ATOMS AND MOLECULES

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ATOMS AND MOLECULES

• THE CHEMICAL
• BASIS OF LIFE

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ATOMS AND MOLECULES

• Elements are not changed in normal chemical
  reactions
• Each element has a unique chemical symbol
• 92 naturally occurring elements range from
  hydrogen to uranium

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ATOMS AND MOLECULES

• Four elements make up 96 of most living
  organisms
• What are they?
• What other elements are necessary for US to live
  (think about what you eat)?
• Trace elements are necessary, but present in
  small quantities

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http//periodic.lanl.gov/
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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• Atoms are the smallest component of an element
  that retains the chemical properties of the
  element
• Atoms contain protons, neutrons, and electrons

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• An atom is uniquely identified by its number of
  protons
• A proton is a subatomic particle with one unit of
  positive charge

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• An atom is uniquely identified by its number of
  protons
• A proton is a subatomic particle with one unit of
  positive charge

• The periodic table depicts the elements in order
  of their atomic numberthe number of protons in
  the nucleus A proton is a subatomic particle with
  one unit of positive charge

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• An atom is uniquely identified by its number of
  protons
• A proton is a subatomic particle with one unit of
  positive charge

• The periodic table depicts the elements in order
  of their atomic numberthe number of protons in
  the nucleus A proton is a subatomic particle with
  one unit of positive charge

• Atomic numbers are written in subscript to the
  left of the chemical symbol

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• Proton plus neutrons determine atomic mass
• Atomic mass units (amus) are also known as
  daltons
• One amu equals the approximate mass of a proton
  or neutron

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• Isotopes differ in number of neutrons
• Some isotopes are unstable (radioisotopes)
• Many radioisotopes are important in scientific
  research

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ATOMS ARE THE FUNDAMENTAL PARTICLES OF ELEMENTS

• Electrons occupy orbitals corresponding to energy
  levels
• The outer electrons are known as the valence
  electrons and contain the most energy
• These outer electrons occupy the valence shell

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ATOMS UNDERGO CHEMICAL REACTIONS

• Atoms form molecules and compounds
• Two or more atoms combined chemically form a
  molecule
• Molecules may be composed of different or similar
  atoms

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ATOMS UNDERGO CHEMICAL REACTIONS

• A substance can be defined by a chemical formula
• Chemical formulas indicate ratios of atoms in a
  molecule
• Structural formulas show the arrangement of atoms
  in a molecule

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ATOMS UNDERGO CHEMICAL REACTIONS

• One mole of any substance contains the same
  number of units
• The molecular mass of a substance is the sum of
  the atomic masses of the atoms composing the
  molecule
• The molecular weight is dimensionless

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ATOMS UNDERGO CHEMICAL REACTIONS

• One mole of any substance contains the same
  number of units
• The molecular mass of a substance is the sum of
  the atomic masses of the atoms composing the
  molecule
• The molecular weight is dimensionless
• The number of units in a mole is Avogadros
  number- One mole is 6.02 X 1023 atoms or molecules

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Avogadro
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ATOMS UNDERGO CHEMICAL REACTIONS

• Chemical equations describe chemical reactions
• Reactants are written on the left side of the
  equation
• Products are written on the right side of the
  equation
• Reversible reactions are indicated by double
  arrows between reactants and products

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ATOMS ARE JOINED BY CHEMICAL BONDS

• In covalent bonds electrons are shared
• The electrons in the outer shell are the valence
  electrons
• Atoms tend to be reactive if the valence shell is
  not full
• The Lewis structure of the atoms represents the
  valence electrons

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ATOMS ARE JOINED BY CHEMICAL BONDS

• In covalent bonds electrons are shared
• The electrons in the outer shell are the valence
  electrons
• Atoms tend to be reactive if the valence shell is
  not full
• The Lewis structure of the atoms represents the
  valence electrons

• Covalent bonds result in filled valence shells
• A single electron pair shared between two atoms
  is a single covalent bond
• Double and triple covalent bonds are formed by
  two or three shared electron pairs, respectively
• Hydrogen forms one covalent bond
• Carbon forms a maximum of four covalent bonds

