Isotopes
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Isotopes. Of the Atom. Isotopes At the conclusion of our time together, you should be able to:. Define an isotope Determine the number of protons, neutrons and electrons for an isotope Define average atomic mass Determine the average atomic mass for an element given the isotopes.

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Isotopes

Isotopes

Of the Atom


Isotopes at the conclusion of our time together you should be able to

IsotopesAt the conclusion of our time together, you should be able to:

  • Define an isotope

  • Determine the number of protons, neutrons and electrons for an isotope

  • Define average atomic mass

  • Determine the average atomic mass for an element given the isotopes


Isotopes1

Isotopes

Atoms with the same number of protons & electrons but a different number of neutrons.

They are the same element, are chemically identical and undergo the exact same chemical reactions

They have different masses (different mass number).

All isotopes are used to calculate average atomic mass (this mass is usually a decimal).

Most elements consist of a mixture of isotopes.


Isotopes2

11B

10B

Isotopes

  • Atoms of the same element but different mass number.

  • Boron-10 (10B) has 5 p and 5 n

  • Boron-11 (11B) has 5 p and 6 n


Two isotopes of sodium

Two Isotopes of Sodium.


Isotopes

Isotopes

  • According to international convention all atomic weights derive from the isotope carbon-12.

  • One atomic mass unit (amu) is exactly 1/12 of the mass of a C-12 atom.

  • The natural atomic mass of an element is the average of the atomic masses of the isotopes:


15 helpful hints on the lab report from mr t s vast lab experience

15 Helpful Hints On The Lab Report from Mr. T’s Vast Lab Experience!!!

Hint #12. The probability of a given event occurring is inversely proportional to its desirability.


Schematic diagram of a mass spectrometer

Schematic Diagram of a Mass Spectrometer


Neon gas

Neon Gas


Mass spectrum of natural copper

Mass Spectrum of Natural Copper


Isotopes

Another Interesting Boat Name


Determining average atomic mass

Determining Average Atomic Mass

Because of the existence of isotopes, the mass of a collection of atoms has an average value.

Boron is 20%10B and 80%11B. That is, 11B makes up 80% of the boron in the earth’s crust.

For boron average atomic mass

= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

11B

10B


How to determine average atomic mass

How to Determine Average Atomic Mass

Determine Relative Abundance –

% abundance divided by 100

Determine mass of each isotope and multiply relative abundance by this mass

(keep all digits your calculator gives you)

Determine Average Atomic Mass by adding up all the individual masses, round to “2” decimal places


1 nitrogen example

#1 Nitrogen Example

  • Because of the existence of isotopes, the mass of a collection of atoms has an average value.

  • 14N = 99% abundant and 15N = 1%

  • (0.99 x 14 amu) + (0.01 x 15 amu) =

    Avg. Atomic mass of N = ______________

    Avg. Atomic mass of Sb = ______________

14.01 amu

121.84 amu


Isotopes

Average Atomic Mass

Example Problem:

There are three naturally occurring isotopes of neon: Ne-20, 90.51%, 19.99244 amu;

Ne-21, 0.27%, 20.99395 amu;

Ne-22, 9.22%, 21.99138 amu. Calculate the average atomic mass of neon.

Atomic mass = (0.9051 x 19.99244 amu)

+ (0.0027 x 20.99395 amu) +

(0.0922 x 21.99138 amu)

Atomic mass = 18.10 amu + 0.057 amu

+ 2.03 amu =

20.18 amu


Isotopes average atomic mass

Isotopes & Average Atomic Mass

  • Because of the existence of isotopes, the mass of a collection of atoms has an average value.

  • 6Li = 7.5% abundant and 7Li = 92.5%

    • Avg. Atomic mass of Li = ______________

  • 28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10%

    • Avg. Atomic mass of Si = ______________

6.93 amu

28.11 amu


Isotopes

Wish I’d of Thought of It!!!


Isotopes let s see if you can

IsotopesLet’s see if you can:

  • Define an isotope

  • Determine the number of protons, neutrons and electrons for an isotope

  • Define average atomic mass

  • Determine the average atomic mass for an element given the isotopes


Let s see what you learned

Let’s see what you learned…

Get your clickers ready!!!


Isotopes3

Isotopes?

Which of the following represent isotopes of the same element?

Which element?

234 X234 X235 X238 X

92939292

Uranium


Self check

Self-Check

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C14C

6 6 6

#p+ _______ _______ _______

#no _______ _______ _______

#e- _______ _______ _______

6

6

6

7

8

6

6

6

6


Self check continued

Self-Check Continued

An atom has 14 protons and 20 neutrons.

A.Its atomic number is

a) 14b) 6c) 34d) 20

B. Its mass number is

a) 14b)20c) 16d) 34

C. The element is

a) Sib) Cac) Sed) C

D.Another isotope of this element is

a) 34X b) 34X c) 36X

16 14 14


Average atomic mass practice

Average Atomic Mass Practice

Silicon has 3 isotopes with the following % abundances.

Si-28, 92.23%

Si-29, 4.67%

Si-30, 3.10%

Calculate silicon’s average atomic mass.


Answer

Answer

(28 amu x 0.9223) + (29 amu x 0.0467) + (30 amu x .031)

= 28.11 amu


Isotopes

Element “X” has three naturally occurring isotopes. 78.70% of “X” atoms exist as X-24, 10.03% exist as X-25 and 11.17% exist as X-26. What is the average atomic mass of element “X” in amu’s?

  • 24.00

  • 24.29

  • 24.30

  • 24.99

  • 25.00


Candium lab

Candium Lab


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