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November 25, 2014
Chemical Bonding: Ch 7 and 8
http://www.youtube.com/watch?v=QqjcCvzWwww
http://www.youtube.com/watch?v=UR4eG60jjQQ
http://www.youtube.com/watch?v=QXT4OVM4vXI
Chemical BondingA chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.
Why are most atoms bound together?Most atoms are at relatively high potential energy by
themselves and are more stable when combined with other elements!
We will be discussing ionic vs. covalent bonding.Chapter 7- Ionic BondingChapter 8- Covalent Bonding
Chemical Bonding-Vocabulary
A chemical bond
-Attractive force between atoms or ions that binds them together as a unit.
-bonds form in order to:-decrease potential energy (PE)-increase stability
Chemical Bonding-Vocabulary
Chemical Formula
covalentionic
Formula Unit
NaClMolecular Formula
H2O
Chemical Bonding-Vocabulary
Compound
more than 2 elements2 elements
Binary Compound
NaClTernary Compound
NaNO3
Chemical Bonding-Vocabulary
Ion
2 or more atoms1 atom
Monoatomic Ion
Na+
Polyatomic Ion
NO3-
November 25, 2014B) Types of Bonds
Ionic Covalent Metallic
Bond Formation
electrons transferred from metal to nonmetal
electrons shared between two nonmetals
electrons are delocalized among metal atoms.
Type of Structure crystal lattice true molecules "electron sea"
Physical State solid liquid or gas solid
Melting Point high low very high
Solubility in Water yes usually not no
Electrical Conductivity
yes (solution or liquid) no yes (any form)
Other Properties odorousmalleable, ductile, lustrous
Example NaCl, BaCl2, CaO, etc. H2O, NO, NO2 Al, Fe, etc.
1) Ionic Bonding
-Transfer of electrons from one atom to another.
Metal + Nonmetal Ionic Compound
Valence electrons are usually the only electrons used in chemical bonds.
Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level.
Atoms of some non-metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete octet.
Example: Sodium ChlorideThe chemical formula: NaCl because Na+1 and Cl-1
Steps:1. Look at the charge2. Determine the ratio of charges3. Criss-Cross the charges and simplify to the lowest ratio.
Practice Problems:
Determine the charge of the ions and the final formula unit of the following:
1. potassium and iodine
2. aluminum and oxygen
3. magnesium and chlorine
Nomenclature of Ionic Compounds1. Keep the name of the cation the same and change the name of the anion to an -ide ending.
a) NaCl= sodium chlorideb) CaCl2= calcium chloride
c) BaF2=
d) KCl=
e) MgO=
November 25, 2014
Coordination patterns and packing depends on the size of the ions. Remember the trends from the Periodic Table!
Body Centered Cubic Every atom has 8 neighborsEx: (Na, K, Fe)
Face Centered CubicEvery atom has 12 neighborsEx: (Ag, Au, Al, Pb)
Hexagonal close-packedEvery atom ALSO has 12 neighbors but is pattern is different. Ex: (Zn, Mg, and Cd)
http://www.youtube.com/watch?v=ZVqocQLAEr0
http://www.youtube.com/watch?v=Rm-i1c7zr6Q&feature=related
http://www.youtube.com/watch?v=KNgRBqj9FS8Oxidation Numbers (Honors)
-Can figure out from the formula-Unpaired electrons in d orbitals
Fe: (+2 and +3)
Section 7.3 Bonding in Metals*Similar to structure of ionic!The valence electrons of metal atoms can be modeled as a sea of electrons.The valence electrons are mobile and can drift freely from one part of the metal to another.The electrons can drift because of the vacant d orbitals just below their highest energy level.
These orbitals can overlap and the overlapping is what causes the electrons to move about freely.
http://www.drkstreet.com/resources/metallic-bonding-animation.swf
Bonding in MetalsMetallic bonds:consist of the attraction of the free-floating valence electrons for the positively charged metal ions.
