Chemical Bonding

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Chemical Bonding
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Chemical Bonds Chemical Bonds Chemical Bonds
are the forces that hold atoms together in compounds are the forces that hold atoms together in compounds are the forces that hold atoms together in compounds

Ionic bond Covalent bond Metallic bond
Polar Covalent bond
Nonpolar Covalent bond
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Lewis theory,

• valence electrons play a fundamental role in
  chemical bonding
• e- transfer leads to ionic bonds.
• Sharing of e- leads to covalent bonds.
• Atoms tend to have the electron configurations of
  the noble gas, (octet rule.)

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Lewis symbols (electron dot symbols) is the
simple way of showing the valence electrons of
atoms.

Si



valence electrons are the electrons that occupy
the outer shell (principal shell number (n)) of
an atom. Core electrons are the electrons in
inner shells.
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Lewis Structures for Ionic Compounds
BaO
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MgCl2
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Iyonik Bilesikler

• Suda çözünürler
• Yüksek kaynama noktasina sahiptirler - iyonlar
  arasi çekim kuvveti yüksektir
• Eritilmis halleri veya sulu çözeltileri elektrigi
  iletir. Iyonik bilesikler kati halde elektrigi
  iletmez.

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Lewis Structures of covalent bonds
Lone pair (nonbonding or unshared) electrons are
the electrons are not used for bonding.
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Coordinate Covalent Bonds
If both electrons of the bond are contributed by
the same atom, this type of bond is called as a
coordinate cocalent bond.
Cl
H
Cu2 4 NH3 ? Cu(NH3)4
(type of covalent bond in which both electrons
are donated by the same atom
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Kovalent Bilesikler

• En temel yapitaslari moleküllerdir
• Erime ve kaynama noktalari düsüktür
• Elektrik akimini iletmezler
• Çogu suda çözünmez

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• Bond Order
• Single bond, order 1 Double bond,
  order 2
• Higher bond order
• Shorter bond - Stronger bond

• Multiple bonds In many molecules atoms attain
  complete octets by sharing more than one pair of
  electrons between them.
• The sharing of a pair of electrons
  represents a single covalent bond, usually just
  referred to as a single bond, if two electron
  pairs are shared it is a double bond, if three
  electron pairs are shared it is called as a
  triple bond
• Bond length is the distance between the nuclei of
  two atoms joined by covalent bond. As a general
  rule, the distance between bonded atoms decreases
  as the number of shared electron pairs increases
• Bond energy (strength) is the quantity of energy
  required to break one mole of covalent bond.

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Bond energy (strength) is the quantity of energy
required to break one mole of covalent bond.
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Bond Energies and Enthalpy of Reaction
?Hrxn ?H(product bonds) - ?H(reactant bonds)
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?Hrxn ?H(product bonds) - ?H(reactant bonds)
?H bonds formed - ?H bonds broken -770
kJ/mol (657 kJ/mol) -114 kJ/mol
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Bond polarity
In covalent bonds the atoms do not share the electrons equally. The atom which has greater electronegativity, attract the electrons more strongly in covalent bond. In covalent bonds the atoms do not share the electrons equally. The atom which has greater electronegativity, attract the electrons more strongly in covalent bond. In covalent bonds the atoms do not share the electrons equally. The atom which has greater electronegativity, attract the electrons more strongly in covalent bond.

nonpolar covalent bond polar covalent bond
electrons are shared equally between two atoms in a chemical bond one atom has a greater attraction for the electrons than the other atom in a chemical bond.

