Chapter 3 - Bonding and Chemical Reactions Flashcards
what is a covalent bond?
atoms share electrons; attraction that each electron in the shared pair has for the two positive nuclei of the bonded atoms
what are characteristics of molecules with covalent bonds?
lower melting and boiling points, poor conductors of electricity
what are single, double, and triple bonds?
Two atoms sharing one, two, or three pairs of electrons are said to be joined by a single, double, or triple bond
what is bond order?
the number of shared electron pairs (ie. bond order of a single bond is 1)
what is bond length?
average distance between two nuclei of atoms in a bond
how does bond length change
as number of pairs of shared electrons increases, the two atoms are pulled closer together; triple bond shorter than double bond, which is shorter than a single bond
what is bond energy?
energy required to break a bond by separating its components into their isolated, gaseous atomic states
how does bond energy change?
greater the number of pairs of electrons shared between the two atoms, the more energy required to break the bonds holding the atoms together; triple bonds have greatest bond energy, single bonds have lowest bond energy; greater the bond energy, the stronger the bond
when does polarity occur?
when two atoms have relative differences in electronegativity, the atom with the larger electronegativity gets the larger share of electron density
what is a nonpolar covalent bond?
when atoms that have identical or nearly identical EN share electron pairs, they do so with equal distribution of the electrons; EN difference of 0.5 or less, no separation of charges
what are the diatomic molecules?
H, O, F, Br, I, N, Cl
what is a polar covalent bond?
atoms that differ moderately in their EN will share electrons unevenly, difference in EN between 0.5-1.7
what is a partial positive charge?
occurs when less electronegative atom takes on less of the electron density
what is a partial negative charge?
occurs when the more electronegative atom takes on more of the electron density
what makes a polar molecule?
separation of positive and negative charges
what is the equation for a dipole moment?
p=qd (charge x distance)
what is a coordinated covalent bond?
both of the shared electrons originated on the same atom; lone pair of one atom attacks another atom with an unhybridized p-orbital; typically found in Lewis acid-base reactions
what are bonding electrons?
electrons involved in a covalent bond
what are nonbonding electrons?
electrons in the valence shell that are not involved in covalent t bonds, aka lone pairs
what is a Lewis structure?
system of notation developed to keep track of bonded and nonbonded electron pairs
what is formal charge?
difference between the number of valence electrons of each atom and the number of electrons the atom is associated with
what is the equation for formal charge?
FC= # of valence electrons in atom – number of bonds- nonbonded electrons
what is the assumption made by formal charge?
Assumes equal sharing of all bonded electron pairs regardless of actual differences between EN
what is a lewis dot diagram?
chemical symbol of element surrounded by dots, each representing one of the s or p valence electrons
what are resonance structures?
two or more Lewis structures that demonstrate the same arrangement of atoms but differ the specific placement of the electrons, represented with a double headed arrow between them
what is a resonance hybrid?
actual electronic distribution in the compound is a hybrid or the possible resonance structures (more stable a structure, the more it contributes to a resonance hybrid)
what makes a structure more stable?
- lewis structure with small or no formal charges is preferred over a Lewis structure with large formal charges
- lewis structure with less separation between opposite charges is preferred over a Lewis structure with a large separation of opposite charges
- lewis structure in which negative formal charges are placed on more electronegative atoms is more stable than one in which the negative formal charges are placed on less electronegative atoms
what is valence shell electron pair repulsion theory (VSEPR)?
uses Lewis dot structures to predict the molecular geometry of covalently bonded molecules, 3D arrangement of atoms is determined by the repulsion between bonding and nonbonding electron pairs in the valence shell of the central atom, arrange themselves as far apart as possible, minimizing repulsive forces
what are electronic geometries?
are concerned only with the basic geometry (just with the steric number, not differentiating between bonding and non-bonding electrons) ie. Electronic geometry of water is tetrahedral, not bent
what are molecular geometries?
are concerned with the actual specific geometry, which includes the nonbonding vs. bonding electrons; ie. Molecular geometry of water is bent
what is steric number?
number of bonded species (not bond order!!, triple bond is 1) and number and electron pairs on the central atom
what determines the ideal bond angle?
the electronic geometries?
what exerts more repulsion - bonding electrons or nonbonding electrons
nonbonding electrons
what happens to bond angle as nonbonding electrons increase?
the bond angle decreases
molecular geometry: steric #2
linear
molecular geometry: steric #3, no lone pairs
trigonal planar
molecular geometry: steric #3, 1 lone pair
bent
molecular geometry: steric #4, no lone pairs
tetrahedral
molecular geometry: steric #4, 1 lone pair
trigonal pyramidal
molecular geometry: steric #4, two lone pairs
bent
molecular geometry: steric #5, no lone pairs
trigonal bipyramidal
molecular geometry: steric #5, one lone pair
seesaw
molecular geometry: steric #5, two lone pairs
T-shaped
molecular geometry: steric #5, three lone pairs
linear
molecular geometry: steric #6, no lone pairs
octahedral
molecular geometry: steric #6, one lone pair
square pyramidal
molecular geometry: steric #6, two lone pairs
square planar
molecular geometry: steric #6, three lone pairs
T-shaped
molecular geometry: steric #4, four lone pairs
linear
what is the ideal bond angle of steric #2?
180
what is the ideal bond angle of steric #3?
120
what is the ideal bond angle of steric #4?
109.5
what is the ideal bond angle of steric #5?
90 and 120
what is the ideal bond angle of steric #6?
90
when is a compound nonpolar?
compound only has nonpolar bonds, or compound has polar bonds but the molecular geometry is in such a way that the dipole moments cancel each other out
when is a compound polar?
when the molecular geometry is arranged such that the bond dipoles do not cancel each other out
what is a molecular orbital?
• when two atoms bond to form a compound, the atomic orbitals interact to form a molecular orbital, which describes the probability of finding the bonding electrons in a given space; obtained by combining wave functions of the atomic orbitals
o if signs of the two atomic orbitals are the same a bonding orbital forms
o if the signs are different, an antibonding orbital forms
what is a sigma bond?
when orbitals overlap head to head, allows free rotation about their axes
what is a pi bond?
when orbitals overlap so that there are two parallel electron cloud densities, does not allow for free rotation
