Calculate the number of neutrons in the following elements: (i) H 1 3 (ii) Cl 17 37 (iii) Ar 20 40 (iv) U 92 235

H 1 3 in this, numeral 1 indicates the atomic number and 3 indicates the mass number of hydrogen. The atomic number is the total number of protons present in the atom and the sum of the numbers of protons and neutrons in an atom is called the mass number. We know that, Mass number = Number of protons + Number of neutrons The number of neutrons = Mass number - Number of protons . Therefore , number of neutrons = 3 - 1 = 2 . Cl 17 37 in this, numeral 17 indicates the atomic number and 37 indicates the mass number of chlorine. The atomic number is the total number of protons present in the atom and the sum of the numbers of protons and neutrons in an atom is called the mass number. We know that, Mass number = Number of protons + Number of neutrons The number of neutrons = Mass number - Number of protons . Therefore , number of neutrons = 37 - 17 = 20 . Ar 20 40 in this, numeral 20 indicates the atomic number and 40 indicates the mass number of argon. The atomic number is the total number of protons present in the atom and the sum of the numbers of protons and neutrons in an atom is called the mass number. We know that, Mass number = Number of protons + Number of neutrons The number of neutrons = Mass number - Number of protons . Therefore , number of neutrons = 40 - 20 = 20 . U 92 235 in this, numeral 92 indicates the atomic number and 235 indicates the mass number of uranium. The atomic number is the total number of protons present in the atom and the sum of the numbers of protons and neutrons in an atom is called the mass number. We know that, Mass number = Number of protons + Number of neutrons The number of neutrons = Mass number - Number of protons . Therefore , number of neutrons = 235 - 92 = 143 .

Write the electronic configuration of the following elements: (i) Cl 17 35 (ii) C 6 12 (iii) K 19 39 (iv) P 15 31

The maximum number of electrons that could be present in a shell is given by the rule 2 n 2 , where n is the shell number. That is the first shell K shell can accommodate a maximum of 2 electrons, second shell L can accommodate a maximum of 8 electrons, and the M shell can accommodate a maximum of 18 electrons. The atomic number of chlorine is 17, therefore the electronic configuration of Cl 17 35 = 2, 8, 7 The atomic number of carbon is 6, therefore the electronic configuration of C 6 12 = 2, 4 The atomic number of potassium is 19, therefore the electronic configuration of K 19 39 = 2, 8, 9 The atomic number of phosphorous is 15, therefore the electronic configuration of P 15 31 = 2, 8, 5