Fewer than four, or more than four

The idea

An atom with fewer than four valence electrons generally donates them to become stable, while an atom with more than four usually gains or shares electrons to complete its octet.

Give or take?

Sodium has 1 valence electron and chlorine has 7.

Which of the two do you think is more likely to give away its valence electron?

• Sodium
• Chlorine
• Both are equally likely

Count the valence electrons

Change the number of valence electrons in the outer shell.

A rule of thumb

If the valence shell has fewer than four electrons, the atom would generally donate them to become stable. If it has more than four, the atom usually gains electrons, or shares them, to complete an octet.

An atom with fewer than four valence electrons generally donates them to become stable, while an atom with more than four usually gains or shares electrons to complete its octet.

Notes

Fewer than four valence electrons: the atom generally donates them. More than four: it usually gains or shares electrons to complete its octet.

Check yourself

A sodium atom has 1 valence electron. What would it generally do?

A chlorine atom has 7 valence electrons. What does it usually do?

A sulfur atom has 6 valence electrons. How many electrons does it need to gain to complete its octet?

Answer: 2

8 − 6 = 2. Sulfur gains two electrons to complete its octet.

Atom X has 2 valence electrons. Atom Y has 6. Which is more likely to donate its valence electrons?

• Gain seven electrons. An atom with fewer than four valence electrons generally donates them, rather than gaining seven.
• Gain one electron. An atom with fewer than four valence electrons generally donates its valence electrons.
• Donate that electron — correct. Yes!
• Gain or share electrons to complete its octet — correct. Yes!
• Donate seven electrons. An atom with more than four valence electrons usually gains or shares electrons.
• Donate one electron. An atom with more than four valence electrons usually gains or shares electrons.
• Atom Y, because it has more valence electrons. An atom with more than four valence electrons usually gains or shares electrons.
• Atom X, because it has fewer than four — correct. Yes!
• Neither can donate. An atom with fewer than four valence electrons generally donates them.