Presentation on theme: "Chapter 2 The Chemical Context of Life. Comment u Much of this chapter should be review from a basic chemistry course. Much of the material is unlikely."— Presentation transcript:
Isotopes u Atoms of the same (iso-) element with different atomic mass. u Caused by changes in the number of neutrons. u Used as “tracers”.
Types of Isotopes 1. Radioactive - where the nucleus decays spontaneously, giving off particles and energy. 2. Heavy - has a stable nucleus, but masses more than the standard isotope for the element.
Electron Energy Levels u Energy levels around the nucleus of an atom. u 1st level can have 2 electrons and has the lowest potential energy. u Other levels can hold more than 2 electrons and have higher energy levels.
Electron Orbitals u The three dimensional space where an electron is found 90% of the time. u Different orbitals have different shapes. u Each orbital can hold only 2 electrons.
Chemical Behavior Of An Atom u Is determined by its electron configuration in the energy levels and orbitals.
Valence Electrons u The electrons in the outermost energy level. u Electrons available chemical bonds.
Octet Rule u The most stable condition is to have an outer level of 8 electrons. u Exception - 1st level is stable with only 2 electrons. u When stable - no chemical reactions will take place. Ex: Ne, He, (Noble gases)
Hydrogen Bonds u When a hydrogen atom bonded to one molecule is attracted to the slightly negative area (often N or O) of another molecule. u Very weak individual bond. u Can be a “strong” force if there are many H bonds.