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Who is going to win this game of tug-of-war?

Who is going to win this game of tug-of-war?. How can we determine which atom will get the shared electrons the most?. Electronegativity. The ability of an atom, while in a bond, to attract electrons to itself .

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Who is going to win this game of tug-of-war?

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  1. Who is going to win this game of tug-of-war? How can we determine which atom will get the shared electrons the most?

  2. Electronegativity The ability of an atom, while in a bond, to attractelectronstoitself. ***Basically, a measure of how hard the atom “pulls” on the shared electrons (ice cream)

  3. Increasing electronegativity Most electronegative element = Fluorine (F) We ignore the noble gases because they don’t form bonds. They already have an octet, so they never share electrons with other atoms

  4. Electronegativity is measured using an arbitrary scale of 0-4, with 4 being the highest electronegativity (strongest attraction for the electrons)

  5. Using Electronegativity • We can use electronegativity to determine the type of bond formed: • NONPOLAR COVALENT • POLAR COVALENT • IONIC

  6. NonPolar Covalent Bonds • Electrons are shared equally • The two atoms have equal “pull” on the shared electrons/ice cream • The atoms have equal electronegativities

  7. NonPolar Covalent Bonds • Difference in electronegativity is between 0 and 0.5 • example: P (2.19) and H (2.10). Difference = 0.09  Nonpolar bond YOUR TURN: Identify 3 different combinations of atoms that would be nonpolar using the table.

  8. Polar Covalent Bonds Electrons areshared unequally One atom “pulls” harder on the electrons than the other Negative side = side with greater “pull” (largerelectronegativity) Positive side = side with weaker “pull” (smallerelectronegativity)

  9. Polar Covalent Bonds Difference in electronegativities is between 0.5 and 2.1 • Example: C (2.55) and Cl (3.16). Difference = 0.61  POLAR BOND YOUR TURN: Identify 3 different combinations of atoms that would form a polar bond.

  10. Dipoles • Polar molecules are also called dipoles • Dipole: a molecule with two partiallycharged ends, or poles • Polar bonds are also referred to as dipoles or having a “dipole moment”

  11. Ionic Bond • One atom takes electron(s) away from the other atom (no sharing) • this happens when electronegativity difference is very large! • What holds the ions together is the +/- attraction

  12. Forming Ions • Metals have lowelectronegativity, so they have less of a “grip” on their electrons. They tend to loseelectrons to form positive ions (cations). • Non-metals are the opposite- they have highelectronegativities, they pull harder on their electrons, and are more likely to takeelectrons from other atoms, forming negative ions (anions)

  13. Ionic Bonds • Difference in electronegativities is greater than 2.1 • Example: K (0.82) and F (3.98). Difference = 3.16  IONIC BOND YOUR TURN: Identify 3 different combinations of atoms that would create an ionic bond using the electronegativity table.

  14. 2 ways in which a molecule can be NONpolar… Example: the polar bears are pulling with the same amount of strength on the ice cream #1: the atoms in the molecule have equalelectronegativities (ie. same atom)

  15. 2 ways in which a molecule can be NONpolar… #2: The pulls from the polar bonds “cancel out” Example: the bears are pulling equally in opposite directions. There is no net movement of the ice cream

  16. Example: CO2 Dipoles can “cancel out” In this case, the Oxygens are pulling equally hard on the shared electrons from opposite directions, so overall this is NON-POLAR There is no net dipole: there are no positive and negative ends

  17. For a molecule to be POLAR… There needs to be an “overall pull” of the electrons in a certain direction example #1: two atoms, one atom (bear) pulls harder than the other (penguin) example #2: 3 or more atoms, the individual pulls add up to a general dipole in one direction

  18. Shape Matters!

  19. Wrap-Up • Electronegativity measures how strongly an atom will attract shared electrons. • The greater the difference in electronegativity between two atoms, the more polar the bond will be. • In the case of an ionic bond, the electronegativities between two atoms are so greatly different that the electron(s) of one atom is(are) completely given up to the other atom.

  20. Activity 3.3.4 • Answer questions #1-9 and HW #1-7

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