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Chapter 9

Chapter 9 - Chemical Bonding I Lewis Theory

8 Pages
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Department
Chemistry
Course Code
CHMA10H3
Professor
Xiao- An Zhang

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Chapter 9 Chemical Bonding I: Lewis Theory
9.1 Bonding Models and AIDS Drugs
- Bonding Models are central to chemistry because:
1) Explains why and how atoms attach together to form molecules
2) Explain why some combinations are stable while other are not
3) Can be used to predict shapes (structure) of molecules
4) Can be used to predict the chemical and physical properties of compounds
-Chemical Bonds form because they lower the potential energy between charged particles
(Potential energy of bonded atoms < potential energy of separate atoms
9.2 Types of Chemical Bonds
- Chemical Bonds: Interactions between atoms (from elements to molecules
- Ionic Bond: Between metal and nonmetal, electron transferred
- Covalent Bond: Between Nonmetal and nonmetal, electrons shared
- Metallic Bond: Between metal and metal, electrons pooled
9.3 Representing Valence Electrons with Dots
- Simplest bonding theory is Lewis Theory (emphasizes valence electrons to explain
bonding and predict molecular properties such as molecular stability, shape, size and
polarity (can draw models called Lewis Structures/ Electron Dot Structures), focuses
on behavior of valence electrons
- Valence Electrons: Electrons in all sublevels with highest principal energy shell, very
important in bonding
- Core Electrons: Electrons in lower energy shells
- Lewis Structure of Atoms: Represent the valence electrons surrounding the symbol of the
element, use symbol of element to represent nucleus and inner electrons. Use dots to
represent valence electrons
www.notesolution.com
- Octet Rule: Stable configuration of 8 electrons in outermost shell, ns2np6
- There are some exceptions to this rule the key to remember is to try to get an electron
configuration like a noble gas
1) He = 2 valence electron = duet (stable)
2) Li loses 1 valence electron
3) H shares or gains 1 electron (commonly loses 1 electron to become H+)
4) Be loses 2 electron to become Be 2+ (commonly shares 2 electrons, resulting in 4 valence
electrons)
5) B loses 3 electron to become B 3+ (commonly shares 3 electrons, resulting in 6 valence
electrons)
9.4 Ionic Bonding: Lewis Structures and Lattice Energies
- Cation metals usually have Lewis symbols without valence electrons (lost in formation to
gain same electron configuration as previous noble gas) while anions have Lewis Symbols
with 8 valence electrons (gained in formation to get same electron configuration as next
noble gas)
- Atoms bond because it result in a MORE STABLE ELECTRON CONFIGURATION (lower
potential energy)
- Electrons are transferred until metal loses all valence electrons and nonmetal has
octet
- Ionization Energy of metal is endothermic while Electron Affinity of nonmetal is
exothermic
- Generally the ionization energy of metal > electron affinity of nonmetal (formation of
ionic compound is endothermic B UT the heat of formation is exothermic and
generally large)
- Extra energy released from the formation of a structure (crystal lattice) where every
cation is surrounded by anions and vice versa, held together by electrostatic attraction
(NONDIRECTIONAL no direct anion-cation pair) , maximizes attraction between cations
and anions (MOST STABLE ARRANGEMENT)
www.notesolution.com
- Lattice Energy: Extra stability that accompanies the formation of the crystal lattice
(exothermic, hard to measure directly, but can be calculated from knowledge of other
processes), depends directly on size of charges and inversely on distance between ions
- Determining Lattice Energy: Born-Haber Cycle: Hypothetical series of reactions
representing the formation of an ionic compound from the elements (reaction are chosen so
the enthalpy change is known except the last one Lattice energy)
1) Use Hesss Law to add enthalpy to determine the lattice energy
- Trends in Lattice Energy Ion Size
1) The force of attraction between charged particle is inversely proportional to the
distance between them, larger ions mean the center of positive charge is farther away from
the negative charge
2) The force of attraction between oppositely charged particles is directionally product of the
charges larger charge means the ions are more strongly attracted (larger
charge=stronger attraction =larger lattice energy
- Ionic Bonding: Model Theory predicts ionic VS. Reality
1) Implies that the attractions between ions are strong
2) Predicts that ionic compounds should have high melting points and boiling points
because breaking down the crystal should require a lot energy Ionic compound have high
melting points and boiling points
3) Implies that positions of ions in crystal lattice are critical to stability of structure
4) Predicts that moving ions out of position should be difficult IONS ARE HARD
(compared to most molecular solids) ions are displaced from their position, repulsive forces
should occur (will be unstable and break apart and be BRITTLE)
5) To conduct electricity, a material must have charged particles, in the ionic solid,
ions are locked in position and cannot move around ionic solids should not conduct
electricity
-6) In liquid state or when dissolved in water, the ions will have the ability to move around
both a liquid ionic compound and an ionic compound dissolved in water should
conduct electricity
9.5 Covalent Bonding: Lewis Structures
- Electrons that are shared by atoms are called bonding pairs, electrons not shared are
called lone pairs (non bonding pairs)
www.notesolution.com

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Description
Chapter 9 Chemical Bonding I: Lewis Theory 9.1 Bonding Models and AIDS Drugs - Bonding Models are central to chemistry because: 1) Explains why and how atoms attach together to form molecules 2) Explain why some combinations are stable while other are not 3) Can be used to predict shapes (structure) of molecules 4) Can be used to predict the chemical and physical properties of compounds -Chemical Bonds form because they lower the potential energy between charged particles (Potential energy of bonded atoms < potential energy of separate atoms 9.2 Types of Chemical Bonds - Chemical Bonds: Interactions between atoms (from elements to molecules - Ionic Bond: Between metal and nonmetal, electron transferred - Covalent Bond: Between Nonmetal and nonmetal, electrons shared - Metallic Bond: Between metal and metal, electrons pooled 9.3 Representing Valence Electrons with Dots - Simplest bonding theory is Lewis Theory (emphasizes valence electrons to explain bonding and predict molecular properties such as molecular stability, shape, size and polarity (can draw models called Lewis Structures Electron Dot Structures), focuses on behavior of valence electrons - Valence Electrons: Electrons in all sublevels with highest principal energy shell, very important in bonding - Core Electrons: Electrons in lower energy shells - Lewis Structure of Atoms: Represent the valence electrons surrounding the symbol of the element, use symbol of element to represent nucleus and inner electrons. Use dots to represent valence electrons www.notesolution.com
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