Chapter 8 Covalent Bonding. General Chemistry I T.ARA. Chemical Bonding. Now that we know something about electron configurations, we can take a closer look at the ways atoms form bonds. There are two main types of chemical bonds: Ionic Bonds Covalent Bonds. A. Ionic Bonding.
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General Chemistry I
Na [Ne]3s1 Na+ [Ne] + e-
Cl [Ne]3s23p5 + e- Cl- [Ar]
Na+ + Cl- NaCl (ionic bond)
Using Lewis symbols:
a polyatomic ion are
polyatomic ions form
ionic bonds with other
eg. NO3- is a polyatomic anion.
H• + H• H : H
H : H
eg. The Lewis structure for H2 can be drawn in two ways:
H : H or H–H
a) A single line represents two covalently shared electrons – also known as a single bond.
Draw a Lewis structure for water (H2O) that obeys the octet rule.
Draw a Lewis structure for ammonia (NH3) that obeys the octet rule.
Draw a Lewis structure for methane (CH4) that obeys the octet rule.
In this structure, each nitrogen atom would have only six valence electrons – two short of an octet.
Ethane (C2H6), Ethylene (C2H4) & Acetylene (C2H2)
4 total bonds
3 total bonds
2 total bonds
When necessary, atoms will form any combination of single, double and triple covalent bonds to gain a full octet.
Lewis Structures of Ions: Add one additional valence electron for every negative charge & subtract one valence electron for every positive charge.
Formal charge: the charge a bonding atom would have if its bonding electrons were shared equally
Formal Charge = Atomic Group #
– # lone pair electrons
– ½ (# bonding electrons)
eg. Resonance Structures of Ozone
Which N2O resonance structure(s) are lowest in energy?
B & C both have only two formal charges – lower in energy than A.
High in Energy:
Too many formal charges!!
C is lowest in energy because the negative charge is on O (more electronegative than N) – more on this in a minute!
Single Bond (1) > Double Bond (2) > Triple Bond (3)
Covalent Polar Ionic
- electrons shared - electrons shared - electrons not
equally unequally shared at all
- No separation - some separation - complete separation
of charge of charge of charge
- held together by - held together by - held together by
shared electrons shared electrons electrostatic
Electronegativity: the ability of an atom in a covalent bond to attract shared electrons to itself; the “electron-pulling” power of an atom
The higher the EN, the more tightly an atom holds its electrons.
+ = less electronegative atom
- = more electronegative atom
H2 LiF HCl MgO CsI N2