THE CHEMICAL BOND
Stability represents the decrease of energy in a system. There is a general trend in all systems to achieve a lower energy state. The energy of two chemically bonded atoms is less than that exists between than two that are free.
Energy and Bonds
• If energy is released (exothermic) in the formation of a bond, the strength is proportional to the energy released (energy of formation) • Table I
• NaCl vs NI3 http://www.youtube.com/watch?v =2mzDwgyk6QM http://www.youtube.com/watch?v=-F cVuYuFx6o&feature=related
Bonds & Energy
• When bonds are broken,energy is absorbed.
• When bonds are formed energy is released.
3 Major Bond Types
• Covalent: shared electrons
(molecules: carb’s, fats, protein, nucleic acid). Elements tend to be close to each other, from right of Periodic table.
• Ionic: transferred electrons (salts:
NaCl, MgSO4, KNO3). Elements tend to be far fromeach other, opposite sides of Periodic table.
• Metallic: mobile electrons in a “sea of positive nuclei”.
• Using the element______________________ complete the following methods of mapping electron placement.
• Determine the complete electron configuration by sublevel.
(1s22s22p63s2…….)
• Determine the electron configuration by energy level. (2-3-……)
• Determine the orbital notation
•
•
__
1s
__
2s
__ __ __
2px py pz
__ __
3s
__ ___ ___
3px py pz
• Determine the Lewis Structure (Electron dot diagram)
Lewis dot diagrams: model of valence electron placemen t
Only for Groups
1,2 & 13-18.
Li
Be
2-1
2-2
B
C
N
O
F
Ne
2-3
2-4
2-5
2-6
2-7
2-8
Lewis dot diagrams
• Lewis dot overview: plotting valence electrons. Diagrams for elements.
• Single Covalent Bonds
– Hydrogen
– Chlorine
– HCl
Home work
• Read 213-216
• Do p 216 SA #1-6
• Read 217-229
• Do p 229 #13-15,20,21
Lewis dot Diagram:
Salts
• Ionic (opposite sides of reference table). – Potassium iodide (KI)
– Calcium Chloride***(CaCl2)
• Sodium Hydroxide (NaOH)
• Salts
Potassium
(K2SO4) withsulfate Polyatomic
bonds).
Ions (covalent
Homework
• Read p 187-193
• Do SA p193 #1-11
• Read p 194-199
• Do SA p 199 #14-22
Lewis dot diagrams
• Covalent molecules
Polar
Hydrochloride (HCl) dipole: Unsymmetrical charge distribution in a neutral molecule; polar covalent molecules.
Water
Ammonia
Nonpolar
Carbon dioxide
Lewis dot diagrams
• Covalent molecules
Fluorine (F2)
Nonpolar molecule.
Hydrochloride (HCl)
Dipole: Unsymmetrical charge distribution in a neutral molecule; polar covalent molecules.
Ionic Substances- opposite sides
• Octet Rule (isoelectronic ions)
• Ionic compounds
– NaCl
• Electrons do not belong to one nuclei, valence electrons jump.
• Tend to form between Active metals and nonmetals
Ionic bonding
• transferring electrons to gain filled valence shells ergo increasing stability.
• Ions become isoelectronic to noble gases. K0 e—> K+
2-8-8-1
e—> [Ar]
- 2-8-8
•
F0
+
e—> F2-7
+e- —> [Ne]
- 2-8
Homework
• Review book
– P 98-99
– 99-103
– 103-105
Table S, Ionization Energies and
Electronegativities
Intramolecular attractions and bond type.
• Differences in electronegativity predict the type of bonding between particular atoms.
If the difference is:
0.0-0.4 nonpolar covalent. F2 or BrCl.
o.41-1.69 polar covalent. HBr, HO
1.7-4.0 ionic. NaBr, KF
Intramolecular attractions and bond type scale (not in tables!) Ionic Compound
• High melting and boiling points because of the strong chemical attraction of the ions.
Dissolve in polar solvents (water).
Crystals hard but brittle.
Conduct electricity in aqueous and liquid phase (molten).
• Metal and nonmetal/polytatomic ion.
Covalent compound
• Low melting and boiling points because of the weak chemical attraction of the atoms. • Some dissolve in polar
