Chemical Bonding

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Chemical Bonding

• Chapter 6

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Types of Chemical Bonds

• Chemical Bond mutual electrical attraction b/
  the nuclei and valence e- of different atoms
• Atoms make bonds b/c they become more stable

3
Types of Chemical Bonds

• Ionic Bonding
• Results from the electrical attraction between
  cations and anions
• Atoms completely give up e-s to other atoms

4
Types of Chemical Bonds

• Covalent Bonding
• Results from sharing of e- pairs between two
  atoms
• Shared e- are owned equally by two atoms

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Determining the Type of Bond

• Bonds fall somewhere b/ purely Ionic and purely
  Covalent
• Depends on electronegativity how much is the
  atom pulling the e-s
• Calculate the difference in electronegativities

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Determining the Type of Bond

• Types
• Ionic electronegativity dif 1.7 3.2
• Polar-Covalent dif 0.3 1.7 (1.7 ionic)
• Nonpolar-Covalent dif 0 0.3 (0.3 NP)

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Determining the Type of Bond

• Ionic
• One atom is so electronegative it strips the
  other atom of electrons making cation and anion
• NaCl

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Determining the Type of Bond

• Polar-Covalent
• Bond where atoms have unequal attraction for
  shared e-s
• More electronegative atom has stronger attraction
  for e-s

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Determining the Type of Bond

• Nonpolar-Covalent
• Bond where atoms have equal sharing of e-s,
  balanced distribution of charge
• Bonds b/ two atoms of the same element

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Determining the Type of Bond

• Determine the type of bond b/ these elements and
  sulfur, which is more electronegative element?
• H, Cs, Cl

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Covalent Bonding
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Covalent Bonding

• Molecule neutral group of atoms that are held
  together by covalent bonds.
• Molecular compound covalent compound

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Covalent Bonding
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Covalent Bonding

• Chemical formula NaCl, MgCl2, H2O (Ionic or
  Covalent)
• Molecular formula only for molecules (covalent)

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Covalent Bonding
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Covalent Bond

• Bond length average distance b/ two bonded atoms
• Forming bonds atoms release energy
• Same amount of energy needed to break bond ? bond
  energy (kJ/mol)

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Forming Covalent Bonds

• Share e-s to get noble gas configuration

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Octet Rule

• Def atoms gain, lose or share e-s to have octet
  (8) of electrons in outer energy level
• H exception, only needs 2 e-s
• Ex HF

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Exceptions to Octet

• B happy with 6 e-s in outer level
• Other elements can have more than 8 valence e-s
  PF5, SF6 d orbitals invovled in bonding

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Electron-Dot Notation

• Use element symbol and dots to indicate valence
  e-s.
• Period 2

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Lewis Structures

• Def Use electron-dot notation for molecules
• H2
• F2 shared pair with dash (-)
• lone pair unshared pair

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Lewis Structures

• Structural formula shows structure w/o lone
  pairs
• H F , H H
• Single bond covalent bond where one pair of e-
  being shared b/ two atoms

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Lewis Structures

• Draw Lewis Structure
• NH3
• H2S

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Multiple Covalent Bonds

• C, N, and O can share more than 1 pair of e-s
• Double bond two pairs, 4 e-s, being shared
• C2H4

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Multiple Covalent Bonds

• Triple Bond three pairs, 6 e-s, being shared
• N2
• Lengths of multiple bonds?
• More bonds shorter more energy to break
• p.187

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Resonance Structures

• Molecules cant be shown with one Lewis structure
• Ex O3

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Lewis Structure

• CH2O
• CH3Br
• C2HCl
• SO3

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Recap Ch. 6

• Bonds Ionic and Covalent
• Ionic, Polar-Covalent, and Nonpolar-Covalent
• Drawing Lewis Structures
• C2H2
• Type of bonds?

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Ionic Bonding
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Ionic Compounds

• Def () and (-) ions that combine so charges
  balance out
• Crystalline solids
• Formula Unit simplest unit of ionic compound
  where charges are balanced
• NaCl Na Cl-
• Video (68)

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Forming Ionic Compounds

• NaCl use electron dot diagrams
• Compound with Ca and F

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Characteristics of Ionic Bonds

• Ions in crystal lattice are more stable lower
  potential energy
• Lattice energy energy released when 1 mole of
  gaseous ions form a lattice
• More negative energy more stable stronger
  bonds

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Ionic vs. Covalent

• Ionic
• stronger bonds b/ formula units than b/ molecules
  in covalent compounds
• HIGHER melting and boiling points
• hard but brittle
• conduct electricity in molten or dissolved state

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Ionic vs. Covalent

• Covalent
• Weak bonds b/ molecules
• Most compounds are gases at room temp.
• LOW boiling and melting points

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Polyatomic Ions

• Def charged group of covalently bonded atoms
• Result from excess or lack of electrons in bonding

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Metallic Bonding

• Excellent conductors in solid state due to
  highly mobile valence electrons
• Filled outermost sublevel is s
• p orbitals empty and some d
• Vacant orbitals overlap and valence e-s are free
  to move throughout entire metal

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Metallic Bonding

• Valence e-s are delocalized, do not belong to any
  one atom but move freely
• Sea of electrons around metal atoms

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Metallic Properties

• High electrical and thermal conductivity
• Malleability hammered into sheets
• Ductility drawn into wires