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Question
A nucleus of stable phosphorus has 15 protons and 16 neutrons.
a) What is its atomic number and mass number?
b) The nucleus of radio phosphorus has one neutron more than the stable nucleus. What will be its atomic number and mass number?
c) What will be the atomic number and mass number of new nucleus formed by the decay of a β-particle by the radio phosphorus in part (b)?
a) What is its atomic number and mass number?
b) The nucleus of radio phosphorus has one neutron more than the stable nucleus. What will be its atomic number and mass number?
c) What will be the atomic number and mass number of new nucleus formed by the decay of a β-particle by the radio phosphorus in part (b)?
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Solution
a) The total number of protons and neutrons in the nucleus is called the mass number (symbol, A).
The total number of protons in the nucleus of an atom is called the atomic number (symbol, Z).
Atomic number, Z = Number of protons = 15
Mass number, A = Number of neutrons + Number of protons
A = 16 + 15 = 31
b) Given, radio phosphorus has 1 neutron higher than that of stable (or parent) nucleus. Thus, radio phosphorus has 15 protons and 17 neutrons.
Atomic number, Z = Number of protons = 15
Mass number, A = Number of neutrons + Number of protons
A = 15 + 17 = 32
c) In β decay one neutron decays to one proton with the emission of a beta particle. Hence, in the daughter nucleus the number of protons increases by one and the number of neutrons decreases by one.
Number of neutrons = 17 - 1 = 16
Atomic number, Z = Number of protons = 15 + 1 = 16
Mass number, A = Number of neutrons + Number of protons
A = 16 + 16 = 32
3215P→3216S +0−1β
Here the phosphorus atom changed into sulphur nuclei.
The total number of protons in the nucleus of an atom is called the atomic number (symbol, Z).
Atomic number, Z = Number of protons = 15
Mass number, A = Number of neutrons + Number of protons
A = 16 + 15 = 31
b) Given, radio phosphorus has 1 neutron higher than that of stable (or parent) nucleus. Thus, radio phosphorus has 15 protons and 17 neutrons.
Atomic number, Z = Number of protons = 15
Mass number, A = Number of neutrons + Number of protons
A = 15 + 17 = 32
c) In β decay one neutron decays to one proton with the emission of a beta particle. Hence, in the daughter nucleus the number of protons increases by one and the number of neutrons decreases by one.
Number of neutrons = 17 - 1 = 16
Atomic number, Z = Number of protons = 15 + 1 = 16
Mass number, A = Number of neutrons + Number of protons
A = 16 + 16 = 32
3215P→3216S +0−1β
Here the phosphorus atom changed into sulphur nuclei.
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