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Introduction to Atomic Theory Some old people, facial hair and some science Aristotle • Various combinations of simple properties existed as undifferentiated matter to create every substance known • Water, air, fire and earth Dalton’s Atomic Theory • Elements are all made up of small particles called atoms • All atoms of a particular molecule are identical • Chemical compounds are unique and are made up of a particular combination of specific atoms, put together in a specific way • Chemical reactions are reshuffling of atoms to create new compounds. The new compounds are made of the original atoms in the reaction Law of Definite Proportions • Pure samples of a particular compound always contain the same proportions by mass of the elements in the compound Law of Multiple Proportions • When different masses of one element combine with a specific mass of a second element, the mass ratios of the first element are small whole number ratios. Law of Conservation • The mass of reactants and products are the same J.J. Thomson • Spherical ball of positive charge with negative charges buried inside. • Discovered the electron • Plum Pudding model. Also known as the chocolate chip cookie model. RutherfordGeiger-Marsden • Very important experiment in figuring out the atom Gold Foil Experiment • Fired alpha particles at thin sheet of gold foil • Some of the alpha particles bounced off at strange angles • Showed there was a concentration of mass in the atom: the nucleus Atom Structure • Atom is made up of tiny positively charged nucleus • Nucleus is surrounded by negatively charged electrons • Almost all the mass of the atom is in the form of protons and neutrons • # protons = # electrons to give it a neutral charge Atomic Number and Atomic Mass • Atomic number: The number of protons in an atom OR charge on the nucleus • Neutral atoms: # electrons = # protons • Ion: If electrons are added or removed from a neutral atom, then it is called an ion On the Periodic Table • Atomic Number: Always a whole number • Atomic Symbol • Atomic mass: Always a decimal number o # of protons + # of neutrons o Electrons are so light they are negligible Isotopes • Isotopes are different flavors of the same element • Same # protons, different # of neutrons • Example: Hydrogen, deuterium and tritium Mixtures of Isotopes • The reason we have decimal points for the masses on the periodic table is because they are averages of the different isotopes • Example: Chlorine is a mixture, which is 75.77% Cl-35 24.33% Cl-37 Calculation: The molar mass of Cl-35 is 34.968852g and Cl-37 is 36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of chlorine is Cl-37, what is the average molar mass of the chlorine atom in such a mixture? Calculation: The molar mass of Cl-35 is 34.968852g and Cl-37 is 36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of chlorine is Cl-37, what is the average molar mass of the chlorine atom in such a mixture? Take the percent average Calculation: The molar mass of Cl-35 is 34.968852g and Cl-37 is 36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of chlorine is Cl-37, what is the average molar mass of the chlorine atom in such a mixture? Take the percent average Mass of Cl-35= 75.77% x 34.968852 = 26.4959 Mass of Cl-37= 24.23% x 26.865803 = 8.9568 Calculation: The molar mass of Cl-35 is 34.968852g and Cl-37 is 36.965903. If 75.77% of chlorine is Cl-35 and 24.23% of chlorine is Cl-37, what is the average molar mass of the chlorine atom in such a mixture? Take the percent average Mass of Cl-35= 75.77% x 34.968852 = 26.4959 Mass of Cl-37= 24.23% x 36.965803 = 8.9568 Total mass of mixture = 26.4959+8.9568 = 35.453g Two Projects One big, one small Small Project • Using the atomic number you have drawn from the hat, please make an 8.5x11 periodic box • Include: o o o o o o Name of Element Atomic Symbol Atomic Mass Some different isotopes and their uses A picture representing the element Leave a third of the page open, as we will be adding onto this later down the road This will also be posted online on my website Big Project! • Research a scientist who was instrumental in figuring out what we know now about the atom. • Work in teams of 3 or 4 • Please sign up at the front with Mr. Lam. Know: o o o o Your teammates Your team name The scientist you want to research How you may want to present it