A calcium atom has {Fill in the blank} valence electrons. It needs to transfer {Fill in the blank} electrons to oxygen to have a full outer shell. An oxygen atom has {Fill in the blank} valence electrons. It needs to accept {Fill in the blank} electrons from calcium to have a full outer shell.

After the transfer of electrons, calcium becomes an ion with a charge of {Fill in the blank} and oxygen becomes an ion with a charge of {Fill in the blank}.
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The atomic number of calcium is 20. Its electronic configuration is 1s2 2s2 2p6 3s2 3p6 4s2. Since the outer most shell (4s) has two electrons in it, its valency is 2.

Similarly atomic number of oxygen is 8. Its electronic configuration is 1s2 2s2 2p6. Since the outer most shell (2s 2p) has total of 6 electrons in it, its valency is 6.

Calcium will gain the stable configuration by loosing two electrons where as oxygen will gain the stable octet configuration by gaining two electrons. Loss of electrons result in the formation of cation and gain of electron result in formation of anion. Thus calcium cation is formed with a charge of +2 and oxygen anion is formed with a charge of -2. The formula of calcium oxide will be CaO.

ahsan57900 ahsan57900 · Answer 2 · 2021-09-21T19:24:46+02:00

Calcium belongs to second group whereas oxygen belongs to six group.

A calcium atom belongs to second group of periodic table which means calcium has 2 electrons in its outermost shell. To make the calcium stable, it needs to transfer 2 valance electrons to oxygen.

An oxygen atom has 6 electrons in its outermost shell so calcium needs 2 electrons in order to complete its last outermost shell to become stable. After the transfer of electrons, calcium becomes a cation with a charge of +2 and oxygen becomes a anion with a charge of -2 so we can conclude that calcium needs to loose two electrons and oxygen needs to accept two electrons to become stable.

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