Chemistry · Periodic Classification Of Properties · NEET
He plotted atomic volume on the y-axis (vertical) and atomic weight on the x-axis (horizontal). Atomic volume means the volume taken by one mole of the solid element. He also tried melting point and boiling point, but the atomic volume graph is the famous one. When the points are joined, they form a repeating up-down wave, not a straight line.
Atomic volume is the space occupied by one mole of an element in the solid state. You get it by dividing the atomic weight (in grams) by the density of the solid: atomic volume = atomic weight / density. So even though he uses atomic weight on the x-axis, atomic volume already contains density information, which is why the graph shows a pattern.
Alkali metals (Li, Na, K, Rb, Cs) have low density and large size, so their atomic volume is very high. That is why each peak of the wave is an alkali metal. Right after each peak, the atomic volume drops. This regular return of high peaks is the periodicity Meyer wanted to show.
It proves periodicity: if you arrange elements by increasing atomic weight, similar elements come back at fixed intervals. Every peak is an alkali metal, every valley region has the same kind of element. So a physical property (atomic volume) is a periodic function of atomic weight. This was direct visual support for the Periodic Law.
They worked separately but reached a similar idea in 1869. Both said properties repeat with increasing atomic weight. But Meyer focused mostly on physical properties (like atomic volume) shown as a curve, while Mendeleev built a full table using both physical and chemical properties, and even left gaps for undiscovered elements. Mendeleev's table was more detailed and is why he is remembered more.
The transition metals and elements with high density (like the middle-of-period metals) sit low in the curve because they have small atomic volume. The ascending slope toward a peak passes through less dense elements. So the shape goes: valley (dense metals) up to a peak (alkali metal), then down again for the next period.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Lothar Meyer (1830-1895) was a German chemist. In 1869, working on his own, he showed that physical properties of elements repeat at regular intervals when elements are arranged by increasing atomic weight.
It is a repeating wave (a periodic curve). It rises to sharp peaks and falls into valleys again and again. Each sharp peak is an alkali metal because of its large atomic volume.
Yes, for the 'Classification of Elements' history part. NEET can ask what he plotted, why alkali metals form peaks, and how his work compares with Mendeleev. It is a quick, high-return topic to memorise.
Because the value (atomic volume) keeps returning to high peaks at fixed gaps as atomic weight increases. A quantity that repeats its pattern like this is called a periodic function, which is the meaning behind the word 'Periodic Law'.
Mendeleev built a full periodic table and even predicted missing elements like eka-aluminium and eka-silicon. That prediction is the next big step in the classification story.
