What is an atom?
Atoms are the building blocks of universe.
They are very tiny particles.
Its very hard to imagine even its size.
- The centre of atom is called nucleus.
Atom is made of tiny particles called protons and neutrons.
Electrons circle around the nucleus in clouds, or shells, far from the nucleus.
When an atom is in balance, it has the same number of protons and electrons.
Atom can have a different number of neutrons.
Electrons stay in their shells because a special force holds them.
Protons and electrons of atom are attracted to each other.
We say protons have a positive charge (+) and the electrons have a negative charge (-).
An atom consists of electrons orbiting around a nucleus. But, the electrons cannot choose any orbit they wish.
The orbits of atom are restricted to certain energies.
Consider a neutral hydrogen atom.
Its energy levels are given in the image shown below.
The x-axis shows the allowed energy levels of electrons in a hydrogen atom, numbered from 1 to 5. The y-axis shows each level's energy in electron volts (eV).
Electrons in a hydrogen atom must be in one of the allowed energy levels.
If an electron is in the first energy level, it must have exactly -13.6 eV of energy. If it is in the second energy level, it must have -3.4 eV of energy.
An electron in a hydrogen atom cannot have -9 eV, -8 eV or any other value in between.
Let's say the electron in atom wants to jump from the first energy level, n = 1, to the second energy level n = 2.
The electron of an atom can gain the energy it needs by absorbing light.
If the electron in a atom jumps from the second energy level down to the first energy level, it must give off some energy by emitting light.
The atom absorbs or emits light in discrete packets called photons, and each photon has a definite energy.
The energy of the photon depends on its wavelength.
The wavelength, ? can be found by the following equation,
E is the energy of the photon (in eV), h
is Planck's constant (4.14 x 10-15 eV s)