BSC 2010C Lecture Notes - Lecture 2: Atomic Mass, Ionic Compound, Covalent Bond
Document Summary
Life depends on chemical reactions (cid:0) matter takes up space and occupies mass. 25 of the 92 elements are essential to life. Four elements: hydrogen, oxygen, carbon, nitrogen; make up 96% of living matter (cid:0) most of the remaining 4% is accounted for by p, ca, s, k. Trace elements are required in small amounts, usually as catalysts. Definition: an element can"t be broken down to any other substance by a chemical reaction. = protons + neutrons, we will not differentiate the two terms. The outermost orbital is called the valence shell. This is the part of the atom that takes part in chemical reactions. Valence denotes the bonding capacity of an atom. Valence electrons = the number of unpaired electrons in the outermost orbital {valence. Octet rule = when atoms react they do so to obtain stability in the valence shell. In most of the atoms we will deal with in this class, 8 electrons will confer the stability.
