Question

Teacher wrote the electronic configuration of an atom of an element as 2,8,7.what is the atomic number of this element

Answer 1

Since, electronic configuration is 2,8,7(17). Means number of protons in it is 17. If protons are 17 means atomic number is 17. Therefore, the element is Chlorine (Cl).

$\rule{200}2$

Additional Information

• Atomic mass of Chlorine is 35 atomic mass units. (Atomic mass is the sum of number of protons and of neutrons.)
• It contains 17 protons, 18 neutrons and 17 electrons in it.
• As, there are 7 electrons in the outer most shell. Therefore, the valency of the Aluminium is 1 (will gain electron).
• It's symbol is Cl.
• It belongs to 3rd period and 17th group number in periodic table.
• It's melting point is -101°C.
• It is greenish-yellow in colour.
• Used to kill microorganisms in power plant, extraction of bromine etc.
• It is the second-most-abundant halogen.
• It consists of two stable isotopes i.e. chlorine-35 and chlorine-37.

Answer 2

Explanation:

Electronic configuration of an is 2,8,7 and its atomic number is 17.

Name of the elements is Chlorine.

Additional information:

Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine is a yellow-green gas at room temperature.

Symbol: Cl

Atomic mass: 35.453 u

Atomic number: 17

Electron configuration: [Ne] 3s²3p⁵

Electronegativity: 3.16

Van der Waals radius: 175 pm