Chapter 2 Study Guide

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University of Toronto Scarborough
Biological Sciences
Mark Fitzpatrick

Chapter 2 The Chemistry of Life Chemical Elements -all matter is composed of atoms -atom consists of a dense, positively charged nucleus & negatively charged electrons orbit around the nucleus -nucleus contains protons & neutrons -atomic mass unit (amu) is mass of proton -mass of electrons can be ignored because its mass is very low -proton has positive electric charge, +1 -electron has negative charge equal to that of proton, -1 -neutron is neutral & has no charge -when number of proton equals number of electron, atom is neutral Element -element is pure substance that contains only one kind of atom -6 main elements found in organism: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur Protons -atomic number is the number of proton -mass number is the total number of proton & neutron in the nucleus -atomic number is written at the lower left, mass number at the upper left Neutrons -isotope is element that has the same number of proton, but different number of neutron -atomic mass atomic weight is the average mass of element based on the relative abundance of various isotopes -radioisotope is unstable & gives off energy in the form of alpha, beta or gamma radiation from atomic nucleus -can be used as tag and label to trace organism -radioactive decay is the release of energy that transforms original atom ->can change number of protons, resulting in different elements Electrons -impossible to determine the exact location of electron at any given time -can only estimate the volume of space electron is located in orbital -1 electron shell contains 1 s-orbital, hold up to 2 electrons -2 electron shell contain 4 orbitals (1 s-orbital, 3 p-orbital), hold up to 8 electrons -higher energy level means electron needs more energy to overcome the pull of positively charged nucleus -s-orbital (the lowest energy level) fills with electrons first -valence (outermost electron shell) determines how atom behaves chemically -atom is stable when valence shell reaches maximum number of electrons -stable elements are helium neon, argon (noble gas)
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