Nitrogen has two isotopes. one has an atomic mass of 14.003
amu and a relative abundance of 99.63% while the other
isotope has an atomic mass of 15.000 amu and a relative
abundance of 0.37%. what is the average atomic mass for
nitrogen?
a
14.456 amu
b
14.778 amu
c 14.993 amu
d 14.007 amu

d= 14.007 amu

Explanation:

Abundance of N¹⁴ = 99.63%

Abundance of N¹⁵ = 0.37%

Atomic mass of N¹⁴ = 14.003 amu

Atomic mass of N¹⁵ = 15.000 amu

Average atomic mass = ?

Solution:

Average atomic mass = (abundance of 1st isotope × its atomic mass) +(abundance of 2nd isotope × its atomic mass)  / 100

Average atomic mass = (14.003 × 99.63)+(15.000× 0.37) /100

Average atomic mass =  1395.12 + 5.55 / 100

Average atomic mass  = 1400.67/ 100

Average atomic mass = 14.007 amu.

"among the transition metal elements, manganese and zinc have a slight lowering of electronegativities. the reason behind this is that the nuclear charges of these elements are slightly weaker than the other transition metal elements due to the way their valence electrons are filled up. both manganese and zinc have their valence electrons filled up to the 4th shell with 1 pair of electrons (4s2) completely occupying it. although the electrons in the 3rd shell (3d) are yet to be paired since the outer most shell is filled up, the ability of the nucleus to attract electrons is lessened. hence,   the electronegativity (or the ability to attract electrons) is lessened."