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Chemistry

Chemistry. Chapter 4: How Atoms Differ : Atomic number = # p + AND e - (assume neutral atom for charge). Rounded (whole number) mass number = # p + + # n 0 . Rounded average mass number – Atomic number = #n 0 . Symbol notation (Element; mass # and atomic #). 1. Chemistry. Ions :

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Chemistry

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  1. Chemistry Chapter 4: How Atoms Differ: Atomic number = # p+ AND e- (assume neutral atom for charge). Rounded (whole number) mass number = # p+ + # n0. Rounded average mass number – Atomic number = #n0. Symbol notation (Element; mass # and atomic #). 1

  2. Chemistry Ions: When atoms are NOT balanced for charge they are called ions. Positive ion: Atom has lost electrons. Called cations (symbol). Negative ion: Atom has gained electrons. Called anions (symbol). Symbol system for ions. 2

  3. Chemistry Isotopes: When the number of neutrons is different BUT the proton number is the same…: Chemical behavior is the same. The more neutrons, the greater the mass number (mass). Most elements found in nature are a mixture of isotopes. Isotopes differ for their relative abundance in nature (show as a %). 3

  4. Chemistry Atomic and Mass # Review: The atomic number provides the number of protons in the nucleus and the number of electrons in a neutral atom. The mass number tells us the number of protons and neutrons in the nucleus. The mass # minus the atomic # provides the number of neutrons. The mass # is different for isotopes of the same element. 4

  5. Chemistry Isotopes and Ions Review: Different isotopes of the same element that are neutral for charge are different for neutron # and mass #; they are the same for electron # andproton #. Ions of the same element are different for electron # and charge ; they are the same for atomic # and mass #. Cations have a positivecharge because electrons have left the atom. Anions have a negative charge because electrons have entered into the atom. 5

  6. Chemistry Average Atomic Mass: Chemists used a standard of C-12 as being 12 amu; 1 amu is 1/12 of C-12. Calculating average atomic mass need number of naturally occurring isotopes, their masses AND their abundance (percentage of the total found in the environment). 6

  7. Chemistry Average Atomic Mass: Round I: Calculate the atomic mass of element X and identify the element from the periodic table using the following data: 63X (62.930 amu; 69.2% abundance). 65X (64.928 amu; 30.8%) Answer: 63.5 amu; Copper (Cu) 7

  8. Chemistry Average Atomic Mass: Round II: Calculate the atomic mass of element Y and identify the element from the periodic table using the following data: 54Y (53.940 amu; 5.9% abundance). 56Y (55.935 amu; 91.72%) 57Y (56.935 amu; 2.1% abundance) 58Y (57.933 amu; 0.28% abundance). Answer: 55.844 amu; Iron (Fe) 8

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