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Warm-up: To be turned in. Fill in the blanks: According to Bohr, electrons move in certain _______ around the nucleus. When an electron moves from a lower energy level to higher one, it _________ energy. One problem with Bohr’s atomic model is that it only works with the _____________ atom.
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Warm-up: To be turned in Fill in the blanks: According to Bohr, electrons move in certain _______ around the nucleus. When an electron moves from a lower energy level to higher one, it _________ energy. One problem with Bohr’s atomic model is that it only works with the _____________ atom.
Configuration of Electrons Valence Electrons and Lewis Dot Structure
Recall from last unit… • Bohr model: electrons orbit the nucleus in certain paths (orbits) around the nucleus • Different paths correspond to different energy levels • Each energy level can have a maximum number of electrons • 1= 2 electrons • 2= 8 electrons • 3= 18 electrons • 4+= 32 electrons
Valence Electrons • Electrons available to be lost, gained, or shared in the formation of chemical compounds • Located in the highest energy level of that atom • Any atom can have up to 8 valence electrons • Number of valence electrons increases as you move from group 1 to group 18
Valence Electrons, cont. • Group 1 (alkali metals)= 1 valence electron • Group 2 (alkaline-earth metals)= 2 valence electrons • Group13= 3 valence electrons • Group 14= 4 valence electrons • Group 15= 5 valence electrons • Group 16= 6 valence electrons • Group 17 (halogens)= 7 valence electrons • Group 18= 8 valence electrons (except He)
Practice! • How many valence electrons do these atoms have? Phosphorous Chlorine Silicon Xenon Sulfur
Lewis-dot Structure • Also known as electron-dot notation • Electron configuration notation in which only the valence electrons of an atom are shown • Represented as dots surrounding the chemical symbol • Ex: F N • When you draw the dots, draw one on each side BEFORE pairing them • Remember: like repels like, so the electrons want to be away from each other
Practice! • Draw the Lewis-dot structure for the following elements: Phosphorous Chlorine Silicon Xenon Sulfur
Homework: Due Weds. 10/10/12 • For each of the following atoms, identify the number of valence electrons and draw the Lewis-dot structure: Lithium Fluorine Boron Calcium Cesium Magnesium Krypton Iodine Carbon Silicon Aluminum Indium Nitrogen Helium Hydrogen