Models of Chemical Bonding 3 ways that metals and nonmetals combine
The three bonds
Electronegativity Scale Difference in electronegativity is one way to determine type of bond
Electronegativity Difference and Bond Type • If the difference in electronegativity between bonded atoms is 0, the bond is pure covalent . – Equal sharing • If the difference in electronegativity between bonded atoms is 0.1 to 0.4, the bond is nonpolar covalent . • If the difference in electronegativity between bonded atoms is 0.5 to 1.9, the bond is polar covalent . • If difference in electronegativity between bonded atoms is larger than or equal to 2.0, the bond is ionic .
Ionic Bond • An ionic bond forms from electrostatic attraction of ions. • Usually it is between a metal and a nonmetal or a metal and a polyatomic ion.
Lattice Energy • A quantitative measurement of the stability of any ionic solid is its lattice energy • Can also be used to compare bond strengths in ionic compounds. • chemists compare the amounts of energy released when separated ions in a gas come together to form a crystalline solid. Yup – another enthalpy H lattice
Lattice Energy • Trends: – As you move up in a column, lattice energy increases: - higher up, higher lattice energy Li + Na + K + Rb + Cs + F - 1036 923 821 785 740 Cl - 853 787 715 689 659 Br - 807 747 682 660 631 I - 757 704 649 630 604 The force of attraction between oppositely charged particles is directly proportional to the product of the charges on the two objects ( q 1 and q 2 ) and inversely proportional to the square of the distance between the objects ( r 2 ). Lattice energy increases as Q increases and/or as r decreases . Moving up a column = smaller ionic radii
Lattice Energy versus Ion Size
Lattice Energy • Trends: – As you increase the magnitude of the charge (becomes more positive or more negative), lattice energy increases Na + Mg 2+ Al 3+ OH - 900 3006 5627 O 2- 2481 3791 15916 Lattice energy increases as Q increases and/or as r decreases . Higher charge = higher q
Trends in Lattice Energy: Ion Charge • The force of attraction between oppositely charged particles is directly proportional to the product of the charges. • Larger charge means the ions are more strongly attracted. – Larger charge = stronger attraction – Stronger attraction = larger lattice energy • Of the two factors, ion charge is generally more important.
13 Born-Haber Cycle for Determining Lattice Energy H overall = H 1 + H 2 + H 3 + H 4 + H 5 o o o o o o Uses Hess’ Law: Also known as heat of formation You will get to do this in a cool powerpoint for part of the Lewis Quiz
Metallic Bonding • Metallic Compounds – Are a crystal made out of just metals – like an iron nail or a clump of aluminum – In a metallic bond the electrons are delocalized – which means they do not belong to any one specific atom, but are free to move about the metal crystal.
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