2.  Made of only 1 type of atom  92 naturally occurring ◦ H, Fe, O, Ca, N, C  Compounds – H 2 O, CO 2, C 6 H 12 O 6 (glucose)  C,H,N,O,P,S found in all life ◦ Previous + Ca = 99% of human body  > 20 elements in body (Table 2-1)

3.  Smallest part of an element retaining element’s properties  Consists of protons (+), neutrons (0), and electrons (-) ◦ Protons, neutrons in nucleus ◦ Electrons orbiting nucleus in electron cloud (shell)  Atomic number = # of protons  Atomic weight = #protons + #neutrons

5.  # protons = # electrons ◦ Atom is neutral  Electrons bond to other atoms to form molecules ◦ Molecule – combination of atoms that are tightly bound and behave as a single unit  Electrons orbit nucleus in shells (energy levels) ◦ First – holds 2 electrons (stable) ◦ Second – holds 8 electrons (stable) ◦ Higher– stable with 8 or a multiple of 8 electrons

6.  Few atoms are naturally stable (He, Ne)  Most atoms gain, lose, or share electrons to fill their outer shell ◦ Atoms form chemical bonds with other atoms to become stable

7.  Force or attraction between (+) and (-) charges that joins atoms to form a molecule  Molecules often have characteristics different from original elements ◦ H 2 and O 2 are gases, but H 2 O is a liquid  4 kinds of bonds ◦ Ionic ◦ Covalent ◦ Disulfide ◦ Hydrogen

8.  Involves loss of electron(s) by one atom and gain of electron(s) by another atom(s) (Fig. 2-2)  1. Na loses electron in outer shell  2. Has a charge of (+1); now a sodium ion  3. Cl atom gains an electron in outer shell  4. Has a charge of (-1); now is a chloride ion  5. (+) and (-) charges attract  6. Result in NaCl (table salt) ◦ Held together by ionic bond

10.  CaCl 2 is another example  Cations – ions with (+)  Anions – ions with (-)  Ionic bonds are strong in solid form, but weakened in aqueous (water) solution ◦ Dissociation  e.g. sodium chloride ionizes into Na and Cl ions

11.  Sharing of electrons b/w atoms  An oxygen atom shares 2 electrons with another oxygen atom, also sharing 2 electrons (Fig. 2-3)  Oxygen atom may share 2 electrons with 2 hydrogen atoms, each sharing a single electron (Fig. 2-3)  Single covalent bond – pair of shared electrons; single line  Double covalent bond – 2 pairs of shared electrons; double line

13.  C forms 4 covalent bonds ◦ e.g. CH 4 (methane)  May form bonds with other C, H, O, N, etc.  Covalent bonds are relatively strong; not weakened in water sol’n

14.  Disulfide bonds (disulfide bridge) – covalent bond between 2 sulfur atoms ◦ Insulin has 2 disulfide bonds ◦ Straightening curly hair breaks disulfide bonds

15.  H atom shares electron in a covalent bond with another atom  Its proton is slightly (+) and may be attracted to nearby O or N atom, which are slightly (-)  Weak bonds, but important ◦ Proteins, DNA ◦ Make water cohesive (water molecules stick together)

16.  Change brought about by forming or breaking chemical bonds  Two types ◦ Synthesis – bonds are formed to make a new compound  Require energy ◦ Decomposition – bonds are broken, resulting in smaller molecules  Release energy

17.  Inorganic compounds - simple molecules often consisting of 1 or 2 different elements  Water ◦ Essential to life  Solvent  Lubricant  Changes temp. slowly

18.  Solvent ◦ solutes can dissolve in water  Lubricant ◦ prevents friction where surfaces meet & move  Changes temperature slowly ◦ Has high heat capacity  Will absorb a lot of heat before temp. rises much  Must lose a lot of heat before temp. drops much ◦ Has high heat of vaporization  Can release a great deal of heat, without much water loss

19.  Intracellular fluid (ICF) ◦ Water within cells; 65% of total water  Extracellular fluid (ECF) ◦ 35% of total water  Plasma – in blood vessels  Lymph – in lymphatic vessels  Tissue or interstitial fluid – in small spaces b/w cells  Specialized fluids – synovial, cerebrospinal fluid (CSF), aqueous humor in eye

21.  O 2 is 21% of atmosphere, which we inhale  Essential for cell respiration ◦ Cells break down glucose to release energy ◦ ATP used for cellular processes requiring energy

22.  Waste product of cell respiration  If amount in body fluids increases, fluids become too acidic (acidosis)

23.  Energy production within cells  Involves oxygen, carbon dioxide C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + ATP + heat  CO 2 is exhaled  Water becomes part of intracellular fluid  Heat contributes to normal body temp.  ATP used for cell processes