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Chapter 2: The Chemical Context of Life

Everything we know and love is made of matter.

"Matter" is anything that takes up space or has mass.

The word "matter" is only a general term to describe everything that exists in the known universe.

Of the 92 natural elements, 25 are essential for life.

Of those 25, only 4 make up 96% of living matter:

  • Carbon (C)
  • Oxygen (O)
  • Hydrogen (H)
  • Nitrogen (N)

Trace elements are those that are required for life, but are

only necessary in small quanities.

However, if essentail elements aren't present, organisms will suffer from disease.

The properties of elements are dependent on the structure of the atoms.

  • Atoms are composed of subatomic particles (Neutrons, Protons (+) and Electrons (-)

Isotopes:

  • Isotopes are atoms of the same element that have a different number of neutrons
  • Isotopes may be radioactive, spontaneously emiting particals and energy
  • Among other things, isotopes are commonly used to date fossils and as medical tracers

ENERGY!

Energy:

Energy is the capacity to cause change. It exists in two possible states.

The volatility of elements is dependent on their number of valence electrons.

  • Valence electrons are those in the outermost shell
  • The most volatile elements are those that possess only one valence electron as well as those that are missing only one electron to complete their outermost shell.

Chemical Bonds

Covalent bonds:

  • In this situation, two atoms share valence electrons to complete their respective shells.
  • They are the strongest of bonds.
  • Molecules consist of two or more atoms covalently bonded together

With covalent bonding comes electronegativity.

-groan-

Electronegativity is the attraction of one atom to the electrons in a covalent bond.

Atoms with high electronegativity pull shared electrons with more strength.

Bonds between two atoms of different electronegativities are "polar-covalent bonds"

Ionic Bonds:

  • When two atoms bond ionically, one atom strips valence electrons from the second atom.
  • Atoms that have a charge are called ions.

Ions come in two varieties:

  • Anions are negatively charged (have gained electrons)
  • Cations are positively charged (have lost electrons)

Hydrogen Bonds:

  • Hydrogen bonds form when a hydrogen atom that is covalently bonded to an electronegative atom is -also- attracted to another electronegative atom
  • They are among the weakest bonds

Chemical Reactions!

Chemical reactions make and break chemical bonds and lead to changes in the composition of matter

Examples of chemical reactions include photosynthesis and cellular respiration.

Also

EXPLOSIONS!

...the end.

Matter

atoms

Elements and Compounds

Organels

Cells

etc.

The energy possessed by an atom's electrons vary in relation to the electron's distance from the nucleus

  • Electrons have more energy the farther they are from the nucleus
  • When electrons absorb energy, the enter an "excited" state and move to a higher level of the atom's electron shell
  • When electrons lose energy, they descend to a lower level

Protons and neutrons make up

an atom's nucleus, while electrons

orbit in the "electron cloud."

Elements differ in their number of subatomic particles:

  • The total number of protons in an atom's nucleus makes up the atomic number
  • Protons + neutrons make up an atom's atomic mass

Like ice cream, chemical bonds come in a few different flavors.

Double covalent bond (two pairs of shared electrons)

Single covalent bond (one pair of shared electrons)

Energy

In a non-polar covalent bond, two atoms with similar electronegativities share electrons equally.

Because water is very electronegative, one end of the molecule has a slight negative charge that repels the slightly positive hydrogen molecules.

Kinetic energy: energy of motion

Potential energy: the energy that matter possesses because of location or structure

Thus, an ionic bond is an attraction between an anion and a cation.

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