History of the Periodic Table Flashcards

All 6 cards in this deck

Before protons, neutrons and electrons were discovered, how did scientists try to classify the elements?

By arranging them in order of their atomic weights.

What two things did Mendeleev do to overcome the problems with earlier periodic tables?

He left gaps for elements not yet discovered, and in some places changed the order based on atomic weights.

Why did Mendeleev reverse the order of some pairs of elements?

So that their properties matched the rest of the group.

True or false? Mendeleev swapped some pairs of elements so that they were in order of atomic number.

False. Atomic number is the number of protons, and protons had not been discovered yet — he swapped them so properties matched the group.

What discovery explained why ordering elements by atomic weight was not always correct?

The discovery of isotopes — atoms of the same element can have different masses, so atomic weight does not always follow atomic number.

How did the discovery of new elements such as gallium help Mendeleev's table become accepted?

They fitted into gaps he had left, and their properties matched the ones he had predicted.