Consider the elements cobalt, nickel, argon and potassium. What would be wrong w
ID: 574141 • Letter: C
Question
Consider the elements cobalt, nickel, argon and potassium. What would be wrong with ordering these elements according to atomic weight? 1a. 1b. Explain why pair reversals occur in terms of protons and neutrons3) 1c. Draw a left-step periodic table and indicate the labels for each of the four blocks. Do not attempt to include symbols for actual elements into the table apart from H and He which should be indicated. 1d. State one possible advantage compared with the conventional periodic table, other than its having a regular or possibly more pleasing shape. (2) e. State one possible disadvantage
Explanation / Answer
1a. In spite of the corrections made by the redetermination of atomic weights, some of the elements in the Mendeleyev tables of 1871 were still required by their properties to be put in positions somewhat out of the order of atomic weights(instead of atomic number). In the pairs argon , potassium, cobalt and nickel the first element had the greater atomic weight but the earlier position in the periodic system. The solution to this difficulty was found only when the structure of the atom was better understood. Hence,it was wrong ordering these elements according to the atomic weight.
1b. This occurred when the periodic table was made according to the increasing atomic weight. Even though the second element had fewer protons the neutrons made the atomic weight higher. This caused confusion because both elements were placed in columns that did not share their chemical or physical properties. This is why the periodic table is now lined up by atomic number(Z) and not the atomic weight.
1d. Some of the advantages are
*. The systematic grouping of elements into four blocks; s, p, d and f has made the study of the elements more simple.
*. The position of some elements which were misfit on the basis of atomic mass is now justified on the basis of atomic number. For example, argon precedes potassium because argon has atomic number 18 and potassium has 19.
*. The lanthanoids and actinoids which have properties different from other groups are placed separately at the bottom of the periodic table.
*. Since this classification is based on the atomic number and not on the atomic mass, the position of placing isotopes at one place is fully justified.
1e. Disadvantages are
a.The position of hydrogen is not settled. It resembles with alkali metals as well as halogens. However, it has been placed with alkali metals.
Lanthanoids and actinoids have not been accommodated in the main body of the periodic table.