Atomic Models
* Atoms are made of charged particles.
According to Thomson’s Model:
* An atom is a positively charged sphere with electrons set within it.
* An atom is electrically neutral.
Rutherford’s model states that:
* There is a positively charged centre in an atom called the nucleus. Almost all the atom lies in the nucleus.
* The electrons revolve around the nucleus in well-defined orbits.
* The nucleus is much smaller than the atom.
The postulates of Bohr’s model are:
* Electrons revolve in discrete orbits called shells. Shells are called energy levels.
* Electrons do not radiate energy. Within an orbit, the energy of an electron is constant.
Structure of an Atom
* An Atomic Number is the number of protons in an atom.
* The arrangement of electrons in various energy levels of an atom is known as electronic configuration.
* The maximum number of electrons in any energy level of the atom is given by 2n2.
* The outermost shell of an atom cannot accommodate more than eight electrons.
* Combining capacity of the atoms to form molecules either with the same or different elements is known as valency.
* Neutron is a neutral particle present in the nucleus.
* The total number of protons and neutrons present in one atom of an element is referred as atomic mass.
* Isotopes are atoms with same atomic number but different mass numbers.
* Isotopes of certain elements are used in a nuclear reactor, and in the treatment of cancer and goitre.
* Atoms of different elements with different atomic numbers that have the same mass number are called Isobars.