Question

In the early periodic tables some elements were placed in the wrong groups. Mendeleev overcame some of these problems in his periodic table. Give two ways Mendeleev did this

Answer 1

Explanation:

left some places for noble gases as he knew that there are many other elements would discovered

Answer 2

Mendeleev made a few changes to his order to make his classification work: he left gaps for yet-to-be-discovered elements and switched the order of a few elements to keep the groups consistent.

Mendeleev's periodic table:

• Mendeleev's periodic table is a tablet-sized arrangement of elements in increasing atomic mass order that reflects similarities and trends in element behavior.
• Mendeleev initially arranged elements in increasing atomic weight order, one beneath the other.
• Elements with similar properties are grouped together.
• The same horizontal row contains elements with similar properties.
• The following is Mendeleev's original periodic table, published in 1869.
• Mendeleev's periodic table can be better understood by reversing the element arrangement.
• Elements are arranged in a horizontal line in increasing order of atomic mass.
• A 'period' is a horizontal arrangement of elements.
• When an element has a high degree of similarity to an earlier element, the new element is placed just below the earlier element with the same property to begin a new period.
• A 'column' is formed by the periods one below the other (group).
• Thus, Mendeleev's periodic table is made up of horizontal rows and vertical columns, or periods and groups.
• If the element is similar but not identical, it is placed below but slightly away from the other to differentiate it.
• Each column will have two sub-columns (A and B), so elements in the same sub-columns will be more similar.

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