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Lewis Structures and Chemical Bonds
Lecture 4 Lewis Structures and Chemical Bonds Chapter 7 Suggested HW 7.1, 7.3, 7.7, 7.15, 7.17, 7.23, 7.31, 7.37, 7.39, 7.59, 7.61, 7.63, 7.67, 7.69, 7.73, 7.75, 7.77, 7.81, 7.97, 7.99, 7.101, 7.105, 7.107, 7.109, 7.111, 7.115, 7.119, 7.121, 7.125, 7.127, 7.129, 7.139, 7.143, 7.145, 7.147
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Electrons dictate the chemistry of an atom
Review Electrons dictate the chemistry of an atom Electrons fill orbitals in order or increasing energy 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p … We can represent the electron configuration of an element by showing the orbital designation or orbital configuration Shell Number of electron in subshell 1s1 subshell S 1s2 2s22p6 3s23p4 [Ne]3s23p4
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The Octet Rule – Atoms prefer to have 8 electrons in their outer shell
Octet Rule and Ions The Octet Rule – Atoms prefer to have 8 electrons in their outer shell (or dublet for H and He). Valence electrons = outer shell Ions tend to form such that they satisfy the Octet Rule An ion is an atom that has gained or lost electrons This results in a net charge on the atom If an ion has a net (+) charge cation If an ion has a net (-) charge anion
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Noble gas configuration ALWAYS satisfy the octet rule
Forming Ions Noble gas configuration ALWAYS satisfy the octet rule Na (Z = 11) [Ne] 3s1 Mg (Z = 12) [Ne] 3s2 Cl (Z = 17) [Ne] 3s2 3p5 S (Z = 17) [Ne] 3s2 3p4
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Lewis Representation American chemist G.N. Lewis had a profound impact on our understanding of chemical bonding. One of his many contributions was a simple way to represent chemical bonds. We call these Lewis Symbols. Valence Electrons are represented by dots. A single dot represents an electron A pair of dots represents two paired electrons sharing an orbital H He N O O2- K Mg2+ I- 1s1 1s2 2s22p3 2s22p4 2s22p6 3s1 [Ne] 5s25p6
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Composed of Charged components
Compounds Compound Bond Type Inorganic Compound Organic Compound Covalent Composed of Charged components Ionic Bonds Contains Carbon Cations Anions
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Electronegativity X-Y Some atoms attract electrons more than others
Electronegativity difference Ionic Bond < Covalent
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Predict the type of bond that will form between:
Electronegativity Predict the type of bond that will form between: Ca and F B and H C and F
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Ionic Bonds Ionic bonds do not share electrons – bond forms through charge attraction NaCl Ion Na+ Cl- Electron Configuration [Ne] [Ne]2s22p6 Lewis Symbol CaCl2 Ion Ca2+ Cl- Electron Configuration [Ar] [Ne]2s22p6 Lewis Symbol
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Electrons pair and are shared between both atoms
Covalent Bonds Covalent bonds electrons shared between two atoms. This involves an overlap of atomic orbitals Let’s consider H2 - two hydrogen atoms share electrons. Octet Rule NOT satisfied! Electrons pair and are shared between both atoms Commonly represented as: H H Solid line represents covalent bond
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Covalent Bonding Energy Energy 1s1 1s1 s bond Hydrogen Hydrogen
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Covalent Bonding – Fluorine (F2)
Energy Energy Atomic Orbitals are NOT optimized for bonding 2p5 2p5 2s2 2s2 sp3 sp3 Fluorine Fluorine
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Covalent Bonding Energy Energy sp3 sp3 s bond Fluorine Fluorine
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Covalent Bonding
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Covalent Bonding – CH4 2p2 sp3 2s2 1s1 Carbon Hydrogen (x4)
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Covalent Bonding – CH4 sp3 1s1 Carbon Hydrogen (x4)
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Covalent Bonding – CH4 sp3 1s1 Carbon Hydrogen (x4)
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Covalent Bonding – CH4
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Covalent Bonding – NH3
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Covalent Bonding – NH3
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Covalent Bonding – NH3
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Covalent Bonding – NH3
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VSEPR Valence Shell Electron Pair Repulsion
Each region of electrons (bond or lone pair) counts as a balloon Balloons want to spread out as much as possible
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Molecular Shapes
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Will each of these molecules be polar?
Molecule Polarity Will each of these molecules be polar? CH4 CH3F CH2F2 CHF3 CF4
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