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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 !!!
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
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 (+)
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.
© 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
© 2009, Prentice-Hall, Inc.
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
Copyright © Cengage Learning. All rights reserved
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.