Atomic%20Structure

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Atomic Structure
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What Is an Atom?

• Atom the smallest unit of matter that retains
  the identity of the substance.

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Atomic Structure

• Atoms have two regions
• Nucleus the center of the atom that contains
  protons and neutrons which is most of the mass of
  the atom.
• Electron Cloud surrounds the nucleus and takes
  up most of the space of the atom.

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Inside the Atoms Nucleus

• Protons positively charged subatomic particles.
• Mass of 1 amu

• Neutrons neutrally charged subatomic particles.
• Mass of 1 amu

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Inside the Electron Cloud

• Inside the electron cloud are electrons which are
  subatomic particles with a negative charge and
  relatively no mass. ? Mass of 1/1836 amu

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Subatomic Particles
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Protons

• Atomic Number Number of Protons in an Atom
• Ex Hydrogens atomic number 1
• Hydrogen has one proton
• Ex Carbons atomic number 6
• Carbon has six protons
• The number of protons
• identifies the atom.
• It is the atoms fingerprint.

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Learning Check
State the number of protons for atoms of each
of the following A. Nitrogen 1) 5 protons
2) 7 protons 3) 14 protons B. Sulfur
1) 32 protons 2) 16 protons 3) 6
protons C. Barium 1) 137 protons 2) 81
protons 3) 56 protons
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Solutions
State the number of protons for atoms of each
of the following A. Nitrogen
2) 7 protons B. Sulfur 2) 16
protons C. Barium 3) 56 protons
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Neutrons

• Atomic Mass Number of Protons and Neutrons in
  an Atom
• of Neutrons Atomic Mass - Atomic Number
• Ex Lithiums atomic mass 7
• Lithiums atomic number 3
• Neutrons 7 3 4
• Lithium has 4 neutrons

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Electrons

• Most atoms are neutral--having no overall charge.
• Because the only charged subatomic particles are
  the protons and electrons they must balance each
  other out in an electrically neutral atom.
• Therefore..
• p e-
• in a neutral atom.

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Calculating p, n, and e-

• Beryllium
• Protons
• Neutrons
• Electrons
• Magnesium
• Protons
• Neutrons
• Electrons

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Calculating p, n, and e-

• Beryllium
• Protons 4
• Neutrons (9 4) 5
• Electrons 5
• Magnesium
• Protons 12
• Neutrons (24 12) 12
• Electrons 12

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Subatomic Particle Arrangement
All of the protons and the neutrons
Orbit 3 holds up to 8 e-
Orbit 1 holds up to 2 e-
Orbit 2 holds up to 8 e-
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Carbons Arrangement
Atomic Number 6 Atomic Mass 12
e- 6
6 p and 6 n live in the nucleus
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Atomic Mass
Atomic mass is the weighted average mass of all
the atomic masses of the isotopes of that
atom. Atomic Mass Unit amu Your remember
this. 1 amu the mass of 1 p or 1 n You do
NOT have to remember this. Atomic Mass Unit (amu)
is defined as one-twelfth the mass of a carbon-12
atom.
Atomic Number
11 Na 22.99
Symbol
Atomic Mass
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Why Average Atomic Mass?

• Q How heavy is an oxygen atom?
• A It depends because there are different oxygen
  isotopes.
• We are more concerned with the average atomic
  mass. This is determined based on the abundance
  of each isotope.
• The standard unit for mass grams. But, for
  atomic mass amu (atomic mass unit) is used. It is
  too small to use grams.

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Calculating Average Atomic Mass
Cl-35 is about 75.5 and Cl-37 about 24.5 of
natural chlorine. 35 x 75.5
26.43 100 35.50 37
x 24.5 9.07 100

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Calculating Average Atomic Mass for Carbon
Isotope Symbol Composition of the nucleus in nature
Carbon-12 12C 6 protons 6 neutrons 98.89
Carbon-13 13C 6 protons 7 neutrons 1.11
Carbon-14 14C 6 protons 8 neutrons lt0.01
Atomic mass is the average of all the naturally
occurring isotopes of that element.
Carbon 12.011
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Daltons Atomic Theory

• Daltons first postulate was wrong. Atoms of the
  same element can be different.
• They can have different of neutrons. Thus,
  different mass numbers.
• These are called isotopes.

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Isotopes

• Atoms with the same number of protons, but
  different numbers of neutrons.
• Atoms of the same element (same atomic number)
  with different atomic masses (aka mass numbers).
• Isotopes of Chlorine
• 35Cl 37Cl
• 17 17
• chlorine-35 chlorine-37

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Isotopes
Elements occur in nature as mixtures of isotopes.
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Hydrogen Isotopes
Isotope Protons Electrons Neutrons Nucleus
Hydrogen1 (protium) 1 1 0
Hydrogen-2 (deuterium) 1 1 1
Hydrogen-3 (tritium) 1 1 2
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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
carbon atoms. 12C 13C 14C
6 6 6 p
_______ _______
_______ n _______ _______
_______ e _______
_______ _______
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Solutions
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 13C 14C
6 6 6 p
___6___ ___6___
___6___ n ___6___ ___7___
___8___ e ___6___
___6___ ___6___
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Learning Check
An atom of zinc has an atomic mass of 65 amu.
Find the atomic number then answer the questions.
A. Number of protons in the zinc atom 1)
30 2) 35 3) 65 B. Number of neutrons in the
zinc atom 1) 30 2) 35 3) 65 C.
What is the mass number of a zinc isotope with
37 neutrons? 1) 37 2) 65 3) 67
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Solutions
An atom of zinc has an atomic mass of 65 amu.
Find the atomic number then answer the questions.
A. Number of protons in the zinc atom 1)
30 B. Number of neutrons in the zinc atom
2) 35 C. What is the mass number of a
zinc isotope with 37 neutrons? 3) 67
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Learning Check
Write the atomic symbols for atoms with the
following A. 8 p, 8 n, 8 e- ___________ B.
17 p, 20 n, 17 e- ___________ C. 47 p, 60
n, 47 e- ___________
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Solutions
Write the atomic symbols for atoms with the
following A. 8 p, 8 n, 8 e- ___________ B.
17 p, 20 n, 17 e- ___________ C. 47 p, 60
n, 47 e- ___________
16O 8 p, 8 n, 8 e- 8 17p, 20n,
17e- 37Cl 17 47p, 60 n, 47 e-107Ag
47
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Isotope Nomenclature

• We name the isotope based on its mass number.
• Carbon-12 C-12 12C
• Carbon-14 C-14 14C
• Uranium-235 U-235 235U