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The Structure of the Atom Mr. O’Brien (SFHS) Chapter 4 Standard 1.E&A Structure of an Atom (std.1E) (figure 1) Early model of an atom. If atoms were empty space then the experiment would have showed no deflection. • What is the Earliest Idea of an Atom – the atom was EMPTY SPACE with (-) particles “floating around”. • What is the Current Idea of an Atom? – Rutherford Experiment. • Exposed a thin gold foil to a stream of particles. • 99.8% of particels went through. • 0.2% of particles were deflected or bound back! THIS PROVED DISCOVERY OF A VERY SMALL NUCLEUS! (figure 2) ACTUAL RESULTS! The particles bounced back. Discovery of Nucleus! (figure 2) Imagine the atom’s nucleus to be the size of a bean, the atom itself will become the size of a stadium. The electrons will be like tiny fleas whizzing frantically somewhere around the stands. Structure of an Atom (std. 1E) Atom: smallest particle of an element that retains the properties of the element. – ex: Copper (Cu) • There are 29,000,000,000,000,000,000,000 Copper atoms in a penny! • What’s in an Atom? NUCLEUS (figure 1) Illustrates the size of a nucleus (the golf ball) and the distance between the nucleus and the edge of an atom. • tiny & dense center of an atom • contains protons (+) charge particles • contains neutrons (have NO CHARGES) Cool Facts of the Nucleus •100,000x smaller than its atom •Contains 99.9% of the atoms mass •Protons & neutrons have the same mass (1a.m.u.). (figure 2) If there are 29,000,000,000,000,000,000 ,000 atoms in one copper penny, what does that say about the size of one atom? So What Does Atom Look Like??? What is the net charge of the nucleus? ELECTRON CLOUD • contains electrons (é) (-) charge particles • Move very fast and unpredictable around the nucleus Cool Facts of the Electron Cloud •An electron is 1/2000 a.m.u. the size of a proton. BEST representation Not a good representation Recap Structure of an Atom (std.1E) • Atom is smallest particle that retains element property. • Atom is mostly made up of empty space. – Atom contains an electron cloud. – Electrons are 2000x smaller than a proton or neutron! • Atom has a tiny dense core called the nucleus. – Nucleus is virtually all the mass of the atom. – Protons mass (1a.m.u.) = Neutron mass (1a.m.u.) – An atom can be up to 100,000x bigger in diameter than the nucleus! • Atom is electrically neutral: – Electron charge (-1) cancels out proton charge (+1) Atoms & Isotopes (std.1a) • What makes elements unique from each other? • Atomic Number • The number of protons in an atom. • The atomic number can never be changed in an element. • The Periodic Table organizes all known elements by increasing atomic number. (figure 1) the image to the left shows liquid nitrogen rapid evaporating. Pencil lead is just one product made from carbon atoms • What unit is used to measure the mass of atoms? • Atomic Mass Units (a.m.u.) • Standard is based on 1/12 a carbon atom Atoms & Isotopes (std.1a) • Is there more of than one type of nitrogen or one type of carbon? • Isotopes • Atoms of the same element with different number of neutrons but same number of protons. • Why is the mass number different than the atomic mass on the periodic table? • Atomic mass is an average of all isotopes. • Mass number is the sum of the number of protons + neutrons (of specific isotope) • Why is carbon atomic mass 12.011 a.m.u.? • More carbon-12 exist than any other isotope. • That’s why the average is closer to 12. Atoms & Isotopes (std.1.A) • How do you calculate number of particles? • Protons are found on the periodic table (atomic number) • Neutron are found by subtracting protons from Mass Number. Mass number – protons = neutrons • Electrons = protons = atomic number isotope Protons Neutrons electrons Carbon-12 6 6 6 Carbon-13 6 7 6 Carbon-14 6 8 6 Experimental Discoveries (std.1H) • The Discovery Recap: – J.J. Thomson: Use a Cathode Ray Tube to discover that gas particles carried a negative charge. – Robert Millikan: confirmed Thomson’s experiment that electrons are identical particles by balancing tiny, electrically charged oil droplets that separated into equal distances. – Ernest Rutherford: Shot positive alpha particles through gold foil and discovered that atoms had positive dense nucleus. Calculating Atomic Mass of Isotopes (hnrs) Isotope Abundance for Element X Isotope Atomic Mass % abundance X6 6.015 7.5% X7 7.016 92.5% • Example: Calculate the atomic mass of unknown element X. Then, identify the unknown element, which is used to medically treat some disorders. • 1st step: multiply mass of Isotope X6 by the percent abundance (how much there is in the world). Do the same for Isotope X7. – (6.015a.m.u.)(0.0750) = 0.451a.m.u. – (7.016a.m.u.)(0.925) = 6.49a.m.u. • 2nd step: Sum the mass contributions. – (0.451a.m.u. + 6.490a.m.u.) = 6.941a.m.u. • 3rd step: Match the new atomic mass with the periodic table. – 6.941a.m.u. is Lithium.