SPM Form 4 Chemistry Notes — Chapter 5『5.1』Formation of Compounds

Stability of Noble Gases

1. Noble gases are chemically non-reactive（inert），stable and exist as monoatomic gases.
2. This is because the outermost occupied shell of all noble gases are full. They have very stable duplet / octet electron arrangement.
3. Noble gases do not donate，receive or share electrons with other atoms.
4. But the atoms of elements from Group 1 to Group 17 are tend to donate，receive or share electrons to achieve the stable duplet / octet electron arrangement and form chemical bonds.

Formation of compounds

• A compound is a chemical substance which consist of two or more elements chemically bonded together.
• A compound is in a more stable state than the elements comprising it.

Examples of natural compounds：

An ion is a positively-charged or negatively-charged particle formed after an atom donate / receive electrons. （ Cation=Positive ion ；Anion=Negative ion ）

When an atom，X donate 1 electron，it form X⁺

When an atom，X donate 2electrons，it form X²⁺

When an atom，X donate 3 electrons，it form X³⁺

When an atom，Y receive 1 electron，it form Y^-

When an atom，Y receive 2electrons，it form Y^2-

When an atom，Y receive 3 electrons，it form Y^3-