Chemistry · Periodic Classification Of Properties · NEET
Eka is a Sanskrit word meaning 'one'. Mendeleev used it to mean 'one place below' the known element in the same group. So eka-aluminium means the missing element sitting one box below aluminium. Eka-silicon means the missing element one box below silicon. It is just his naming style for a gap, not a real element name.
Eka-aluminium is gallium (Ga), discovered in 1875. Eka-silicon is germanium (Ge), discovered in 1886. When their true properties were measured, they matched Mendeleev's predicted values very closely. This match made scientists trust his periodic table.
He kept elements with similar properties in the same group. Sometimes the next known element did not fit the pattern, so he left an empty box instead of forcing a wrong element in. He believed a real element that fit the gap was simply not discovered yet. This is why his table had blank spaces on purpose.
He used the trend in the group. He took the average of the neighbours (the element above, below, left, and right in the table) to estimate atomic mass, density, melting point, and formula of oxides. For eka-silicon he predicted mass about 72 and a dioxide; germanium later showed mass 72.6 and forms GeO2. For NEET, remember this shows periodic properties change in a regular, predictable way.
They are different gaps in different groups. Eka-boron is the element one below boron, which turned out to be scandium (Sc). Eka-aluminium is one below aluminium, which turned out to be gallium (Ga). Eka-silicon is one below silicon, which is germanium (Ge). Do not mix them up: eka-B = Sc, eka-Al = Ga, eka-Si = Ge.
They proved that properties are a periodic function of atomic weight, as Mendeleev claimed. Because the guesses came true, his periodic table was accepted over rivals. In NEET, a common one-line fact is: the success of these predictions was the biggest merit of Mendeleev's table.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. Eka-aluminium was Mendeleev's placeholder name for the missing element below aluminium. It was later discovered and named gallium (Ga).
He predicted an atomic mass near 72, a grey metal-like solid, an oxide of the form EO2 (a dioxide), and a chloride ECl4. Germanium later matched all of these closely.
Eka-boron is the gap one place below boron. It was later filled by scandium (Sc). Note it is different from eka-aluminium (gallium).
They are the strongest proof of Mendeleev's periodic law and a favourite exam fact. Questions often ask you to match eka-names with the modern element.
Eka is Sanskrit for 'one', meaning one step below the named element in the same group of the table.
