Question

The atomic mass of the lithium-7 atom is 7.016003 amu. The mass of a proton is 1.007277 amu and the mass of a neutron is 1.008665 amu. Moreover, the mass of the electron is 0.000548597 amu. From this information, calculate the mass defect of the lithium-7 atom. [6 points]

Answer 1

Mass defect is the difference between the mass of an atom and the mass of its individual particles. It can be calculated by using the following formula :

∆m = Z(m_p + m_e) + (A -Z)m_n - M_atom

here ∆m is mass defect Z is atomic number , m_p mass of proton , m_e mass of electron , A is atomic mass number , m_n is mass of neutron and M_atom is mass of the atom

(1)

Lithium

Atomic mass of Lithium A = 7.016003 amu

number of protons = 3

number of neutrons = 7-3

=4

mass defect = Z(m_p + m_e) + (A -Z)m_n - M_atom

= [3(1.007826 amu) + (7-3)1.008665 amu] - 7.016003 amu

mass defect  ∆m   = 0.0421335 amu

therefore mass defect for lithium = 0.0421335 amu

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