Biology 6th Edition Campbell, Reece - Ch 2

            
             Distinguish between an element and a compound.
             An ELEMENT is a substance that cannot be broken down to other substances by a chemical reaction. While a COMPOUND is a substance consisting of two or more elements combined in a fixed ratio.
             Exploring Life on its Many Levels.
             2. Identify the four elements that make up 96% of living matter. .
             The 4 elements that make up 96% of living matter are: Carbon (C), oxygen (O), hydrogen (H), and nitrogen (N).
             The remaining 4% consist of: Phosphorus (P), sulfur (s), calcium (Ca), potassium (d), and a few others.
             Atoms and Molecules.
             3. Describe the structure of an atom.
             Atom: is the smallest unit of matter that still retains the properties of an element. Atoms consist smaller parts called SUBATOMIC PARTICLES. Only 3 types of particles are stable enough to be of significance: Neutron: An electrically neutral particle (a particle having no electrical charge), found in the nucleus of an atom. Proton: A subatomic particle with a single positive electrical charge, found in the nucleus of an atom. Electron: A subatomic particle with a single negative charge; one or more electrons move around the nucleus of an atom. .
             4. Define and distinguish among atomic number, mass number, atomic weight, and valence.
             Atomic Number: a subscript to the left of the symbol of the element. It tells us the number of protons and electrons in an electrically neutral atom.
             Mass Number: The sum of protons plus neutrons in the nucleus of an atom. .
             Atomic Weight: The total atomic mass, which is the mass in grams of one mole of the atom. .
             Valence: The bonding capacity of an atom generally equal to the number of unpaired electrons in the atom's outermost shell.
             5. Given the atomic number and mass number of an atom, how do you determine the number of its neutrons?.
             Mass number - Atomic Number = # of Neutrons.
             6. Explain why radioactive isotopes are important to biologists.
             Radio Isotopes: An isotope (an atomic form of a chemical element) that is unstable; the nucleus decays spontaneously, giving off detectable particles and energy.