Chemistry Helpers
Bonding Definitions
Bonding

 

Energy and Chemical Bonds
1) Chemical Bond: A force of attraction between atoms in a compound
 
2) All elements bond for one reason
To acquire an electron configuration of a noble gas (8 valence electrons =stable octet(or 2 valence for He)
 
3) Bonds and Energy changes
·        As bonds are formed, energy is released. This is a(n) exothermic process.
·        As bonds are broken, energy is absorbed. This is a(n) endothermic process.
 
4) Bonds and Stability
·        Bonds form to make elements/compounds stable.
·        The greater the release of energy, the stronger the bond.
 
5) Electronegativity (review)
·        The measure of attraction an atom has for electrons
·        Metals have low electronegativity
·        Non metals have high electronegativity
 
 
Types of chemical bonds
1)    Ionic bonding
·        Results from the complete transfer of electrons between metals (that lose electrons) and nonmetals(that gain electrons)
·        Metals form positive ions called cations
·        (memory hint: has a “t” in the name—looks like a plus sign for positive)
·        Non metals form negative ions called anions
Example of ionic bonding:
Na                                           Cl
2-8-1                                       2-8-7
           
 
               Result is:
                             Na +1                                        Cl -1
2-8                                                                                                          2-8-8
 
How do you know?
          Electronegativity Difference (ED)
·        If the difference between the electronegativities (higher minus lower) is 1.7 or more, the bond is ionic.
Example:
Na  0.9              Cl 3.2                  3.2 - 0.9 = 2.3 
                                                          
·        Exception: the bond is always ionic for a metal hydride:
(group 1 and 2 + hydrogen is always ionic)
Example:
Na  0.9             H 2.1                 2.1 - 0.9 = 1.2
                                             
 
 
2)    Covalent Bond: Results from the sharing of electrons between two atoms
 
Polarity:
·        Unequal sharing of electrons
·        Each atom attracts electrons by different amounts (like a tug of war)
 
A.   Polar Covalent Bond:
·        one atom has a slightly higher affinity for electrons
·        electronegativity difference (ED) is between 0.1 and 1.6
 
 
example of polar covalent bonds
NH3                                H2O
          N =    3.0                       O =   3.4
          H =    2.1                       H =   2.1
                    0.9                                1.3
 
B.   Non polar Covalent Bond:
·        Atoms share the electrons equally
·        Electronegativity difference (ED) is 0.0
·        Most common in diatomics or ‘triatomics’
·        Br2 H2 O2 N2 Cl2 I2 F2       and     O3
 
example:
          O = 3.4
          O = 3.4
                  0.0
      
 
C. Coordinate Covalent Bond:
·        Atoms share the electrons, but one atom donates both electrons
·        **usually the bond is shared with a proton (H+)
 
example     NH3 + H+ NH4+
 
 
 
3)    Metallic Bond:
·        These bonds are only found in metals
·        Metals do not have a strong attraction for electrons. The electrons are loosely held, so therefore, their electronegativity is very low.
·        **These are often described as “positive ions surrounded by a sea of mobile electrons
·        the positive ions form a strong attraction for the electrons surrounding them causing strong bonds
SUMMARY
E. D. = 0 --------------------------------------------1.7 -------------------------------3.3
                         Nonpolar Covalent                                                   Ionic
                                                             Polar Covalent
         
TYPES OF SOLIDS
1)           Ionic solids
·        contains ionic bonds
Properties
-         regular geometric pattern - lattice
-         relatively high melting and boiling points
-         in the solid form, a poor conductor of electricity
-         in the liquid or aqueous form, a good conductor of electricity
-         ionic solids dissolve in water
 
2)              Solids with Covalent Bonds:
Molecular Solids                              Network Solids
covalently bonded                      covalent in a 3-D network
       
1. soft                                              1. hard, brittle    
2. poor conductors                         2. poor conductors
3. low melting points                      3. high melting points
 
examples:                                        examples: 
NH3, HCl, H2O, CH4                                   * C , SiC, and SiO2
(diamond, silicon carbide, silicon dioxide)
 
