Electronegativity and Polarity Chapter 8 Section 5 Electronegativity and Polarity

Electron Affinity, Electronegativity, and Bond Character The type of bond formed during a reaction is related to each atom’s attraction for electrons. Electron affinity is a measure of the tendency of an atom to accept an electron. Excluding noble gases, electron affinity increases left to right across a period and bottom to top within a group.

Electron Affinity, Electronegativity, and Bond Character

Electronegativity The chart below shows the electronegativity values for individual elements.

Bond Character A chemical bond between two different elements is never completely ionic or covalent. The character of the bond depends on how strongly each of the bonded atoms attracts electrons. The character and type of chemical bond can be predicted using the electronegativity difference of the elements in the bond.

Bond Character Electrons in bonds between identical atoms have an electronegativity difference of zero – meaning that the electrons are equally shared between the two atoms. This type of bond is considered nonpolar covalent, or simply covalent. Electrons pairs in most other covalent bonds are not equally shared based on their different electronegativities. Unequal sharing results in a polar covalent bond.

Electronegativity Difference Bond Character When there is a large difference in the electronegativity between bonded atoms, an electron is transferred from one atom to the other. This results in an ionic bond. Electronegativity Difference Bond Character >1.7 Ionic 0.4 – 1.7 Polar Covalent <0.4 Mostly Covalent Covalent

Bond Character Calculate the electronegativity difference and determine the bond character of the following: CH4 NH3 HF

Polar Covalent Bonds A polar covalent bond is similar to a tug of war in which the two teams are not of equal strength. When a polar bond forms, the shared electron pair is pulled toward one of the atoms. Therefore, the electrons spend more of their time around one atom than the other. This results in partial charges at the ends of the bonds.

Polar Covalent Bonds The Greek letter delta (δ) is used to represent a partial charge. An atom can have a partial positive or a partial negative charge. The more electronegative atom is at the partially negative end, while the less electronegative atom is at the partially positive end. The resulting polar bond is often referred to as a dipole (two poles).