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

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B. Types of Bonds

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B. Types of Bonds

Ionic Bonding - Crystal Lattice

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B. Types of Bonds

Covalent Bonding - True Molecules

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B. Types of Bonds

Diatomic Molecule

Metallic Bonding - “Electron Sea”

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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