Review – Packet #7

Bonds can be classified as being either polar or non-polar.

Polarity: tendency of a molecule, or compound, to be attracted or repelled by electrical charges because of an asymmetrical arrangement of atoms around the nucleus.

Think of it like a game of tug of war, if one end of the compound is pulling on the electrons more than the other, there is an unequal pull, and therefore, the substance is polar. If there is an equal pull, then the substance is non-polar.

This concept of polarity is determined by electronegativity.

Ionic Bond Attraction between oppositely charged ions Occurs when electrons are transferred

from one ion (charged particle) to another Electronegativity difference 1.7+ Metals react with Nonmetals to form ionic

compounds Always

Polar !!!

Lewis Dot Structure of Ionic Compounds

KCl

CaBr2

KNO3

(NH4)3PO4

Possible Combinations for Ionic Compounds

Formula

(+) ( - ) Examples

M NM NaCl, KI, and CaF2

M P LiNO3 and Sr(CN)2

P NM NH4Br, Hg2S, and (H3O)2Se

P P NH4NO3 and H3OMnO4

Properties of Ionic Compounds

Hard Good conductors of electricity in

liquid or aqueous form only, because ions can move in solution and in liquid form, but not in solid form.

High melting and boiling points Solid at room temperature Dissolve in polar substances: like

water. (Polar – opposite charges).

Covalent Bonds Formed when 2 atoms (both nonmetals) share

electrons. [Example Cl2 or H2O] Neither atom pulls strongly enough to remove an

electron from the other The EN difference is < 1.7 Unpaired electrons pair up in such a way that the

atoms complete their outer shells Covalent compoundsalso referred to as molecularcompounds

Properties of Covalent Bonds

Gases, liquids or solids Soft Nonmetals Poor conductors of heat and electricity

because they are not charged particles. (No ions or mobile electrons)

Low melting and boiling points because of weak attraction between molecules.

Polar vs. Non-Polar Covalent Bonds

Unlike an ionic compound, a covalent compound can be classified as either a polar covalent bond, or a non-polar covalent bond.

If the EN of the atoms are different then it is a polar covalent bond.

If the EN of the atoms are the same or very similar then it is a non-polar covalent bond.

0.0 - 0.4 = non-polar covalent0.5 - 1.6 = polar covalent

Number of Covalent Bonds

Single covalent bond: one pair of shared electrons; 2 electrons total

-Double covalent bond: two pairs of shared electrons; 4 electrons total

-Triple covalent bonds: three pairs of shared electrons; 6 electrons total

Must know how to draw these!!

HF H2O CO2 CH4 NH3

HCl H2S CS2 CF4 PH3

HBr SiO2 CCl4HI SiS2 CBr4

CI4

Partially Positive & Negative

In a polar covalent bond, both of the elements are non-metals, and therefore there is no “true” + or – charges; instead there are partially (+) and partially (-) charges.

The element with the higher EN is partially (-)and the one with thelower EN is partially (+)

This is a SNAP!

•Symmetric are

•Nonpolar

•Asymmetric are

•Polar

Other Types of Covalent Bonds

Coordinate Covalent Bond: When one atom donates both of the electrons that

are shared Example: NH4

+ and H3O+

Nitrogen donates a pair of electrons to share with H+ forming a coordinate covalent bond between nitrogen and hydrogen

Other Types of Covalent BondsNetwork Solids:

Solids that have covalent bonds between atoms linked in one big network or one big macromolecule with no discrete particles. This gives them some different properties from most covalent compounds.

They are hard, poor conductors of heat and electricity, and have high melting points

Examples include: Diamond (C), silicon carbide (SiC), and silicon dioxide (SiO2)

Metallic Bond Occurs only in metals (Example Copper)

Metals have low ionization energy meaning they hold onto their valence electrons very loosely

As a result the electrons in metallic substances move about very easily and are not associated with any particular atom

Therefore, the particles of a metal are usually positive ions surrounded by a mobile sea of electrons

The attraction between the positive cations and the moving electrons is what holds the metal together

Properties of Metallic Bonds are that of metals: hard, good conductors of heat & electricity, malleable, ductile, etc . . .

Dipole-Dipole Attractions

• Positive end of a polar molecule is attracted to the negative end of an adjacent polar molecule.

Hydrogen Bonding• An intermolecular attraction between a

hydrogen atom in one molecule to a nitrogen, oxygen, or fluorine atom in another molecule

• The strongest intermolecular force

• Substances with hydrogen bonds tend to have much higher melting and boiling points than those without hydrogen bonds

• Example: The boiling point of H2O is much higher than H2S

London Dispersion Forces

AKA: van der Waals Forces Weak intermolecular forces between non-polar molecules (like diatomic

molecules) Dispersion forces make it possible for small,

non-polar molecules to exist in both liquid or solid phases under conditions of high or low temperatures.

Increases with molecular size, Ex. As you go down group 17, dispersion forces increase and boiling point increases.

Molecule-Ion Attraction Attraction between the

ions of an ionic compound such as NaCl, and a molecule such as water (or any other polar covalent compound).

When you put NaCl into water, the Na+ from the salt is attracted to the O from the water which is partially (-), and the Cl- from the salt is attracted to the H+ of the water.

THE VSEPR Model

180°

120°

THE VSEPR Model

104.5°

107°

109.5°

THE VSEPR Model

120°

90°

THE VSEPR Model

90°

© 2009, Prentice-Hall, Inc.

sp Hybrid Orbitals

• Consider BeF2

– In beryllium’s ground electronic state, it would not be able to form bonds with fluorine because it has no singly-occupied orbitals

– Linear structure

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sp2 Hybrid Orbitals• Using a similar model lets consider BF3

• Boron (1s2 2s2 2p1) does not have three single electrons to share with the three F atoms

• An electron is promoted to the 2p orbital• s,p,p (sp2)• Trigonal Planar

© 2009, Prentice-Hall, Inc.

sp3 Hybrid Orbitals• Using a similar model lets consider CH4

• Carbon (1s2 2s2 2p2) does not have four single electrons to share with the four hydrogen atoms

• An electron is promoted to the 2p orbital• s,p,p,p (sp3)• Tetrahedral

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27

sp3d Hybrid Orbitals• Combination of one s orbital, three p

orbitals, and one d orbital• Gives a trigonal bipyramidal

arrangement of hybrid orbitals.

• Examples include: PF5, SF4, BrF3

sp3d2 Hybrid Orbitals Combination of one s orbital, three p

orbitals, and two d orbital Gives a octahedral arrangement of

hybrid orbitals. Examples include: SF6, ClF5, XeF4, PF6

-

Hybrid Orbitals

• The type of hybridization can be determined based on the electron-domain geometry of a particular molecule.

Hybrid Orbitals