4.1.2 - The Periodic Table: 4.1.2.2 - Development of the Periodic Table Flashcards
Students should be able to describe these steps in the development of the periodic table. Explain how testing a prediction can support or refute a new scientific idea.
What did Dobereiner discover?
He discovered triads - groups of 3 elements that react in a similar way.
What law did Newlands create?
The law of octaves - every 8th element reacted similarly (this was untrue for some)
What did Mendeleev create?
The periodic table, with elements arranged in order of increasing relative atomic mass.
How did Mendeleev create the periodic table?
- Placed elements in order of atomic mass.
- Arranged elements in periodic pattern (elements with similar chemical properties occurred at regular intervals)
- Left gaps for elements not yet discovered
- Predicted properties of elements that would fill gaps.
- Presence of isotopes sometimes gave elements different masses, so they ended up in the wrong groups
How is the modern-day periodic table arranged?
In atomic number order (proton number order) so elements that react similarly are now in groups together.
How did scientists classify elements before the discovery of protons, neutrons & electrons?
They attempted to classify the elements by arranging them in order of their atomic weights.
Why were the early periodic tables not accurate?
The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
How did Mendeleev overcome some of the problems with the periodic table?
He left gaps for elements that he thought had not been discovered & in some places changed the order based on atomic weights.
Why was the order based on atomic weights not always correct?
Because of isotopes.
What are isotopes?
An atom of the same element with the same number of protons and a different number of neutrons.