November 25, 2014
Crystalline Structure of Metals Alloys:Mixtures composed of two or more elements, at least one of which is a metal.
*Alloys are important because their properties are often superior to those of their component elements.
Types of AlloysSubstitutional- atoms of different components are of similar size.Ex: Brass
Interstitial- solute atoms occupy "gaps" because they are different sizes.Ex: Carbon for steel
Electrons shared between nonmetals
3) Covalent Bonding
Potential Energy Diagram
1. The separated atoms do not affect each other.2. Potential energy decreases as the atoms are drawn together.3. Potential energy is at a minimum when attractive forces are balanced by repulsive forces.4. Potential increases when repulsion between like charges outweighs attraction between opposite charges.
1. 2. 3. 4.
Mr. BrINClHOF
B(r)illiantHarvardNerdsOftenFindC(l)hemistry Interesting
Most elements can form diatomics, HOWEVER, only at very high temperatures.
Kinetic Theory (Random movement)
The "7" exist free at normal conditions.
November 25, 2014
The Nature of Covalent BondingIn covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.
Why would atoms want to do that?
We will be looking at three different types of covalent bonds:
1. Single Covalent2. Double and Triple Covalent
3. Coordinate Covalent
1. Single Covalent BondStructural formula:Represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms. One dash represents two electrons.
Unshared Pair:
A pair of valence electrons that are not shared between atoms.
(lone pair or nonbonding pair).
2. Double and Triple Covalent Bonds
Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.
Double covalent bond: A bond that involves two shared pairs of electrons
Triple covalent bond: A bond formed by sharing three pairs of electrons.
3. Coordinate Covalent BondsCoordinate Covalent Bond:
A covalent bond in which one atom contributes both bonding electrons.
In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.
Electron-Dot Notation (Lewis Dot Structures)Why the exceptions??
Incomplete Octet: (Group 3A)
Group 3A: Boron 1s2 2s2 2p1 (only 3 valence electrons)
Expanded Octet: (3rd Period)
Beyond the 3rd period with the "d" orbitals
Sulfur: [Ne]3s2 3p4 (6 valence electrons)
Odd-Electron Molecules (Radicals)(NO and NO2 )
Lewis Structures-Steps1. Find the total # of valence electrons2. Arrange atoms-singular atom is usually in the middle (usually carbon)3. Form bonds between atoms (2 electrons)4. Distribute remaining electrons to give each atom an octet.5. If there are not enough electrons to go around, you will have to make double or triple bonds.· Don't forget the exceptions.· Boron and Aluminum only need 6· Sulfur and Phosphorus can have an expanded octet.
November 25, 2014
Lewis Structures-Practice
NH3
CO2
Polyatomic Ions
-a tightly bound group of atoms that have a positive or negative charge and behaves as a unit.
The charge is on the whole ion but the individual components can be held together covalently.
Example is the ammonium ion (NH4+ )
Polyatomic Ions-Practice
ClO4-
NH4+
Exceptions to Lewis Structures1. Odd number of valence electrons
*Central atom will not have an octet*Examples: ClO2 and NO
2. Central atom with less than eight electrons*These compounds tend to be very reactive*Examples: BF3, BH3
3. Central atom with more than eight electrons*Most common exception*Expanded octet*extra electrons fill in the empty d-sublevel*Examples: SF6, XeF4
Resonance
Resonance-Practice
O3
SO3
November 25, 2014
Bond Dissociation EnergiesBond Dissociation Energy:The energy required to break the bond between two covalently bonded atoms.
The larger the bond dissociation energy, the stronger the bondExample: C2H2 vs. C2H6
Nomenclature (Intro)
Nomenclature (Intro)Name the following binary molecular compounds:
1. SF6 is sulfur hexafluoride
2. CO
3. CO2
4. N2 O
5. Cl2 O8
Nomenclature (Intro)
Resonance(Honors Only)
Formal Charge is used to determine the best overall resonance structure.
Handout