Bonding and Intermolecular Forces Flashcards
lewis dot structures
each dot represents the valence electrons, we place dots around the symbol of the element . one on each side and if there are more then 4 , then we start to pair them up.
electrons in the d subshells
these are not considered valence electrons for the transition metals since valence electrons are in the highest n level
single bond
2 electrons between atoms
lone pairs:
non bonding electrons (unshared pair of valence electrons)
double bonds and triple bonds use how many electrons ?
double bonds use 4 electrons
triple bonds use 6 electrons
what is the formal charge?
helpful way to evaluate a proposed lewis structure is to calculate the formal charge of each atom in the structure. the formal charges won’t give us the actual charges but they tell us if the atoms are sharing their valence electrons in the best way possible, which will happen when the formal charges are all zero.
what is the formula for calculating the formal charge?
FC= V-1/2 B-L
= Valence electrons - 1/2 bonding electrons - lone pairs.
the best lewis structures have?
octet of electrons and a formal charge of zero on all the atoms. if there is a charge, the best structures have negative formal charges on the more electronegative element.
resonance
accurately depict bonding in a molecule.
these structures are depicted when there are double or triple bonds in a molecule with one or more lone Paris of electrons.
what is bond dissociation energy?
energy required to break a bond homolytically.
in homolytic bond cleavage, one electron of the bond being broken goes to each fragment of the molecule. – so two radicals form.
heterolytic bond cleavage:
both electrons of the electron pair that make up the bond end up on the same atom : forms a cation and an anion
these processes are diff and therefore have diff energies associated with them.
for similar bonds, the higher the bond order , the shorter and stronger the bond.
a single bond has a bond order of 1
while a triple bond will have a bond order of 3
bond length/ bond dissociation energy comparisons should only be made for similar bonds. so compare C-C bonds with other C-C and c-o with other c-o bonds.
bc of varying radii.
when comparing the same types of bonds, the greater the s character
the shorter the bond
also , the longer the bond, the weaker it is . the shorter the bond, the stronger it is.
covalent bonds
each atom contributes one or more of its unpaired valence electrons.
the electrons are shared by atoms to help complete both octets.
polarity of covalent bonds
a bond is polar if the electron density between the two nuclei is uneven. this occurs if there is a difference in electronegativity of the bonding atoms, and the greater the difference the more uneven the electron density and the greater the dipole moment.
non polar bonds
electron density between the two nuclei is even. little or no diff in electronegativity.
coordinate covalent bonds
when one atom will donate both of the shared electrons in a bond. ex would be : F3BNH3
here N donates both electrons , therefore its the Lewis base.
F3B will be the Lewis acid as its accepting the electrons
ionic bonds
gaining or loosing electrons.
electrostatic interactions between the cation and the anion.
the strength of the bond is proportional to the charges
on the ions and the strength will decrease as the ions get farther apart or if the ionic radii increase.
VSEPR theory
valence shell electron pair repulsion theory
electrons repel one another, electron pairs weather they are bonding or non bonding will attempt to move as far apart as possible.
therefore, the Total number of electron GROUPS on the central atom of a molecule determines its bond angles and orbital geometry.
what are electron groups?
any type of bond (single, double, triple) and lone pairs of electrons
double and triple count ONLY as one electron group.
the shape of the molecule is called the molecular geometry.
however, when lone Paris are present on the central atom of molecule, the shape is not the same as the orbital geometry.
what is the orbital geometry with ZERO lone pairs on the central atom?
linear if 2 electron groups
if 3 electron groups: trigonal planar
if 4 : tetrahedral
what if there is 1 lone pair of electrons?
1 lone pair and two other electron groups: bent
1 lone pair and three other electron groups: trigonal pyramid
what if there are 2 lone pairs?
if two lone Pairs and two other electron groups: bent