Question

Boron has atomic number 5. It comprises two isotopes, one with five neutrons, the other with six. a) Define the term "isotope". b) Calculate the mass numbers of the two isotopes and represent them in the form In naturally occurring boron, 20% of the atoms contain five neutrons and 80% six neutrons. Calculate relative atomic mass of boron. Given the atomic numbers of the following elements, write their simple electronic structures: a) Beryllium (AL No.24) b) Aluminium (At. No. 13) c) Fluorine (At, No. = 9) d) Argon (ALN:18) Sulfur (At. No-16) 12. The folloing figure is the successive lonization energy of some element » 5.5 5.0 4.5 3.5 3.0 2.5 1st 2nd 3rd 4th Sth 6th 7th 8th 9th 10th 11th 12th Electron removed Figure 223 The energy required for the removal of successive electrons Predict which element should be?

Answer 1

10. a) Isotope: it is defined as the atoms having same number of protons but mass numbers are different or isotopes are the atoms with same atomic number but different mass number due to have different number of neutrons.

example: $_{6}^{12}\textrm{C}$ and $_{6}^{13}\textrm{C}$ are isotopes. Both of the atoms have same proton number 6 but different mass number (12 and 13)

b. proton number = 5

neutron number = 5, mass number = 5+ 5 = 10 . so, the atom is $_{5}^{10}\textrm{B}$

another one has neutron number = 6, mass number = 5+6 = 11. so, the atom is $_{5}^{11}\textrm{B}$

c. relative mass = $(_{5}^{10}\textrm{B}*20 + _{5}^{11}\textrm{B}*80)/100$ = $(10*20 + 11*80)/100 = 10.8$

11. a. Be $1s^{2}2s^{2}$

b. Al $1s^{2}2s^{2}2p^{6}3s^{2}3p^{1}$

C. F $1s^{2}2s^{2}2p^{5}$

d. Ar $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}$

e. S   $1s^{2}2s^{2}2p^{6}3s^{2}3p^{4}$

12. It is a digram for elimination of 12 electrons . so it is an atom having 12 electrons. therefore, the atom must have 12 protons. so . it will be magnesium (Mg).