Introduction to Chemical Bonding

Atoms bond to reach a stable, full outer shell (like the noble gases). There are two main ways for the first-20 elements:

• Ionic bonding — between a metal and a non-metal. The metal gives away its outer electron(s) and the non-metal takes them. The atoms become charged ions ($+$ and $-$) that attract each other. Example: $\text{Na}^{+}$ and $\text{Cl}^{-}$ in table salt, $\text{NaCl}$.
• Covalent bonding — between two non-metals. The atoms share electron pairs. Example: two hydrogens share to make $\text{H}_2$; oxygen and hydrogens share in $\text{H}_2\text{O}$.

Rule of thumb: metal + non-metal → ionic (transfer); non-metal + non-metal → covalent (sharing).