The answer is 64.907 amu.

The atomic mass of an element is the average of the atomic masses of its isotopes. The relative abundance of isotopes must be taken into consideration, therefore:
atomic mass of copper = atomic mass of isotope 1 * abundance 1 + atomic mass of isotope 2 * abundance 2

We know:
atomic mass of copper = 63.546 amu
The atomic mass of isotope 1 is: 62.939 amu
The abundance of isotope 1 is: 69.17% = 0.6917
The atomic mass of isotope 1 is: x
The abundance of isotope 2: 100% - 69.17% = 30.83% = 0.3083

Thus:
63.546 amu = 62.939 amu * 0.6917 + x * 0.3083
63.546 amu = 43.535 amu + 0.3083x
⇒ 63.546 amu - 43.535 amu = 0.3083x
⇒ 20.011 amu = 0.3083x
⇒ x = 20.011 amu ÷ 0.3083 = 64.907 amu

7 0

4 years ago

How many protons electrons and neutrons respectively does 29 CS have

irakobra [83]

$55 \; \text{e}^{-}$ , $55 \; \text{p}^{+}$ , and $74 \; \text{n}^{0}$ - in case cesium-129 is what you were referring to.

Cesium has atomic number $55$ as seen on a modern periodic table. A cesium atom nucleus would thus contain an equal number of protons; in addition to that, a neutral atom of cesium would contain the same number of electrons in its electron cloud.

For a particular isotope,

$\text{Mass number} = \text{Number of protons per nuclei} + \text{Number of Neutrons per nuclei}$ .

This isotope of cesium has a mass number of $129$ and contains $55$ protons in each atomic nucleus. One cesium nuclei would therefore contain $129 - 55 = 74$ neutrons.

8 0

3 years ago