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Physical Science Chapter 17: Atoms and the Periodic Table Atomic Structure Notes Review What is an atom? An atom is the smallest particle of an element that still retains the properties of that element. Atomic Symbol - The shorthand abbreviation that is used to identify an element (element name) - Atomic symbols have o A capital letter at the beginning of the symbol (all symbols have this) o Some have a lower case letter after the capital letter Be careful! The letters of the atomic symbol do not always match the name of the element o o Examples: Hydrogen Helium Magnesium Potassium Iron Sodium __________ __________ __________ __________ __________ __________ Label the element name and atomic symbol on the diagram above Nucleus (discovered by Rutherford in 1911) - The center of the atom - Contains a majority of the mass of the atom (99.9%), but a small portion of the volume - Relative size of the nucleus: IF the atom was the size of a stadium, the nucleus would be the size of a marble. - The nucleus contains: o Protons Have a positive charge Have a mass of 1.6726 x 10-24 grams or 1 atomic mass units (amu) The number of protons determines the type of atom that you have!! (If you change the number of protons, you change the element!) We call this the atomic number Label the atomic number on the diagram above Complete the table below. Use the Periodic Table on p. 518 to help you. Element Atomic Symbol Atomic Number # of Protons Copper Cu 29 29 Bromine Br 35 35 Lead Pb 82 82 o Neutrons (Discovered by Chadwick in 1932) Are neutral, which means they have no charge Have a mass of 1.6749 x 10-24 grams or 1 atomic mass units (amu) To determine the number of neutrons in an atom, you need to know the atom’s mass number Mass number: the sum of the number of protons and the number of neutrons in the nucleus of an atom # of Neutrons = Mass Number – Atomic Number If you are given the mass number and the number of neutrons, how can you figure out the number of protons? - o Subtract the number of neutrons from the mass number Protons and Neutrons can both be broken down even farther into quarks. More info on pg. 508 Electrons (Discovered by JJ Thompson in 1904) - Have a negative charge - Have a very small mass (approximately 9.1093 x 10-28 grams or 0.00055 amu) - In a neutral atom, the total number of electrons equals the number of protons - Can be found in electron clouds surrounding the nucleus (Developed in 1926) o Electrons are so small and move so quickly that it is impossible to determine their exact location (fan example) however we can predict it based on probability o The electron cloud is approximately 100,000 times larger than the nucleus o Each electron cloud has a different amount of energy o The electron clouds closest to the nucleus have the lowest amount of energy, and the electron clouds furthest from the nucleus have the most energy o Electrons fill the energy levels from the inner levels to the outer levels Each level can hold a specific number of electrons 32 electrons 18 electrons 8 electrons 2 electrons *Note: Remember the Bohr model (proposed in 1913 by Niels Bohr) is no longer the accepted model for the atom, however it is easier to understand the behavior of electrons and where they are located if we imagine the electron clouds as orbits. Drawing Atomic Structure Draw a diagram of a neutral atom for the element that contains 2 protons and has a mass number of 4. Element name: Helium Protons: 2 Electrons: 2 Neutrons: 2 p+= 2 n =2 Draw a diagram of a neutral atom for the element that contains 12 protons and has a mass number of 24. Element name: Magnesium Protons: 12 Electrons: 12 Neutrons: 12 p+= 12 n = 12 Draw a diagram of a neutral atom for the element that contains 9 electrons and has a mass number of 19. Element name: Fluorine Protons: 9 Electrons: 9 Neutrons: 10 p+= 9 n = 10 Isotopes Atoms of the same element that contain the same number of protons, but a different number of neutrons Because isotopes have a different number of neutrons, they also have different mass numbers. Most elements have more than one isotope, and therefore have an average atomic mass. o The average atomic mass is the weighted average mass of an element’s various isotopes (takes into consideration which isotopes are more abundant than others). The average atomic mass can be found on the Periodic Table. Label this on the diagram on the first page. Isotopes can be symbolized in a few ways: 1) Atomic symbol, mass number, and atomic number Mass number Atomic number 14 6 C Atomic Symbol 2) Atomic name or symbol with a hyphen and mass number Carbon-14 or C-14