BIOLOGY 172 Lecture Notes - Lecture 2: Null Hypothesis, Characteristic Class, Mass Number
Document Summary
Hypothesis: testable statement that can be used to build more complex explanations. Law: descriptive generalization, does not explain why something happens. Theory: overarching explanation that is well-substantiated and can incorporate facts, laws, inferences, tested hypotheses. Based on results, revise hypothesis and repeat process. Every different atom has characteristic number of protons (atomic number) Atoms with same atomic number are same element, have same chemical properties. Forms of element with different numbers of neutrons are isotopes. Mass number: number of protons + neutrons of most common isotope. Move around atomic nuclei in specific regions called orbitals: each orbital holds up to 2 electrons. Orbitals grouped into levels called electron shells: electron shells numbered, with smaller numbers closer to nucleus, electrons in outermost shell are called valence electrons. Elements commonly found in organisms have at least one unpaired valence electron. Number of unpaired electrons is an atom"s valence. Atoms are most stable when each orbital has 2 electrons.
