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BIOL 102 (99)
Chapter 2


3 Pages

Course Code
BIOL 102
Dr.Ada Mullett

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CHAPTER 2 Atom- smallest functional unit of matter, forms all chemical substance, cannot be broken down Chemical Element- each specific type of atom Atomic nucleus- where protons and neutrons are confined to a small space  Protons have one unit of positive charge  Electrons have one unit of negative charge  Nucleus has a net positive charge equal to the number of protons  Nucleus has no electric charge because the protons attract an equal number of electrons  Electrons do not orbit the nucleus in an organized path  Electrons travel within in regions that surround the nucleus  Orbitals- where there is a high probability of finding electrons  Some orbitals are spherical (s orbitals)  Some orbital are propeller or dumbbell shaped (p orbital)  The energy shell closest to the nucleus fills up with the lowest energy electrons first and then higher  Orbitals occupy energy shells that are associated with specific energy levels  Innermost energy shell: spherical orbital (1s)  Second energy shell: two orbitals, one spherical (2s) and three dumbbell (2p)  Electrons determine how many orbitals and energy shells  Atoms that have unfilled energy shells obtain, share or release electrons to fill their outer energy shell  Valence electrons- electrons in the outer energy shell that are available to combine with other atoms  Daltons (Da)- units atomic mass is measured in  Weight is derived from the gravitational pull on a given mass, depends on location  Avagadro’s Constant: 6.022 x 10 23  Isotopes- defer in the number on neutrons but same protons  Radioisotopes- lose energy through radiation by emitting subatomic particles  Two or more atoms bonded together make a molecule  Compound- molecule made of two or more elements  Covalent bond- sharing of electrons, between atoms whose energy levels are not full  Atoms most stable when outer energy level is full  Double bond occurs when atoms share two pairs of electrons  Electronegativity- measure of an atoms ability to attract electrons in a bond from another atom  In a covalent bond the shared electrons orbit is closer to the atom with a higher electronegativity creating a polarity in the distribution of the charge  Polar covalent bonds- skewed distribution of electrons towards one of the atoms which creates a polarity across the molecule  The molecule itself is called a polar molecule or dipole  H 2 is a polar molecule: the shared electrons are closer to the oxygen, the unequal sharing gives water a region of partial negative charge and two regions of positive charge, this leads to its physical properties  High EN atoms have strong attraction for electrons (oxygen, nitrogen)  Ion- when an atom gains or loses electrons  Cations- net positive charge  Anions- net negative charge  Ionic Bond- cation and anion bind together  Free Radical- an atoms with a single unpaired electron  Free radicals can do harm to living cells, causing cell membranes to rupture or damage the genetic material  Chemical reaction- when one or more substances are changed into another substance  Chemical rxn all require energy  Heat energy causes atoms to vibrate and move (Brownian Motion)  Catalyst- speeds up chemical rxn without itself being affected  Chemical rxn proceed in a certain direction until they reach a state of equilibrium Van der waals forces- electrostatic interactions between molecules of opp
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