Question

The graph illustrates the correlation between the number of protons (x-axis) and the number of neutrons (y-axis) for elements A, B, C, D, and E in the periodic table. These elements are denoted by the letters rather than their conventional symbols.

1. Identify the radioactive radiation emitted when element C decays into element E. Represent this using a nuclear reaction.  (1)
2. What is the special name given to elements D and E?  (1)
3. If element C transforms into element B by emitting a radioactive ray, how will this ray behave in an electric field?  (2)

Answer 1

a. From the graph,

Number of proton in C = 92

Number of neutron in C = 146

Mass number of C = Number of proton in C + Number of neutron in C

= 92 + 146

= 238

Number of proton in E = 93

Number of neutron in E = 145

Mass number of E = Number of proton in E + Number of neutron in E

= 93 + 145

= 238

Since element C has one excess proton and one neutron less than element E, if C decays into E, then its proton number increases by one and its neutron number decreases by one, keeping the mass number the same, which is only true in the case of beta radiation.

Thus, the reaction will be as follows:

\[\ce{^238_92C -> ^238_93E + ^0_-1\beta}\]

b. As points D and E are situated on the same vertical line but on different horizontal lines, it means they have the same number of protons but different numbers of neutrons; i.e., their atomic number is the same but their mass number is different, so they are isotopes of each other.

c. Number of protons in B = 90

Number of neutron in B = 144

Mass number of B = Number of proton in B + Number of neutron in B

= 90 + 144

= 234

As element B has two protons less than element C and has a mass number four less than C, during a decay of C into B two protons and two neutrons are emitted, which is nothing but an alpha particle.

Alpha particles shift towards the negative plate in an electric field.