Chemical Context of Life

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Chemical Context of Life

• Chapter 2

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• Matter - anything that takes up space, has mass.
• Element - substance cannot be broken down by
  chemical reaction (i.e. copper)
• Represented by a symbol (Cu)

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• Compound - consists of 2 elements combined in
  fixed ratio.
• 92 natural elements, 25 essential.
• Carbon, oxygen, nitrogen, hydrogen, phosphorus,
  sulfur included.

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• Atom - smallest unit of matter still has
  properties of original element.
• Composed of subatomic particles.
• Neutrons are neutral, protons positive charge,
  and electrons negative charge.

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http//serc.carleton.edu/images/usingdata/nasaimag
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• Protons and neutrons - found in atomic nucleus
  electrons orbit nucleus.
• Atoms of one element have same number of protons
  in nuclei (atomic number)
• Protons and neutrons together - mass number.

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Negative charge
Positive charge
Neutral charge
http//www.bartleby.com/images/A4images/A4atom.jpg
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• Mass - atomic number of neutrons.
• Atomic weight - total mass of atom.
• Electrons weigh very little mass number is
  approximation of atomic weight of atom.

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Isotopes

• Isotopes - atoms of element have different
  numbers of neutrons (different weights)
• Element exists as mixture of isotopes.
• Radioactive isotope (carbon-14) - nucleus decays
  spontaneously and gives off energy.

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http//education.jlab.org/glossary/isotope.gif
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Energy

• Energy - ability to do work.
• Potential energy - stored energy kinetic energy
  - energy of motion.
• Top of a hill, potential energy rolling down the
  hill, kinetic energy.
• Electrons change positions while orbiting nucleus.

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• Positions around nucleus - electron shells or
  energy levels.
• Move away from the nucleus, energy levels
  increase.
• Electron absorbs energy as it moves away from
  nucleus.
• Gives off energy as moves closer to nucleus.

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Bonding

• Atoms share or transfer atoms (bonding)
• Atoms held together by electrons they share or
  transfer.
• Covalent bonding - pair of electrons shared.
• 2 atoms held together by covalent bond
  molecule.

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• Covalent bonds either polar or nonpolar.
• Electrons shared equally - nonpolar.
• Electrons closer to 1 atom polar (1 atom more
  electronegative than other).

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• Ionic bonds - 1 atom donates electrons to other
  atom - form compounds (i.e. salt).
• Ionic and covalent bonds - strong.

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Sodium donates electron to chlorine.

• Ionic bond

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Polar covalent bond electrons pulled closer
to oxygen.

• Polar bond

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• There are weaker bonds that exist briefly.
• Hydrogen bonds form when H atom covalently bonds
  to one atom but attracted to another atom.
• Occurs mostly with O2 (like in water).

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Reactions

• Chemical reaction - making and breaking of
  chemical bonds.
• Starting materials reactants ending materials
  - products.
• Concentration of reactants determines how fast or
  slow reaction will go.

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Rusting is an example of a chemical reaction
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