Basic Chemistry

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Basic Chemistry

• REVIEW

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Chemistry is the study of Matter

• Matter anything that takes up space and has
  mass (ex. solid, liquid, gas)

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Elements

• Cannot be broken down into smaller substances
• Make up all matter
• 92 occur in nature
• Designated by a symbol of 1 or 2 letters

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4 Elements make up 96 of most living organisms

• Carbon
• Hydrogen
• Oxygen
• Nitrogen
• The other 4 calcium, phosphorous, potassium,
  sulfur, sodium, chlorine, magnesium, and TRACE
  ELEMENTS

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Trace Elements

• Required by organisms in minute (small)
  quantities
• They are critical for life
• Ex. Iron, Zinc

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Compounds

• A molecule composed of atoms or two or more
  elements combined in a fixed ratio.

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Atoms

• Units of matter.
• The smallest component of an element that retains
  the chemical properties of the element.
• Atoms contain subatomic particles.

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Subatomic Particles

• (1) Proton (2) Neutron (3)
  Electron
• Found Nucleus Nucleus Outside
• Charge () ()/(-) (-)
• Weight 1 amu 1 amu 1/2000 amu

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Atoms are defined by

• There number of Protons
• Protons Atomic , which are generally written
  in subscript to the left of the chemical symbol
• Ex. 2 He

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Atomic Mass

• protons neutrons
• This is because the mass of an electron is so
  insignificant that it is ignored (1/2000 of a
  proton or neutron)
• Atomic mass units are known as AMUs (or Daltons)
  1 amu the approximate mass of a proton or
  neutron, written as a superscript.
• Ex. 4 2He

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Isotopes

• Atoms with the same atomic but different mass
  .
• Ex. 12 6C 13 6C 14 6C
• Unstable isotopes are radioactive. Often they
  are used as tracers or labels.

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Electrons

• Found in orbitals corresponding to energy levels.
• Outermost electrons are called Valence Electrons
  and contain the most energy.
• They have great potential energy because they are
  attracted to the () nucleus
• The further the distance between the e- and the
  nucleus greater potential energy!

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Electrons

• The e- in the first shell closest to the nucleus
  is the lowest in energy.
• Electrons can change their shell by absorbing or
  losing energy.
• To move a shell out, e- must absorb energy.
• To move a shell in, e- must lose energy.

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Orbitals

• The 3-D space where an e- spends 90 of its
  time.
• It is NOT a defined pathway of movement.
• No more than 2 e- can occupy the same orbital.

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Orbitals

• orbitals/shell orbitals/level max e-
• 1s 1 1 2
• 2s 1 4 8
• 2p 3 4 8
• 3s 1 9 18
• 3p 3 9 18
• 3d 5 9 18

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Chemical Behavior

• Determined by its e- configuration.
• Chemical properties depend mostly on the of e-
  in the outer most or valence shell.
• An atom with a complete valence shell is
  unreactive or inert.

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Chemical Bonds

• Attractions that hold molecules together.
• Atoms undergo chemical rxns. to form molecules
  and compounds.
• Molecules can be composed of different or similar
  atoms.

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Covalent Bonds

• One or more pairs of valence electrons are
  shared. Results in full valence shells.
• Can be
• Single
• Double
• Triple

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Molecular Shapes

• Molecules composed of 2 atoms are linear.
• Molecules composed of more than 2 atoms form
  complicated shapes.
• Shape is important because it is the basis for
  how molecules recognize and respond to one
  another.

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Electronegativity

• A measure of an atoms ability to attract and
  hold electrons.
• The more electronegative the atom, the more
  strongly it pulls shared e- towards itself.

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Polar vs. Nonpolar

• Covalent bonds can be polar or nonpolar.
• In a nonpolar bond e- are shared equally
  (symmetry)
• H-H, CH4
• Same electronegativity!

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Polar vs. Nonpolar

• In a polar bond e- are shared unequally
• ex H2O
• Oxygen is more electronegative than Hydrogen
• e- spends more time around Oxygen
• The oxygen in water has a slight negative charge
  and each hydrogen has a slight positive charge.
  (Its a POLAR molecule)

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Ionic Bonds

• Feature the transfer of e- from a donor to an
  acceptor.
• A charged atom is called an ION
• A () charged atom is called a CATION
• A (-) charged atom is called a ANION
• Ionic bonds are formed between anions and
  cations. (NaCl)

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Salts

• Ionic compounds are called salts
• Ionic bonds tend to dissociate in water (ionize)
• Na loses an e- OXIDIZED
• Cl- gains e- REDUCED

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Hydrogen Bonds

• Weak attractions involving partially charged
  hydrogen atoms.
• Forms when a hydrogen atom covalently bonded to
  one electronegative atom is also attracted to
  another electronegative atom
• There is a weak attraction between the (-)
  charged oxygen atom and the () hydrogen atom of
  adjacent water molecules.

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Why are hydrogen bonds important?

• Contact can be brief - used as signals or
  recognition sites
• Weak bonding force - DNA replication
• Proteins - reinforce 3-D shape
• Energy used to vaporize water breaks the
  hydrogen bonds between adjacent water molecules.

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Hydrogen bonds and Water

• Cohesion (sticking together)
• Adhesion (sticking to something)
• Hydrophilic (water loving)
• Hydrophobic (water fearing) NON SOLUBLE IN
  WATER
• Due to hydrogen bonding the evaporation of water
  requires large amounts of heat!

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Chemical Reactions

• Making and breaking of chemical bonds.
• Starting materials reactants
• End materials products
• Some reactions go to completion - all reactants
  get converted to products
• Most reactions are reversible
• Chemical Equilibrium rate forward rxn rate
  backward rxn

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Acids, Bases and pH

• Acids donate H ions when they dissociate in
  water
• Bases reduce the H concentration of a solution,
  dissociate to form OH- ions (accept H or donate
  OH-)
• pH scale 0 -14
• 1 strong acid
• 7 neutral
• 14 strong base

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Acids, Bases and pH

• The lower the pH, the GREATER the concentration
  of H ions.
• If H concentration of a solution is 10-12
  Molar then the OH- concentration must be 10-2 M
  (exponents must add to 14)
• Buffers prevent great fluctuations in pH