151F09_W5_LV_short - UA GenChem General Chemistry General...

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Unformatted text preview: UA GenChem General Chemistry General Chemistry CHEM 151 CHEM 151 Week 5 UA GenChem Unit 2: Zooming In Unit 2: Zooming In What are they made of? What holds them together? Why are they joined in this way? Why are there forces between them? ( intermolecular forces ) They could be atoms, molecules, ions UA GenChem Electrical Nature Electrical Nature How do we explain this? We assume atoms and molecules have an electrical nature ( they are made of + and - charges ) Understanding charge distribution in atoms and molecules is of central importance in chemistry. UA GenChem Atoms are characterized by the number of protons in the nucleus ( atomic number, Z ). In a neutral atom , the number of protons is equal to the number of electrons . Mass Number, A (protons+ neutrons) Atoms Atoms Made of electrons (- ) , protons ( + ), and neutrons (no charge). old new A X Z 12 6 C 6 12 C Periodic table UA GenChem Atomic Number, Atomic Number, Z Z , and , and Mass Number, Mass Number, A A Mass Number Mass Number A A = # protons + # neutrons = # protons + # neutrons A boron atom can have A boron atom can have A A = = 5 p + 5 n 5 p + 5 n A Z 10 5 B A Z 10 5 B All atoms of the same element have the same All atoms of the same element have the same number of protons number of protons in the nucleus, in the nucleus, Z, Z, b but they may differ in the number of neutrons UA GenChem Isotopes Isotopes Atoms of the same element ( Atoms of the same element ( same Z same Z ) but different mass ) but different mass number ( number ( A A ). ). Boron-10 ( Boron-10 ( 10 10 B) has B) has 5 p 5 p and and 5 n 5 n Boron-11 ( Boron-11 ( 11 11 B) has B) has 5 p 5 p and and 6 n 6 n 10 B 11 B How many p and n in this atom? C 12 6 ?? 208 82 What is this? UA GenChem What is the nuclide symbol for plutonium-246? How many protons, neutrons and electrons are in the isotope? Pu 246 94 UA GenChem Atomic Mass Atomic Mass The scale of atomic masses is defined relative to a standard: 12 g/mol 1.00728 g/mol 10.0129 g/mol 11.0093 g/mol 78.918 g/mol Because of the existence of Because of the existence of isotopes isotopes , the mass of , the mass of an atom in the periodic table is expressed as an an atom in the periodic table is expressed as an average value of the mass of the different natural average value of the mass of the different natural isotopes....
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151F09_W5_LV_short - UA GenChem General Chemistry General...

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