Lecture 30 Flashcards
What is ionic bonding
Ion is attracted by other ions with opposing charges
What happens when there is a strong force in ionic bonding
More energy is needed to break the forces holding the particles together. There is a higher mp and bp
What are ion-dipole attractions
Attraction between the charge of the ion and opposite dipole (nearby polar molecule)
Ion charge - dipole charge
What is dipole-dipole attractions
Molecules with permanent dipole moments experience dipole-dipole interactions
Molecules will either maximize positive & negative attractions or minimize like charge repulsion
Dipole - dipole
What gives rise to dipole-dipole forces
The polar molecules in liquids & solids lie near each other so their partial charges act as tiny electric fields which give rise to dipole-dipole forces
Do polar or non polar substances have a higher bp
Polar has a higher bp
What is H-bonding
An H-atom bonded to a small, highly electronegative atom (N,O, or F)
A hydrogen bond forms when the H of one molecule is attracted to the lone pair on the N, O, or F on another molecule
Why is ice less dense than water
Because when water solidifies, the H-bonding between molecules creates space between the molecules which increases the overall volume of the solid
Lower density & higher volume
What are London-dispersion forces
- they occur in all molecules
- a temporary instantaneous dipole that makes one point of the molecule negatively charged and the rest positively charged
What trend does LDF follow
LDF increases in strength with atomic size;
More e-: greater opportunity to disturb e- cloud = stronger induced dipole
What is polarizability ***
- The ease with which the electron cloud can be distorted to create a charge separation.
- polarizability increases with greater number of electrons and larger molecular size
- increases down a group
- decreases across a period
Why does polarizability increase down a group
Because atomic size increases, and electron clouds are easier to distort
Why does polarizability decrease across a period
Because increasing Zeff makes the atoms smaller & holds the electrons more tightly
Explain the polarizability of anions & cations
Anions are more polarizable because they are larger
Cations are less polarizable because they are smaller
