Question

What is the atomic mass of Barium?

Answer 1

Hint :Barium is a highly reactive member of the alkaline earth metal family which undergoes a different chemical reaction.it shows a very high melting point and boiling point range. It presents in a solid state at normal room temperature.

Complete Step By Step Answer:
Atomic mass of any element is calculated with reference to carbon isotope $\left(C^{12}\right)$.
Atomic mass is defined chemically as the average relative mass of an atom of barium as compared to the mass of an atom of carbon $\left(C^{12}\right)$ which is considered as $12$.
Atomic mass of barium is calculated with the help of its isotopes present naturally and their respective abundance.
 $M={\displaystyle \frac{m_1{c}_1\times m_2{c}_2\times m_n{c}_n}{c_1+c_2+c_3}}$
where $M$ is the average atomic mass of the element
 $\left(m\right)$ is atomic mass of particular isotope
 $\left(c\right)$ is relative abundance of particular isotope
Different isotope of barium present in nature are-

ISOTOPE	RELATIVE ABUNDANCE
$B{a}^{130}$	$0.0011$
$B{a}^{132}$	$0.0010$
$B{a}^{134}$	$0.0242$
$B{a}^{135}$	$0.0659$
$B{a}^{136}$	$0.0785$
$B{a}^{137}$	$0.1123$
$B{a}^{138}$	$0.7170$

Substituting the values from table into the formula of average atomic mass of barium we get,
$M={\displaystyle \frac{m_1{c}_1\times m_2{c}_2\times m_n{c}_n}{c_1+c_2+c_3}}$
After calculation we get,
$M={\displaystyle \frac{130\times 0.0011+132\times 0.0010+134\times 0.0242+135\times 0.0659+136\times 0.0785+137\times 0.1123+138\times 0.7170}{100}}$
Atomic mass of barium is 137.327 amu.
mass of barium is accurately calculated using the instrument spectrophotometer which is used extensively in laboratories to determine mass of element.
Atomic mass of barium is also expressed in terms of gram atomic mass which expressed as,
Atomic mass of barium $=137.327amu$
Gram atomic mass of barium $=137.327g$ .

Note :
Barium comes under the alkaline earth metal family with atomic number $56$ . Electronic configuration of barium is $\left[Xe\right]6s^2$ . Barium gives grassy green to green colour flames when heated over flame which further help in qualitative analysis of elements.