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Atoms define the structure of elements. They are composed of mainly three particles; protons, neutrons and electrons. Here protons and neutrons are heavier compare to electrons and are placed at center of the atom. The center part of the atom is known as nucleus. The lightweight electrons exist in a cloud orbiting around the nucleus. The mass of nucleons; protons and neutrons is approximately same but mass of 1 proton is more than 1,800 electrons.

Atoms are neutral as they have same number of electrons and protons. Neutrons are neutral particles and do not contribute to the charge of an atom. Entire mass of the atom is localized at the center of the atom that is called as nucleus whose volume is much less compare to the atom. In the nucleus, protons and neutrons are held together due to energy transfer. In this article we will see different aspects of electrons.


Electrons Definition

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Let’s start with the electrons definition. Electrons are negatively charged particles of an atom which are extremely small and electron charge is same as charge on protons with opposite sign. The electron mass is 1800 times less compare to mass of protons. Electrons are elementary particles with symbol e or ß.

Electron Charge

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The charge on electron is represented as coulomb and symbolized by C. It is about $1.60 x 10^{-19}C$. Electrons were first discovered in Cathode rays experiment by J.J. Thomson in 1897. Later the Irish physicist George F. Fitzgerald named them as electrons.

Electron Mass

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Similarly the mass of an electron at rest; me, is approximately $9.11 x 10^{-31} kilogram (kg)$.  Electrons move with the speed of light and have greater mass due to relativistic effects.

Electron Spin

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Like other charge particles; electron spin is also on their axis and electron subshells contain two electrons with opposite spins. The electrons present in the outermost shell are known as valence electrons. 

Electron Subshells

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The pathways where electrons are present around the nucleus are known as orbitals. The orbitals near the nucleus are spherical and outer orbitals have complicated shapes. The electronic configuration of an atom represents the orbital description of the locations of the electrons and helps to predict an atom's properties like stability etc.

The electronic configuration can be written in the form of noble gas configuration in which inner orbitals will come as noble gas symbol and valance shell will come with formal notations like electronic configuration of beryllium can be written as 1s22s2 or [He] 2s2

Here Letters, s, p, d, and f indicate the shape of the orbitals and number in superscript indicates the number of electrons in that orbital. Similarly electronic configuration of carbon can be written as 1s22s22p2 or [He] 2s22p2

Carbon Atom
The electronic clouds around the nucleus of an atom are placed at the specific distances from the nucleus and are organized into shells. Due to fast movement of electrons, they cannot define at certain position at a moment so scientists discovered specific areas of maximum probability of finding the electrons around the nucleus. The overall shape of the shells depends on the number of electrons present in that shell and also on the distance from the nucleus.

Valence Electrons

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The outermost shell or valence shell of an atom plays a major role in formation of chemical bonds as valence electrons participate in the formation of chemical bonds. There are mainly two types of bonding between atoms; electrovalent or ionic and covalent bonding.

Electrovalent bonds between atoms are formed by the complete transfer of electrons that results the formation of anion and cation which attract each other to form ionic compound. The covalent bonds are formed by the complete and equal sharing of valence electrons between bonding atoms. Electrons can stream through wires and circuits to create the currents of electricity.

They can move from negative charge to positive charge through the system. Since the number of electrons and protons is same in a neutral atom therefore the atomic number which is total number of protons in an atom can be used to write the electronic configuration of an atom.

The Modern periodic table is based on the atomic number and depicts the electronic configuration of the atom. The atomic number is located in the upper left corner and the atomic weight is located on the bottom of the notation of the element.

The transfer of electrons from an atom results the formation of ions. If an atom loses electrons, it forms cation with positive charge because as an atom loses electrons, the number of protons becomes more compare to the number of electrons and the atom will be no more neutral. Similarly if an atom accepts electrons, it gets some extra negative charge and forms anion.

An atom can accept or lose electrons only when it does not have some stable noble gas configuration (octet configuration). As the atom gets the stable octet configuration, it will show no more transition of electrons.  There is no contribution of electrons in the mass number of an atom as they have negligible mass. The mass number represents total number of protons and neutrons in an atom. Any change in the number of neutrons does not create a new atom but only change its mass. These different forms of an element with different mass number or different number of neutrons but same atomic number are called as isotopes.

So we can say that number of protons in an atom is called as atomic number and that is equal to the number of electrons in a neutral atom. The sum of number of neutrons and protons in an atom is called as mass number of an atom.
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