Stability in bonding

1. Stability in bonding • In covalent bonds, electrons aren’t always shared equally between the two nuclei. • This is because some elements have a greater affinity for electrons than others.

2. The pull that an element has on electrons INCREASES as you go from LEFT TO RIGHT and from BOTTOM TO TOP.

3. H H How does this affect bonds? H2 has the same amount of pull in both directions. It would look something like:

4. H F HF is made of elements from opposite sides of the periodic table. The fluorine has a much greater affinity for electrons than hydrogen. The electrons would concentrate around the fluorine, and the bond would look something like:

5. Polar bond H H H F Nonpolar bond When electrons in a bond are concentrated near one of the nuclei, the bond is POLAR. If the electrons are shared equally between the nuclei, the bond is NONPOLAR.

6. Now, you try some... Do the following have polar or nonpolar bonds? F2 H2O HCl C60 BCl3 SO2 S8 BN

7. Writing formulas Properly written formulas start with the element that is farthest to the left. For example: NaCl not ClNa MgI2 not I2Mg BN not NB

8. Name that compound!!! • 1. The name of the first element in the compound is unchanged. • 2. The name of the second element in the compound is changed so that it ends in -ide • If you’re naming a covalent compound, indicate that there’s only one of the second element with the prefix mon- • 3. If there is more than one of the second element AND it is a COVALENT compound, use… • di- to indicate two (CO2 is carbon dioxide) • tri- to indicate three (BCl3 is boron trichloride) • tetra- to indicate four (CCl4 is carbon tetrachloride) Example: CO is called carbon monoxide

9. Now, you try some... HF HCl BCl3 Al2S3 SO2