Presentation is loading. Please wait.

Presentation is loading. Please wait.

FINDING THE ATOMIC MASS OF AN ELEMENT weighted average by finding the weighted average of the masses of each of the element’s isotopes.

Similar presentations


Presentation on theme: "FINDING THE ATOMIC MASS OF AN ELEMENT weighted average by finding the weighted average of the masses of each of the element’s isotopes."— Presentation transcript:

1 FINDING THE ATOMIC MASS OF AN ELEMENT weighted average by finding the weighted average of the masses of each of the element’s isotopes.

2 Mass number The mass number of an individual atom is the sum of protons and neutrons in the nucleus. The mass number of an individual atom is the sum of protons and neutrons in the nucleus. Mass number = p + n Mass number apply to individual atoms or to an element with just one isotope in it. Mass number apply to individual atoms or to an element with just one isotope in it. Mass number is always a whole number. Mass number is always a whole number.

3 Elements, as found on earth consist of a mixture of isotopes of that element. Example: Nearly all of the carbon in a sample of pure carbon is carbon-12. However, the sample also has traces of carbon-13 and carbon-14 isotopes.

4 Atomic mass The atomic mass of an element is the WEIGHTED AVERAGE of the mass numbers of all of the isotopes in the sample.

5 atomic mass What is the atomic number of chlorine? What is the atomic mass of chlorine?

6 Mass number ≠ atomic mass = protons + neutrons Mass number = protons + neutrons weighted average Atomic mass = weighted average of the mass numbers of all of the isotopes of an element present in a sample.

7 What is a weighted average?

8 Weighted average A total of 50 students at Carmel HS took the AP exam in U. S. History. Here are the results of the test. What is the weighted average score? Test scoreNumber of students 512 418 314 26 10

9 50 students A total of 50 students at Carmel HS took the AP exam in U. S. History. What is the weighted average score ? Test score Number of students MultiplyProduct 5125 x 12 =60 4184 x 18 =72 3143 x 14 =42 262 x 6 =12 101 x 0 =0 Sum =186 Weighted average score Weighted average score = 186/50 =3.72

10 The Eminemium exercise M & M s

11 Eminemium The element Eminemium has several isotopes Each color represents an isotope of the element. For example red is E-20. Count your M&Ms and figure % abundance of each isotope. The weighted value for each isotope is: mass number x % abundance.

12 The weighted average of the mass numbers of each of the isotopes of eminemium is the sum of the weighted values for each of the isotopes (colors) of eminemium. This weighted average is the atomic mass of that sample of eminemium atoms.

13 Let’s try the exercise.

14 In case you’re curious… The M&M website shows the relative distribution (% abundance) of it products. http://us.mms.com/us/about/products/milkchocolate/

15 Let’s do a calculation for using the real isotopes of the element magnesium.

16 The truth about mass numbers Modern chemical instrumentation enables us to determine the actual masses of each of the isotopes to a tremendous degree of accuracy! Therefore, magnesium-24 has been found to have an actual mass of 23.985 atomic mass units.

17 Calculation of the weighted average of isotopes of magnesium IsotopeActual mass (AMU) Relative abundance (%) Mg-2423.98578.99 Mg-2524.98610.00 Mg-2625.98211.01 100.00%

18 Isotope Atomic mass Relative abundance Weighted value 23.98578.99%18.946 24.98610.00 2.499 25.98211.01 2.861 100.00% 24.306 Sum: 24.306

19 The weighted average of mass number of magnesium isotopes as found in nature is its ATOMIC MASS. Atomic mass of Mg = 24.306


Download ppt "FINDING THE ATOMIC MASS OF AN ELEMENT weighted average by finding the weighted average of the masses of each of the element’s isotopes."

Similar presentations


Ads by Google