How many electrons to reach an octet?
Valency.
Counting to eight
Sodium has the configuration 2, 8, 1 and can lose electrons. Oxygen has 2, 6 and can gain electrons.
How many electrons must sodium lose and oxygen gain to complete an octet?
What this lesson covers
The idea
The valency, or combining capacity, of an element is the number of electrons its atom gains, loses or shares to complete its octet.
Counting to eight
Sodium has the configuration 2, 8, 1 and can lose electrons. Oxygen has 2, 6 and can gain electrons.
How many electrons must sodium lose and oxygen gain to complete an octet?
- Sodium 1, oxygen 2
- Sodium 7, oxygen 6
- Sodium 8, oxygen 8
Complete the octet
Choose an atom. Orange shows the valence electrons.
Valency
The number of electrons that an atom gains, loses or shares to complete its octet is its valency. It is also its combining capacity.
The valency, or combining capacity, of an element is the number of electrons its atom gains, loses or shares to complete its octet.
Notes
Valency (combining capacity) is the number of electrons an atom gains, loses or shares to complete its octet.
Check yourself
Sodium has the configuration 2, 8, 1 and can get an octet by losing one electron. What is its valency?
Answer: 1
It loses 1 electron, so its valency is 1.
Oxygen has the configuration 2, 6 and gains electrons to attain an octet. How many does it gain? That number is its valency.
Answer: 2
6 + 2 = 8, so it gains 2 electrons and its valency is 2.
Carbon has the configuration 2, 4. How does it complete its octet?
Chlorine has the configuration 2, 8, 7 and gains electrons to complete its octet. What is its valency?
Answer: 1
7 + 1 = 8, so it gains 1 electron and its valency is 1.
- By losing its four valence electrons. Carbon cannot easily lose four electrons, so it shares them.
- By gaining four electrons from other atoms. Carbon cannot easily gain four electrons, so it shares them.
- By sharing four electrons with other atoms — correct. Yes!