 
3)              Metallic Solids
·        Contains metallic bonds
·        Good conductors of heat and electricity in due to
“sea of mobile electrons”
 
          examples:   Cu, Ag, Au
 
BONDING SUMMARY
The four types of solids:
a)    Ionic Solids:
           ·        bonding between metals and nonmetals
           ·        results from the transfer of electrons
           ·        high melting and boiling points
           ·        do NOT conduct electricity in the SOLID state
           ·        conducts only in the liquid (molten) or aqueous phases
           ·        ions are held together by electrostatic attraction
           ·        examples: NaCl (salt), MgO, MgCl2
 
 
b)    Metallic Solids:
           ·        bonding between metal atoms
           ·        "sea of mobile electrons"
           ·        good conductors of heat and electricity in all phases
           ·        malleable
           ·        ductile
           ·        shiny luster
           ·        examples: Cu, Fe, Na, Ag
 
 
c)    Molecular (Covalent) Solids:
                   ·        bonding between two or more nonmetals
                   ·        results from the sharing of electrons
                   ·        poor conductors ( good insulators)
                   ·        soft *
                   ·        low melting points *
                   ·        examples: water (H2O), methane (CH4),
                                              ammonia (NH4), hydrogen (H2)
 
d)    Network Solids
                   ·        Atoms are covalently bonded in a network (3-D)
                   ·        hard
                   ·        high melting points
                   ·        examples: diamond (C), silicon carbide (SiC),
                                             silicon dioxide (SiO2)
 
 
Types of Molecules, Symmetry and Polarity
1)    Polar Molecules (dipoles)
·        This represents unbalanced charge distribution along the bond
Examples:
 
H2O       +H-O-H+                      NH3           +H-N-H+
                                                                                                                           H+
 
  NaCl           +NaCl-
 
 
 
2.    Nonpolar Molecules
·        This represents balanced charge distribution
Examples:
CO2                                                       CH4
 
 
·        All diatomics contain nonpolar molecules and nonpolar covalent bonds
Examples:
O2                                                     F2
 
 
 
Molecular Attraction
·        These are forces between molecules, not to be confused with attractive forces between atoms which are bonds.
 
1. Dipole – Dipole attraction
·        Neighboring polar molecules orient themselves so that oppositely charge regions line up.
Example:
H - Cl                             H-Cl H-Cl
                                                                        H-Cl
 
 
                   H                                             H       H       H       H
                             O                                        O      O      O      O
                   H                                             H       H       H       H
 
 
2.    Hydrogen “bonds”
·        This happens when hydrogen is bonded to a small highly electronegative element.
·        Only happens with F, O and N
·        3 substances are HF, H2O, and NH3
·        these attractive forces are SO strong they have been called bonds
·        hydrogen bonds are the reason that water has such a relatively high boiling point; this also gives insects the ability to “walk on water”
 
3. van der Waal’s Forces:
·     weak intermolecular forces of attraction between individual molecules
a.     as molecular mass increases, van der Waal’s forces increase
b.    as the distance between molecules increases, van der Waal’s forces decrease.
c.     The stronger the van der Waal’s forces, the higher the melting and boiling point.
 
b.p    C5H12    >        b.p. C4H10    >       b.p. C3H8
                   b.p.   I2      >             b.p. B2    >             b.p. Cl2    >       b.p. F2
 
4. Molecule-Ion Attraction:
·     Ions are attracted to the negative and positive ends of water molecules or other polar solvents
·     Example: NaCl in water—sodium have a positive charge and is attracted to the negative or oxygen end of the water molecules
 
Multiple Covalent Bonds
1. Double covalent bond
·        2 pairs of electrons are shared
·        Stronger than a single bond
·        Shorter than a single bond
·        More stable than a single bond
 
 
2. Triple Covalent Bond
·        3 pairs of electrons are shared
·        stronger than a single or double bond
·        shorter than a single or double bond
·        more stable than a single or double bond
      
 
SUMMARY:         Bond strength
          Single                  <                 double                 <       triple


Write Your Questions Below



Some molecules contain polar covalent bonds but are not themselves polar. Explain, with diagrams, how this is possible.
November 24, 2013

 Hi Emma, your question is discussing two different pieces to the overall picture. The bonds that are between two elements can be polar, nonpolar or ionic. The overall compound can also be polar or nonpolar. For example, methane has a formula of CH4. Each of the C-H bonds is polar with carbon having a stronger "pull" of electrons. However, because the shape of methane is symmetrical the overall "pull" of electrons balances out and is nonpolar. Water is an example of polar  bonds and polar mollecule because it is asymmetrical.

January 9, 2014 -  Replied By Expert

what are all the ways zolpidem can form hydrogen bonds with water?
April 29, 2013

Hydrogen bonds are only formed when hydrogen is bonded to F, O or N.

April 30, 2013 -  Replied By Expert

what are the hydrogen bonds in zolpidem?
April 29, 2013

This is the IUPAC  name for zolpidem which is a prescription drug for sleep problems (AKA Ambien):

N,N-dimethyl-2-(6-methyl-2-p-tolylimidazo[1,2-a]pyridin-3-yl)acetamide

each hydrogen can only hold one bond

April 29, 2013 -  Replied By Expert

 
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