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Chapter 3
Atoms
Atoms and Elements;
Isotopes and Ions;
Minerals and Rocks
A Review of Chemistry:
What geochemistry tells us
Clicker 1
Chemistry Background?
A.
B.
C.
D.
No HS or College Chemistry
High School Chemistry
1 semester College Chemistry
2+ semesters College Chemistry
Atoms
• Atoms are composed of Protons,
Neutrons and Electrons
– A proton has an electric charge of +1 and
a rest mass of 1.67 x 10-24 gm.
– A neutron has a charge of 0 and a rest
mass of 1.67 x 10-24 gm. (about the same
as a proton).
– An electron has a charge of -1 and a rest
mass of 9.11 x 10-28 gm. (much, much
less than a proton). [0.055%]
• The electron mass is negligible
relative to protons and neutrons.
Atoms:
Learning Goals
• Atoms are composed of Protons,
Neutrons and Electrons.
• The protons and neutrons are bound
into the nucleus and contain all the
mass.
• The electrons orbit the nucleus.
• The electrons interact with
neighboring atoms and determine the
chemistry.
Atoms and Elements
• The chemical properties of an element
depend on the number and configuration
of electrons (i.e. the net electric charge).
• The number of protons in the nucleus is
known as the atomic number of the
element.
• Atomic numbers for natural
elements range from 1 (hydrogen) to 92
for uranium.
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Atomic Number
Chemistry
• The number of protons in the nucleus is the
atomic number.
• A neutral atom will have the same number
of electrons as protons
• The elements are arranged by chemistry
into the Periodic Table. (by atomic number)
• The chemical reactions an element
is capable of is determined by the
electron configuration.
• Neutral atoms with complete outer
shells don’t enter chemical reactions
(Inert). (He, Ne, Ar, Kr, Xe)
• The number of lost electrons (net
electric charge) is the valence.
Ions and Valence
• Atoms with 1,2, 3, or 4 outer electrons may
lose them and form positive ions (cations).
• Atoms with 6 or 7 outer electrons may gain
electrons to form negative ions (anions).
• The number of lost electrons is the valence
– The valence is thus the net electric charge.
• The elements are arranged by chemistry
into the Periodic Table.
Ions and Valence
Charge Denoted by Superscript
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Cations
H+1
Na+1
Mg+2
Al+3
Si+4
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Anions
F-1
O-2
S-2
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Chemical Compounds
Chemical Compounds
• Elements occur in integer ratios
• Elements occur in integer ratios
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to maintain charge balance
H2
hydrogen gas
H 2O
water, ice
SiO2
quartz, cristobalite
CaCO3
calcite, aragonite
Atomic Number and Ions
• The atomic number of an element is the
number of protons (positive charges) in the
nucleus.
• H is atomic number 1, He 2, O 8, Ne 10
etc.
• A neutral atom has the same number of
electrons as protons.
• Ions are charged atoms and have more or
fewer electrons than protons.
Atomic Number and Ions
• Cations have fewer electrons than
protons and a net positive charge.
– Examples: H+, Mg2+, Al3+, Si4+
• Anions have more electrons than
protons and a net negative charge.
– Examples: F-, O2-, Cl-
• Atoms will gain or lose electrons to
have a filled outer electron shell.
to maintain charge balance
H2
H 2O
SiO2
CaCO3
Isotopes
• The number of protons plus
neutrons in the nucleus is known
as the mass number of the atom.
• Atoms of a given element (atomic
number) may have differing
numbers of neutrons.
• Atoms of the same element with
different mass numbers are
known as isotopes.
Mass Number
• The mass numbers or isotopes of an
element are denoted as preceding
superscripts.
• For example the stable isotopes of the
element oxygen are denoted 18O, 17O, and
16O.
• Oxygen has an atomic number of 8 (eight
protons).
• The nucleus of 16O thus contains eight
protons and eight neutrons.
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Ions, isotopes, and molecules
• Ions are denoted with superscripts
– H+1, Na+1, Si+4, O-2
• Isotopes are denoted with
preceding superscripts
– 2H, 3H,
(mass number)
14C, 16O, 18O, 90Sr, 137Cs, 235U
• Molecules and compounds are
denoted with subscripts
Nucleosynthesis
• Large stars undergo successive fusion
reactions until Fe is formed by direct fusion.
• Heavier elements are formed by neutron
capture.
