chemical bond--shamim

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Chapter 04 Basic Concepts Of Chemical Bonding

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Chemical Bonding – is the force of attraction between any two atoms in a compound. This attraction is the force that overcomes the repulsion of the positively charged nuclei Lewis Symbols Lewis Symbols (or Lewis Structures) – is a convenient way of representing atoms singly or in combination. Only the valence electrons are shown 4.1 Chemical Bonding

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Principal Type of Chemical Bonds: Ionic Bond - complete transfer of one or more electrons from one atom to another Covalent Bond – two atoms share electrons 4.1 Chemical Bonding

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Ionic Bonding Metal + Nonmetal Covalent Bonding - Nonmetal + Nonmetal 4.1 Chemical Bonding

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Ionic Bond – complete transfer of electrons Covalent Bond – sharing of electrons Polar Covalent Bond – a bond made up of unequally shared electron pairs. Non-polar Covalent Bond – a bond made up of equally shared electron pairs 4.1 Chemical Bonding

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Electronegativity Difference in Electronegativity ( Δ E n ) 4.1 Chemical Bonding

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Ionic Bond – complete transfer of electrons Covalent Bond – sharing of electrons Polar Covalent Bond – a bond made up of unequally shared electron pairs. Non-polar Covalent Bond – a bond made up of equally shared electron pairs 4.1 Chemical Bonding EN Cl = 3.0 3.0 - 3.0 = 0 Non-Polar Covalent EN Cl = 3.0 EN H = 2.1 3.0 – 2.1 = 0.9 Polar Covalent EN Cl = 3.0 EN Na = 1.0 3.0 – 0.9 = 2.1 Ionic

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Electron-Dot Structures (Lewis Structures) : A representation of an atom’s valence electrons by using dots and indicates by the placement of dots how the valence electrons are distributed in the molecule. 4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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Example 4.8 Draw the Lewis Structure of Carbon Dioxide (CO 2 ) Example 4.9 Draw the Lewis Structure of Ammonia (NH 3 ) Example 4.10 Draw the Lewis Structure of the ammonium ion (NH 4 + ) Example 4.11 Draw the Lewis Structure of the sulfate ion (SO 4 2- )

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Example 4.12 Draw the Lewis Structure of the acetate ion (CH 3 COO) - Example 4.13 Draw the possible resonance structures of the nitrate ion, NO 3- , and represent them as a resonance hybrid.

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Example 4.14 Draw the Lewis structure of beryllium hydride, BeH 2 . Example 4.15 Draw the Lewis structure of phosphorus pentafluoride , PF 5 .

Common Bonding Patterns:

Common Bonding Patterns B C N O C + N + O + C - N - O - B - F F + - F

Practice - Lewis Structures:

Practice - Lewis Structures CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4

Practice - Lewis Structures:

Practice - Lewis Structures CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4 : O :: C :: O : : : 16 e - 26 e - 18 e - 26 e - 32 e - 14 e -

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Lewis Structures and Formal Charges 4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Formal Charge # of valence e - in free atom - 2 1 - # of nonbonding e - # of bonding e - = Calculate the formal charge on each atom in O 3 . O O O 6 - (2) - 6 = -1 1 2 6 - (4) - 4 = 0 1 2 6 - (6) - 2 = +1 1 2

Practice - Assign Formal Charges:

Tro, Chemistry: A Molecular Approach 17 Practice - Assign Formal Charges CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4

Practice - Assign Formal Charges:

Tro, Chemistry: A Molecular Approach 18 Practice - Assign Formal Charges CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4 all 0 -1 P = +1 rest 0 S = +1 Se = +1 -1 -1 all 0 -1 -1 -1

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Resonance Resonance – there is more than one Lewis structure for a molecule that differ only in the position of the electrons and they are called resonance structures. - the actual molecule is a combination of the resonance forms – a resonance hybrid- it does not resonate between the two forms, though we often draw it that way

Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them:

Tro, Chemistry: A Molecular Approach 20 Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4 all 0 -1 P = +1 S = +1 Se = +1 -1 -1 all 0 -1 -1 -1

Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them:

Tro, Chemistry: A Molecular Approach 21 Practice - Identify Structures with Better or Equal Resonance Forms and Draw Them CO 2 SeOF 2 NO 2 -1 H 3 PO 4 SO 3 -2 P 2 H 4 none -1 -1 -1 +1 all 0 +1 all 0 -1 none S = 0 in all res. forms

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Lewis Structures and Molecular Geometry; VSEPR Theory Valence Shell Electron Pair Repulsion Theory (VSEPR) “… electron pair arrange themselves so that they can be as far as possible from each other.” -Electrons in bonds and in lone pairs can be thought of as “charge clouds” that repel one another and stay as far apart as possible, this causing molecules to assume specific shapes. 4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Two Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Three Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Four Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Four Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Five Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Five Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Six Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Six Charge Clouds

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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Lewis Structures and Polarity 4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions Polar Nonpolar

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Nonpolar Polar Nonpolar Polar

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4.4 Drawing Lewis Structures of Molecules and Polyatomic Ions

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