Bonding continued

Types of Chemical Bonds Covalent (molecular) bond – results from the sharing of e- between two atoms (usually done w/ nonmetal atoms) The e- are not always equally shared (like tug of war)

Covalent Bonds Bonds between 2 unlike atoms are never completely covalent Non-polar covalent – e- are shared equally ( which only happens between two identical atoms) Polar covalent – e- are not equally shared (due to differences in electronegativity)

Determining Bond Type… Using Periodic Table Metal Element (left of staircase) + Nonmetal Element (right of staircase) Ionic Bond Two Nonmetal Elements (right of staircase) Covalent Bond

Determining Bond Type… Using Electronegativity Values Page 161 has a EN chart Determine the EN difference between the two elements in the bond Go to page 176 and find the chart of bond types. Use the EN difference to determine type of bond (greater difference = more ionic character). Nonpolar covalent: difference of 0 to 0.3 Polar covalent: difference of 0.3 to 1.7 Ionic: difference of 1.7 to 4.0

Determining Bond Type… Using Observed Properties from Lab Activity Conducts electricity while dry Metallic bonding (valence electrons are free to move from one atom to another) Dissolves in water Rule for dissolving is “like dissolves like” Compounds with either polar covalent bonds or ionic bonds (which are very polar bonds) may dissolve because water has polar covalent bonds

Determining Bond Type… Using Observed Properties from Lab Activity Conducts electricity while dissolved in H2O Ionic bonds Dissolving ionic compounds allows ions to separate and this lets electric current flow from one ion to the next

Polar Molecules Molecules with ends

Polar Bonds When the atoms in a bond are the same, the electrons are shared equally. This is a nonpolar covalent bond. When two different atoms are connected, the electrons are not shared equally. This is a polar covalent bond.

How to show a bond is polar Isn’t a whole charge just a partial charge d+ means a partially positive d- means a partially negative The Cl pulls harder on the electrons The electrons spend more time near the Cl d+ d- H Cl

Dipole interactions Occur when polar molecules are attracted to each other. Slightly stronger than dispersion forces. Opposites attract but not completely hooked like in ionic solids.

Dipole interactions H F d+ d- H F d+ d- Occur when polar molecules are attracted to each other. Slightly stronger than dispersion forces. Opposites attract but not completely hooked like in ionic solids. H F d+ d- H F d+ d-

+ - + -

Hydrogen Bonding H O d+ d- H O d+ d-

- + H - F H - F H - F H - F H - F H - F H - F H - F d+ d- d+ d- d+ d-

Electronegativity A measure of how strongly the atoms attract electrons in a bond. The bigger the electronegativity difference the more polar the bond. Use table 12-3 Pg. 285 0.0 - 0.4 Covalent nonpolar 0.5 - 1.0 Covalent moderately polar 1.0 -2.0 Covalent polar >2.0 Ionic