Determine the Level of Ionic/Covalent Bonding Electronegativity

Content Objectives SWBAT describe the difference in pull on electrons within chemical bonds between atoms based on differences in size of atomic radii and strength of nuclear pull.

Electronegativity The tendency of one atom to pull an electron toward it when bonded with another atom It is a relative scale from 0 to 4 It is called the Pauling Scale The difference between the atoms determines the level of ionic, polar covalent, or non-polar covalent bonding.

Electronegativities Do you notice a pattern here?

Electronegativity

Ionic or Covalent Ionic bonds represent the near total removal of an electron from one atom to another Polar covalent bonds are shared electrons that have a tendency to move toward the more electronegative atom Nonpolar covalent bonds are situations where electrons are shared equally between two atoms.

Ionic or Covalent? A difference > than 1.7 (about halfway) will make it more ionic A difference between 0.4 and 1.7 will make it polar covalent A difference less than 0.4 is non- polar covalent When two of the same element bond, they are automatically non-polar covalent

Why does electronegativity increase across a period? Consider sodium at the beginning of period 3 and chlorine at the end (ignoring the noble gas, argon). Both sodium’s and chlorine’s valence electrons are in the 3 rd level. The electron pair is screened from the nuclei by the 1s, 2s and 2p electrons, but the chlorine nucleus has 6 more protons. Electronegativity increases across a period because the number of charges on the nucleus increases. That attracts the bonding pair of electrons more strongly.

Why does electronegativity fall as you go down a group? Think of hydrogen fluoride and hydrogen chloride. The bonding pair is shielded from the fluorine's nucleus only by the 1s 2 electrons. In the chlorine case it is shielded by all the 1s 2 2s 2 2p 6 electrons. In each case there is a net pull from the center of the fluorine or chlorine of +7. But, F is at the 2 nd level and Cl is at the 3 rd level. If it is closer to the nucleus, the attraction is greater. As you go down a group, electronegativity decreases because the bonding pair of electrons is increasingly distant from the attraction of the nucleus.

Examples Same Electronegativity So electrons are shared equally (covalent) 0.93 to 3.16 The difference is 2.23 so it is more ionic

More Ionic or Covalent?

Content Objectives SWBAT describe the difference in pull on electrons within chemical bonds between atoms based on differences in size of atomic radii and strength of nuclear pull.