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Molecular motion can be defined as the motion or movement of constituent particles in solid, liquid, or gas. Do you wonder why liquid takes the shape of the container in which it has been filled & is impossible for solid to do so? The reason behind this is due to the constant movement of the constituent particles. The particles of solid have no free movement instead it only vibrates in their mean position because of this reason the solids are rigid. On the other hand, gaseous particles have a very high degree of freedom to move and therefore expand in the entire volume of the vessel. Liquid shows the intermediate property of both solid and gases, the particles show slow movements but are notionally fixed.
Read Also: What are Electrons?
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Key Takeaways: Molecular Motion, solid, liquid, particles, gaseous, translation motion, rotational motion, vibrational motion, electronic motion.
Types of Molecular Motion
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The different types of molecular motion are described below.
Translation Motion- The movement of particles or molecules from one point to another within the same axis is known as translation motion.
Rotational Motion- It is the movement of particles around the axis.
Vibrational Motion- one of the best examples of this type of motion is seen in solid-state. The molecules do not move and only vibrate in their mean position.
Electronic motion- The motion of electrons from higher energy state to lower energy state or lower energy state to higher energy state is called electronic motion in other words movement of electrons from orbitalto orbital.
Types of Molecular Motion
Check Important Notes for Change of State
Different Types Of Movement Shown By Solid, Liquid & Gas
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Different types of movement seen in the different states of matters are tabulated below.
| Types of Motion | Solid | Liquid | Gas |
|---|---|---|---|
| Vibrational Motion | Present | Present | Present |
| Rotational Motion | Absent | Present | Present |
| Translation Motion | Absent | Present | Present |
| Reason | Strong intramolecular forces | Weak intramolecular forces when compared to solids | Weakest intramolecular force & highest degree of freedom |
Check Also: Intermolecular Forces
Measurement of Movement of Particles or Molecules
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Every atom or molecule requires energy for its motion. They can get this energy by absorbing a certain amount of light such as infrared and can then show their characteristic motion. Different types of atoms and molecules require a different amount of energy to undergo their motion, hence they all have a characteristic value for absorbance of light. The entire phenomenon from absorbing light by the molecules and later measuring this value of absorbance is known as spectroscopy techniques and can be used for analysing or measuring the movement of constituent particles as well as for identification of the types of atomic or molecular species present in an unknown sample.
Things to Remember
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- Molecular motion can be defined as the motion or movement of constituent particles insolid, liquid or gas.
- Order of intramolecular forces of attraction → Solid > liquid > gas
- Order of Degree of freedom → Solid < liquid < gas
- Order of random motion → Solid < liquid < gas
- The different types of motion are Translation, Rotation, Vibration and Electronic motion.
- Vibrational motion can be defined as the movement of particles back & forth along with their mean position.
Read More: Atomic and Molecular Masses
Sample Questions
Ques 1. Describe the degree of freedom? (2 marks)
Ans- Degree of freedom can be best described as the total number of independent ways a gaseous atom can move, vibrate or rotate in space. Translational, vibrational & rotational motion are three different types of degrees of freedom that depend on the total number and geometry or arrangement of atoms in space.
Ques 2. The conversion of liquid into its vapour state is known as evaporation. How can you link and explain this phenomenon on the basis of molecular motion? (2 marks)
Ans. If we take the example of heating of water, the molecule water has more intramolecular spaces and less intramolecular forces when compared to solid. But while comparing it to gases it has fewer intramolecular spaces and more intramolecular forces. On heating, the water molecules overcome these attraction forces by gaining kinetic energy and escaping from liquid to gaseous state.
Ques 3. How is molecular motion significant for life? (2 marks)
Ans. molecular motion is living plants and animals occurring at the cellular level and cannot be observed by the naked eye. The movement of molecules across the living tissue helps in repairing & nourishing the tissue. It also plays an important role in the process like respiration, photosynthesis and transportation of oxygen in each cell of the body. The molecular motion is independent of locomotory motion and only stops once the body is dead.
Ques 4. What are the possible ways in which an atom or molecule moves? (2 marks)
Ans. An atom or molecule can show the following different types of movement:
- Translation Motion- The movement of particles or molecules from one point to another within the same axis is known as translation motion.
- Rotational Motion- It is the movement of particles around the axis.
- Vibratiotional Motion- one of the best examples for this type of motion is seen in solid-state. The molecules do not move and only vibrate in their mean position.
- Electronic motion- the motion of electrons from higher energy state to lower energy state or lower energy state to higher energy state is called electronic motion in other words movement of electrons from orbital to orbital.
Ques 5. Describe factors that affect molecular motion. (2 marks)
Ans. The kinetic energy of the molecules depends upon the mass and average velocity of the molecules. Heavier molecules will be the slow mover and lighter molecules will move faster. Temperature is another such factor that affects molecular motion. The increase in temperature increases the kinetic energy of the molecules.
Ques 6. Describe the Brownian motion? (2 marks)
Ans. Brownian motion is the movement of particles suspended in a liquor gases medium, the movement results due to collision between the particles of gaseous particles and suspended particles. Example- Movement of pollen grains in water. Brownian motion is named after the scientist Robert Brown who observed this for the first time in 1927.
Ques 7. How can you measure the Movement or motion of particles at the molecular level? (2 marks)
Ans. Every atom or molecule requires energy for its motion. They can get this energy by absorbing a certain amount of light such as infrared and can then show their characteristic motion. Different types of atoms and molecules require a different amount of energy to undergo their motion, hence they all have a characteristic value for absorbance of light. The entire phenomenon from absorbing light by the molecules and later measuring this value of absorbance is known as spectroscopy techniques and can be used for analysing or measuring the movement of constituent particles as well as for identification of the types of atomic or molecular species present in an unknown sample.
Ques 8. Explain molecular motion in the case of liquids? (2 marks)
Ans. Liquid shows the intermediate property of both solid and gases, the particles show slow movements but are notionally fixed. Thus liquids possess vibrational motion like solids because of intramolecular forces and translation and rotational motion like gases due to intramolecular spaces. Due to this property of liquid, it takes the volume and shape of the vessel in which it is kept.
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