Sharing or transferring electrons

The idea

Atoms with an incomplete valence shell become stable by combining with other atoms, either by sharing valence electrons or by transferring them (giving or accepting electrons); stable atoms like helium exist singly.

Which atoms are happy alone?

Atoms with a full valence shell are stable. Look at helium, hydrogen, oxygen, chlorine and sodium.

Which one do you think stays as a single atom?

• Helium
• Hydrogen
• Chlorine

Look at the valence shell

Choose an atom. Blue dots are its valence electrons. Empty rings show the room for more.

Two ways to become stable

An atom with an incomplete valence shell can become stable by combining. It either shares valence electrons with another atom, or transfers them: it gives electrons or accepts them. Helium needs neither, so it exists on its own.

Atoms with an incomplete valence shell become stable by combining, either by sharing valence electrons or by transferring them (giving or accepting electrons). Stable atoms like helium exist singly.

Notes

Atoms become stable by sharing or transferring valence electrons. Atoms that are already stable, like helium, stay single.

Check yourself

What are the two ways in which atoms with an incomplete valence shell combine to become stable?

Why does helium exist as single atoms?

A chlorine atom has 7 valence electrons. How many more does it need to complete an octet?

Answer: 1

An octet is 8 electrons, and 8 − 7 = 1.

A sodium atom has 1 valence electron. How can it attain a stable configuration?

• Splitting the nucleus or joining the nucleus. The book describes sharing and transferring of valence electrons, not changes in the nucleus.
• Sharing electrons or transferring electrons — correct. Yes!
• Heating or cooling. Heating and cooling are not how atoms become stable. They share or transfer valence electrons.
• It has no electrons. A helium atom has 2 electrons in its K-shell, which is its valence shell.
• It has too many valence electrons to share. A helium atom is stable, with 2 electrons in its K-shell, so it has no need to share.
• Its valence shell is already complete, so its atoms are stable — correct. Yes!
• By losing that electron — correct. Yes!
• By sharing 7 electrons. Sodium has only 1 valence electron, so it cannot share 7. It can lose that electron.
• By gaining 7 electrons. The book says sodium becomes stable by losing its single valence electron.