Chapter 2 Study Guide

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University of Toronto Scarborough
Biological Sciences
Mark Fitzpatrick

Chapter 2: The Chemistry of Life 2.1 What are the chemical elements that make up living organisms? N All matter is composed of atoms J protons, neutrons, and electrons N The mass of a proton serves as a standard unit of measure called the atomic mass unit or Dalton (1.7E-24 g) N Breakdown: Type Charge Mass (da) Info Provided Proton +1 1 Atomic number Neutron 0 1 Isotope Electron -1 negligible Reactivity N An element is a pure substance that contains only one kind of atom N 98% of the mass of a living organism is composed of six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur. N Atomic number J number of protons in an atom N Mass number J the total composition of protons and neutrons in the nucleus N Isotopes of an element have the same number of protons but different number of neutrons N Atomic weight J average of mass numbers of isotopes in their normally occurring proportions N Radioisotopes are unstable isotopes, and thus spontaneously give off energy in the form of alpha, beta, or gamma radiation N The radioactive decay transforms the atom, including the atomic number N The radioactivity can be used as a marker (such as tumor marking) N The number of electrons determine how the atoms will interact N The region of space ZZo }L]Z}LoZ}Z]K]Z ooZo }L[Z orbital N Orbitals occur in series called electron shells or energy levels N The s orbitals fill with electrons first and then subsequent shells are filled according to their energy level N Reactive atoms have unpaired electrons in their outermost (valence) shell N Atoms can share electrons, lose, or gain electrons J resulting in bonding N The octet rule J the tendency of atoms in a stable molecule to have eight electrons in their outermost shells
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