightly negative (oxygen end) and one

end is slightly positive. (hydrogen end)

The e- in water are not equally shared.

Overall, the water molecule has a neutral

charge.

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Polar Water Molecule

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Polar Molecules form Hydrogen Bonds.

A Hydrogen bond is an attraction

between the + hydrogen atom and the –

atom of another molecule.

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Due to it’s hydrogen bonds, water has

some unique properties:

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1. High Specific Heat- water resists

changes in temperature. Water must

absorbe a great deal of heat before it

changes temperature. This helps regulate

cell temperature.

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2. Cohesion- water molecules are

attracted to each other – they stick

together. They form drops of rain, water

beads up on a window. They also form

Surface tension- like the “skin” on the

water.

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A Waterstrider

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3. Adhesion- water molecules are

attracted to other molecules.Water sticks

to a glass- forms the meniscus in a

graduated cylinder. Water is also pulled up

the vessels in plants.

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Meniscus

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Water dissolves many substance.

A solution is a mixture of substances

that is equally mixed throughout.

The solvent is the substance that is

present in a greater amount.

The solute is the substance that is

dissolved in the solvent.

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Ex. Saltwater

Solution: Saltwater

Solvent: water

Solute: salt

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Ionic compounds dissolve in water.

Non-polar substances, like oils and fats,

rarely dissolve in water.

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Acids and Bases

An Acid is a compound that releases a

proton – H+ when it dissolves.

A Base is a compound that removes

protons- H+ from a solution.

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pH 0-14

Acids- below 7

Neutral – 7

Bases- above 7

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Most organisms need to be near neutral,

7 pH.

Buffers are compounds that can bind to

H+ or release H+ to maintain

Homeostasis.

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Cells work best at a narrow pH

range!

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