Final answer:
The Law of Octaves states that every eighth element by mass has similar chemical and physical properties.
Step-by-step explanation:
The theory that describes a pattern where every eighth element by mass has similar chemical and physical properties is The Law of Octaves. This theory was proposed by John Newlands in 1864, who arranged the known elements at that time in order of increasing atomic mass.
According to the Law of Octaves, when the elements were arranged in rows of seven, similar properties would repeat every eighth element. For example, the eighth element, sodium (Na), would have similar properties to the first element, lithium (Li), and so on.
This pattern is similar to the musical scale where notes repeat every eighth note, hence the name 'Law of Octaves'.
Learn more about The Law of Octaves