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ATOMS ARE JOINED BY CHEMICAL BONDS

• Ionic bonds form between cations and anions
• An atom becomes an ion when it gains or loses one
  or more electrons
• Cations are positively charged ions
• Anions are ions with a negative charge, and are
  named with the suffix -ide

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ATOMS ARE JOINED BY CHEMICAL BONDS

• Ionic bonds form between cations and anions
• An atom becomes an ion when it gains or loses one
  or more electrons
• Cations are positively charged ions
• Anions are ions with a negative charge, and are
  named with the suffix ide
• An ionic bond forms between cations and anions
• Ionic compounds tend to dissociate in water
  (ionize)

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ATOMS ARE JOINED BY CHEMICAL BONDS

• Hydrogen bonds are weak attractions involving
  partially charged hydrogen atoms
• In the water molecule, hydrogen is partially
  positively charged
• Hydrogen bonds form between the hydrogen atom in
  a water molecule and a partially negatively
  charged atom
• Hydrogen bonds individually are weak, but
  collectively very strong

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ELECTRONS AND THEIR ENERGY ARE TRANSFERRED IN
REDOX REACTIONS

• Oxidation and reductions reactions occur
  simultaneously, hence they are called redox
  reactions
• Reduction is a process in which an atom, ion, or
  molecule gains electrons
• Reduction is so named because the gain of
  electrons reduces the positive charge.

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REDOX REACTIONS
Redox reactions are important in both cellular
respiration and photosynthesis
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WATER IS ESSENTIAL TO LIFE
Water is important because most organisms are
composed of water and may live in water
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WATER IS ESSENTIAL TO LIFE

• Water molecules are polar
• Hydrogen atoms in the water molecule have a
  partial positive charge
• Each water molecule can form up to 4 hydrogen
  bonds

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WATER IS ESSENTIAL TO LIFE

• Hydrogen make water cohesive and adhesive
• Water molecules tend to hydrogen bond to each
  other, making water cohesive
• Water molecules tend to hydrogen bond to other
  molecules, making water adhesive
• Capillary action is a result of adhesion and
  cohesion

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WATER IS ESSENTIAL TO LIFE

• Hydrogen make water cohesive and adhesive
• Water molecules tend to hydrogen bond to each
  other, making water cohesive
• Water molecules tend to hydrogen bond to other
  molecules, making water adhesive
• Capillary action is a result of adhesion and
  cohesion
• Cohesion results in water moving upwards in
  plants
• Hydrogen bonding also results in surface tension

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Water with dish washing detergent
Distilled Water
Water with food coloring added
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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• Water tends to slightly dissociate into hydrogen
  and hydroxide ions
• The concentration of hydrogen ions in pure water
  is 10-7 moles per liter, equals the hydroxide ion
  concentration

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• Acids are substances that dissociate in a
  solution to yield H ions and Hydronium ions
• Acids are proton donors
• Acidic solutions have a higher hydrogen ion
  concentration than hydroxide ion concentration

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• Bases dissociate in solution to yield hydroxide
  ions
• Bases are proton acceptors
• Basic solutions have a lower hydrogen ion
  concentration than hydroxide ion concentration

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• pH is a convenient measure of acidity
• The pH of a solution is the negative log of the
  hydrogen ion concentration expressed in moles per
  liter
• A pH below 7 is acidic, above 7 is basic
• The pH of most living cells is slightly above 7.0

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• Buffers minimize pH change
• Weak acids and weak bases act as buffers

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• An acid and a base react to form a salt
• When an acid and base are mixed, water is formed
  from the hydrogen ions of the acid, and the
  hydroxide ions of the base
• The cation of the base and the anion of the acid
  form the salt

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ACIDS ARE PROTON DONORS AND BASES ARE PROTON
ACCEPTORS

• An acid and a base react to form a salt
• When an acid and base are mixed, water is formed
  from the hydrogen ions of the acid, and the
  hydroxide ions of the base
• The cation of the base and the anion of the acid
  form the salt
• Electrolytes are salts, acids, or bases that can
  conduct an electrical current when dissolved in
  water
• Nonelectrolytes are molecules that do not
  dissociate in water and therefore do not conduct
  an electrical current