Difference Between Valence and Core Electrons

Posted on February 12, 2012 by Dunee Last updated on: February 12, 2012

Valence vs Core Electrons

Atoms are the small building blocks of all existing substances. They are so tiny that we can’t even observe with our naked eye. Normally atoms are in the Angstrom range. After many experiments, the atomic structure was described during the 19th century. Atom is made up of a nucleus, which has protons and neutrons. Other than neutrons and positrons there are other small sub atomic particles in the nucleus. And there are electrons circling around the nucleus in orbitals. Most of the space in an atom is empty. The attractive forces between the positive charged nucleus (positive charge due to protons) and the negatively charged electrons maintain the atom’s shape.

Electron is shown by the symbol e. This has a negative (-1) electrical charge. Electron has a mass of 9.1093×10−31 kg, which makes it the lightest sub atomic particle. Electron was discovered by J.J. Thompson in 1897, and the name was given by Stoney. Discovery of the electron was a turning point in sciences as it led to explanation of electricity, chemical bonding, magnetic properties, thermal conductivity, spectroscopy and so many other phenomena. Electrons reside in orbitals in atoms and they have opposite spins.

What are Valence Electrons?

Valence electrons are the electrons in an atom which are participating in the chemical bond formation. When chemicals bonds are forming, either atom can gain electrons, donate electrons, or share electrons. The ability to donate, gain, or share depends on the number of valence electrons they have. For example, when a H2 molecule is forming, one hydrogen atom gives one electron to the covalent bond. Thus, two atoms share two electrons. So a hydrogen atom has one valence electron. When sodium chloride is forming, one sodium atom gives out one electron, whereas a chlorine atom takes an electron. This happens in order to fill an octet in their valence orbitals. Therefore, sodium has only one valence electron, and chlorine has seven. Therefore, we can conclude that, by looking at the valence electrons, we can tell the chemical reactivity of the atoms.

Main group elements (group I, II, III, etc..) have valence electrons in the outermost shells. This number is equivalent to their group number. Inert atoms have completed shells with the maximum number of valence electrons. For transition metals, some inner electrons also act as valence electrons. Number of valence electrons can be determined by looking at the electron configuration of the atom. For example, nitrogen has the electron configuration of 1s2 2s2 2p3. The electrons in the 2nd shell (which is the highest principal quantum number in this case) are taken as valence electrons. Therefore, nitrogen has five valence electrons. Other than participating in bonding, valence electrons are the reason for thermal and electrical conductivity of elements.

What are Core Electrons?

Core electrons are the rest of the electrons in an atom which are not valence electrons. Core electrons do not participate in bond formation. They reside in inner shells of an atom. For example, as in nitrogen, five electrons out of all seven are valence electrons, whereas two are core electrons.

What is the difference between Valence Electrons and Core Electrons?

• Valence electrons are participating in the chemical bond formation, but core electrons are not.

• Valence electrons are residing in the outer most shells (in the main group elements) whereas core electrons reside in inner shells.

• The energy that should be supplied to remove core electrons is higher than that of valence electrons.