Download Atomic Structure Summary Sheet

Atomic Structure and Stoichiometry Summary Sheet 2 “An atom is the smallest particle of an element that retains the chemical properties of that element.” (Modern Chemistry, p.64, 2002) I.
Atomic Structure A. Basic structure of an atom 1. Nucleus – center of the atom a. Proton i. Positive charge ii. Determines atomic number iii. Have a mass unit of 1 AMU iv. Used to calculate atomic mass b. Neutron i. Neutral charge ii. Have a mass unit of 1 AMU iii. Used to calculate atomic mass iv. Number of neutrons varies in isotopes 2. Electron cloud—outer portion of the atom a. Electron i. Negative charge ii. Mass not significant to be counted in the mass of the atom. iii. Arrangement determines how reactive an atom is. iv. Makes up most of the volume of an atom. b. Orbital i. A three dimensional region around the nucleus where a particular electron might be found. ii. Elements in the same GROUP have the same number of valence electrons. B. Atoms are electrically neutral. II.
Atomic Theories A. Law of Conservation of Mass 1. Mass is neither destroyed nor created during ordinary chemical reactions or physical change. B. Law of Definite Proportions 1. Chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of the sample or the compound. C. Law of Multiple Proportions 1. If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the first element is always a ratio of small whole numbers. D. Dalton’s Atomic Theory 1. All matter is composed of extremely small particles called atoms. 2. Atoms of a given element are identical in size, mass and other properties; atoms of different elements differ in size, mass and other properties. 3. Atoms cannot be subdivided, created or destroyed. 4. Atoms of different elements combine in simple whole number ratios to form chemical compounds. 5. In chemical reactions, atoms are combined, separated or rearranged. E. Discovery of the Electron 1. Cathode Rays Tubes (Joseph John Thomson) a. When current is passed through a cathode ray tube the surface directly opposite the cathode glows. b. Made observations using cathode ray tubes to discover the negatively charged particle called the electron because they were deflect (repelled) by the negatively charged side. 2. Millikan’s experiments a. Mass of the electron is one two-­‐thousandth the mass of the simplest type of hydrogen atom. b. Electron mass is 9.109 x 10-­‐31 kg F. Discovery of the nucleus 1. Ernest Rutherford a. The volume of the nucleus is very small compared to the total atom. b. Gold Foil experiment III.
Counting atoms A. Atomic number = number of protons B. Isotopes = have a different atomic mass, different number of neutrons than the “normal” atom. 1. Are used to calculate the atoms average atomic mass. C. Mass Number (Atomic Mass)=Number of protons + neutrons 1. Average atomic mass=weighted average of the atomic masses of the naturally occurring isotopes of an element. D. Molar Mass/Atomic Mass/Formula Weight 1. The mass of one mole of a pure substance (g/mol)