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| matter consists of chemical elements in pure form and in combinations called compounds. |
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| elements cant be broken down chemically to other substances. A compound contains two or more different elements in a fixed ratio. |
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| essential elements of life |
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| carbon, oxygen, hydrogen, and nitrogen make up approximately 96% of living matter. |
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| an element's properties depend on the structure of its atoms. |
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| an atom, the smallest unit of an element, has the following components |
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| atomic number & atomic mass |
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| an electronically neutral atom has equal numbers of electrons and protons; the number of protons determines the atomic number. The atomic mass is measured in daltons and is roughly equal to the sum of protons plus neutrons. |
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| isotopes of an element differ from each other in neutron number and therefore mass. unstable isotopes give off particles and energy as radioactivity. |
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| The energy levels of e-... |
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| in an atom, e- occupy specific energy shells; the e- in a shell have a characteristic energy level. |
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| e- distribution & chemical properties |
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| e- distribution in shells determines the chemical behavior in an atom. An atom that has an incomplete valence shell is reactive. |
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| e- exist in orbitals, 3d spaces with specific shapes that are componenets of e- shells. |
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| The formation & function of molecules depend on chemical bonding between atoms. |
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| chemical bonds form when atoms interact & complete their valence shells. Covalent bonds form when pairs of e- are shared. |
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| a hydrogen bond is an attraction between a H atom carrying a partial + charge and an electronegative atom - charge. van der waals interactions occur between transiently + and - regions of molecules. weak bonds reinforce the shapes of large molecules and help molecules adhere to each other. |
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| molecular shape & function |
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| a molecule's shape is determined by the positions of its atoms' valence orbitals. Covalent bonds result in hybrid orbitals, which are responsible for the shapes of water, methane, and many more complex biological molecules. shape is usually the basis for the recognition of one biological molecule by another. |
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| chemical rxns make & break chemical bonds |
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| chemical rxns change reactants into products while conserving matter. all chemical rxns are theoretically reversible. chemical equilibrium is reached when the forward and reverse rxn rates are = |
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