Isotopes 2016 filled in.notebook November 21, 2016

Isotopes and Average Atomic MassAim: -How do isotopes of the same element differ from each other with regards to atomic structure?-How can we calculate average atomic mass?

http://www.brainpop.com/science/matterandchemistry/isotopes/

Isotope 1 Isotope 2

Properties of Isotope 1Atomic #: 6Mass: 12 amuColor: Blackish-grayLuster: None/DullHardness: BrittleRadioactivity: Stable. Geiger counter does not detect radiation.

1. What element is Isotope 1? What element is Isotope 2?

2. How did you identify the above elements?

3. What is different for the two isotopes?

DO NOW

Properties of Isotope 2Atomic #: 6Mass: 14 amuColor: Blackish-grayLuster: None/DullHardness: BrittleRadioactivity: Unstable. Geiger counter detects radiation.

Carbon and Carbon

The atomic number is 6

The mass a radioactivity. The mass is different due to a different number of neutrons

Isotopes 2016 filled in.notebook November 21, 2016

Isotope: two of the same element (same atomic number) with a different mass number, due to a different number of neutrons.

Isotopes must always have the SAME atomic number (# of protons)

12 14

Isotopes are represented with different notations for the mass number:

C-14

14C

Carbon – 14

Isotope Notations

The 14 in each notation represents the mass number of that isotope.

Isotopes 2016 filled in.notebook November 21, 2016

Determine the number of protons, neutrons and electrons in each of the following isotopes:

16O Oxygen-18 O-15

REMEMBER! Isotopes can have a different mass number from the mass of the periodic table.

mass= 16 amu mass= 18 amu mass= 15 amuprotons= 8 protons= 8 protons= 8neutrons= 8 neutrons= 10 neutrons= 7electrons= 8 electrons= 8 electrons=8

Why is the atomic mass not a whole number?

Isotopes 2016 filled in.notebook November 21, 2016

Why is the atomic mass not a whole number?Every element has different isotopes that occur naturally on Earth. Some isotopes are more abundant than others.

The percent abundance's are shown for each elements isotope and the weighted average will be closer to the MOST ABUNDANT isotope.

Average atomic mass: a weighted average that uses the percent abundance and mass of all naturally occurring isotopes of the element.

Carbon-12 is 98.2% abundant while Carbon-13 is 1.8% abundant. The atomic mass of carbon is 12.0111 amu and is closer to the more abundant isotope, carbon-12.

This is done the same way you would find any weighted average:

Calculating the Atomic Mass

1) Convert given percent abundances to decimals (divide by 100)2) Multiply the mass of each isotope by its decimal abundance.3) Add resulting numbers.

Ex 1) Find the average atomic mass of carbon given the following:

Isotope Mass (amu) Percent AbundanceCarbon-12 12.01 98% Carbon-13 12.99 1.2% Carbon-14 13.84 0.8%

atomic mass= (0.98)(12.01 amu) + (0.012)(12.99 amu) + (0.008)(13.84 amu) = 11.7698 + 0.15588 + 0.11072= 12.0364 amu *closest to 12 because carbon-12 is the most

abundant isotope

Isotopes 2016 filled in.notebook November 21, 2016

Ex 2) Find the average atomic mass of chlorine given the following:

Isotope Mass (amu) Percent Abundance35Cl 34.969 amu 75.53 % 37Cl 36.966 amu 24.47 %

Isotope 1 Isotope 2

Nucleus of Isotope 1 Nucleus of Isotope 2

Summary Questions

Properties of Isotope 1Atomic #: 6Mass: 12 amu

Properties of Isotope 1Atomic #: 6Mass: 14 amu

1.) Explain in terms of subatomic particles, why isotope 1 and isotope 2 have a difference mass number?

2.) Explain in terms of subatomic particles, how the two isotopes represent the same element?