The Aufbau principle regarding the structure of atoms is that electrons will first enter the lower energy orbitals and gradually enter the higher energy orbitals. Due to the greater stability in the lower energy levels, the electron follows such a continuum in entering orbitals.

The formula for determining the energy of an orbital in Aufbau’s principle is-
E = n + l
Where n is the principal energy level number or principal quantum number of any orbital.
l is the value of the associated quantum number of the energy level. which-
• For s orbitals, l = 0
• For p orbital, l = 1
• For d orbital, l = 2
• For f orbitals, l = 3
E.g. If we determine the energy of 3s orbital-
For 3s, n = 3 and l = 0
Then the energy, E = n + l = 3 + 0 = 3
Similarly, for 4d, E = n + l = 4 + 2 = 6

We have a total of 7 main orbitals for the electron arrangement of all the elements in the periodic table. Among them-
• For the Kth energy level, n = 1; which has orbital – 1s
• For the Lth energy level, n = 2; which has orbitals – 2s 2p
• For the Mth energy level, n = 3; which has orbitals – 3s 3p 3d
• For the Nth energy level, n = 4; which has orbitals – 4s 4p 4d 4f
• For the Oth energy level, n = 5; which has orbitals – 5s 5p 5d 5f
• For P the energy level, n = 6 ; which has orbitals – 6s 6p 6d 6f
• For the Qth energy level, n = 7; which have orbitals – 7s 7p 7d 7f
If we arrange them in order of strength, the order we get is-
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s < 5f < 6d < 7p

However, if two energy levels are equal in energy value, then the energy level in which the value of n is lower, the electron will enter first.
• For example-
• Energy for 4s, E = 4
• Energy for 3p, E = 4
The energy of these two orbitals is equal. So which one will the electron enter first? At 3p! Because 4s and 3p have equal strength. Since the n value of the 3p orbital is low (n = 3), the electron will enter the 3p orbital first.

Even if we arrange the electrons according to the order of energy, we have to keep one more thing in mind.

• When an orbital is filled with electrons, it is the most stable.
• When an orbital is half-filled with electrons, it is fairly stable.
• If an orbital is neither filled nor unfilled with electrons, it is the least stable.
Since the inner energy levels are full, we will try to fill or half-fill the orbital in the outermost energy electron configuration.

Many may think that Aufbau is the name of a scientist or researcher. But no! Aufbau is a German word. Which means – to build or rise.

Newton’s third law of force is: For every acting force there is an equal and opposite reaction force.

Newton’s third law tells us that whatever action force we apply, there will be an equal and opposite reaction force. That is, if you push a wall with 10 newtons, the wall will also push you back with 10 newtons.

Newton’s first law of force is: If no external force acts, a stationary object will remain at rest, and a moving object will continue to move in a straight path with uniform velocity.

That is, if no force is applied from outside, there will be no change in the kinetic state of the object. Here it is called external force because the force must be applied from outside. Not from within the object. That is, if you sit inside a bus and apply force on the bus itself, it will not. Rather, the bus should be pushed from outside.

In practical terms, Newton’s first law gives an idea of the nature of force. That is, force must be applied to change the motion of an object. So we can define the ball from here.

Also, this formula gives the idea of inertia. If no force acts, the object will remain as it is, from this idea we can also define inertia.

Everything has both good and bad sides. Science also has. While making our daily life much easier, there is no way to neglect the cursed aspects of science. Where science is saving our daily time, science is making us dependent again. We now depend on technology in every aspect of life. From small children to adults, everyone is now a smartphone lover. No one thinks how much this smartphone hinders the intellectual development of the child.

This smartphone causes a lot of mental and physical damage to the child. When there was not so much technology, children used to play outside the house. At that time, children developed friendly behavior, and a mentality of getting along with each other, which is not commonly seen today.

The null law of thermodynamics is that if two of three objects are in thermal equilibrium with the third object separately, then the first two objects will be in thermal equilibrium with each other.

Here the first and second objects are separately in equilibrium with the third object. So it can be said that the first and second objects are in equilibrium with each other.

Thermometers are made based on the zeroth law of thermodynamics.

A system is a system in which thermodynamic variables are measured by varying the effectors.

The system is basically of three types. These are-
1. Isolated system
2. Closed system
3. Open system

1. Isolated system
An isolated system is a closed system that does not exchange any mass or energy with its surroundings. Such as flux for tea. It cannot exchange any heat or water or mass with the environment. But no system can be completely isolated. Thinking in short time intervals can lead to disjointed thinking.

2. Closed System
The closed system is a closed system that cannot exchange mass with its surroundings but can exchange energy. Like a covered teacup. It can exchange heat energy with the environment around the neck of the teacup, but cannot exchange any water or mass. In other words, steam is formed and water does not fly away.

3. Open System
An open system is a system that can exchange both mass and energy with its environment. For example, cooking rice in a rice cooker. It can exchange heat and water or mass with the environment. Both heat gain and loss occur, as well as evaporation of water.

If some molecules of gas are released into a closed container, surely the molecules will move around inside that container. Molecules can run along the length, width, or height of the container. That is, the molecule can move along three dimensions. The number of degrees along which molecules of an ideal gas can move is called its degrees of freedom.

Since the molecules of an atomic gas such as helium, neon, argon, etc. have only one molecule, we can think of them as a ball. These balls can move freely along three dimensions. So we say, an atomic gas has three degrees of freedom.

Now diatomic gases such as nitrogen, oxygen, etc. are joined by two atoms in one molecule. As we can imagine, two balls are connected by a rod. Since two atoms are connected here, we can think that their degrees of freedom will be three and six in total. But it is not. Due to being connected through bonds, a degree will be reduced between them both. That’s why two atoms individually two by two give a total of four and a common one together will give them a total of five dimensions. So the degrees of freedom of a diatomic gas will be five.

Similarly, triatomic gases will have seven degrees of freedom instead of nine. The energy along one degree of freedom of any molecule or atom is 1/2.KT. then,

The total energy of one atomic gas molecule = 3.1/2.KT
The total energy of molecules of diatomic gas = 5.1/2.KT
The total energy of molecules of tri-atomic gas = 7.1/2.KT

Thus the total energy of gas molecules is distributed equally along their degrees of freedom. It is called the principle of power-sharing.