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Matter Proton Neutron Electron Nucleus Atomic Number Mass Number Isotope Electron Shell Ion Atoms consist of: ◦ Positively charged, heavy protons in the nucleus. ◦ Heavy neutrons with no charge in the nucleus. ◦ Negatively charged, light electrons orbiting the nucleus. Atoms of different elements have different numbers of protons. He Li Pb Ag To save time when describing elements chemists use symbols instead of full words. ◦ ◦ ◦ ◦ ◦ Eg. Sodium = Na Potassium = K Mercury = Hg Lead = Pb Hurry up, I’m a busy man. We classify atoms by the number of protons that they have in their nucleus. In nature we find atoms with up to 92 protons, therefore there are 92 different types of atom. We call these ‘the elements’. Atomic Number (symbol = Z) Mass Number (symbol = A) + + + + + + O 16 + + The number of protons that an atom has in its nucleus is represented by its atomic number which may be written in either of the ways above. 8 The atomic number is the number of protons an atom has (symbol Z). The mass number is the number of protons PLUS the number of neutrons (symbol A). Helium + =Z=2 + + + + =A=4 + + + + Sometimes an atom can have more or less neutrons than another atom of the same element. This is known as an isotope (iso = same, tope = place) ‘Where do these go?’ + + ‘Same place.’ To distinguish between isotopes of an element, physicists often write the mass number as part of the symbol. Uranium-235 How would you write the isotopic symbol for the following isotopes? ◦ ◦ ◦ ◦ ◦ ◦ Carbon with seven neutrons Carbon with eight neutrons Deuterium (Hydrogen with one neutron) Tritium (Hydrogen with two neutrons) Uranium 238 Uranium 235 An atom suddenly lost two protons and two neutrons? ◦ What would happen to the mass number? ◦ What would happen to the atomic number? One of the neutrons in an atom suddenly turned into a proton? ◦ What would happen to the mass number? ◦ What would happen to the atomic number? + + + + + + O 16 + + 8 Electron Shells 2, 8, 18, 32, 50 2n2 (n = shell number) An atom can have a MAXIMUM of: ◦ ◦ ◦ ◦ 2 electrons in the first shell 8 in the second 18 in the third 32 in the fourth HOWEVER, an outer shell is considered FULL if it has EIGHT electrons. The exceptions to this are hydrogen, helium, lithium, beryllium and boron. Their outer shell is full if it has TWO electrons. F - S 2- + Na + K Atoms are most stable when they have a full outer shell. This means that atoms other than those in group eight need to gain or lose electrons. The period (row) that the element is in gives you the number of shells. The group (column) that it is in gives you the number of outer shell electrons. Draw electron shell diagrams for these atoms. How many electrons are in their outer shells? H O Li B Cl Ca Al K What do they need to do to get a full outer shell? ‘Plum Pudding Model’ By Kurzon (Own work) available at http://upload.wikimedia.org/wikipedia/commons/2/26/Plum_pudding_mod el.svg via Wikimedia Commons ‘J.J. Thompson’ By Not Mentioned (First World War.com) available at http://upload.wikimedia.org/wikipedia/commons/c/c1/J.J_Thomson.jpg, via Wikimedia Commons ‘Thompson Cathode Ray Exp’ By Kurzon (Own work) available at http://upload.wikimedia.org/wikipedia/commons/0/08/Thomson_cathode_r ay_exp.gif, via Wikimedia Commons ‘John Dalton by Charles Turner’ by Charles Turner available at http://upload.wikimedia.org/wikipedia/commons/d/d4/John_Dalton_by_Cha rles_Turner.jpg, via Wikimedia Commons ‘Ernest Rutherford LOC’ By George Grantham Bain Collection (Library of Congress) available at http://upload.wikimedia.org/wikipedia/commons/6/6e/Ernest_Rutherford_L OC.jpg, via Wikimedia Commons ‘Geiger-Marsden Experiment Expectation and Result’ By Kurzon (Own work) available at http://commons.wikimedia.org/wiki/File:GeigerMarsden_experiment_expectation_and_result.svg, via Wikimedia Commons ‘Atom Diagram’ By Fastfission at en.wikipedia available at http://upload.wikimedia.org/wikipedia/commons/d/d8/Atom_diagram.png, from Wikimedia Commons ‘Niels Bohr’ By The American Institute of Physics credits the photo [1] to AB Lagrelius & Westphal, which is the Swedish company used by the Nobel Foundation for most photos of its book series Les Prix Nobel. (Niels Bohr's Nobel Prize biography, from 1922) available at http://upload.wikimedia.org/wikipedia/commons/6/6d/Niels_Bohr.jpg, via Wikimedia Commons ‘Erwin Schrodinger’ available at http://commons.wikimedia.org/wiki/File:Erwin_Schr%C3%B6dinger.jpg via Wikimedia commons. ‘D3M0’ By Dhatfield (Own work) available at http://upload.wikimedia.org/wikipedia/commons/5/57/D3M0.png, via Wikimedia Commons ‘Periodic Table (polyatomic)’ By DePiep (Own work) available at http://upload.wikimedia.org/wikipedia/commons/9/98/Periodic_table_%28p olyatomic%29.svg, via Wikimedia Commons ‘Build an Atom’ by Kelly Lancaster et al available at https://phet.colorado.edu/en/simulation/build-an-atom courtesy of PhET Interactive Simulations at the University of Colorado. ‘Blausen 0342 ElectronEnergyLevels’ By BruceBlaus (Own work) available at http://upload.wikimedia.org/wikipedia/commons/2/2c/Blausen_0342_Electr onEnergyLevels.png, via Wikimedia Commons ‘Blausen 0476 HeliumAtom’ By BruceBlaus (Own work) available at http://upload.wikimedia.org/wikipedia/commons/d/de/Blausen_0476_Heliu mAtom.png, via Wikimedia Commons