chapter02 - Focus What are atoms made of? How are they...

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1 Focus • What are atoms made of? • How are they arranged in molecules and ions that make up the substances that we encounter every day? • How do we associate the name of a substance with its chemical formula? (Covered in experiment #2 lab too!) 2 The Nuclear Atom • 1900’s - atom consisted of positively charged matter with electrons scattered throughout (chocolate-chip cookie model by Thomson) • 1910 - Rutherford performed “gold-foil” experiment. Proposed a new model of the atom; nucleus contained positive charges (later called protons) 3 Rutherford’s Experiment 4 The Nuclear Atom • Rutherford’s model left one problem; if H has a mass of 1; then He should have a mass of 2 ….but its mass is 4! • 1932 - James Chadwick discovered the neutron. The mystery was solved.
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5 2.3 Atomic Number • The chemical identity of an atom can be determined solely from its atomic number atomic number (Z) - number of protons in the nucleus of each atom of an element • also indicates number of electrons in the atom—when atoms are neutral 6 Mass Number mass number (A ) - total number of neutrons and protons present in the nucleus • Standard notation follows: mass number (number of protons + neutrons) A Z X Element symbol atomic number (number of protons) 7 8 Isotopes • Many elements consist of atoms that differ slightly in mass. Heavy isotopes (for the most part) behave the same as lighter isotopes. • Isotopes: same atomic number ( Z ) but different mass numbers ( A )
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9 Isotopes of Hydrogen • Hydrogen-1 • Deuterium (hydrogen -2) • Tritium (hydrogen -3) • How many protons, neutrons and electrons in each isotope of hydrogen? 1 1 H 1 2 H 1 3 H 10 Mass Spectrometer Measuring atomic masses Sample In Data Out 11 2.4 Periodic Table 12 Periodic Table • Periods - horizontal rows • Families (Groups) - vertical columns – Elements in the same family have similar chemical and physical properties
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13 Periodic Table Metals - good conductors of heat and electricity (majority of elements on the table-located to the left of the stair step)
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chapter02 - Focus What are atoms made of? How are they...

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