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Atomic Structure: Atomic Number, Mass Number, Isotopes, and Average Atomic Mass, Study notes of Chemistry

An overview of atomic structure, focusing on atomic number, mass number, isotopes, and average atomic mass. It includes examples of determining the number of protons, neutrons, and electrons in atoms of different elements, as well as understanding isotopes and their significance in atomic mass determination.

What you will learn

  • How do isotopes affect the average atomic mass of an element?
  • What is the atomic number and how is it determined?
  • What is the difference between atomic mass and average atomic mass?

Typology: Study notes

2021/2022

Uploaded on 09/12/2022

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NOTES 4.3: Atomic Number, Mass Number, Isotopes and Atomic Mass
Summary of atomic structure (sketch diagram):
ATOMIC NUMBER:
● Designates the in a nucleus of an atom
● Each element has a (the same
atomic # for ALL atoms of the same element)
● The number of electrons
MASS NUMBER:
● Designates the
● Number of neutrons =
● Atoms of the same element can have
Periodic Table Symbol Key:
Determining # p+, n, and e- from chemical symbols:
Example 1:
# protons =
# electrons =
# neutrons = =
Example 2:
# protons =
# electrons =
# neutrons = =
6
C
Carbon
12.011
_____________ (Z)
_____________
_____________
_____________ (A)
# of protons = Z
# of electrons = (in a neutral atom)
# of neutrons =
14
C
6
15
N
7
Mass #
Atomic #
pf2

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NOTES – 4 .3: Atomic Number, Mass Number, Isotopes and Atomic Mass

Summary of atomic structure (sketch diagram): ATOMIC NUMBER: ● Designates the in a nucleus of an atom ● Each element has a (the same atomic # for ALL atoms of the same element) ● The number of electrons MASS NUMBER: ● Designates the ● Number of neutrons = ● Atoms of the same element can have Periodic Table Symbol Key: Determining # p+, n, and e- from chemical symbols: ● Example 1:

protons =

electrons =

neutrons = =

● Example 2:

protons =

electrons =

neutrons = =

C

Carbon

_____________ (Z)

_____________

_____________

_____________ (A)

of protons = Z

of electrons = (in a neutral atom)

of neutrons =

14

C

N

Mass # Atomic #

ISOTOPES:

● Atoms with the , but. ● Isotopes of an element have the , but. ● Nuclear Symbol or isotopic symbol – shows number of protons, neutrons and electrons in an atom **ISOTOPE CHART: Element Isotope symbol

protons # electrons # neutrons**

Boron- 10 Boron- 11 Chlorine- 35 Chlorine 37 AVERAGE ATOMIC MASS (= Atomic Weight) ● the ( ) in a naturally occurring sample of an element ● masses are based off of the atomic mass unit (amu) defined as one twelfth the mass of a carbon- 12 atom ● Average Atomic Mass Example ● In nature carbon is composed of 98.890% 12 C atoms and 1.1100% 13 C atoms. 12 C has a mass of 12.000 amu and 13 C has a mass of 13.0034 amu. What is the average atomic mass of carbon? Example : There are 3 isotopes of magnesium that occur in nature. Their abundances and masses are listed below: Isotope % Abundance Mass (amu) What is the atomic weight of magnesium?