Electronegativity and Polarity Section 9 5 Electron affinity

Electronegativity and Polarity Section 9 -5

Electron affinity • Tendency of atom to accept electron • Usually increases as atomic numbers increase within period • Usually decreases as atomic number increases within a group

Linus Pauling • Developed scale of electronegativity • Figure 9 -15, pg 263 • Fluorine has the highest: 3. 98 • Francium has the lowest: 0. 7 • Noble gases are not given (0)

Electron Affinity tells us… • Character and type of bond – Never completely ionic or covalent – Sharing is not always completely equal

Ionic Bond • Large differences in electronegativity indicate that electrons are transferred

Nonpolar covalent bonds • Difference in electron affinity of atoms involved is very small • Electrons shared fairly equally

Identical Atoms • Difference in electronegativity is 0 • Electrons are shared equally.

Polar Covalent Bonds • Unequal sharing • Electron tug-of-war • Stronger affinity = greater strength

Differences • Less than 0. 4 = nonpolar covalent bond • 0. 4 – 1. 7 = polar covalent bond • Greater than 1. 7 = ionic bond

Examples: • H and Br 2. 20 and 2. 96 = 0. 76 • C and O 2. 55 and 3. 44 • Li and 0. 98 and F 3. 98 polar covalent = 0. 89 polar covalent = 3. 00 ionic bond

Solubility of Polar Molecules • Like dissolves like – Polar (and ionic) compounds are soluble in polar substances – Nonpolar only soluble in non-polar substances

Properties of Covalent Compounds • Van der Waals forces: weak forces of attraction between individual molecules

Types of Intermolecular Forces • Nonpolar – Weak attraction – Dispersion or induced dipole • Polar – Stronger attraction – Dipole-dipole force • Hydrogen bond – Very strong – Between H and another dipole

Physical properties • Melting/boiling points lower than ionic • Many are gases at room temp • Non-conductors of heat or electricity • Extremely hard *Due to the intermolecular forces!!