Covalent Bonds

1. Covalent Bonds Forming single, double, and triple bonds

2. Covalent Bonding • Remember, when atoms bond covalently, there is a sharing of electrons between the two atoms. • However, not all of the electrons are involved in the bond, so there are two different types of electron pairs. • Bonding Pair: Shared (shown by lines) • Lone Pairs: Unshared (shown by pairs of dots)

3. There are also a few types of covalent bonds and the type of covalent bond depends on how many pairs of electrons are shared.

4. Single Covalent Bonds 1 The sharing of ______ pair of electrons Double Covalent Bonds 2 The sharing of ______ pair of electrons Triple Covalent Bonds 3 The sharing of ______ pair of electrons

5. Strength of Bonds bond • Distance separating nuclei - _________ ___________ • Depends on the size of the atoms - _________ ___________ • Pairs shared – more electrons shared, _________ ___________ (_____________ has smallest bond length) • Smaller bond length - _________ ___________ length atomic radii closer together Triple bond stronger bond

6. Strength of Bonds • Bond dissociation energy – energy to _________ ___________ • Energy must be _________ to break bonds • Direct relationship between bond energy and bond length - _________ bond length, _________ bond, _________ bond energy break bonds added smaller stronger more

7. So, how do scientists decide how many electrons are shared? One way is by drawing Structural Formulas a.k.a. Lewis Formulas

8. NASL Method:Let’s look at H3P Single Least Hydrogen H H P H Create a skeleton of the chemical formula _____________element in center first _____________electronegative in center if there is a choice ­_____________ is never in the middle

9. N Needed 8 2 Hydrogen H H H P Determine number of electrons__________ Atoms want ____ electrons. __________only wants ___ electrons.

10. A Available valence H H H P Determine number of electrons __________ Add total number of _________ electrons.

11. N A S = ____- ____ Shared 2 2 Hydrogen bond single H H P H Determine ___________ electrons. Divide by ____ to get number of bonds Remember a line represents ____ electrons. ___________ can only make a ___________ ___________.

12. N A S = ____- ____ Shared 2 2 Hydrogen bond single H H P H Determine ___________ electrons. Divide by ____ to get number of bonds Remember a line represents ____ electrons. ___________ can only make a ___________ ___________.

13. A S L = ____- ____ Lone-pair outside Happy center H H P H Determine ___________ electrons. If any electrons are left, place pairs of electrons on the _______________ atom(s) until they are “______________”. Next, if any electrons are left, place them on the ___________ atom.

14. 2 electrons 8 electrons  H    H P H Check to make sure all atoms are “happy”. Happy Hydrogen :___________ Happy everything else:__________

15. Let’s try some examples • H2O • CF4

16. NCl2Br • CO2

17. Polyatomic Ions • Take charge into consideration. (Add negative to total, subtract positive from total of electrons.) • Put brackets around structure with charge on outside right corner

18. Let’s look at CO32- and NH4+1