#STRUCTURE OF AN ATOM SERIES#

Since they are ones that are participate in a chemical reaction.Įlements having valence electrons 1, 2 or 3 are called metals. The chemical properties of an atom are dependent on these valence electrons. Hence the number of valence electrons present in sodium is 1. In sodium 3 rd shell is the outermost shell (valence shell). The electrons, which are present in the outermost shell of an atom are called valence electrons.Įlectronic configuration of sodium is 2 8 1 ∴ Electronic configuration of sodium atom = 2, 8, 1 The nucleus of sodium has 11protons and 12 neutrons and it is surrounded by 11 electrons. Sodium has atomic number 11 and mass number 23. 'f' sub shell can hold a maximum of 14 electrons. 'd' sub shell can hold a maximum of 10 electrons, 'p' sub shell can hold a maximum of 6 electrons, 's' sub shell can hold a maximum of 2 electrons, The various sub shells are s, p, d and f.Įvery sub-shell can accommodate a fixed number of electrons. Electrons are distributed in these sub-shells.

#STRUCTURE OF AN ATOM SERIES#

The maximum number of electrons that can be filled in a valence shell is eight even if it has capacity to accommodate more than eight.Īfter a series of experiments and a detailed study by scientists like louis de broglie, schrodinger, somerfeld and others proved that shells or energy levels have sub shells within them. Hence, filling of electrons in an atom follows a stepwise approach. Similarly, for M and N shells, maximum number of electrons that can be accommodated are 2X3 2 = 18 and 2X4 2 = 32 respectively.Įlectrons in an atom do not occupy a new shell unless all inner shells like K, L, M, N…. Where n is the number of that energy level.Īccording to Bohr’s model of an atom, the first energy level K can have 2 electrons, the maximum number of electrons which can be accommodated in shell L is 2X2 2 = 8. The maximum number of electrons that can be accommodated in any energy level of the atom is given by a formula 2n 2. Rules for accommodating electrons in various shells ( Bohr-bury scheme) The arrangement of electrons in the shells is known as electronic configuration. These orbits or shells are represented by the letters K, L, M, N,… or the numbers n=1, 2, 3, 4,…. Number of neutrons = Mass number – Atomic numberĮlectrons are placed in fixed energy levels called shells.

In an atom number of electrons = Number of protons

Question: An atom X has mass number 40 and atomic number 18.Find out the number of protons, number of electrons and number of neutrons present in the atom X? The mass number (A) is defined as the sum of the number of protons and neutrons present in the nucleus of an atom. Example: Mass number of Nitrogen atom is 14 then it contains 7 protons and 7 neutrons.Ītomic number Element Mass number Z X AĮxample: Nitrogen atom has notation as 7 N 14. Atomic number (z) is the number of protons in an atom it is also equal to the number of electrons in the atom.Įxample: The atomic number of an element is 12 then its atom contains 12 protons and 12 electrons.

Structure of an atom