★ Must-know
📌 Periods are horizontal rows corresponding to the number of electron shells, whereas groups or families are vertical columns whose elements share similar properties due to their external electron configuration.
Further detail
The periodic table is generally divided into four blocks: s, p, d, and f.
The table's organization helps explain trends in electronegativity, atomic radius, and ionization energy and helps predict element behavior.
Periods run horizontally; groups run vertically.
Mendeleev observed sequences in the properties of elements, establishing the idea of periodicity. - Mendeleïev
In 1913, Moseley discovered the atomic number Z, establishing it as the most important criterion for periodic classification.
1. A student uses the periodic table to classify an element and predict its behavior. Which statements describe features that support this task?
2. Which statements correctly identify Moseley's contribution to periodic classification?
3. An element has atomic number 16 and is being located within the third period. Which statements apply?
By what two criteria does the periodic table arrange chemical elements?
By atomic number and recurring chemical and physical properties.
What do periodic table periods represent in terms of electron shells?
The number of electron shells.
How are groups or families arranged in the periodic table?
They are vertical columns whose elements share similar properties due to their external electron configuration.
What pattern in element properties did Mendeleïev observe?
Sequences in their properties.
Which scientist established the idea of periodicity by observing sequences in element properties?
Mendeleïev.
In which year did Moseley discover the atomic number ?
1913.
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