Stars: Element Factories

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Stars Element Factories

• Review of last class
• Dimitri Mendeleev and the
• Periodic Table
• What is an isotope?
• Internal structure of the Sun
• Stars and nuclear fusion

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Whats a Mole???
Mole (abbr. mol) An amount of an element (or
compound) whose mass, expressed in grams, is
numerically equal to its atomic (or molecular)
weight.
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Avogadros Number

• Avogadros number the number of atoms in 1 mole
• 6.022 ? 1023 mol-1

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Dimitri Mendeleev

• At 33, Russian chemist Dimitri Mendeleev was
  appointed as chair of chemistry at the University
  of St. Petersburg.
• In 1871 he published a periodic table of the
  elements and predicted the properties of 3 new
  elements (Gallium, Scandium and Germanium,
  discovered in 1875, 1879 and 1886)

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Mendeleevs Periodic Law

• The properties of elements are periodic
  functions of their atomic weight

Cs
Rb
K
Julius Meyer, 1870
Na
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Mendeleevs Periodic Law

• The periodicity led him to organize the elements
  into the PERIODIC TABLE OF ELEMENTS

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Sample calculation

• Atomic weight of copper (Cu) 63.55 g
• A 63.55 g sample of Cu ( 1 mole) contains 6.022
  ? 1023 atoms.
• A penny weighing 1 g contains 6.022 ? 1023
  ?63.55 9.48 ? 1021 atoms (to 3 significant
  digits)

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Atomic isotopes

• Mass number (A) number of protons number of
  neutrons in an atom
• A is often indicated in the top left corner of
  the element symbol

16O, 18O
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Whats an Isotope???

• Definition An Isotope is one of two or more
  atoms having the same atomic number but different
  mass numbers.

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Molecules

• Definition Molecules are two or more atoms
  joined together by chemical bonds.
• E.g., H2O

• The molecular weight is the sum of the atomic
  weights.
• ? one mole of water weighs 18.02 g.

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Composition of the universe
Hydrogen (92)
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How are the elements created?
The Sun
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The suns size in perspective
To scale
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Interior of the Sun

• The sun has multiple layers (like an onion)
• The suns energy source is generated by H fusion
  at the core
• Heat escapes the core by radiation
• In the outer part of the sun, heat is
  transferred by convection

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Solar Data
Compared to energy consumption of U.S.A.
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Nuclear fusion reactions

• Definition Nuclear fusion is the process of
  combining two (or more) atomic nuclei to create a
  new element.
• Requires extremely high temperature and pressure
• Energy release E mc2

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Hydrogen fusion the suns energy source (at the
present)

• All naturally occurring elements are created by
  fusion in the interiors of stars
• 4 H nuclei are required to make 1 He nucleus
• Net mass reduction 0.7
• H -gt He is a 3-step process

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Evolution of a 15 solar-mass star
Source In Quest of the Universe, Kuhn, 1998