2. Nucleosynthesis and the origin of the chemical elements
In the beginning….
The Big Bang “quark soup” nuclei of H and He
(all in ~13.8 s)
Today’s topic:
Nucleosynthesis and the origin of the chemical elements

3. The origin of the chemical elements
Nucleosynthesis —
The origin of the chemical elements
Proton-proton chain or
Hydrogen “burning”
CNO cycle

4. Standard notation 4 He 2

5. Mass number 4 He
Element symbol 2
Atomic number

6. He 4 2 Mass number (# of protons and neutrons) Atomic number

7. Atomic weight is the sum of the masses of all natural isotopes
of that element weighted based on their abundance
The atomic weight
you see on the
periodic table

8. O 16 8 Mass number (# of protons and neutrons) The most common
isotope of oxygen is
oxygen-16 16 8
Atomic number
(# of protons)

9. O 18 8 Isotopes have a Mass number different number of
neutrons so their
mass number will be
different, but the
atomic number of an
element is always the
same
Mass number
(# of protons
and neutrons) 18 8
Atomic number
(# of protons)

11. The origin of the chemical elements
Nucleosynthesis —
The origin of the chemical elements
Proton-proton chain or
Hydrogen “burning”
CNO cycle

12. The triple-alpha process
Helium burning —
The triple-alpha process
Key to synthesis of all
elements beyond He
Nuclei of higher atomic number than C
are produced by fusing alpha particles (He)
…but the heaviest atom produced this way is Nickel-56

13. Neutron capture This process is responsible for elements with
atomic number > 26 (Fe)

14. (electron) or (positron) b_ + b
(electron) or (positron) b
S-process
(Neutron-capture)
Beta decay

15. Stars’ nuclear fires Diameter of the star expands while the
core contracts leading
to “giant” stars

16. Blue giants Red giants Hydrogen burning White dwarfs Red dwarfs
Betelgeuse and Rigel
Red
giants
The Sun
in 5 Ga
Hydrogen burning
White
dwarfs
Red
dwarfs
most
common

17. When a mid- to heavy-weight star dies, a supernova explosion ejects
Blue
giants
Betelgeuse and Rigel
When a mid- to
heavy-weight star
dies, a supernova
explosion ejects
the outer layers of
the star (and the
elements therein)
into the universe
creating the raw
material for planets
Red
giants
The Sun
in 5 Ga
Hydrogen burning
White
dwarfs
Planets form by
gravitational
collapse and/or
accretion
Red
dwarfs
most
common

18. Abundances of elements
in the solar system
• H and He most abundant
(90-95% H, 5-10% He)
• Abundances of first 50
elements decreases
exponentially
• Even atomic numbers
are more abundant

19. Most abundant

20. The abundance of the elements is related to their nuclear properties
Mass number
# protons
# neutrons
The most
“even”
isotopes are
more
abundant
The abundance of the elements is related to their nuclear properties
rather than their chemical properties…

22. Abundances of elements
in the solar system
• Elements with Z ≥ 83
have no stable isotopes
but occur naturally
because they are
daughters of long-lived
radio-isotopes of
U and Th

23. No stable isotopes

24. 1s
2s, 2p
3s, 3p
4s, 3d, 4p
5s, 4d, 5p
6s, 4f, 5d, 6p
7s, 5f, 6d, 7p
etc….
Periods are numbered based
on the first quantum number
of the orbitals that are being
filled with increasing atomic
number

25. Electron clouds or
orbitals

27. 1s
2s, 2p
3s, 3p
4s, 3d, 4p
5s, 4d, 5p
6s, 4f, 5d, 6p
7s, 5f, 6d, 7p