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Chapter 5 Atomic Structure and the Periodic Table Section 5.1 Atoms Q OBJECTIVES: –Summarize Dalton’s atomic theory. –Describe the size of an atom. Adapted from notes by Stephen L. Cotton © History of the atom Greek philosopher: –. ~400 B.C. Q Smallest possible piece of stuff (matter)? –. - not to be cut Q Dalton’s Atomic Theory (late 1700s) 1 All matter is made of tiny particles called atoms. 2 Atoms of the same element are . 3 Atoms of different elements combine in to form compounds. 4 Chemical reactions involve the of atoms… atoms are neither created or destroyed. How Small Is an Atom? of cutting a piece of aluminum foil into smaller and smaller pieces… How many times can it be cut and still be aluminum? Q An is the smallest particle of an element that retains the properties of that element Section 5.2 Structure of the Nuclear Atom Q Think Q OBJECTIVES: – Distinguish among protons, electrons, and neutrons in terms of relative mass and charge. – Describe the structure of an atom, including the location of the protons, electrons, and neutrons with respect to the nucleus. 1 Thomson’s Experiment Parts of Atoms Q J. J. Thomson (1897) - made a piece of equipment called a . –Consists of a lined vacuum tube. - Thomson’s Experiment Thomson’s Experiment Voltage source Voltage source - + Q By Other particles Q. + - positively charged pieces 1840 times heavier than the electron – E. Goldstein Q. - no charge but the same mass as a proton – J. Chadwick Q Where are these “pieces” in the atom? adding an electric field… Rutherford’s Gold Foil Experiment Ernest Rutherford - English physicist. (1910) Q Alpha particles – helium atoms without their electrons Q Shot alpha particles at a very thin piece of . Q 2 What did Rutherford Expect? Q The alpha particles would pass through the atom changing direction very much. Q Thought the negative charges were spread out evenly in the atom and that most of the alpha particles right through the gold would foil. What he expected Since he thought the mass was evenly distributed in the atom Because What he got 3 How he explained it Atom is mostly Q Small, dense, positive piece at center = Q Alpha particles are deflected if they get close enough to the Q . + + Subatomic particles – p.111 Relative Actual mass (g) Name Symbol Charge mass Electron Proton Neutron Counting the Pieces = number of protons in the nucleus Q. determines which atom you have. Q Atomic number is the same as the in a neutral atom. Q. = the number of protons + neutrons. Section 5.3 Distinguishing Between Atoms Q OBJECTIVES: – Explain how the atomic number identifies an element. – Use the atomic number and mass number of an element to find the numbers of protons, electrons, and neutrons. – Explain how isotopes differ, and why the atomic masses of elements are not whole numbers. – Calculate the average atomic mass of an element from isotope data. Symbols Q. X Z A Note: The arrangement of X, Z, and A may vary!!! 4 Symbols the: –number of protons –number of neutrons –number of electrons –atomic number –mass number Symbols Q Determine Q Determine F199 the: –number of protons –number of neutrons –number of electrons –atomic number –mass number Symbols Q If an element has an atomic number of 34 and a mass number of 78 what is the: –number of protons –number of neutrons –number of electrons –complete symbol Isotopes Dalton was wrong… atoms of the same element are always identical!!! Q. . – Have number of protons so are same element, but number of neutrons, so are isotopes of the same element… Ex: C-12 & C-13. Q 80 35 Br Symbols Q If an element has 91 protons and 140 neutrons what is the: –atomic number –mass number –number of electrons –complete symbol Measuring Atomic Mass Q Unit is the Q 1 amu = the mass of a C-12 atom… which happens to have protons and neutrons in its nucleus!!! 5 Average Atomic Mass Q Calculate the average atomic mass of copper if copper has two isotopes. 69.1% of the isotopes have a mass of 62.93 amu and 30.9% of the isotopes have a mass of 64.93 amu. Atomic Mass Q Magnesium has three isotopes. 78.99% magnesium-24 with a mass of 23.9850 amu, 10.00% magnesium-25 with a mass of 24.9858 amu, and the rest is magnesium-26 with a mass of 25.9826 amu. What is the average atomic mass of magnesium? Average Atomic Mass not usually a whole number because it is an . Q Is the number with the decimal places for each element in the periodic table usually printed above or below the element symbol… we will use average atomic mass a lot in the future!!! Section 5.4 The Periodic Table: Organizing the Elements Q Is Development of the Periodic Table Q mid-1800s, about elements known by Q Elements arranged in order of increasing Q Father of the first “ ” Q Developed Q OBJECTIVES: –Describe the origin of the periodic table. –Identify the position of groups, periods, and various other locations in the periodic table. Mendeleev Left blanks spaces for undiscovered elements based upon “ ” Q Examples of periodic Trends – – – – Q Ex: Mendeleev predicted Ekasilicon existed, which was later discovered and named . Q 6 Modern Day Periodic Table Q Henry Moseley – arranged elements according to increasing . Q Developed the Periodic Table. Periodic table Q Horizontal Q Vertical column = Areas of the periodic table Q Group A elements = . rows = Metals Q Generally: Group IA – Group 2A – Q Group B Q Q Nonmetals Q Generally: and . Metalloids Q Have properties intermediate between . Q Located along the “ ” of the periodic table. Q Group 7A – Q Group 0 – 7