Observation information obtained through the senses; observation in science often involves measurement

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1 Review Sheet Unit 1: The Atom Chemistry the study of the composition of matter and the changes matter undergoes Scientific Method Scientific method a logical, systematic approach to the solution of a scientific problem; steps in the scientific method include making observations, testing hypothesis, and developing theories Observation information obtained through the senses; observation in science often involves measurement Hypothesis a proposed explanation for an observation Experiment a repeatable procedure that is used to test a hypothesis Dependent variable the variable that is observed during the experiment Independent variable the variable that is changed during an experiment by the scientist Scientific law a concise statement that summarizes the results of many observations and experiments Theory a well-tested explanation for a broad set of observations Matter Density the ratio of the mass of an object to its volume Mass a measure of the amount of matter that an object contains Volume a measure of the space occupied by sample of matter Matter anything that has mass and takes up space Solid a form of matter that has a definite shape and volume Liquid a form of matter that flows, has fixed volume, and an indefinite shape Gas a form of matter that takes the shape and volume of its container; a gas has no definitive shape or volume Mixture a physical blend of two or more substances that are not chemically combined Heterogeneous mixture a mixture that is uniform in composition; components are evenly distributed and not easily distinguished

2 Homogeneous mixture a mixture that is uniform in composition; components are evenly distributed and not easily distinguished Compound - two or more atoms of DIFFERENT ELEMENTS chemically combined; always the same ratio Element the simplest form of matter that has a unique set of properties; an element cannot be broken down into simpler substances by chemical means Physical change a change during which some properties of a material change; but the composition of the material does not change Chemical change a change that produces matter with a different composition than the original matter Physical property a quality or condition of a substance that can be observed or measured without changing the substance s composition Chemical property the ability of a substance to undergo a specific chemical change Chemical reaction a change in which one or more reactants change into one or more products; characterized by the breaking of bonds in reactants and the formation of bonds in products Extensive property a property that depends on the amount of matter in a sample (e.g. mass and volume)

3 Intensive property a property that depends on the type of matter in a sample; not the amount of matter (e. g. density) Energy the capacity for doing work or producing heat Atomic Structure Atom The smallest particle of an element that retains its identity in a chemical reaction; cannot be broken down into its components by chemical means Chemical symbol a one or two letter representation of an element (oxygen O, sodium Na) Dalton s Atomic Theory- the first theory to relate chemical changes to events at the atomic level Law of conservation of mass in any physical change or chemical reaction, mass is conserved; mass can be neither created nor destroyed Nucleus - the DENSE, POSITIVE, CENTRAL core of an atom Neutrons - subatomic particle with a MASS of 1 amu (atomic mass unit), and a CHARGE of zero found WITHIN THE NUCLEUS; (NEUTRAL) Protons - subatomic particle with a MASS of 1 amu (atomic mass unit), and a CHARGE of +1 found WITHIN THE NUCLEUS Nuclear charge - electric charge within the nucleus of an atom; equal to the # of protons (always positive!) Electron a negatively charged subatomic particle; located in the electron cloud

4 Isotopes - an atom of an element with the same number of protons (atomic #) but a different number of neutrons Ex: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) Mass number - the mass of a given isotope of an element; the sum of the masses of protons and neutrons Ex: The mass number for Carbon-12 is exactly 12 amu, even though the atomic mass (average mass) of all carbon isotopes is Atomic number the number of protons in the nucleus of an atom of an element Average atomic mass the weighted average of the masses of the isotopes of an element Models of the atom Rutherford god foil experiment atoms have a positive center Bohr model (planetary model) - atomic model constructed by Neils Bohr that proposes all electrons can be found in orbits or paths outside nucleus (electrons must gain or lose energy to jump from one orbit to another) Wave mechanical Model (electron cloud model) - states that electrons don t travel in fixed orbits, but that we can use mathematic principals to predict where electrons are most likely to be found

5 The Electron Cloud Model and Atomic Orbitals Energy Level the specific energies an electron in an atom or other system can have Atomic Orbital a mathematical expression describing the probability of finding an electron at various locations; usually represented by a region of space around the nucleus where there is a high probability of finding an electron Electron configuration the arrangement of electrons of an atom in its ground state into various orbitals around the nuclei of atoms Aufbau diagram- fill lower sublevels first

6 Valence electrons are the electrons in the outer shell. Exceptions to the Aufbau Principle Chromium: Cr's electron configuration, following the model would be: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 4 4s 2, but instead it is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1, because there is extra stability gained from the half-filled d orbital. Copper: Cu's electron configuration, following the model would be: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 9 4s 2, but instead it is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1, because there is extra stability gained from the half-filled d orbital. Emission Spectrum Ground state the lowest possible energy level of an electron described by quantum mechanics; when the electrons are where they would normally be Excited state - when an atom absorbs energy and one or more of its electrons jump to an orbital further from the nucleus Atomic Emission Spectrum The pattern formed when light passes through a prism or diffraction grating to separate it into the different frequencies of light it contains Amount of energy emitted by the electron when jumping from the n=5 energy level to the n=2 energy level. The amount of energy released is equal to the amount of energy absorbed when excited