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  1. Lesson Standards:Protons and electrons have equal but opposite charges. The number of protons equals the number of electrons in an atom 3.1e.The outermost electrons in an atom are called the valence electrons. In general, the number of valence electrons affects the chemical properties of an element 3.1l.3.1viii Draw a Lewis electron-dot structure of an atom. DO NOW Answer the Regents Practice questions regarding isotopes and WAM on your Guided Notes sheet.

  2. Regents Practice • A meteor crashes to Earth, is collected and analyzed. To everyone’s surprise, a new element is discovered with an atomic number of 120. Calculate the weighted average atomic mass for this new element, Ubn(Unbinnulium). Show all your work.

  3. Electrons: A particle with a net charge of –1 and a mass of 1/1836 amu, found in the energy levels outside the nucleus. • Why is it important to know how many electrons are in each energy level of an atom? • Because the outermost (valence) electrons in an atom are responsible for all physical and chemical properties of elements and compounds. • Basic Configuration • Valence Electrons • Electron-Dot (Lewis Dot) Diagrams

  4. Basic Configuration • The number of electrons is determined from the atomic number (number of protons = number of electrons in an atom) • Look up the basic configuration below the atomic number on the periodic table—it shows how many electrons are found in each shell or energy level • (PEL or Principal Energy Level = shell). • He: 2 (2 e- in the 1st PEL) • Na: 2-8-1 (2 e- in the 1st PEL, 8 in the 2nd and 1 in the 3rd) • Br: 2-8-18-7 (2 e- in the 1st PEL, 8 in the 2nd, 18 in the 3rd and 7 in the 4th)

  5. Valence Electrons • The valence electrons are responsible for all chemical bonding. • The valence electrons are the electrons in the outermost PEL (shell). • Co: 2-8-15-2 (2 valence electrons) • Ag: 2-8-18-18-1 (1 valence electron) • S: 2-8-6 (6 valence electrons) • Pb: ___________________________ • The maximum number of valence electrons an atom can have is EIGHT, called a STABLE OCTET.

  6. Electron-Dot Diagrams • The number of dots equals the number of valence electrons. • The number of unpaired valence electrons in a nonmetal tells you how many covalent bonds that atom can form with other nonmetals or how many electrons it wants to gain from metals to form an ion. • How many bonds can carbon form? • The number of valence electrons in a metal tells you how many electrons the metal will lose to nonmetals to form an ion. Caution: May not work with transition metals.

  7. EXAMPLE DOT DIAGRAMS Carbon can also have this dot diagram, which it has when it forms organic compounds.

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