The Chemical Bond: Covalent vs. Ionic and Polar vs. Nonpolar — Transcript

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1. 0:00professor Dave here, let's learn about chemical bonds
2. 0:09a molecule is made up of atoms that are participating in chemical bonds with one another. there are
3. 0:13different types of bonds that we will want to be able to describe and the key
4. 0:17to their formation has to do with the difference in electronegativity between
5. 0:21the two atoms participating in the bond. if the difference is more than about 2
6. 0:25like with sodium and chlorine, chlorine will steal an electron from sodium
7. 0:30chlorine really wants another electron, sodium really wants to get rid of one so
8. 0:35everybody wins. the result is a positively charged sodium ion and a
9. 0:40negatively charged chloride ion. particles of opposite charge have an
10. 0:44electrostatic attraction so these two ions hang out together by forming an
11. 0:48ionic bond. this is a very strong attraction because it is happening
12. 0:53between ions that have a formal charge. bond, ionic bond. electrons taken not
13. 1:01shared. speaking of shared electrons if the difference in electronegativity
14. 1:04between the two atoms is less than about 1.7 no electrons are stolen but instead
15. 1:11the two atoms share two electrons. the electron from this atom feels the
16. 1:16attraction from the other nucleus and so does the electron from this atom, so the
17. 1:20atoms share the two electrons to form a covalent bond. covalent bonds can be
18. 1:26polar or nonpolar. if the electronegativity difference between the
19. 1:30atoms is not high enough to cause ionization but is at least more than
20. 1:340.5, like with hydrogen and chlorine, instead of completely stealing the
21. 1:39electron the chlorine will just sort of hog the electrons in the resulting
22. 1:43covalent bond. the more electronegative atom in a polar covalent bond pulls the
23. 1:48electron density towards itself and as a result of the slight electron excess we
24. 1:53call this atom partially negative, denoted by the symbol Delta minus. the
25. 1:58atom whose electron is getting pulled away is slightly electron deficient and
26. 2:03therefore partially positive or Delta plus. if the electronegativity difference
27. 2:08is less than 0.5 the covalent bond is said to be
28. 2:12non polar. in a nonpolar covalent bond the electrons are shared more or less evenly
29. 2:18or in the case of two atoms of the same element, precisely evenly. the atoms will
30. 2:23have no partial charges at all. other than strange phenomena like metallic
31. 2:27bonding these are the main ways atoms bind to one another
32. 2:31remember that you can predict the type of bond that will form between two
33. 2:34elements by comparing their electronegativites. if the difference
34. 2:39is very low, less than 0.5 or so, it will be a nonpolar covalent bond where the
35. 2:45electrons are shared evenly. between about 0.5 and 1.7 it'll be a polar
36. 2:51covalent bond with the electrons are shared but one atom holds them more
37. 2:55tightly. if above 2 or so one atom will simply steal an electron from the
38. 3:00other and you'll get ions that are joined by on ionic bond. thanks for
39. 3:05watching guys, subscribe to my channel for more tutorials and as always feel
40. 3:09free to email me