Hume Rotherys Rules for solid solutions by Dr.Ram

The Hume-Rothery Rules

How can you tell if two solids will form a solid solution? A great place to start is the Hume-Rothery Rules. William Hume-Rothery researched metal mixtures and created these rules to predict whether two elements can form solid solutions. The Hume-Rothery rules state that two elements must be very similar to each other in order to form a solid solution, because any dissimilarities can cause separation like in the case of oil and water. The two elements must therefore meet all of the following conditions in order to mix and form a solid solution.

• Atomic Size: The atomic radii of the elements must be within about 15% of each other.
• Crystal Structure: The two elements must have the same crystal structure. This means that the atoms in one element must arrange in the same way as the atoms in the other element.
• Electronegativity: The two elements must have similar electronegativity values. Electronegativity is a measure of an atom's ability to attract electrons. Electronegativity values can be found online or in chemistry books.
• Valency: The two elements must have the same valency, which is a measure of an atom's ability to combine with other atoms. Valency values can be found online or in chemistry book.