Electronegativity is the relative ability of atoms to attract electrons in a chemical bond. Electronegativity is the relative ability of atoms to attract electrons in a chemical bond. Electronegativity is the relative ability of atoms to attract electrons in a chemical bond.
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if the electronegativity difference of atoms is
0, the bond is non-polar covalent If the
difference in electronegativities between the two
atoms is greater than 0, but less than 2.0, the
bond is polar covalent, If the difference in
electronegativities between the two atoms is 2.0,
or greater, the bond is ionic
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if the electronegativity difference of atoms is
0, the bond is non-polar covalent If the
difference in electronegativities between the two
atoms is greater than 0, but less than 2.0, the
bond is polar covalent, If the difference in
electronegativities between the two atoms is 2.0,
or greater, the bond is ionic
Compound F2 HF LiF
Electronegativity Difference 4.0 - 4.0 0 4.0 - 2.1 1.9 4.0 - 1.0 3.0
Type of Bond Nonpolar covalent Polar covalent Ionic (non-covalent)
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Writing Lewis structure

• Skeletal structure shows how atoms are attached
  to one another, the skeletal structure consist of
  one or more central atoms and terminal atoms.
• A central atom bonds to two or more atoms in the
  structure. The atom with the lowest
  electroneagtivity is generally central atom.
• Terminal atom bonds to one another atom. Hydrogen
  atom are terminal atoms.

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In writing Lewis structure

• first determine the total number of valence
  electrons
• write a possible skeletal structure, connect the
  atoms by a single covalent bond. (Molecules and
  polyatomic ions usually have compact, symmetrical
  structures, but organic compounds are based on
  long chains of carbon atoms. In oxyacids hydrogen
  atoms are usually bonded to oxygen atoms)
• place pairs of electrons as lone pairs around the
  terminal atoms, according to octet rule.
• place the remaining electron as lone pairs around
  the central atom
• If there are not enough electrons to give the
  central atom an octet, try multiple bonds (use
  one or more of the unshared pairs of electrons on
  the atoms bonded to the central atom to form
  double or triple bonds, the double bonds form
  generally among carbon, nitrogen oxygen and
  sulfur.)

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• question write a plausible Lewis sturucture for
  phosgene COCl2 NO3-

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• Formal Charge is the differences between number
  of valence electrons in a free (uncombined) atom
  and number of electrons assigned to that atom in
  the Lewis structure.
• FC (number of valence electrons)- ½(number of
  bonding electrons)-(number of lone pair
  electrons)
• Total formal charges on the atoms in a lewis
  structure must be 0 to for a neutral atom
  (and/or to the net charge of a polyatomic ion)
• - negative formal charges should appear on the
  most electronegative atoms
• - where formal charges are required, these should
  be as small as possible.

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FC valence e- - lone pair e- -
bond pair e-
2
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• question write a plausible Lewis structure and
  calculate the formal charge each atom in that
  formula for each compound given below,
• NO3-, CO2, NH4, HNO3, C2H4 SO42- PCl5, SF6
  NO SOCl2 ICl4

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Resonance

• sometimes a molecule or ion can be represented
  by two or more plausible Lewis structure that
  differ only by the distribution of electrons. The
  different plausible structures are called
  resonance structures.
• O-OO ? O-OO

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Exceptions to the octet rule

• Odd-electron species NO
• Incomplete octets BF3
• Expanded octets PCl5, SF6

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H

OH

HCH




F

B


F
F






Cl

P



Cl
Cl




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Dipole moments and molecular shape

• In many cases, covalent bonds are polar covalent
  because the bound atoms have different
  electronegativities but whole molecule might be
  nonploar. The "charge distribution" of a molecule
  is determined by
• - The shape of the molecule
• - The polarity of its bonds
• A Polar Molecule
• The center of the overall negative charge on the
  molecule does not coincide with the center of
  overall positive charge on the molecule
• The molecule can be oriented such that one end
  has a net negative charge and the other a net
  positive charge, i.e. the molecule is a dipole
• A Nonpolar molecule
• Has no charges on the opposite ends of the
  molecule
• Or, has charges of the same sign on the opposite
  ends of the molecule
• Molecule is not a dipole
• question determine the polarity of following
  molecules CH4, CH3Cl

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