Drawing Dot Structures for Molecules
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Questions and Answers

What is the first step in drawing the dot structure for a molecule?

  • Identify the group number of the elements
  • Find the total number of valence electrons (correct)
  • Determine the number of covalent bonds
  • Determine the number of energy levels

    • What does the group number of an element correspond to?

  • The number of energy levels
  • The number of periods
  • The number of covalent bonds
  • The number of valence electrons (correct)

    • What is the maximum number of electrons that can be fit in the first energy level?

  • 6
  • 4
  • 2 (correct)
  • 8

    • What is the significance of the octet rule in drawing dot structures?

    <p>It states that the maximum number of electrons in the second energy level is 8</p> Signup and view all the answers

    What is true about the second period of the periodic table?

    <p>Elements have a maximum of 8 valence electrons</p> Signup and view all the answers

    How many valence electrons does hydrogen have?

    <p>1</p> Signup and view all the answers

    What is the relationship between periods and energy levels in the periodic table?

    <p>Periods are horizontal and energy levels are vertical</p> Signup and view all the answers

    What is the purpose of using a modified periodic table when drawing dot structures?

    <p>To show the relationship between group numbers and valence electrons</p> Signup and view all the answers

    What is the purpose of understanding the octet rule in drawing dot structures?

    <p>To help draw dot structures for elements like carbon, nitrogen, oxygen, and fluorine</p> Signup and view all the answers

    Why is it possible for elements in the third period to exceed the octet rule?

    <p>Because they have more orbitals available</p> Signup and view all the answers

    How many valence electrons does a single atom of silicon have?

    <p>Four</p> Signup and view all the answers

    What is the total number of valence electrons in the molecule silicon tetrafluoride?

    <p>32</p> Signup and view all the answers

    Why is silicon chosen as the central atom in the dot structure of silicon tetrafluoride?

    <p>Because it is the least electronegative element</p> Signup and view all the answers

    How many covalent bonds are drawn in the initial dot structure of silicon tetrafluoride?

    <p>Four</p> Signup and view all the answers

    How many valence electrons are represented in the initial dot structure of silicon tetrafluoride?

    <p>Eight</p> Signup and view all the answers

    What is the main goal of step three in drawing dot structures?

    <p>To assign leftover electrons to terminal atoms</p> Signup and view all the answers

    Why do fluorine atoms need to be surrounded by eight electrons?

    <p>Because they are in the second period</p> Signup and view all the answers

    What is the valence electron count for oxygen in the periodic table?

    <p>6</p> Signup and view all the answers

    What is the central atom in the molecular formula CH2O?

    <p>Carbon</p> Signup and view all the answers

    How many valence electrons are needed to represent in the dot structure of CH2O?

    <p>12</p> Signup and view all the answers

    What is the purpose of step four in drawing the dot structure?

    <p>To create multiple bonds if the central atom doesn't have an octet</p> Signup and view all the answers

    Why are hydrogen atoms not considered when deciding the central atom?

    <p>Because they are ignored in this step</p> Signup and view all the answers

    How many valence electrons are left over after assigning electrons to the carbon and hydrogens in CH2O?

    <p>6</p> Signup and view all the answers

    What is the trend for electronegativity in the periodic table?

    <p>It increases as you move from left to right</p> Signup and view all the answers

    What is the purpose of step three in drawing the dot structure?

    <p>To assign the leftover electrons to the terminal atoms</p> Signup and view all the answers

    What is the valence electron count for carbon in the periodic table?

    <p>4</p> Signup and view all the answers

    How many valence electrons are assigned to each fluorine atom in the dot structure?

    <p>6</p> Signup and view all the answers

    What do you do with leftover electrons after step three in drawing a dot structure?

    <p>Assign them to the central atom</p> Signup and view all the answers

    What happens if the central atom has an octet or exceeds an octet after assigning leftover electrons?

    <p>You are usually done with the dot structure</p> Signup and view all the answers

    Why do you not need to worry about formal charges in this example?

    <p>Because formal charges will be discussed in the next video</p> Signup and view all the answers

    What is the typical way to represent the dot structure of xenon pentafluoride cation?

    <p>By putting brackets around the dot structure and a positive charge outside</p> Signup and view all the answers

    What is the purpose of drawing dot structures?

    <p>To predict the shape of a molecule</p> Signup and view all the answers

    What is the total number of valence electrons in the xenon pentafluoride cation?

