If an element has atomic no 17,which type of bond can it form
Answers
This would be a Chlorine Atom. Being atomic no 17 means it has 17 protons (which are positive) in the nucleus. Being a neutral atom - as opposed to an ion) it therefore has 17 electrons.
Electrons are arranged in shells around the nucleus. The inner shell can contain 2 electrons, whilst the next two shells can contain 8 electrons each. For chlorine the 17 electrons would be found in the following configuration: 2,8,7
The outer shell of chlorine is therefore incomplete. It would be more stable if it had eight electrons to complete the outer shell. Chlorine, like all of the elements in group 7 (known as the Halogens) has 7 electrons in their outer shells, and this is what makes them so chemically reactive. During a chemical reaction they will strongly accept an electron from another atom
There are two ways chlorine can gain the additional electron it needs to achieve a full outer shell of electrons. These two methods correspond to two types of bonding: ionic or covalent bonding.
Ionic bonding
This occurs when a non metal, such as chlorine, forms a bond with a metal. In this example I will use sodium (Na) as an example of the metal as together they make up sodium chloride, which is common table salt.
Sodium has atomic number 11, so has 11 electrons. These are arranged in shells in the configuration 2,8,1. So sodium atoms have one electron in their outer shell. To become more stable and have a full outer shell sodium will lose an electron, becoming a positive Na+ ion. When it loses this electron it has the structure 2,8 and a charge of +1.
Chlorine too would like to achieve a full outer shell, which it can do by receiving an additional electron to increase its outer shell from 7 electrons to 8. It then has the electron structure 2,8,8 with a charge of -1. It is now a negative chloride ion (note the change in spelling for non-metal ions, from chlorine atom to a chloride ion).
The positive sodium ions will be attracted to the negative chlorine ions creating the ionic compound sodium chloride.
Covalent Bonding
In covalent bonding electrons are shared not transferred.
For example in the simp,e covalent molecule hydrogen chloride (a gas), the hydrogen atom shares an electron.
Hydrogen is atomic number 1 so has only a single electron which occupies the first, inner, shell. It would like to have 2 electrons so it’s shell is complete. The chlorine and hydrogen form a bond by sharing one electron each, hence both atoms gain a complete shell.
[GCSE CHEMISTRY - Covalent Bonding in a Hydrogen Chloride Molecule - What is the Structure of a Hydrogen Chloride Molecule? - GCSE SCIENCE.]
Note: in both examples of bonding 5he diagrams use dots and crosses to represent electrons. This is simply a convention to illustrate the different initial locations of the electrons (dots for electrons from one atom, crosses for electrons that started with the other atom. In reality electrons are indistinguishable.
if the atomic number is 17 then the bond it will be formed is ionic bond , covalent bond .