Atomic Calculations and Mass Spectrometry

Quantum Orbital Video

Atomic Mass – Atomic Number = # Neutrons

(p + n) - (p) = (n)

Complete the following chart:

protons electrons neutrons

H

Zr

Ca2+

P3-

Al3+

Cl-

1 1 040 40 51

20 18 2015 18 16

13 10 14

17 18 19

Isotopes- same atomic number but different mass

Not all atoms of the same element are identical.

For example, there are 3 types of hydrogen atoms.

1H 2H 3H

Mass Spectrometers   Are used to determine the abundance and mass of the isotopes of elements

Mass Spectrometers

A device known as a mass spectrometer can be used to determine the relative abundance and the mass of the isotopes of elements.  In the graph the isotopes of a sample of the element zirconium can be seen in their relative abundances.

The data can be summarized as follows:      Isotope            Mass` Abundance      90Zr 90.00 amu              51.5 %       91Zr 91.00 amu               11.2 %       92Zr 92.00 amu               17.1 %       94Zr 94.00 amu               17.4 %      96Zr 96.00 amu              2.80 %       atomic mass of isotope                  100 %

Calculate the weighted average mass of zirconium using the data above.   Change each percent to a decimal by dividing by 100.Multiply by the mass.Add it all together.

+ 0.0280(96.00)+ 0.174(94.00)+ 0.171(92.00)+ 0.112(91.00)0.515(90.00)

= 91.3 amu 3 sig figs!

Look up the mass on the periodic chart.

They are the same with uncertainty

= 91.2 amuThe unit amu describes how many times heavier than the mass of H

Calculate the average atomic mass for Germanium

20.52 %69.92428 amu

27.43 %71.92174 amu

7.76 %72.9234 amu

36.54 %73.92115 amu

7.76 %75.9214 amu

(0.2052)(69.92428) + (0.2743)(71.92174) + (0.0776)(72.9234) + (0.3654)(73.92115) + (0.0776)(75.9214) =

= 72.6 amu

Periodic Table = 72.6 amu

Quantum orbitals