12 Questions
What was the primary basis of arrangement of elements in the periodic table according to Dmitri Mendeleev?
Increasing atomic weight
Which scientist is credited with the discovery of the properties of elements in a triad?
Johann Dobereiner
What was the term used by John Newlands to describe the groups of elements with similar properties?
Octaves
What was the innovation introduced by Henry Moseley in the arrangement of elements in the periodic table?
Arrangement by atomic number
What was the significance of the gaps left by Dmitri Mendeleev in his periodic table?
They were predictions for undiscovered elements
Which scientist used X-rays to determine the number of protons in the nucleus of an atom?
Henry Moseley
Which of the following scientists was the first to isolate potassium and sodium?
Humphry Davy
What was the underlying principle behind Johann Dobereiner's triads?
Similar chemical properties
Why did Dmitri Mendeleev place Iodine and Tellurium out of order in his periodic table?
Because of their atomic weights
What was the significance of the eighth element in John Newlands' octaves?
It had properties similar to the first element
What was the main difference between the arrangement of elements by Dmitri Mendeleev and Henry Moseley?
Atomic number vs. atomic weight
Which of the following scientists did not contribute to the development of the modern periodic table?
Ancient Greeks
Study Notes
Development of the Periodic Table
- Ancient Greeks believed in 4 elements: Earth, Air, Wind, Fire.
- Robert Boyle defined an element as a substance that cannot be split into simpler substances by chemical means.
Contributions of Key Scientists
- Humphry Davy used electrolysis to break down water into hydrogen and oxygen and isolated potassium and sodium.
- Johann Dobereiner discovered triads, where elements in a triad have similar chemical properties and the atomic weight of the middle element is halfway between the other two.
- John Newlands arranged elements in increasing atomic weights and found that the eighth element had properties similar to the first, calling these groups octaves.
Dmitri Mendeleev's Contributions
- Arranged elements in order of increasing atomic weight.
- Listed subgroups for elements like Cu & Ag whose properties didn't fit into the main group.
- Placed Iodine & Tellurium out of order of atomic weight.
- Left gaps for undiscovered elements and predicted their properties.
Henry Moseley's Contributions
- Arranged elements in order of increasing atomic number, not atomic weight.
- Used X-rays to determine the number of protons in the nucleus of an atom.
The Modern Periodic Table
- A list of elements arranged in increasing atomic number.
- Arranged into horizontal periods and vertical groups.
Test your knowledge of the development of the periodic table.
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