Bonding and Intermolecular Forces

Question 1

lewis dot structures

Answer 1

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.

Question 2

electrons in the d subshells

Answer 2

these are not considered valence electrons for the transition metals since valence electrons are in the highest n level

Question 3

single bond

Answer 3

2 electrons between atoms

Question 4

lone pairs:

Answer 4

non bonding electrons (unshared pair of valence electrons)

Question 5

double bonds and triple bonds use how many electrons ?

Answer 5

double bonds use 4 electrons

triple bonds use 6 electrons

Question 6

what is the formal charge?

Answer 6

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.

Question 7

what is the formula for calculating the formal charge?

Answer 7

FC= V-1/2 B-L

= Valence electrons - 1/2 bonding electrons - lone pairs.

Question 8

the best lewis structures have?

Answer 8

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.

Question 9

resonance

Answer 9

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.

Question 10

what is bond dissociation energy?

Answer 10

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.

Question 11

heterolytic bond cleavage:

Answer 11

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.

Question 12

for similar bonds, the higher the bond order , the shorter and stronger the bond.

Answer 12

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.

Question 13

when comparing the same types of bonds, the greater the s character

Answer 13

the shorter the bond

also , the longer the bond, the weaker it is . the shorter the bond, the stronger it is.

Question 14

covalent bonds

Answer 14

each atom contributes one or more of its unpaired valence electrons.
the electrons are shared by atoms to help complete both octets.

Question 15

polarity of covalent bonds

Answer 15

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.

Question 16

non polar bonds

Answer 16

electron density between the two nuclei is even. little or no diff in electronegativity.

Question 17

coordinate covalent bonds

Answer 17

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

Question 18

ionic bonds

Answer 18

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.

Question 19

VSEPR theory

valence shell electron pair repulsion theory

Answer 19

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.

Question 20

what are electron groups?

Answer 20

any type of bond (single, double, triple) and lone pairs of electrons
double and triple count ONLY as one electron group.

Question 21

the shape of the molecule is called the molecular geometry.

Answer 21

however, when lone Paris are present on the central atom of molecule, the shape is not the same as the orbital geometry.

Question 22

what is the orbital geometry with ZERO lone pairs on the central atom?

Answer 22

linear if 2 electron groups
if 3 electron groups: trigonal planar
if 4 : tetrahedral

Question 23

what if there is 1 lone pair of electrons?

Answer 23

1 lone pair and two other electron groups: bent

1 lone pair and three other electron groups: trigonal pyramid

Question 24

what if there are 2 lone pairs?

Answer 24

if two lone Pairs and two other electron groups: bent

Question 25

s and p orbital combine

Answer 25

you get sp hybrid orbitals ( 2 hybrids as 2 orbitals originally combined).

Question 26

determining the hybridization for most atoms

Answer 26

add the number of the attatched atoms to the number of the non bonding electron pairs. ( #atoms + # lone pairs )= electron groups.

Question 27

if the electron groups are 2 :

Answer 27

sp hybridization
bond angle is 180
orbital geometry is linear

Question 28

if the electron group is 3

Answer 28

hybridization is sp2
bond angle is 120
trigonal planar

Question 29

if the electron group is 4

Answer 29

sp3
109.5 degrees
tetrahedral

Question 30

sigma bonds

Answer 30

bond consist of two electrons that are localized between two nuclei
end to end overlap whereas pi bonds are side to side overlap

Question 31

pi bonds

Answer 31

is formed by the proper , parallel, side to side alignment of two unhybridized p orbitals on adjacent atoms.

Question 32

in any multiple bonds there is one sigma bond and the remainder are pi bonds

Answer 32

single bond : 1 sigma bond
double bond : 1 sigma bond and 1 pi bond
triple bond : 1 sigma bond and 2 pi bond.

Question 33

what are intermolecular forces?

Answer 33

they are relatively weak interactions that take place between neutral molecules.

Question 34

polar molecules are attracted to ions producing

Answer 34

ion-dipole forces

Question 35

what are dipole to dipole forces?

Answer 35

attractions between the positive end of one polar molecule and the negative end of another polar molecule.

Question 36

what is the strongest dipole-dipole force?

Answer 36

hydrogen bonding

Question 37

what is momentary dipole induced dipole force?

Answer 37

a permanent dipole in one molecule may induce a dipole in a neighbouring non polar molecule .

Question 38

London dispersion forces

Answer 38

instantaneous dipole in non polar molecule may induce a dipole in a neighbouring non polar molecule.
these are VERY weak transient interactions between the instantaneous dipoles in non polar molecules.
every atom with electrons will experience this ! as the size of the molecule increases the # of electrons will also increase therefore the dispersion forces will also increase

Question 39

despite being weak, all intermolecular forces including London dispersion forces can have PROFOUND impact on the physical properties of a molecule.

Answer 39

substances with stronger intermolecular forces will experience a greater melting point, greater boiling point, greater viscosity and lower vapour pressure.

Question 40

dipole forces, hydrogen bonding and London forces are all collectively known as

Answer 40

van der Waals forces!!!

Question 41

hydrogen bond

Answer 41

in order for a hydrogen bond to form, two criteria have to be met:

1) a molecule must have a covalent bond between H and either N,O, F
2) another molecule must have a lone pair of electrons on an N,O,F atom.

Question 42

vapor pressure

Answer 42

is the pressure exerted by the gaseous phase of a liquid that evaporated from the exposed surface of the liquid.
the weaker the substances intermolecular forces , the higher its vapour pressure and more easily it will evaporate.

Question 43

while vapour pressure is determined by the intermolecular forces , what else will influence it?

Answer 43

temperature ! : it will inc with the temperature
if you inc the kinetic energy of the particles (which is proportional to temp) allows them to overcome the intermolecular forces and inc the particles that can move to the gas phase.

Question 44

ionic solid

Answer 44

held together by electrostatic interactions between cations and anions in a lattice structure.
ionic bonds are strong
these will be solid at room temp ! ex NaCl.

Question 45

netword solids

Answer 45

atoms are connected in a lattice of covalent bonds
these are very strong and they are VERY HARD SOLIDS at room temp.
ex) DIAMOND

Question 46

metallic solids

Answer 46

these have freely roaming valence electrons : which are called conduction electrons.
due to this, metals conduct electricity and heat excellently and are malleable and ductile!
almost all metals are solid @ room temp

Question 47

molecular solids

Answer 47

held together by 3 types of intermolecular interactions
hydrogen bonds
dipole-dipole forces
London dispersion forces
these forces are significantly weaker then ionic, network, or metallic bonds
molecular compounds have much lower melting and boiling point then the other types of solids.
these are often liquids or gas @ room temp