    <p>42</p> Signup and view all the answers

    What is the correct dot structure for formaldehyde?

    <p>Carbon with a double bond to oxygen and two lone pairs of electrons</p> Signup and view all the answers

    What type of electrons are involved in bonding between atoms?

    <p>Bonding electrons</p> Signup and view all the answers

    How many valence electrons does xenon have?

    <p>8</p> Signup and view all the answers

    Why does the xenon pentafluoride cation have a positive charge?

    <p>It lost an electron</p> Signup and view all the answers

    What is the total number of valence electrons in the xenon pentafluoride cation?

    <p>42</p> Signup and view all the answers

    What is the central atom in the xenon pentafluoride cation?

    <p>Xenon</p> Signup and view all the answers

    How many valence electrons are represented by the bonds in the xenon pentafluoride cation?

    <p>10</p> Signup and view all the answers

    Why can xenon exceed the octet rule in the xenon pentafluoride cation?

    <p>Because it can expand its outer shell</p> Signup and view all the answers

    How many valence electrons are left over after representing the bonds in the xenon pentafluoride cation?

    <p>32</p> Signup and view all the answers

    How many valence electrons are assigned to each fluorine atom in the xenon pentafluoride cation?

    <p>6</p> Signup and view all the answers

    Study Notes

    Drawing Dot Structures

    • Step 1: Find the total number of valence electrons
      • Look at the periodic table to find the number of valence electrons for each atom in the molecule
      • Group number corresponds to the number of valence electrons
      • Periods (energy levels) determine the maximum number of electrons that can be held
      • The octet rule: elements in the second period (energy level) can have a maximum of 8 electrons
    • Step 2: Decide on the central atom
      • Choose the least electronegative element in the molecule
      • Ignore hydrogen when deciding on the central atom
      • Refer to the periodic table to determine the relative electronegativities of the elements

    Silicon Tetrafluoride Example

    • Step 1: Find the total number of valence electrons
      • Silicon has 4 valence electrons (group 4)
      • Fluorine has 7 valence electrons (group 7)
      • Total valence electrons: 4 (Si) + 28 (4F) = 32
    • Step 2: Decide on the central atom
      • Silicon is the least electronegative element, so it's the central atom
    • Step 3: Assign leftover electrons to terminal atoms
      • Each fluorine needs 8 electrons to follow the octet rule
      • Assign 6 electrons to each fluorine, totaling 24 electrons
      • Remaining electrons: 32 - 8 = 24

    Formaldehyde Example (CH2O)

    • Step 1: Find the total number of valence electrons
      • Carbon has 4 valence electrons (group 4)
      • Hydrogen has 1 valence electron (group 1)
      • Oxygen has 6 valence electrons (group 6)
      • Total valence electrons: 4 (C) + 2 (2H) + 6 (O) = 12
    • Step 2: Decide on the central atom
      • Carbon is the least electronegative element, so it's the central atom
    • Step 3: Assign leftover electrons to terminal atoms
      • Assign 2 electrons to each hydrogen, totaling 4 electrons
      • Remaining electrons: 12 - 4 = 8
      • Assign 6 electrons to oxygen to follow the octet rule
    • Step 4: Create multiple bonds
      • Move an electron pair to create a double bond between carbon and oxygen
      • Carbon has an octet of electrons, and oxygen has 2 lone pairs of electrons

    Xenon Pentafluoride Cation (XeF5+) Example

    • Step 1: Find the total number of valence electrons
      • Xenon has 8 valence electrons (group 8)
      • Fluorine has 7 valence electrons (group 7)
      • Total valence electrons: 8 (Xe) + 35 (5F) = 43
      • Subtract 1 electron for the positive charge: 43 - 1 = 42
    • Step 2: Decide on the central atom
      • Xenon is the least electronegative element, so it's the central atom
    • Step 3: Assign leftover electrons to terminal atoms
      • Assign 2 electrons to each fluorine, totaling 10 electrons
      • Remaining electrons: 42 - 10 = 32
      • Assign 6 electrons to each fluorine to follow the octet rule, totaling 30 electrons
      • Remaining electrons: 32 - 30 = 2
    • Step 4: Assign leftover electrons to the central atom
      • Assign the 2 remaining electrons to the xenon atom, exceeding the octet rule

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    Description

    Learn how to draw dot structures for molecules, such as silicon tetrafluoride, by finding the total number of valence electrons and accounting for them in the dot structure.

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