Chemical Bonding

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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 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 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 Number Preix Number Preix 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 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 pentaluoride N2O5 dinitrogen pentoxide .

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