Warm up
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Warm-Up. Complete the worksheet you received two classes ago regarding subatomic particles & symbols of atoms. If you have already completed that, work on filling out the front side of the “Atomic Structure Vocabulary & Skills” page you got today. Practice.

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Warm up

Warm-Up

Complete the worksheet you received two classes ago regarding subatomic particles & symbols of atoms.

If you have already completed that, work on filling out the front side of the “Atomic Structure Vocabulary & Skills” page you got today.


Practice

Practice

  • How many protons, neutrons, and electrons are in the following ions?

    7Li +1

    40Ca +2

    14N -3

    112Cd +2

    1H +1

    1H -1

3 p+, 4 n0, 2 e-

20 p+, 20 n0, 18 e-

7 p+, 7 n0, 10 e-

48 p+, 64 n0, 46 e-

1 p+, 0 n0, 0 e-

1 p+, 0 n0, 2 e-


Warm up

1

+1

nucleus

1

0

nucleus

outside nucleus

negligible (0)

-1


Looking at the periodic table

17

Cl

35.453

Looking at the Periodic Table

Mass number

Cl

vs.

35

17

Atomic number

symbol

Atomic number

symbol

  • What are the similarities?

  • What are the differences?

(Average) Atomic Mass

Where does the “35.453” come from?


Isotopes

Isotopes

  • Atoms with the same number of protons, but different numbers of neutrons.

  • Atoms with the same atomic number but different mass numbers.

  • Example: isotopes of chlorine

Cl

Cl

vs.

35

17

37

17

18 neutrons

20 neutrons


More on isotopes

More on Isotopes

  • In nature, elements are found as a mixture of isotopes

  • Not all isotopes are equally abundant

Where does the “35.453” come from?


Isotopes atomic mass

Isotopes & Atomic Mass

  • The atomic mass is a weightedaverage of all the atoms of a particular element.

    Weighted average formula: S(% x mass)

    Example:

  • In Ms. Schmoe’s class, tests are worth 50% of the final grade, quizzes are 25%, and homework is 25%.

  • Joe’s grades in those three areas are 92, 100, and 65, respectively. What is Joe’s final grade?


Joe s grade

Joe’s Grade

  • Since each assignment carries a different weight, we must take this into account in our final grade.

(T) 0.50 x92 =46.00

(Q) 0.25 x 100 =25.00

(H) 0.25 x 65 = +16.25

87.25

How can we apply weighted averages to atomic mass?


Average atomic mass

Average Atomic Mass

Where does the “35.453” come from?

  • Apply the same steps to calculate the average atomic mass of chlorine.

  • MASS NUMBER

  • protons + neutrons

  • useful in identifying isotopes

  • refers to one atom

  • WHOLE NUMBER

  • ATOMIC MASS

  • weighted average mass of all the isotopes

  • found on the PToE

  • usually a decimal!

vs.


Isotope vs ion

-

-

0

+

+

0

+

0

-

ATOM

ATOM

-

-

-

-

0

0

+

+

+

+

0

0

+

+

-

0

+

+

+

0

+

-

-

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Isotope vs. Ion

ISOTOPE

ION


Learning check

Learning Check

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

  • Calculate the average atomic mass of carbon, given the relative abundances below (C-14 abundance is negligible).


Learning check answers

Learning Check Answers

  • 12C: 6p, 6n, 6e

  • 13C: 6p, 7n, 6e

  • 14C: 6p, 8n, 6e

  • Atomic mass

    (0.989 x 12.0 amu) = 11.868

    (0.011 x 13.00335 amu) = + 0.01430

    12.011 amu


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