The element lithium has two stable isotopes, li-6 and li-7. how do the atomic structures of these two isotopes compare? a) both have 3 protons and 3 electrons, but li-7 has 4 neutrons. b) both have 3 protons and 4 neutrons, but li-7 has 4 electrons. c) li-6 has 3 protons and 3 electrons; li-7 has 3 protons and 4 electrons. d) li-6 has 3 protons, 3 neutrons, 6 electrons, while li-7 has 3 protons, 3 neutrons, and 7 electrons.

Lithium is the third element in the periodic table and has an atomic number of equal to 3. The atomic number represents the number of proton of the atom. 

The number following the chemical symbol is equal to the mass number which the sum of the number of protons and neutrons. Hence, calculating the number of neutrons for each isotope:

(1)   Li-6:  number of neutrons = 6 - 3 = 3
(2)  Li - 7: number of neutrons = 6 - 4 = 2

If the atom is neutral the number of electron is equal to number of protons. Hence, the answer to this item is,

  (1) Li-6   : number of protons = 3, number of neutrons =3, and number of electron = 3

(2) Li-7    : number of protons = 3, number of neutrons = 7, and number of electrons = 3

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