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6-1 Introduction to Chem Bonding
*a link between atoms that results from the mutual attraction of their nuclei for e-
-Types of chem bonds1. Ionic bond:
transfer of e-2. Covalent bond:
sharing of e-’s-bonds between unlike atoms are never
completely ionic and rarely completely covalent.(Pauling)
3. Metallic bonds: between metals
*nonpolar-covalent bond: cov bond which the bonding e-’s
are shared equally by the bonded atoms
-resulting in a balanced distribution of elect charge
*Polar: meaning that they have an uneven distribution of charge
*Polar-cov bond: the united atoms have an unequal attraction for the shared e-’s
-Why chem bonding occurs
-if their PE is lowered by the change, two atoms will form a chem bond.
6-2 Covalent Bonding and Molecular Compounds
*Molecule: smallest unit quantity of matter which can exist by itself and retains all the prop of the original substances
*Diatomic molecule: 2 like atom
*Molecular cmpnd: chem cmpnd whose simplest units are molecules
*Chem formula: represents the #’s of atoms of each kind in a chem cmpnd by using atomic symbols and numerical subscripts
A. Vocabulary
CHEMICAL FORMULA
MolecularFormula
FormulaUnit
IONIC COVALENT
COCO22NaClNaCl
*Molecular formula:
shows types and numbers of atoms combined in a single molecule
-Formation of covalent bond
*Bond length: aver dist between 2 bonded atoms
*Bond nrg: nrg required to break a chem bond and form neutral atoms
-The Octet Rule
*Octet rule:
8 e-’s in the highest nrg level
-Lewis Structure
(Gilbert Lewis)
*pg 169
-Lewis Structure
*Unshared pair: pair of e-’s that is not involved in bonding
*single bond: cov bond produced by sharing of 1 pair of e-’s between 2 atoms
*structural formula:
indicates kind, number, arrangement, and bonds of the atoms in a molecule.
-Multiple Covalent Bonds
*Double bond:
cov bond between 2 atoms produce by sharing 2 pairs of e-
EX
-Multiple Covalent Bonds
*Triple bond:
cov bond between 2 atoms produced by sharing 3 pairs of e-
Ex
-Sample problem 6.3
-Polyatomic Ions
*charged group of cov bonded atoms
Ex
6.3 Ionic Bonding and Ionic Compounds
*Ionic compound: composed of + and – ions combined so that the + and – charges are equal
6.3 Ionic Bonding and Ionic Compounds
*Formula unit: simplest collection of atoms from which a cmpnds formula can be estab
-Common ions: Na+, K+, Mg+2, Ca+2, Ba+2,O-2, S-2, F-,Cl-, Br-,I-
-Formation of Ionic Bonds
*Lattice nrg:
nrg released when one mole of an ionic crystalline cmpnd is formed from gaseous ions
-Ionic vs Covalent bonds
-ionic bonds are stronger than cov bonds
-cov bonds
~lower mp, bp, and hardness
-Ionic vs Covalent bonds
-ionic bonds
~hard and brittle
~carry a current when
dissolved in water
IONIC COVALENTBond Formation
Type of Structure
Solubility in Water
Electrical Conductivity
OtherProperties
e- are transferred from metal to nonmetal
high
yes (solution or liquid)
yes
e- are shared between two nonmetals
low
no
usually not
MeltingPoint
crystal lattice true molecules
B. Types of Bonds
Physical State solid liquid or gas
odorous
6.4 Metallic Bonding
-metals have a low ionization nrg and low electroneg.
-two metals form at best a weak covalent bond
6.4 Metallic Bonding
-metals tend to form what we call a sea of electrons
6.4 Metallic Bonding
*Metallic bond: chem bond resulting from the attraction between + ions and surrounding mobile electrons
-to compare strengths in metals vaporization heats are used
“electron sea”
METALLICBond Formation
Type of Structure
Solubility in Water
Electrical Conductivity
OtherProperties
MeltingPoint
B. Types of Bonds
Physical State
e- are delocalized among metal atoms
very high
yes (any form)
no
malleable, ductile, lustrous
solid
-Nature of Metals
-the motion of the e- sea helps explain why metals have certain properties
*Malleability*Ductility-luster
RETURN
B. Types of Bonds
RETURN
B. Types of Bonds
Ionic Bonding - Crystal Lattice
RETURN
B. Types of Bonds
Covalent Bonding - True Molecules
RETURN
B. Types of Bonds
Diatomic Molecule
Metallic Bonding - “Electron Sea”
RETURN
B. Types of Bonds
C. Bond Polarity
Most bonds are a blend of ionic and covalent characteristics.
Difference in electronegativity determines bond type.
C. Bond Polarity
Electronegativity Attraction an atom has for a shared pair of
electrons. higher e-neg atom -
lower e-neg atom +
C. Bond Polarity
Electronegativity Trend (p. 151) Increases up and to the right.
Nonpolar Covalent Bond e- are shared equally symmetrical e- density usually identical atoms
C. Bond Polarity
+ -
C. Bond Polarity
Polar Covalent Bond e- are shared unequally asymmetrical e- density results in partial charges (dipole)
Nonpolar
Polar
Ionic
View Bonding Animations.
C. Bond Polarity
C. Bond Polarity
Examples:
Cl2
HCl
NaCl
3.0-3.0=0.0Nonpolar
3.0-2.1=0.9Polar
3.0-0.9=2.1Ionic
6.5 The properties of molecular compounds
-VSEPR Theory
*electrostatic repulsion between valence e- pairs surrounding an atom causes these pairs to be oriented as far apart as possible
(table 6-5 pg 186)
1. Linear
2. Tetrahedral
3. Trigonal pyramidal
4. Bent
-Hybridization(fig.6-23 p188)
*mixing of two or more atomic orbitals of similar nrg’s on the same atom to give new orbital of equal nrg’s
-Hybridization
ex: CH4
-hybridization of s and p yield 4 new identical orbits
*hybrid orbitals: orb of = nrg produced by the combination of 2 or more orb on the same atom
-Intermolecular Forces
*force of attraction between molecules
-generally weaker than the bonds that join atoms in molecules, ions in ionic cmpnds, or metal atoms in solid metals
~dipole-dipole forces and molecular polarity
-strongest intermol forces act between polar molecules
*dipole: = but opp charges separated by a short distance.
- arrow points toward the neg pole
*DD force: forces of attraction between polar molecules
ex: polar vs nonpolar
~hydrogen bonding
*an intermolecular attraction between a H atom and an unshared pair of e-’s on a strongly electroneg. Atom
~hydrogen bonding
-H bond represented by dotted lines connecting the H to the unshared e- pair of the electroneg atom
~london dispersion forces
(Fritz London 1930)
*attraction resulting from the constant motion of e-’s and the certain instantaneous dipoles and induced dipoles
~london dispersion forces
-between all atoms and molecules-only intermolecular forces acting
among noble-gas atoms and nonpolar molecules
-LF increases with increasing mass of atoms and molecules