VII Atomic Structure C Bonding

Bonding Bonding between atoms in a compound comes from the sharing of electrons The kind of bond formed between the two atoms depends on the amount of sharing of the electrons

Bonding in Compounds Kinds of Bonds Ionic electron transferred from one atom to another generally between a metal cation and a non metal anion Covalent electrons shared between 2 atoms in a bond

Electronegativity Li Be B C N O F 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Measure of the ability of an atom in a bond to attract the bonding electrons Across a Period: EN increases Down a Group: EN decreases Most electronegative element is fluorine Li Be B C N O F 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Na Mg Al Si P S Cl 0.9 1.2 1.5 1.8 2.1 2.5 3.0 K Ca Ga Ge As Se Br 0.8 1.0 1.6 1.8 2.0 2.4 2.8

Determine the amount of covalent or ionic character in a bond Using Electronegativity The difference in electronegativity between two atoms can be used to determine how ionic or how covalent the bond is

Difference in electronegativity EN = 1.7 = 50% ionic EN > 1.7 more ionic EN < 1.7 more covalent The larger the EN, the more ionic the bond The smaller the EN, the more covalent the bond So the farther apart the atoms are the more ionic the bond

Compare three bonds: A) C--F B) O--F C) N--F Which is the most ionic?

Compare three bonds: A) C--F B) O--F C) N--F Which is the most covalent?

Determine the amount of covalent or ionic character in a bond Fajan’s Rules of Covalency The bond with the smaller cation is the more covalent bond The bond with the larger anion is the more covalent bond The bond with the larger charge on the cation or anion is the more covalent bond The bond with a transition metal cation is the more covalent bond

Predict which is the more covalent SbCl3 BiCl3 BeO BeS Tl2O Tl2O3 NaCl CuCl Sb is smaller than Bi, so the SbCl3 is more covalent S is larger than O, so the BeS is more covalent Compare Tl+ and Tl+3 , thallium(III) oxide more covalent Cu is a transition metal, CuCl more covalent

Which is the Most Covalent? MgCl2 MgBr2 CaCl2 CaBr2

Which is the Most Covalent? MgCl2 MgBr2 CaCl2 CaBr2 Compare: Mg cation and Ca cation. Mg smaller than Ca so Mg compounds more covalent Compare: Cl anion and Br anion. Br larger than Cl, so Br compounds more covalent

Which is the Most Ionic? MgCl2 MgBr2 CaCl2 CaBr2

Which is the Most Ionic? MgCl2 MgBr2 CaCl2 CaBr2 Most ionic is the same as least covalent Compare: Mg cation and Ca cation. Mg smaller than Ca so Mg compounds more covalent, Ca more ionic Compare: Cl anion and Br anion. Br larger than Cl, so Br compounds more covalent, Cl more ionic

Which of the following is least covalent? Cu2O CuO Cu2S CuS

Which of the following is least covalent? Cu2O CuO Cu2S CuS Compare anions O and S. S is the larger anion, so it forms more covalent bonds. Therefore, Cu2O and CuO are less covalent Cu2O is Cu+1, CuO is Cu+2 , the larger charge is more covalent, so Cu2O is the least covalent

Which of the following is least ionic? AgCl NaCl AuCl RbCl

Which of the following is least ionic? AgCl NaCl AuCl RbCl Least ionic is Most covalent Ag and Au are transition metals, so they are more covalent than Na and Rb which are Group 1 Alkali metals. Compare Ag and Au. Ag is the smaller size so it forms the most covalent bond.

Bond polarity Because electrons are shared unequally in a bond due to the difference in electronegativity, a covalent bond has a positive end and a negative end. (poles) The bond is said to be polar H ---Cl Bond dipole - occurs when you have a polar bond Dipole moment () - is a measure of the bond dipole (the amount of polarity) - +

Bond Polarity The more ionic the bond the more polar the bond The more ionic the bond, the larger the bond dipole The more ionic the bond, the greater the dipole moment.

Compare three bonds: A) C--F B) O--F C) N--F Which is the least polar bond?