The Development of the Periodic Table Flashcards
(19 cards)
- Q: Who is considered the father of the modern periodic table?
A: Dmitri Mendeleev.
Dmitri Mendeleev
How did Mendeleev arrange elements in his periodic table?
By increasing atomic mass and grouping elements with similar properties
Keyword: Atomic mass - the mass of an atom based on protons + neutrons
What was unique about Mendeleev’s table?
He left gaps for undiscovered elements and predicted their properties.
Example: He predicted the properties of gallium before it was discovered
Why was Mendeleev’s periodic table accepted over time?
Because elements he predicted (like germanium) were later discovered and matched his predictions
What were some problems with arranging elements by atomic mass?
Some elements seemed out of order when grouped only by mass, not properties.
Example: Iodine comes before tellurium based on properties, despite having a lower atomic mass.
What is the modern periodic table arranged by?
Atomic number (number of protons)
Who discovered the proton and helped correct the periodic table order?
Henry Moseley
What did Moseley’s work show about atomic number?
That it is a better basis for organizing elements than atomic mass
What is a “periodic” pattern?
A repeating pattern of properties across periods in the table
Why did Mendeleev swap some elements from their atomic mass order?
To group them with others that had similar chemical properties
How did Mendeleev deal with elements that didn’t fit the pattern?
He left gaps or moved elements to maintain group similarities
Give an example of a prediction Mendeleev made that was correct.
He predicted “eka-aluminum,” which matched the properties of gallium
How many elements were known in Mendeleev’s time?
Around 63
What is one limitation of Mendeleev’s original table?
It didnt include noble gases, as they weren’t discovered yet
Why did Mendeleev’s predictions gain credibility?
Later discoveries of new elements confirmed the accuracy of his predicted properties
What group of elements was added after Mendeleev’s table?
Group 0 - the noble gases
Why was the development of the periodic table important for chemistry?
It organized elements in a way that made patterns and relationships predictable
What is meant by “periodicity” in the periodic table?
The regular recurrence of element properties
What scientific change helped explain why Mendeleev’s adjustments worked?
Discovery of atomic number and subatomic structure
