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Ch. 6 Chemical Bonding 6-1 Introduction to chemical bonding

Ch. 6 Chemical Bonding 6-1 Introduction to chemical bonding

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Ch. 6 Chemical Bonding

6-1 Introduction to chemical bonding

Chemical bond-a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together

Types of Bonds

Ionic-results from the electrical attraction between large numbers of cations and anions

Covalent-results from sharing of electron pairs between two atoms

Rarely are bonds ever purely ionic or purely covalent but most lie somewhere between

fig. 6-3

1. nonpolar covalent bond-the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge

polar- uneven distribution of charge

2. polar-covalent bond-unequal attraction for the shared electrons

Fig. 6-2

1. nonpolar-covalent: 0-5% ionic character; electronegativity difference of 0-0.32. polar-covalent: 5-50% ionic character; electronegativity difference of 0.3-1.73. ionic: 50-100% ionic character; electronegativity difference of >1.7

6-2

6-2 Covalent Bonding and Molecular Compounds

Molecule-neutral group of atoms that are held together by covalent bonds

Molecular compound-chemical compound whose simplest units are molecules

Chemical formula-indicates the relative numbers of atoms of each kind in a chemical compound by using symbols and subscripts

Molecular formula-the types and numbers of atoms combined in a single molecule of a molecular compound

Diatomic molecule-a molecule containing only two atoms

Forming of a bond

The electrons-protons of two atoms are attracted to each other while the electrons-electrons are repelled by each other

The bond forms at a distance at which these two forces become equal, potential energy is at a minimum and a stable molecule forms

Covalent Bonds

Bond length-the distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atoms

Bond energy-the energy required to break a chemical bond and form neutral isolated atoms

Octet Rule

Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level

Exceptions: H, B (6), Be(4), P, S, Xe

Electron-Dot Notation

An electron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the element’s symbol

Pg. 170

Lewis Structures

Formulas in which atomic symbols represent nuclei and inner-shell electrons, dot-pairs or dashes between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons

Lone pair (unshared pair)-pair of electrons that belongs exclusively to one atom and not involved in bonding

Structural formula-indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule ex: F-F

Multiple Bonds

single bond-covalent bond produced by the sharing of one pair of electrons between two atoms

Double bond-covalent bond by sharing two pair of electrons

Triple bond-bond by sharing of three pair of electrons

Resonance structures

Structure that cannot be correctly represented by a single Lewis structure

Ionic Bonding and Compounds

Ionic compound-composed of positive and negative ions that are combined so that the charges are equal

Ions minimize their potential energy (form bonds) by combining in an orderly arrangement known as a crystal lattice

Pg. 177

Ionic Bonds/Compounds

Form between a metal (+) and nonmetal (-)

+ and – ions attracted to each other

Hard, brittle

High melting pt/boiling pt

Form crystal lattices

Do not vaporize at room temp

Good electrical conductors

Covalent Bonds/Compounds

Share electrons

Between 2 nonmetals

Form molecules

Lower melting pts

Vaporize at room temp

Polyatomic Ions

Pg. 180

Group of covalently bonded atoms with a charge

NO3-

NH4+

6-4 Metallic Bonding

Metals outer orbital overlap each other so electrons are free to roam from atom to atom

The chemical bonding that results from the attraction between metal atoms and the surrounding sea of electrons.

Metallic Properties

Malleable-ability to be hammered or beaten into thin sheets

Ductile-ability of a substance to be drawn into a wire

Bond strength-the amount of heat required to vaporize the metal is a measure of the bond strength

Metallic Bonds

Metals bond with other metalsAttraction b/t metals and a surrounding sea of electronsHigh electrical and thermal conductivityMalleable, ductile, and high luster (shiny)Ability to absorb wide range of light frequencies

6-5 Molecular Geometry

Properties of molecules depend on the bonding and also the geometry or shape.

The polarity depends on the geometry and determines if the molecule is polar

VSEPR Theory

States that repulsion of valence electrons surrounding an atom causes them to be oriented as far apart as possible

1. Linear-2 atoms set equal distance apart (180˚) OR 3 atoms because the electrons repel each other

Ex: AB2

2. Trigonal Planar- AB3 difference of 120º

3. Tetrahedral- AB4 difference of 109.5ºVSEPR with unshared electrons

4. Trigonal Pyramidal- AB3E (107º)-lone electrons will also repel each other but shape only involves the atoms involved in the bonding

5. Bent or Angular (105º) AB2E2 or AB2E

6. Trigonal bipyramidal- AB5 ex: PCl57. Octahedral- AB6 ex: SF6

Pg. 186 Table 6-5

Predict the geometrical shape using the VSEPR theory and by drawing the Lewis Structure for the following:

A. HI E. SO2

B. CBr4 F. Cl4C. AlBr3 G. BCl3D. CH2Cl2

Using a protractor and pg. 186, construct the geometrical shapes using gumdrops and toothpicks

Intermolecular Forces

Forces of attraction b/t molecules

Higher the boiling pt, the stronger the force

These are generally weaker than bonds that join atoms in molecules

Strongest intermolecular forces are those between polar molecules

1. Dipole-dipole=equal but opposite attractions

dipoles that are additive make it more polar ex: NH3

Dipoles in a molecule that cancel each other make it nonpolar ex: CCl4

2. Induced dipole=temporary dipole develops

Weaker than dipole-dipole force

3. Hydrogen bond=strong type of dipole-dipole between H-F, H-O, H-N

Makes them highly polar

Ex: water H2O

4. London dispersion forces- weak, induced instantaneous dipole created by constant motion of electronsOnly among noble gases and nonpolar molecules due to their low boiling pts.Their strength increases with the number of electrons in the molecules or with increased mass