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Atomic Structure. What Is An Atom?. the smallest particle of an element that retains the chemical properties of that element Can be subdivided into electrons (e - ), protons (p + ) and neutrons (n 0 ). Diagram Of An Atom. Important Info About Subatomic Particles.

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What is an atom
What Is An Atom?

  • the smallest particle of an element that retains the chemical properties of that element

  • Can be subdivided into electrons (e-), protons (p+) and neutrons (n0)



Important info about subatomic particles
Important Info About Subatomic Particles

1 amu = (1/12)(mass of C-12 isotope in kg)

1 amu = 1.660540 x 10-27 kg

Amu = atomic mass units


Atomic number z
Atomic Number (Z)

  • Tells us the number of protons in the nucleus of an atom

Z


Isotopes
Isotopes

  • Some atoms of the same element will have different masses.

  • These atoms are called isotopes because they have the same number of protons, but differ in the number of neutrons.

  • Isotopes of the same element have different mass numbers.

  • Mass number (A) is the total number of protons and neutrons in the nucleus of an isotope



Hyphen notation of isotopes
Hyphen Notation of Isotopes

  • Isotopes can also be denoted through hyphen notation

  • The element symbol will be listed, following a hyphen, and then a mass number (p+ + n0)

  • Ex. Hydrogen has 3 isotopes (H-1, H-2, H-3)


Hydrogen isotopes
Hydrogen Isotopes

AKA “Protium”

99.985% Abundant

H-1

.015% Abundant

H-2

Radioactive, Prepared Artifically

H-3


Sample problems
Sample Problems

  • How many protons, electrons, and neutrons are there in a Cl-37 atom?

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

-1


Atomic mass
Atomic Mass

  • What is the atomic mass listed on the periodic table under each element really measuring?

  • This mass is a weighted average of all of the naturally occurring isotopes of an element

  • This mass is a relative average (compared to the C-12 isotope) in atomic mass units (amu)


How to find the atomic mass of hydrogen
How To Find The Atomic Mass of Hydrogen

H-1 is 99.985% abundant with an atomic mass of 1.007825 amu

H-2 is .015% abundant with an atomic mass of 2.016490 amu

H-3 is not counted because of the fact that it is not naturally occurring

To find the weighted average:

(% abundance/100)(relative atomic mass of isotope 1) +

(% abundance/100)(relative atomic mass of isotope 2) +

(% abundance/100)(relative atomic mass of isotope 3)…

*Mass # may be substituted for the relative atomic mass when given

(99.985%/100)(1.007825 amu) + (.015%/100)(2.016940 amu)

= 1.0079 amu


Things to remember
Things To Remember…

  • If you change the number of protons, you change the type of atom itself.

  • If you change the number of electrons, you change the atom to an ion (charged particle).

  • If you change the number of neutrons, you change the isotope of that element.


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