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Chemical Bonding
Chapter 6
Chemical Bond
Chemical Bond – an attraction between atoms to hold the atoms together
Review
Which type of elements are the most stable (least willing to undergo change)?
How many valence electrons do they have?
What would you expect of the other elements to increase their stability?
Octet Rule
Octet Rule- atoms gain, lose, or share electrons in order to acquire a full set of 8 valence electrons.We will address exceptions to octet rule also.
Ex. sodiumA sodium ion is more stable than the neutral sodium atom because it now has 8 valence electrons.
3 types of Bonds
Nonpolar covalent bonds- valence electrons are shared equally between bonded atoms.
Polar covalent bonds- valence electrons are shared unequally between the bonded atoms.
Ionic bonds- valence electrons are transferred from one atom to another forming ions. These oppositely charged ions attract.
Bonding between atoms is rarely purely ionic or covalent. It is usually some degree between the two.
General rule on the type of bond that forms between two atoms:
Ionic bond-a metal and a nonmetal, or a polyatomic
Covalent bond-2 or more non-metals, sharing of electrons
Electronegativity
Electronegativity Differences-Used to determine what type of bond forms (Pg. 151)0-.2 nonpolar covalent.3-1.7 polar covalent>1.7 ionic
Example: Determine the type of bond with electronegativity differences:
H and Cl: Cs and Cl: Cl and Cl:
Prac p163 and section review p163
Molecular Cmpds
Molecule (2 or more nonmetals)-a neutral group of atoms held together by covalent bondsMolecular cmpd
Molecular formula-shows the number and kind of atoms in a molecule of a compound
Diatomic molecule-molecule with only 2 atoms Ex.
Diatomic elements-element that comes as 2 atoms (Memorize:HBrONClIF)
Diagram graph on p165, show why a bond forms at position c and not at d, a.
Show the overlapping of orbitals in H2
Chemical Bonds
Bond Length – distance between 2 bonded atoms
Bond energy – energy required to break a chemical bond into isolated atoms
Electron Dot Notation
Electron Dot Notation – Element symbol represent the nucleus and electrons other than the valence electrons. The dot (s) around the symbol represent the valence electrons
Note: This is an important representation because it is mostly the valence electrons that undergo chemical rxns
Illustrate the electron dot notation for all the elements in period 2:
Lewis Structures
Lewis structures-using electron dot notation to show the way atoms form a compound
Single Bond
Single bond is the sharing of one pair of electrons between 2 atoms, represented by 2 elec dots or a dash.
Ex.
H2 HF
Single Bond
Draw these Lewis structures. Note if C is in the formula, it is the central atom.
H2O, HBr, F2, NH3, H2S, CH3I
Double Bond
Double bond – covalent bond formed by sharing two pairs of electrons b/t atoms.
Illustrate C2H4, CO2
Triple Bond
Triple bond-a covalent bond formed by sharing 3 lone pairs of electrons between two atoms.
Illustrate C2H2, N2
Multiple Bonds
Double bonds and triple bonds are called multiple bonds.
Which type of bond is the strongest? p173Weakest?Which bond is the longest?Shortest?
Practice 174
Resonance
Resonance – bonding that requires several structures to represent the molecule or ion. The actual molecule (ion) is resonating from one structure to another.
Ex. O3, CO3 -2
Section Review p175
Ionic Bond
Ionic cmpd – cmpd made up of positive and negative ions that combine to be neutral.
Formula unit – simplest repeating unit of ionic cmpd
Formation of Ionic Cmpd
Using electron dot structureEx. Na and Cl to Na+ and Cl- = NaCl
Ex. Ca and F to Ca+2 and F-1 = CaF2
Section Review p180
Ionic vs. Molecular Cmpds
1. Ionic cmpds have very strong attractions to hold the formula units together. Attractions holding molecules together is weaker.
2. Ionic cmpds have high melting pt, boiling pt, and high degree of hardness due to above reason.
3. Ionic cmpds are brittle. Illustrate reason. See p179 fig. 6-17
Polyatomic Ions
Polyatomic Ions – group of atoms bonded covalently that have a charge.
Suffix of –ate, if more oxygens
Suffix of –ite, if less oxygens
Metallic Bonding
Metallic Bonding – bonding due to attraction between metal atoms and a sea of electrons. Illustrate concept.
Malleability – metals can be hammered into sheets
Ductility – metals can be drawn into wires
Section Review p182
Molecular Geometry
VSEPR Theory = valence shell electron pair repulsion theory = valence pairs stay as far as possible from each other due to repulsion.
Illustrate and name the 8 different molecular shapes to be memorized (p186)
Practice p187
Hybridization
Hybridization – mixing of 2 or more atomic orbitals to produce new orbitals of the same energy
Ex.
Illustrate:
Polar vs. Nonpolar molecules
To determine if a molecule is polar or nonpolar:
1. Identify the shape of molecule
2. Show bond polarity with aid of electronegativity
Ex. HCl, CO2, CH4, NH3, H2O
Intermolecular Forces
Intermolecular Forces – attractions between molecules
3 types1. Dipole-Dipole – attraction between
polar molecules
Ex. Show dipole-dipole force between two molecules of NH3
2. Hydrogen Bonding – intermolecular force where hydrogen is attracted to an unshared pairs of electrons on another molecule
Illustrate with NH3 and H2O
3. London Dispersion Forces – temporary intermolecular attractions caused by motion of molecules.
Illustrate with H2 and O2
Section Review p193
Polymers
Polymers – large molecules made up of many units joined through rxns
Monomers – small units
Thermoplastic polymer – melts when heated and can be reshaped many times
Thermosetting polymer – doesn’t melt when heated but keeps its original shape
Types of Polymers
There are linear polymers, branched polymers, and cross linked polymers. See diagram p685
Types of Polymers
Addition Polymer – formed from double bonded monomers linked up.
Ex.
CH2=CH2 CH2=CH2 CH2=CH2 →
-CH2-CH2-CH2-CH2-CH2-CH2-
Condensation Polymer – formed by removing a molecule of water between two monomers
See p690 for example
Patterns of Monomers
Possible Patterns of monomers:AAAAAA
ABABAB
AAABBBAAABBB
AABBBBBBABAA