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 vThe greater the electronegativity difference, the stronger the bond is that forms between them vIf 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 Determine the type of bond: Chart Carbon 2.55 1. H and O 3.44-2.20 = 1.2 Nitrogen 3.04 POLAR COVALENT Potassium 0.82 2. Ca and F 3.98-1.00 = 2.98 Fluorine 3.98 IONIC Hydrogen 2.20 Oxygen 3.44 3. Ba and O 3.44-0.89 = 2.55 Calcium 1.00 IONIC Chlorine 3.98 4. C and O 3.44-2.55 = 0.89 Barium 0.89 POLAR COVALENT Bromine 2.96 5. N and N 0-NONPOLAR COVALENT
Covalent Bonds vCharacterized by a sharing of electrons vThe 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 vA compound whose atoms are held together by covalent bonds is a covalent compound vMolecules 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 vThese 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 irst element named -If a pre ix accompanies the name, place a subscript equal to the pre ix after the symbol Example: Dinitrogen N2 2. Write the symbol of the second element - Place a subscript after its symbol if the pre ix means two or higher
- Example: Dinitrogen trioxide N2O3
Formulas for Covalent Bonds Number Pre ix Number Pre ix
1 mon(o)- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- Examples:
Carbon dioxide CO2
phosphorous trichloride PCl3
diarsenic pentoxide As2O5
Naming Covalent Compounds 1. Write the name of the irst element 2. If the symbol is followed by a subscript of 2 or more, use the appropriate pre ix 3. Write the root of the name of the 2nd element with an “–ide” ending 4. Use appropriate pre ix to denote the number of the 2nd element (1 or more) Examples:
CO2 carbon dioxide
IF5 iodine penta luoride
N2O5 dinitrogen pentoxide