This preview shows page 1. Sign up to view the full content.
Unformatted text preview: ve the same chemical
identity but different atomic weights. • Nitrogen (3%) Remember: 65-75% of total body weight is H20 Electron shell • These variations of an element are called isotopes.
• Some isotopes are unstable and emit radioactive energy.
Such isotopes are radioisotopes. Ions • Electrons have
different levels of
• Each energy level is
called an electron shell
• Outer shell called
valence shell • If # p+ = # e–: neutral atom • Only valence shell
electrons participate in
chemical reactions • If the valence shell loses an electron = positive ion (cation). Ions & Isotopes • If # p+ ≠ # e–: charged atom = ion
• If the valence shell gains an electron = negative ion (anion). Chemical reactions occur when bonds
between atoms are formed or rearranged
+ 2 H2 +
Reactants O2 2 H2O
Reaction Products • Molecule: two or more atoms bonded together
– Compound: molecule constructed of more than
one kind of atom.
E.g.: H2 and O2 and H2O are all molecules.
• But H2 and O2 are elemental molecules.
• And H2O is a compound molecule. Heyer 2 Biological Chemistry Molecules can be represented in many ways
(a) Hydrogen (H 2 ).
atoms can form a
single bond. (b) H O Water (H 2O). H O O H Ball-and-stick
model Hybrid-orbital model
model superimposed) •Biological molecules have many atoms bound precisely in complex forms.
•How does the right rearrangement of the right bond at the right time happen? H O H H Methane (CH 4 ).
atoms can satisfy
the valence of
methane. O O Two hydrogen
atoms and one
oxygen atom are
joined by covalent
bonds to produce a
molecule of water.
(d) H Spacefilling
model Oxygen (O 2). Two oxygen atoms
share two pairs of
electrons to form
a double bond.
formula Living cells carry out millions of chemical reactions
that rearrange matter in significant ways C H C 104.5 ° H H H H H H C H H H H H H
H O O H H H
Electron pair C
View Full Document
- Spring '10
- molecular biology