1)why bohr orbit are called stationary orbit? 2)what do you mean by saying energy of electron is quantised?
1) Bohr orbits are called stationary orbits because, according to Niels Bohr's atomic model, electrons in these orbits do not radiate energy and therefore, do not spiral into the nucleus. These orbits are stable and do not change with time. The term "stationary" refers to the fact that the electron remains in a fixed orbit without undergoing any energy changes.
The reason behind the stability of these orbits is the balance between the centripetal force (due to the electron's circular motion) and the electrostatic force of attraction between the electron and the nucleus. According to classical electromagnetic theory, an accelerating electron should radiate energy, causing it to spiral inwards. However, Bohr proposed that electrons can exist only in certain specific orbits, and these orbits are the ones where the electron's angular momentum is quantized.
2) When we say that the energy of an electron is quantized, it means that electrons can only have certain discrete values of energy. This concept arises from the wave-particle duality of electrons and is a fundamental aspect of quantum mechanics.
In the context of Bohr's model, the quantization of energy refers to the fact that electrons can only occupy specific energy levels or orbits around the nucleus. These energy levels are represented by whole numbers known as principal quantum numbers (n = 1, 2, 3, ...). The energy of an electron increases as the principal quantum number increases.
The quantization of energy in atoms was actually a departure from classical physics, which predicted that energy should be continuous and electrons could occupy any orbit. However, experimental observations of atomic spectra showed that only specific wavelengths of light were emitted, indicating that the energy of electrons in atoms was quantized.
To determine the energy of an electron in a specific energy level, one can use the formula E = -13.6 eV / n^2, where E is the energy in electron volts (eV) and n is the principal quantum number. This equation gives the energy of the electron relative to the energy when the electron is at an infinite distance from the nucleus.