Zumdahl Chapter 2 : Molecules and Ions

Molecules and Ions
Chemical bonds: forces that hold atoms together in compound.
Covalent bond formed by sharing electrons.
Molecule: collection of atoms bonded by covalent bonds Example: H2, H2O, O2, NH3, CH4
Chemical Formula consist of element symbol and subscripts to indicate the relative number of atoms. Example: CO2
In structural formula individual bonds are shown by lines.

Ionic bond: Electrostatic attraction between ions.
Ion: atom or group of atoms that net charge: Monoatomic ion: Example: Na+ and Polyatomic ion:NH4+
Ionic compound such as sodium chloride: NaCl.

- Sodium atom loses electron to form positive ion Na+; called cation. 
- Chlorine atom gain electron to form negative ion Cl- called anion.

In NaCl equal number of Na+ and Cl- ion packed together and form beautiful colourless cubic crystals.
Ionic solid consist of oppositely charged ions.