Kinetic Molecular Theory

Preface 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 Fractions of particles the Maxwell speed distribution molecules sorted by speed many different molecular speeds

Kinetic Molecular Theory Considerations 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 NH cm cm NH 4 Cl(s) Choice 2: Lighter gas moves faster; meet closer to heavier gas.

Graham’s Law KE = ½mv 2 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

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 Law Preface 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 Law Considerations 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 Radius The 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)