Chapter 9 (part 2): Chemical Bonding I: Lewis Theory Flashcards
Bond energies are always ____ because it always _____ energy to break a bond
Positive
Takes
A bond is stronger than another when it requires ____ energy to break it (ie. _____ bond energy)
More
Greater
A strong and stable bond will cause a molecule to be relatively ______
Inert
What two things do bond energies depend on?
The kind of atoms involved in the bond and the type of bond (single, double, triple)
The bond energy for tripe bond is _____ than the bond energy for double bonds which is ____ than the bond energy for single bonds
Greater
Greater
Bond energies can be used to estimate _____ change of a reaction
Enthalpy
When bonds break the process is ____ so bond energy is _____
Endothermic
Positive
When bonds form the process is _____ so bond energy is _____
Exothermic
Negative
A reaction is Exothermic when ____ bonds are broken and ____ bonds are formed
Weak
Strong
A reaction is endothermic when _____ bonds break and ____ bonds form
Strong
Weak
Breaking a chemical bond always _____ energy
Requires
Forming a chemical bond always _____ energy
Energy
Define bond length
The average length of a bond between two particular atoms in a variety of compounds
Bond lengths depend on
The kind of atoms involved in the bond and the type of bond (single, double, triple)
Define bond stretching vibration (or stretching vibration)
A molecular motion in which a bond stretched and then contracts
For bond vibrations to take place, energy much be ______ to the molecule
Supplied
Energy that cause bond vibrations can originate from…..
Molecular collisions or from the absorption of electromagnetic radiation in the infrared region
Why is energy that cause bond vibrations specifically cause by the infrared region of the electromagnetic spectrum and not other regions?
Because the infrared frequency range of electromagnetic radiation corresponds to the energies of molecular (E =hv)
Define infrared (IR) absorption spectroscopy
The measurement of molecular absorption of infrared frequency radiation to give information about molecular structure
Define wavenumber
The reciprocal of wavelength
In infrared absorption spectroscopy ______ is determined not the wavelength.
Wavenumber
The higher the wave number, the ____ the energy of light that was absorbed
Greater
As bond strength increases then the wavenumber value of absorption ______
Increases
Define polar covalent bond
A covalent bond between two atoms with significantly different electronegativities, resulting in an uneven distribution of electron density
Most covalent bonds between dissimilar atoms are actually _____ _____
Polar covalent
Define electronegativity
The ability of an atom to attract electrons to itself in a covalent bond
Electronegativity ___ across a row
Increases
Electronegativity _____ down a column
Decreases
Fluorine is the _____ electronegative atom
Most
Francium is the _____ electronegative atom
Least
Also Is sometimes called the most electropositive
Electronegativity follows what rule of thumb perfectly
Righter tighter lower loser
What does the degree of polarity in a chemical bond depend on?
The electronegative difference between the two bonding elements (sometimes abbreviated delta EN)
The greater the electronegativity difference, the more ____ the bond
Polar
If two elements with identical electronegativities form a covalent bond, they share the electrons equals, and the bond is purely _____ or ____ ____
Covalent
Non polar
When the electronegativity difference is small (0-0.4) the bond type is …?
Covalent
When the electronegativity difference is intermediate (0.4-2.0) the bond type is …?
Polar covalent
When the electronegativity difference is large (2.0 and up) the bond type is …?
Ionic
How do you quantify the polarity of a bond?
By the size of its dipole moment
Define dipole moment
A measure of the separation of positive and negative charge in a molecule
What unit is commonly used for reporting dipole moments?
The Debye (D) (1D = 3.34 x 10^-30 C•m)
Define percent ionic character
The ratio of a bonds actual dipole moment to dipole moment it would have if the electron were transferred completely from one atom to the other, multiplied by 100%
In general bonds with greater than ____ ionic character are referred to as ionic bonds
50%
Define bond energy
The energy required to break 1 mole of the bond in the gas phase
