Ionic and covalent bonding and properties of solids
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Ionic and covalent Bonding and Properties of Solids. Chemical Bonding sites. The Orbitron: a gallery of atomic orbitals and molecular orbitals on the WWW http://www.shef.ac.uk/chemistry/orbitron/ Excellent sites for shapes of molecules: http://www.chemmybear.com/shapes.html.

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Ionic and covalent Bonding and Properties of Solids

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Ionic and covalent Bonding and Properties of Solids


Chemical Bonding sites

The Orbitron:a gallery of atomic orbitals and molecular orbitals on the WWWhttp://www.shef.ac.uk/chemistry/orbitron/Excellent sites for shapes of molecules:http://www.chemmybear.com/shapes.html


Electron Dot Structures

  • All chemistry textbooks have a chart like this


Loss & Gain of electron(s)

  • Atoms are stable when they have an “octet” or Nobel gas configuration.

  • Atoms form ions through the gain or loss of electrons

  • Opposites attract and ionic compounds are formed


Formation of an Ionic Compound Using Electron Configurations

  • Sodium looses 1 electron and chlorine gains one electron to form an “octet” or Nobel gas configuration.


Electron Dot Formula of an Ionic Compound

  • Magnesium atoms lose 2 electrons to become stable

  • Nitrogen atoms gain 3 electrons to become stable

  • 3 Mg ions (+6) and 2 nitrogen atoms (-6) = 0 net charge;)


Properties of Ionic Compounds

  • Usually solid crystals @ room temp (types of crystal structure & coordination number)

  • Generally have high melting points

  • Can conduct electricity when melted or dissolved in water

  • Formula represents number of ions in a representative unit


Metallic Bonds

  • Metals are made up of closely packed cations rather than neutral atoms

  • Valence electrons are mobile (sea of electrons)

  • Metallic bonds consist of attractions of the free-floating valence electrons for the positively charged metal ions


Metallic Properties & Structures:

  • Good conductors of electricity

  • Can be drawn into wires (ductile)

  • Can be hammered or forced into shapes (malleable)

  • Arranged in very compact & orderly patterns

  • Alloys are a mixture of 2 or more elements, at least one of which is a metal


Single Covalent Bonds

  • Nitrogen needs 3 additional electrons to satisfy its octet but cannot remove them from hydrogen so they share electrons

  • Carbon needs 4 additional electrons to satisfy its octet but cannot remove them from hydrogen so they share electrons


Double Bonds

  • Oxygen cannot remove 2 electrons from another oxygen so they share 2 pairs (double bond)

  • Nitrogen cannot remove 3 electrons from another nitrogen so they share 3 pairs(double bond)


Coordinate Covalent Bonds

  • Coordinate covalent bond is formed when one atom donates an unshared electron pair to the bond. In this case oxygen donates on of its unshared pairs.

  • This is seen frequently in polyatomic ions!


VSEPR (valence shell electron pair repulsion theory)

Electron pairs repeland molecules adjust their shapes so that

their valence shell electrons are as far apart as possible


VSEPR continued


Molecular Compounds - 2 or 3 pairs of electrons around central atom

Each “-” between atoms represents a shared pair of electrons


Octets - 4 pairs of electrons around central atom


Expanded Octets - 5 pairs


Expanded Octets - 6 pairs


Covalent (polar/nonpolar) or Ionic?

Bond type determined by difference in electronegativity and molecular shape


Intermolecular Forcesattractions between molecules


Intermolecular Forces -attractions between molecules

  • Hydrogen bonds

    • Strongest intermolecular attraction

    • Occurs between the hydrogen atom of one molecule and a very electronegative (O, N, or F) atom in another molecule


Dipole moment u = 1.85 D

Polarizability α = 1.48 x 10-24 cm3

δ-

δ+


Solids

Crystalline:

orderly array

Amorphous:

random jumble


(all crystalline!)

  • Forces in solids:

  • Metallic: metallic bonds (metal ions in electron sea)

  • Ionic: electrostatic (anions and cations)

  • Network: covalent bonds

  • Molecular: London, dipole-dipole, hydrogen bonds


Numerous Unit Cells for Different Crystal Structures

Unit cell: the smallest representation of a crystal that

reproduces the whole crystal.

(do not memorize this table!)


Layered structure of metallic solids

(A and B are same type of atom)


Hexagonal close-packed

metallic structure:

Coordination number is 12

(number of nearest neighbors

for each atom; 6 in same plane

and 3 above and 3 below)

(the other major structure

is cubic close-packed;

Al, Cu, Ag, Au)

Mg, Zn


Bravais Lattices for Unit Cells of Metallic Solids*

* don’t memorize these! No way!


A metal crystallizes in a cubic cell structure with an edge length of 3.308 A. Its density is 4.401 g/cm3. What is the element?

edge


Structures of Ionic Solids

NaClunit cell (coordination # 6)

Note: anions and cations are different sizes!


Billions of “unit cells” to create NaCl crystals


Molecular Solids

  • Sucrose

  • Ice

Ice

H O


Network Solids: Strong covalent bonds

Graphite: hexagonal rings of sp2 hybridized carbons

Others: Diamond, ceramics


Properties of Solids:

Density

Conductivity

“Luster”


Malleability


Alloys: Mixtures of Two or More Metals


Alloys

SubstitutionalInterstitial

Harder and stronger, but less conductive


Catalytic Converter

Pt, Rh

2 NO  N2 + O2

2 CO + O2  2 CO2

hydrocarbons + O2 

CO2 + H2O

Pt, Pd

Pt, Pd

emissions

honeycomb ceramic coated with Pt, Pd, Rh


Semi-Conductor

  • Si doped with P or As (electron rich)

  • Si doped with B or Ga (electron poor)

No current across

junction with this set-up


PROPERTIES OF MATTER


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