Unit 3: Bonds & Properties, Covalent Structures, IMFs Flashcards
Electronegativity Differences and Bond Character
- > 1.7 = Ionic
- 0.4 - 1.7 = Polar covalent
- < 0.4 = Nonpolar covalent
Electronegativities memorized
H = 2.1, B = 2.0, C = 2.5, N = 3.0, O = 3.5, F = 4.0
Covalent AKA Molecular Bond characteristics
- covalent bonds are strong, but physically weak
- most are l and g at room temp.
- insoluble in water, but soluble in organic solutions
- poor conductors
- vaporize readily at room temp
Nonpolar Covalent Bond characteristics
- only dissolves in Nonpolar covalent
- NO dipole moment
Polar Covalent Bond characteristics
- weakly conduct electricity
- dissolve in polar and ionic
- causes a dipole moment (arrow indicates element with higher electronegativity)
Ionic AKA Electrostatic Bond characteristics
- two completely charged atoms or ions
- incredibly strong chemical bonds
- high melting and boiling points
- crystalling solid and room temp
- solid does not conduct electricity, but the aqueous/liquid state does
Metallic bond characteristics
- form an “electron sea” that cements the positive nucleus together, and shields the positive cores from each other
- Delocalized electrons = electrical and thermal conductivity
- Lustrous (shiny)
- Malleable (can be flattened)
- Ductile (drawn into wires)
Bond (Dissociation) Energy
- The amount of energy that is required to break the bond between two specific atoms in a molecule which is EQUAL to: the amount of energy that is released when a bond forms between two specific atoms
When covalent bonds form between two atoms, the two atoms close together follow four electrostatic forces
Two attractive forces between:
1. Nucleus A and electron B
2. Nucleus B and electron A
Two repulsive forces between:
1. Two nuclei
2. Two electrons
**ATTRACTIVE MUST BE GREATER THAN REPULSIVE FOR A BOND TO FORM
Bond Order on Graphs
Highest dip = single bond
Middle dip = double bond
Lowest dip = triple bond
Bond Order
Number of bonds between two atoms; increasing = decreasing distance/bond length
Single = 1, Double = 2, etc.
Bond Energy/Bond Length
As the number of bonds between two atoms increases, the bond length decreases, and the bond energy increases
As the electron density between the positive nuclei increases,
the attractive forces between the protons and the electrons increases
- a greater FoA = more energy to break the bond
As atomic radius increases, bond length
increases, and bond energy decreases
Lewis Structures expanded octet
Atoms in periods 3-7 can bond with other atoms to end up with more than 8 electrons in their octet
BECAUSE they have d-orbitals in their outershells than can accept electrons
EXCEPTIONS: Lewis Structures Need
H = 2
B = 6
Be = 4
CALCULATION: Enthalpy of a Reaction with Average Bond Enthalpies
- Draw Lewis Structures
- Determine bonds and account for coefficients
- Reactants - Products AKA broken - formed
Two Types of Solids
- Crystalline: Made of repetitive units called unit cells; 3D array known as crystal lattice (ex: snow, salt crystals)
- Amorphous: Don’t have a well-defined 3D unit structure (ex: plastic, glass)
Types of Crystalline Solids: Network Covalent Solid
atoms held together chemically in large networks or chains by intramolecular chemical covalent bonds
- intramolecular = covalent
- STRONGEST b/c strong IMFs
- very high melting point
- typically nonconductors
- ex: diamonds, graphite (allotropes)
Crystalline: Metallic Solid
positive core of atoms held together by a surrounding sea of electrons AKA delocalized electrons
- intramolecular = metallic
- high melting point
- hard, Lustrous, Malleable, not brittle
conduct electricity
- ex: iron, silver, copper
2 types of Metallic solids
- Interstitial Alloy = far on periodic table/small + big radius
- steel (C in Fe) - Substitutional Alloy = close on periodic table/same-ish radius
- sterling silver (Ag and Cu)
Crystalline: Ionic Solid
consists of cations and anions held together by the electrical attraction of opposite charges
- intramolecular: ionic
- nonconducting solid but conducting liquid
- high melting point
- brittle, hard
- ex: NaCl
Crystalline: Molecular Solid
consists of atoms or molecules held together by intermolecular forces (physical, not chemical)
- WEAKEST of all solids
- low melting point
- nonconducting
- brittle
- ex: dry ice
