Kinetic Molecular Theory

Kinetic Molecular TheoryPreface for KMT of Gases Questions

1. The pressure of a gas is due to collisions between the gas particles (atoms/molecules) and the walls of the container.

2. The average kinetic energy of the gas particles is directly proportional to the absolute temperature of the gas.

Molecular Velocities

speed

Fra

ctio

ns o

f pa

rtic

les

the Maxwell speed distribution

molecules sorted by speed

many different molecular speeds

Kinetic Molecular TheoryConsiderations for Answering KMT of Gases Questions

1. Temp. goes UP: more frequent collisions, more energetic collisions.

2. Temp. goes DOWN: less frequent collisions, less energetic collisions.

3. # of Particles goes UP: more total collisions.

4. # of Particles goes DOWN: less total collisions.

Graham’s Law

Diffusion– Spreading of gas molecules throughout

a container until evenly distributed.

Effusion– Passing of gas molecules through a tiny

opening in a container

Diffusion

HCl NH3

81.1 cm 118.9 cm

NH4Cl(s)

Choice 2: Lighter gas moves faster; meet closer to heavier gas.

Graham’s Law

KE = ½mv2

Speed of diffusion/effusion– Kinetic energy is determined by the temperature of

the gas.

– At the same temp. & KE, heavier molecules move more slowly.• Larger m smaller v

Coulomb’s Law

F kq1q2 /r2

Coulomb's law helps describe the forces that bind electrons to an atomic nucleus.

• Based on Coulomb’s Law, the force between two charged particles is proportional to the magnitude of each of the two charges and inversely proportional to the square of the distance (radius) between them.

Coulomb’s LawPreface for Coulomb’s Law Questions

1. Opposite charges attract and like charges repel.

2. All things being equal, the greater the number of protons in the nucleus, the greater the force of attraction on the outermost (valence) electrons.

3. The greater the distance that the outermost electrons are from the nucleus, the weaker the force of attraction is on those electrons.

Coulomb’s LawConsiderations for Answering Coulomb’s Law Questions

1. Ionization energy is the energy needed to remove an electron from an atom/ion.

2. As the number of electron shells increases, the distance of the outermost (valence) electrons from the nucleus increases.

3. Because the distance dependence of Coulomb’s Law is “inverse squared,” the dependence of the force of attraction on distance is stronger than the dependence of the force of attraction on the number of protons in the nucleus.

Atomic RadiusThe atomic radius increases from top to bottom down a group. Increasing n (the number

of shells), makes it so that the outermost-electron-populated shell lies farther from the nucleus.

Atomic radius decreases from left to right across a period. Increasing the number of

protons in the nucleus (for the same shell) draws the valence shell closer to the nucleus.

Atomic radii (in picometers)