Answer – The electron configuration of chlorine is 1s² 2s² 2p⁶ 3s² 3p⁵.

Explanation:

The electron configuration of an atom provides information about how the electrons in it are arranged around its nucleus. 

The nucleus of an atom consists of neutrons (which are neutral), and positively charged protons. The protons impart a positive charge to the nucleus as whole, allowing it to attract negatively charged electrons that orbit it. The number of these electrons is equal to the number of protons in the nucleus. However, these electrons also repel each other as their charges are similar. They do not cluster around the nucleus. The attractive force of the protons along with the mutual repulsion of the electrons results in them being held in orbital structures around the nucleus.

The greater the number of protons an atom has, the greater the number of electrons it attracts. At the same time, not all of these electrons can get very close to the nucleus. Instead, they will have to be content with being included in orbitals that are further from the nucleus. 

Electrons close to the nucleus are at lower energy levels as they are bound tighter by the attraction of the protons. Those that are further from the nucleus are less tightly bound, with greater freedom of movement and are hence at higher energy levels. These higher energy levels also have larger circumferences (due to their distance from the nucleus), and can accommodate a larger number of electrons. Thus, they fit in more types of orbitals.

The attraction exerted by the protons also ensures that the orbitals closer to the nucleus fill up before those further away (aufbau principle).

The order in which electrons fill up orbitals is as follows:

Understanding this allows chemists to figure out how the electrons of an atom are arranged around its nucleus and draw up its electron configuration. 

As the atomic number of chlorine is 17, it has 17 electrons. Thus, its electron configuration is as follows:

1s² 2s² 2p⁶ 3s² 3p⁵

The alphabets s and p denote the type of orbital while the numbers next to them indicate the energy level of the electron. The numbers in superscript represent the number of electrons in each orbital. Adding them up (2+2+6+2+5) gives us 17, which is the total number of electrons in chlorine.

A shorter method of expressing the electron configuration is its shorthand notation, or noble gas notation. Here, the symbol of the noble gas that appears in the period above the one in which the element is, and with an atomic number lower than the element’s, replaces part of the full electron configuration. Here, the noble gas neon (Ne) is used as it appears in the period above that of chlorine. The shorthand notation would be 

[Ne] 3s² 3p⁵

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