Valency Jigsaw Puzzle
Use valency to snap ions into formulas
What this lesson covers
Why it matters
Atoms are like puzzle pieces that refuse to sit with jagged edges exposed. They trade or share electrons until their outer shells are perfectly smooth and full.
Predict first
Why does sodium (1 valence electron) want to lose that electron, while chlorine (7 valence electrons) wants to gain one?
Stability is the goal. Atoms react to achieve the electron configuration of the nearest noble gas, usually a full outer shell of 8 electrons (octet rule).
- Sodium is heavier than chlorine
- They both seek a stable octet (full outer shell) — correct
- Sodium is a metal and chlorine is a gas
- They are next to each other in the periodic table
What you do
Pick a cation and an anion and let their charges criss-cross into subscripts. Build all four target formulas — an unbalanced pair simply won't snap together.
Check yourself
What is the valency of Oxygen (atomic number 8, config 2,6)?
Oxygen needs 2 more electrons to complete its octet (2,8). Therefore, its valency is 2.
Why does Magnesium (Mg) have a valency of 2, not 10?
Metals lose electrons from their outermost shell. Mg (2,8,2) loses 2 electrons to reveal the stable inner octet (2,8).
In the compound CO2, Carbon has a valency of 4 and Oxygen has a valency of 2. Why are there two Oxygen atoms?
Valency represents combining capacity. Carbon (4) needs to bond with two Oxygens (2 each) to satisfy the valency requirements of all atoms involved.
- 6
- 2 — correct
- 8
- 0
- It loses its 2 outer electrons to achieve a stable octet — correct
- It gains 2 electrons to reach 10
- Valency is always the atomic number divided by 5
- It shares all 12 electrons
- To balance the total charge to zero
- Carbon needs to share 4 electrons; each Oxygen shares 2, so 2 Oxygens are needed — correct
- Oxygen is smaller than Carbon
- There is no specific reason