Development of the Periodic Table

Question 1

What order are elements in the periodic table sorted by ?

Answer 1

Atomic number

Question 2

Why do elements in the same group have similar chemical properties?

Answer 2

They have the same number of outer shell electrons

Question 3

Are groups columns or rows?

Answer 3

columns

Question 4

What order were early periodic tables placed in?

Answer 4

atomic mass

Question 5

Why were some elements in the early periodic tables placed in the wrong group?

Answer 5

Because not all of the elements had been discovered then and because they were placed in order of atomic weight

Question 6

How did mendeleev overcome some of these problems?

Answer 6

Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the mass order based on properties.

Question 7

What did the gaps left in the table enable Mendeleev to do?

Answer 7

Guess the properties of the elements that hadn’t yet been discovered.

Question 8

What happened when new elements were discovered?

Answer 8

Elements with properties predicted by Mendeleev were discovered and filled the gaps

Question 9

What was discovered that led to the understanding of why the order based on atomic mass wasn’t always correct?

Answer 9

Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct.