Melting Point Trends
Lajoy Tucker & Dr. Davinder Bhachu
Teachers
Contents
Melting Point Trends
Melting points are based on the strength of the forces of attraction holding structure together and as a result the amount of energy required to overcome them.
Giant ionic lattice: A lattice of opposite charged ions held together by many strong electrotastic forces of attraction.
Giant covalent (macromolecular): A 3D network of atoms bonded by strong covalent bonds between atoms throughout the structure.
Simple molecular: Discrete molecules held together by weak intermolecular forces (van der Waals).
Metal oxide | ||||||
Structure | Giant ionic | Giant ionic | Giant ionic (with covalent character) | Giant covalent | Simple molecular | Simple molecular |
Held together by | Strong ionic bonds | Strong ionic bonds | Strong ionic bonds | Strong covalent bonds | Weak intermolecular forces | Weak intermolecular forces |
Relative MP | High↑ | High↑↑ | High↑↑↑ | Highest | Low↓ | Lowest↓↓ |
Period 3 Oxides Melting Point Explainer Video
Explanation of Melting Points
Sodium oxide to Magnesium oxide :
Trend: Melting point increases.
Increasing charge and decreasing size of the metal ions . Stronger electrotastic forces of attraction between positive metal ion and negative oxide ion. More energy needed to break bonds higher melting point.
Note: Although ions are the smallest with the greatest charge, the structure of the lattice results in less efficient packing of ions and therefore a lower than expected melting point. This is not assessed by AQA.
No answer provided.
Silicon dioxide :
Highest melting point
Strong covalent bonds between silicon atoms throughout the structure. Stronger that the ionic bonds and intermolecular forces holding the other structures together. The most energy is required to break these bonds.
Phosphorus oxide and oxides of sulfur and
Trend: Melting point depends on size of molecules . Larger molecules = more electrons = stronger van ders Waals. More energy needed to overcome intermolecular forces higher melting points.
Practice Question
Question:
Which of the oxides below has the strongest ionic bonds?
A.
B.
C.
D.
Answer:
B.
has the strongest bonds, but these covalent.
and are ionically bonded. bonds are stronger due to the smaller size and greater charge of the ion compared to .