1 As Q increases in magnitude the size of the lattice energy increases 2 As Q

1 as q increases in magnitude the size of the lattice

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1) As Q + increases in magnitude the size of the lattice energy increases. 2) As Q - increases in magnitude the size of the lattice energy increases. 3) As the sizes of the ions decreases the size of the lattice energy increases (since smaller ion size means a smaller value for d). So the lattice energy increases as the magnitude of the charges of the ions increases and as the size of the ions decreases.
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Examples of Trends (1) 1) Cations in same group forming ionic compounds with the same anion. Lattice energy decreases in size in moving from top to bottom within a group. Ionic compound E lattice (kJ/mol) LiCl 834. NaCl 787. KCl 701. CsCl 657.
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Examples of Trends (2) 2) Anions in the same group forming ionic compounds with the same cation. Lattice energy decreases in size in moving from top to bottom within a group. Ionic compound E lattice (kJ/mol) LiF 1017. LiCl 860. LiBr 787. LiI 632.
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Examples of Trends (3) 3) As |Q + Q - | increases, the size of the lattice energy increases. E lattice = 910. kJ/mol E lattice = 3414. kJ/mol
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Example Arrange the following ionic compounds in order from largest to smallest size of lattice energy. 1) KF, KCl, KBr, KI 2) MgO, CaO, SrO, BaO 3) KF, K 2 O, K 3 N
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Example: Arrange the following ionic compounds in order from largest to smallest size for lattice energy. 1) KF, KCl, KBr, KI KF > KCl > KBr > KI Cation is the same, anion is larger as we go from F - to I - . 2) MgO, CaO, SrO, BaO MgO > CaO > SrO > BaO Anion is the same, cation is larger as we go from Mg 2+ to Ba 2+ . 3) KF, K 2 O, K 3 N K 3 N > K 2 O > KF Cation is the same, anion has a larger charge as we go from F - to N 3- .
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“Ionic Bonding” in Nonmetals Given the success of ionic bonding in explaining substances composed of metals + nonmetals, it is reasonable to attempt to apply the model for bonding between nonmetal atoms. Cl 2 Cl [Ne] 3s 2 3p 5 Cl - [Ne] 3s 2 3p 6 Cl [Ne] 3s 2 3p 5 Cl + [Ne] 3s 2 3p 4 Problems: 1) While the Cl - anion now satisfies the octet rule, the Cl + cation is worse off than before. 2) Experimentally, both Cl atoms in Cl 2 are the same. 3) Cl 2 exists as molecules and is a gas at room temperature. We would expect ionic substances to exist as crystalline solids.
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Covalent Bonding We can get around the problems associated with transferring electrons by sharing one or more pairs of electrons. The shared electrons can be counted by both atoms in satisfying the octet rule. Bonding by sharing of one or more electron pairs is called covalent bonding . Notation 1) Bonding electron pairs are indicated by lines. 2) Nonbonding electrons, called lone pair electrons , are indicated by dots.
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Molecules A molecule is a neutral combination of two or more atoms held together by covalent chemical bonds. Molecules represent the smallest particle of covalently bonded chemical substances. Because of this, these substances are often called molecular compounds . Note that ionic compounds do not exist as individual molecules in the solid phase, but as collections of cations and anions held together by electrostatic forces.
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  • Spring '08
  • JeffreyJoens
  • Chemistry, Molecular formula, Molecule, Ion, chemical substances

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