What is Matter?

The matter we see around us exists primarily in three states, solid, liquid, and gas. These three states of matter can be easily differentiated based on the degree of motion of constituent particles. In the solid, the particles are restricted to their original positions and cannot move. The only vibration of particles from their mean position is seen. But on the other side, in gasses, the constituent particles can move randomly owing to their high kinetic energy. The gaseous particles don't have a fixed position. In liquids, the particles exhibit an intermediate state of movement. The particles in liquids don't have a fixed position but show a higher degree of movement than solids and lesser than that of gasses. To summarize, gasses have the highest degree of molecular motion, followed by liquids and then by solids. This is mainly because gas molecules have possessed high kinetic energy.


What is Molecular Motion?

Molecular motion is nothing but the movement of constituent particles in a specific direction. The degree of motion of constituent particles is affected by temperature. The temperature is also the measure of the average Kinetic energy of the molecules. The molecular motion is also dependent on the heat as the transfer of heat among molecules increases their kinetic energy.


The mathematical relationship between kinetic energy and temperature is defined as:                                                                        


Types of Molecular Motion:

There are four types of molecular motion:

Translational Motion: 

The movement of molecules may be in a different direction, but the movement axis remains the same. This form of movement is called Translational motion.

Rotational Motion: 

The molecules rotate in and around the axis in this type of motion.

Vibrational Motion: 

This form of movement is prevalent in the solid-state, where the molecules vibrate in their mean position.

Electronic Motion: 

In this type of motion, the movement of electrons takes place from place to place, orbital to orbital. This type of electronic motion causes a change in the color of the substance.

Types of Motion and Intermolecular Forces

Gasses take the shape of the container readily and spread quickly in space. This is because, unlike solids and liquids, molecules in the gaseous state show random movement. Their weak intermolecular forces aid in their free and spontaneous movement. Molecules in a solid-state are capable of only vibrational motion due to their strong intermolecular forces; hence, the solid-state molecules can only vibrate from their mean positions. Thus, solids show the least molecular randomness.

On the other hand, liquids exhibit vibrational motion along with the rotational and translational motion. This is due to their weak intermolecular forces between molecules. Molecular motion in liquids is less than gasses but more than solids. Hence, random motion depends on the intermolecular forces, the kinetic energy of molecules, and heat transfer phenomena.

About Random Molecular Motion in Glasses

These are the properties shown by the gas molecules

  • Gasses are constituted of atoms or molecules that are in constant random motion. 

  • These gas particles (atoms and molecules) continuously collide with each other and the walls of the container. The collisions that hence occur are elastic, and there is no net loss of energy. 

  • Gas particles are microscopic compared to the volume of the container. The relative volume of gas particles is thus negligible.

  • There exist no interactive forces, i.e., attraction or repulsion between the molecules of gas.

  • The average kinetic energy of the gas molecules is directly proportional to the temperature of the gas. If two gasses are at the same temperature, they possess the same kinetic energy.

Measurement of Molecular Motion

Atoms and molecules require different amounts of energy for the different types of molecular motion. The light that is absorbed during motion can be used for the measurement of molecular motion. The frequencies of absorbed light and compare them with bonding arrangements present in molecules. Various modern techniques like UV spectroscopy, mass spectroscopy, and IR spectroscopy can also quantify molecular motion. These modern methods can tell a lot about the structure of molecules.

Kinetic Energy of Molecules

As the gas particles are in constant motion, they possess kinetic energy. The kinetic energy of every single atom can be calculated by the formula Ek = 1/2 mu2, where 'm' is the mass of the atom and u is its speed. The molecules of gas share average kinetic energy but individual molecules have different kinetic energies than the rest due to different speeds. The difference in speeds arises from the collision between themselves that occurs in the gas phase. These collisions are elastic and involve no net loss of energy as a whole, but individual molecular speeds change. One molecule's energy gets transferred to the other in a collision, but the net energy of the system remains intact. 

FAQs (Frequently Asked Questions)

Q1: How is the Arrangement of Particles Different in Solids, Liquids, and Gasses?

Ans: Particles in a solid are closely packed, usually in a regular pattern, and high intermolecular forces exist. On the other hand, particles in a liquid are close together but have no regular arrangement as such. On the contrary, particles in a gas are well separated and have no arrangement. Its molecules are free to move around.

Q2: What is the Difference in the Behavior of Gas, Solid, and Liquid Molecules?

Ans: Particles in solid vibrate from their mean position but do not move from place to place. Liquid particles vibrate, move as well as slide past each other. Gasses vibrate and move freely without any restrictions. Liquids and solids are also called condensed phases because the particles are closely packed to each other.

Q3: What is the Effect of Heat on Molecular Movement?

Ans: When heat is supplied to a substance, its molecules vibrate faster, and the space between the atoms increases. The object expands and tries to occupy more space. The mass of the object remains unchanged. Solids, liquids, and gasses all expand when the heat is supplied. When heat leaves the system, the particle movement slows down, and the vibration decreases. The considerable distance between the particles of gas allows it to be compressed more quickly than solids and liquids. Gasses can be compressed by applying high pressure and decreasing the temperature, or withdrawing the system's heat. For example, LPG, which is used extensively in our kitchen for cooking, is a liquefied form of petroleum gas.