Chemistry: The Basis For Life

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Chemistry The Basis For Life
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Matter
liquid
gas
solid
definite volume definite shape
definite volume No definite shape
No definite volume No definite shape
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Elements

• Element- a substance that can no longer be broken
  down into smaller substances while keeping their
  characteristic properties
• 106 named elements
• 92 elements occur naturally
• 20 are necessary for life

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Essential Elements

• Oxygen
• Nitrogen
• Carbon
• Hydrogen
• Sulfur
• Phosphorous

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99.9

• Magnesium
• Chlorine
• Sodium
• Iron
• Potassium
• Calcium

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The Atom

• Atom- the smallest indivisible unit of an element
  that still has the characteristic of that element
• There are 9 sextillion atoms (9,000,000,000,000,0
  00,000,000) in a penny.

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Subatomic Particles
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Atoms Nucleus

• All atoms of the same element have the same
  number of protons
• Change the number of protons
• change the element
• Atomic (written in subscript to the left of the
  atomic symbol) protons
• The number of neutrons can vary within the same
  element.
• The number of neutrons can be determined by using
  the mass number which is the sum of the protons
  and neutrons (written as a subscript to the left
  of the atomic symbol)(electrons have almost no
  mass).

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Electrons

• Atom- of electrons of protons
• Ion- of electrons ? of protons, as a result
  of the difference the ion has a positive or
  negative charge
• Goal of atomsfill outermost energy level.
• can be done bygaining electrons
• sharing electrons
• losing electrons
• Atoms are most stable when their outermost
  electron level is stable. The electrons in the
  outermost orbital are called valence electrons.

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Electrons and Energy

• Not every electron has the same amount of energy.
  The potential energy that an electron has is
  determined by its distance from the nucleus. The
  more energy the electron contains, the further it
  will be from the nucleus an electron with low
  energy will be closer to the nucleus.
• Electrons can move to a higher energy level by
  having added to it (sunlight and light energy)
  The electron becomes excited by absorbing some of
  the energy and moves to a higher energy level.
  When this electron moves back to its original
  position, the same amount of energy that it took
  to move the electron is released.

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How do atoms fill their energy shell?

• Electronegativity is the tendency of an atom to
  attract a bonding pair of electrons. Florine is
  the most electronegative at 4.0 and down to
  caesium and francium which are least
  electonegative at 0.7
• Depending on the difference of electronegativity
  different types of bonds can form

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• polar covalent bond If the atoms are equally
  electronegative, both have the same tendency to
  attract the bonding pair of electrons, and so it
  will be found on average half way between the two
  atoms. This is called a pure covalent bond.
• nonpolar covalent bond If the two atoms differ
  in electronegativity, the atom with the higher
  elecronegativity will attract the electron more
  and becomes partially negatively charged. The
  other atom becomes partially positively charged.
  The electron is still shared.
• ionic bond If the difference in
  electronegativity is so great the higher
  elecronegativity charged atom will steal the
  electron completely and form a - charge. The
  other atom short an electron form a charge.
  These are ions. The - and ions attract and
  ionic compounds form. Cations are positively
  charged ions and Anions are negatively charged
  ions.
• hydrogen bond These happen between molecules.
  The electrons between hydrogen and the other
  atoms are shared unequally (Hydrogen forms a
  polar covalent bond with an atom with greater
  electronegativity) This unequal sharing causes
  the hydrogen to have a partial positive charge.
  The hydrogen is attracted to another atom or
  molecule with a slight negative charge.

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Examples
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Polarity

• polar molecules
• lopsided molecules / asymetrical
• one side of the molecule is partially positive
  the other is partial negative.

• nonpolar molecules
• symetrical

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Electronegativity
Increase in elecronegativity
Ionic

• Polar covalent

nonpolar covalent
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Acids and Bases

• http//occawlonline.pearsoned.com/bookbind/pubbook
  s/campbell6e_awl/chapter3/deluxe.html

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The EndClick For Part II The Chemistry of
Water