Covalent Bonding: Electronegativity, Bond Character, and Types of Covalent Bonds, Lecture notes of Chemistry

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Chemical Bonding

Part Two: Covalent Bonds

Electronegativity and Bond Character

vElectronegativity-­‐ the relative ability of an

atom to attract electrons in a chemical

bond

vThe greater the electronegativity

difference, the stronger the bond is that

forms between them

vIf the electronegativity difference is:

• Less than 0.5, then the bond is nonpolar covalent
• Between 0.5 and 1.6, the bond is polar covalent
• Greater than 1.6, then the bond is ionic

Covalent Bonds

v Characterized by a sharing of electrons

v The attraction of two atoms for a shared pair of electrons is called a covalent bond v In a covalent bond, atoms share electrons and neither atom has an ionic charge

v A compound whose atoms are held together

by covalent bonds is a covalent compound

v Molecules are formed from covalent bonds

Single and Multiple Covalent Bonds

v When more than one pair of electrons are

shared between atoms multiple covalent

bonds form

vThese can be double or triple bonds

depending on the number of pairs of electrons shared

Characteristics of Covalent Bonds v Low melting points v Do not conduct electricity in any state v Solids are often soft or brittle v Many are gases at room temperature v Most are less soluble in water than ionic compounds and are not electrolytes

Polar vs. Nonpolar Covalent Bonds

Nonpolar Covalent Bond

v Equal sharing of the bonding electron pair

v Example: In H-H each H atom has an electronegativity value of 2.

Polar Covalent Bond

v Unequal sharing of the bonding electron pair

v Example: In H-Cl, the electronegativity of the Cl atom is 3.0, while that of the H atom is 2. v Electron pair is displaced toward the more electronegative atom v Results in a dipole

Formulas for Covalent Bonds

Examples: Carbon dioxide CO 2 phosphorous trichloride PCl 3 diarsenic pentoxide As 2 O 5 Number PreUix Number PreUix 1 mon(o)-­‐ 6 hexa-­‐ 2 di-­‐ 7 hepta-­‐ 3 tri-­‐ 8 octa-­‐ 4 tetra-­‐ 9 nona-­‐ 5 penta-­‐ 10 deca-­‐

Naming Covalent Compounds

1. Write the name of the Uirst element
2. If the symbol is followed by a subscript of 2 or more, use the appropriate preUix
3. Write the root of the name of the 2 nd element with an “–ide” ending
4. Use appropriate preUix to denote the number of the 2 nd element (1 or more) Examples: CO 2 carbon dioxide IF 5 iodine pentaUluoride N 2

O

5 dinitrogen pentoxide