Question

Copper has 29 electrons and 35 neutrons. Find the atomic mass.
(A) 62
(B) 63
(C) 54
(D) 64

Answer 1

Hint: Mass number is also known as atomic weight or nucleon number.
Mass number is the total number of protons and neutrons present in the nucleus.

Step by step answer: Let us discuss how to calculate atomic number and mass number of atoms of elements.
Atomic number is represented by Z and is number of proton or electrons present in nucleus
Mass number is represented by A and is = number of proton$ + $number of neutrons
Since in given problem:
Number of Electron in \[Cu\] is \[ = 29\]
Number of Neutron in \[Cu\] is \[ = 35\]
We know that the number of protons is equal to the number of electrons because the atom of the element is neutral as a whole.
$\therefore$ Number of proton in $Cu = 29$
$\therefore$ Mass number of $Cu = 35 + 29$
$\therefore$ Mass number of $Cu = 64$

Therefore, from the above explanation the correct option is (D) $64.$

Additional Information: Protons, electrons and neutrons are subatomic particles of atoms.
-Protons and neutrons form a part of the nucleus of an atom.
-Since the weight of particles is very small it is represented in\[amu\].
-Electrons are negatively charged particles. They are revolving around the nucleus. Its weight is negligible and taken as zero. Charge on electron is $( - 1)$
-Neutrons are neutral and forms a part of makes they have no charge it weighs about $1amu.$
Therefore, the mass of an atom is mainly due to the mass of protons and the mass of neutrons. These atoms are concentrated in the nucleus.



Note: Protons and neutrons have almost same mass i.e., $1.67 \times {10^{ - 24}}gm.$
Electrons weigh only $9.11 \times {10^{ - 28}}gm.$They do not contribute to the element's atomic mass.
Isotopes have the same atomic number and different mass number.
Different mass numbers due to the different number of neutrons present in the nucleus.
Example:
Isotopes of chlorine.
${17^{C{l^{35}}}} \to 18$neutrons
${17^{C{L^{37}}}} \to 20$neutrons