Chapter 6 Covalent Bonds

Bond between 2 nonmetals The valence electron pair is shared. In a single bond there is one shared pair. In a double bond there are two shared pairs. H:H or H-H = H 2

Molecules A neutral group of atoms joined by 1 or more covalent bonds. Bonds are maintained by the proton/electron attraction.

Polar Covalent Bond A covalent bond where electrons are not equally shared. The atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge. The delta symbol with a + or – sign indicates the charge.

Polar and Non-polar Molecules Determined by the type of atoms in a molecule and their shape Molecules with 2 atoms are polar CO 2 has 2 polar bonds but is non-polar because the bonds are across from each other and cancel each other out 0=C=O H 2 O is polar (0 is – and H’s are +)

Polar and Non-polar Molecules Attractions between polar molecules are stronger than attractions between non-polar molecules. The attraction increases the energy required to make molecules evaporate which raises the boiling point. Non-polar molecules have weak attractions Examples: dry ice (solid CO 2 ) and liquid nitrogen

Why do we need chemical names? Un-uniform names are confusing. Examples: lime, quicklime, un-slaked lime They don’t tell you what elements are in the compound. Chemical names are uniform and provide information about the compound. Example: calcium oxide (CaO) tells us that there is 1 Ca atom and 1 O atom

Chemical Names Distinguish compounds from each other In ionic compounds, the formula gives the ion ratios.

Binary Compound Contains 2 elements The cation is first (metal name without charge) The anion is second (nonmetal with –ide suffix)

Binary Compound Examples: Sodium chloride Cadmium iodide There is an anion chart on page 171 in your book.

Practice (Copy all problems) Is the bond ionic or covalent? 1.NaCl7. KCl 2.MgCl 2 8. HBr 3.H 2 9. I 2 4.HCl10. CH 4 5.CO 2 6.H 2 O

Practice If the bond was covalent, decide if it is polar or non-polar. Label the polar areas with delta symbols and +/- signs. Hint: There are 7 covalent bonds and 3 of them are polar. Write out the names for the ionic bonds. Also, tell how many atoms of what elements are in the molecule.