Structure of atom important points: The structure of an atom consists of the three subatomic particles, namely protons, neutrons, and the electrons. The number of protons in an atom determines the atomic number of an element, while sum of protons and neutrons gives its mass number.
Electrons occupy the specific energy levels or shells in an atom, with the outermost shell being the valence shell containing the valence electrons responsible for the chemical properties of an element. The electronic configuration of an atom follows Aufbau principle, Pauli exclusion principle, and Hund’s rule. The periodic table is a tabular arrangement of the elements based on their electronic configuration and chemical properties.
The modern periodic table is divided into groups and periods, with elements in a group having same number of valence electrons and similar chemical properties, while the elements in a period have the same number of shells and different chemical properties. The main group elements includes the elements in groups 1, 2, and 13-18, while transition metals include elements in groups 3-12. Finally, lanthanides and actinides are two series of inner transition metals placed at the bottom of periodic tables.
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NCERT Class 11 Chemistry Chapter 2 – Structure of atom 25 important points
There are 25 important points on structure of atom:
- Atom is smallest indivisible particle of an element which retains its chemical properties.
- Atoms are made up of three different subatomic particles: protons, neutrons, and electrons.
- Protons are the positively charged particles present in the nucleus of an atom.
- Electrons are the negatively charged particles that revolve around the nucleus in shells.
- Neutrons are the neutral particles present in the nucleus of an atom.
- The number of protons in an atom determines atomic number of an element.
- The sum of the protons and the neutrons in an atom gives its mass number.
- Isotopes are atoms of same element having different mass numbers due to different numbers of neutrons.
- Electrons occupy the specific energy levels or shells in an atom.
- The maximum number of electrons that can occupy a shell is given by 2n^2, where n is shell number.
- The valence shell is outermost shell of an atom, and the electrons in it are called valence electrons.
- Valence electrons are responsible for chemical properties of an element.
- The octet rule states that the atoms tend to gain, lose, or share electrons in order to attain a stable configuration with eight electrons in their valence shell.
- The electronic configuration of an atom is represented using Aufbau principle, Pauli exclusion principle, and Hund’s rule.
- The Aufbau principle states that the electrons fill the lowest available energy levels first.
- The Pauli exclusion principle states that no two electrons in an atom can have same set of four quantum numbers.
- Hund’s rule states that the electrons prefer to occupy different orbitals of the same energy level singly before pairing up.
- The electronic configuration of an atom is represented using a notation that specifies energy level, sublevel, and number of electrons in each sublevel.
- The periodic table is a tabular arrangement of elements based on their electronic configuration and their chemical properties.
- The modern periodic table is based on the electronic configuration of the elements and is arranged in increasing order of atomic number.
- The periodic table is divided into different groups or columns, and periods or rows.
- The elements in a group have same number of valence electrons and similar chemical properties.
- The elements in a period have same number of shells and different chemical properties.
- The main group elements includes the elements in groups 1, 2, 13-18, while the transition metals include elements in groups 3-12.
- The lanthanides and actinides are two series of the inner transition metals placed at the bottom of the periodic table.
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