Post on 09-Mar-2021
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
Calculating Bond Character Electronegativity
Chart Carbon 2.55 Nitrogen 3.04 Potassium 0.82 Fluorine 3.98 Hydrogen 2.20 Oxygen 3.44 Calcium 1.00 Chlorine 3.98 Barium 0.89 Bromine 2.96
Determine the type of bond:
1. H and O
2. Ca and F
3. Ba and O
4. C and O
5. N and N
3.44-2.20 = 1.2 POLAR COVALENT 3.98-1.00 = 2.98 IONIC
3.44-0.89 = 2.55 IONIC
3.44-2.55 = 0.89 POLAR COVALENT 0- NONPOLAR COVALENT
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
Single and Multiple Covalent Bonds
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 2.1 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 2.1
v Electron pair is displaced toward the more electronegative atom
v Results in a dipole
Formulas for Covalent Bonds 1. Write the symbol of the Uirst element named -‐If a preUix accompanies the name, place a subscript equal to the preUix after the symbol Example: Dinitrogen N2 2. Write the symbol of the second element -‐ Place a subscript after its symbol if the preUix means two or higher
-‐ Example: Dinitrogen trioxide N2O3
Formulas for Covalent Bonds
Examples: Carbon dioxide CO2 phosphorous trichloride PCl3 diarsenic pentoxide As2O5
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 2nd element with an “–ide” ending 4. Use appropriate preUix to denote the number of the 2nd element (1 or more) Examples: CO2 carbon dioxide IF5 iodine pentaUluoride N2O5 dinitrogen pentoxide