Trace Elements: required by organisms in minute amounts

Essential elements: C, H, O, N (most abundant)


  • “Smallest unit of an element; consists of nucleus of (+) protons and neutrons”
  • Electrons orbit the nucleus
    • Mostly energy, negligible mass
    • Stay at fixed energy level but if absorb energy can move to shell further
  • The type of bonds that form between atoms and its strength depends on the electronegativities of atom
    • (low to high) nonpolar covalent → polar covalent → ionic

Ionic Bonds

  • Form between atoms when electrons are transferred from one atom to another → Forms ions
  • Occurs when there is a great electronegativity difference

Covalent Bonds

  • Form when electrons are shared; neither atom completely holds electron
  • Single covalent, double covalent, and triple covalent bonds form when two, four, and six electrons are shared respectively

Nonpolar Covalent Bonds

  • When electrons are shared equally → atoms have same/similar electronegativity
  • No charge = hydrophobic                                                                                

Polar Covalent Bonds

  • When electron are shared unequally → atoms have diff electronegativity
  • Single water molecule held by polar covalent bonds
  • Yes charge = hydrophilic

Hydrogen Bonds

  • Weak bonds between molecules; form when (+) charged hydrogen atom in one covalently bonded molecule is attracted to (-) charged area of another covalently bonded molecule → results from polarity
    • Strong in large numbers
  • Bond holds one water molecule to another water molecule


Heat of fusion: energy required to change water from a solid to liquid

Heat of evaporation: energy required to change water from liquid to gas

Mass Number: number of protons and neutrons

Isotopes: atoms of same elements with diff mass/number of neutrons

Electronegativity: measure of an atom’s attraction for electrons

  • Allows oxygen to form polar and hydrogen bonds

Energy: capacity to do work

Potential energy: energy that matter has because of location

  • Electrons have potential energy because of distance from nucleus

Electron Shell: distance from nucleus where electrons found

  • Further = more energy

Valence electrons: outermost electrons

  • Determine chemical behavior

Molecule: 2 or more atoms held by bonds

  • Molecule shape determined by position of valence electrons orbitals

Compound: two or more different elements joined together chemically