The periodic table

Question 1

In Mendeleev’s table atomic number was just the position of an element in the table.
What is atomic number the number of?

Answer 1

Protons in the nucleus of the atom.

Question 2

Does every element have a unique atomic number?

Answer 2

Yes.

Question 3

In Mendeleev’s table, some of the elements are not arranged by relative atomic mass, and were instead moved to groups of elements with similar properties.
What did Mendeleev actually arrange the elements by?

Answer 3

Atomic number

Question 4

What are elements arranged by today?

Answer 4

Increasing atomic number.

Question 5

The horizontal rows are called what?

Answer 5

Periods

Question 6

Which elements are on the left and in the centre?

Answer 6

Metals

Question 7

Elements with similar properties are in the same vertical what?

Answer 7

Groups

Question 8

Which elements are on the right side?

Answer 8

Non-metals

Question 9

What does the higher number represent?

Answer 9

relative atomic mass

Question 10

What does the lower number represent?

Answer 10

atomic number

Question 11

Mendeleev placed tellurium before iodine, despite most of his table being arranged by increasing relative atomic mass.

Relative atomic mass: 128 | 127
Element symbol: Te | I
Atomic number: 52 | 53

1) Mendeleev did not know about atomic structure. How did he explain the pair reversals?
2) Was Mendeleev correct in his placement?

Answer 11

1) He could only explain them by terms of the elements’ properties.
2) Yes.

Question 12

The table shows information about cobalt and nickel. Their positions in the periodic table were difficult to determine in Mendeleev’s time.
Explain how knowledge of atomic structure helps to determine the positions of cobalt and nickel in the periodic table.

Relative atomic mass: 58.9 | 58.7
Element symbol: Co | Ni
Atomic number: 27 | 28

Answer 12

Elements are arranged in order of increasing atomic number(number of protons) in the modern table. The atomic number of cobalt is lower than that of nickel.
When Mendeleev arranged his table, he used a different definition of atomic number

Question 13

The relative mass of an element is often given as a whole number.
Suggest why cobalt and nickel may not appear to be a pair reversal.

Relative atomic mass: 58.9 | 58.7
Element symbol: Co | Ni
Atomic number: 27 | 28

Answer 13

Both relative atomic masses are 59 when rounded to the nearest whole number.
Mendeleev arranged by relative atomic mass, but when he swapped Co and Ni the rounding of the relative atomic mass makes it look like they haven’t been moved.