1.2 Monatomic Elements

1. 1.2 Monatomic Elements Very Weak Attractions LO: I know about the weak forces of attraction between atoms of the noble gases.

2. gas liquid Cooling Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne The noble gases are elements as they exist as single atoms at room temperature. monatomic If a gas like neon is cooled to a low enough temperature it turns into a . liquid

3. liquid solid Cooling Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne Ne solid Further cooling turns neon into a . There must be forces of attraction holding the atoms together. They are called forces. van der Waals Van der Waals forces are very since very little energy is needed to break them in neon. weak

4. Van der Waals Forces LO: I understand how van der Waals forces come about.

5. The van der Waals force is the attraction between a momentary slight charge on one atom and the momentary slight opposite charge it causes in a neighbouring atom. electrostatic Van der Waals forces are due to uneven charge in a atom. neutral The uneven charge is produced when the electron cloud surrounding the nucleus about creating a temporary slightly negative side to the atom and a temporary slightly positive side. wobbles (-) (+)

6. — + van der Waals force dipole The dipole on one atom forces a dipole on a atom to form: This kind of charge separation is called a . neighbouring — + Thus, the two atoms are attracted to each other.

7. The Noble Gas Series LO: I understand how van der Waals forces affect the boiling points of the noble gases.

8. Ra Xe Boiling point (˚C) Kr Ar Ne He Period Number Boiling point trend down the noble gases group: increases The boiling point down a group. increasing This is because the atoms are in size. greater The larger an atom is the the van der Waals forces present. energy More is needed to separate the atoms and so the boiling point is higher.