• The final fusion stage results in a
supernova explosion. (not the Big Bang)
• Our solar system formed from the remnants of
a supernova.
– H2, O2, SiO2, CaCO3, Mg2SiO4
Atomic Weight
Chondrule
• A given element may have
several stable isotopes.
• The average mass number of an
element is the atomic weight.
• This is not an integer.
• The atomic weight of H is 1.008
1mm
Nucleosynthesis
Earth differentiated into core and mantle.
• The elements H, He, and minor amounts of
Li were formed in the original Big Bang.
• (13.7 BILLION YEARs AGO)
• All heavier elements were formed from the
primordial H and He by nuclear fusion and
neutron capture reactions in stars.
• The fusion reaction proceeds in steps in
stars massive enough to undergo the full
sequence.
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Ice H2O
Minerals:
Learning Goals
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How is matter organized in the Earth?
What is a mineral?
What is A CRYSTAL? (periodic array)
How does matter self-organize?
What is a rock?
Rock cycle?
Minerals
• A mineral must occur naturally.
• It must be chemically homogeneous
down to the atomic level
• It must have a chemical formula (e.g.
SiO2, FeS2)
• It must have a defined crystal
structure.
• It must be inorganic (not the result
of biological processes alone).
Some Familiar Minerals
Minerals
• A mineral is a naturally occurring,
homogeneous solid of definite
chemical composition and ordered
atomic arrangement that is usually
formed by inorganic processes.
• A Natural Crystalline Phase
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Quartz (SiO2)
Pyrite (FeS2)
Calcite (CaCO3)
Gold (Au)
Silver (Ag)
Copper (Cu)
Diamond (C)
Graphite (C)
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K-feldspar (KAlSi3O8)
Na-feldspar (NaAlSi3O8)
Olivine (Mg2SiO4)
Garnet (Mg3Al2Si3O12)
Gypsum (CaSO4 2H2O)
Apatite (Ca5 (PO4)3OH)
Ice (H2O)
Halite (NaCl) (Salt)
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Hydrothermal Gold
Ice H2O
Halite NaCl (Salt)
Quartz SiO2
Occurrence: Evaporites,
Salt Domes
Uses: Table salt, De-icing,
Nuclear waste host rock?
Calcite CaCO3
Quartz SiO2
• We often display the crystal structure
of minerals as polyhedra where the
corners of the polyhedra represent
oxygen and center is a cation like Si4+.
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Mineral Properties
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Hardness (Mohs Scale)
Luster
Color
Shape
Density
Which of these is
mineral?
• A. Gold
• B. Diamond
• C.Obsidian
• D. Graphite
• E. Quartz
Polymorphs
Some Non-Mineral Solids
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Obsidian (Glass)
Opal (Amorphous)
Coal (Amorphous)
Wood (Organic)
Amber (Organic)
Which of these is
mineral?
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A. Gold
B. Diamond
C. Obsidian
D. Graphite
E. Quartz
not a
not a
• Same composition - different
structure
– Graphite - Diamond (C)
– Quartz - Tridymite - Cristobalite - Coesite
– Calcite - Aragonite (CaCO3)
– Pyrite - Marcasite (FeS2)
Isomorphs
• Same Structure - Different
Composition
– Olivine (Mg2SiO4) (Fe2SiO4)
– Calcite (CaCO3) - Rhodochrosite
(MnCO3)
– Apatite (Ca5(PO4)3OH) - (Ca5(PO4)3F)
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Rocks are Composed of
Minerals
Sedimentary Rocks form from
weathering products of igneous
and metamorphic rocks.
• Granite weathers to quartz, clay, and
dissolved material.
• Water and air transport these on the
surface and sort them by grain size.
• The different grain size fractions are
deposited in different places.
A Rock is an Aggregate of Minerals
Depositional Environments
• Igneous -
– Crystallized from melts
– Surface - Volcanic;
– Subsurface - Intrusive
• Sedimentary -
– Deposited from air and water on
the surface
• Metamorphic
– Recrystallized from pre-existing
igneous or sedimentary rocks.
Crust and Mantle
Lithosphere and Asthenosphere
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A Rock is an Aggregate of Minerals
• Igneous -
– Crystallized from melts
– Surface - Volcanic;
– Subsurface - Intrusive
A.Igneous
B.Metamorphic
C.Sedimentary
Black Rock
• Sedimentary -
– Deposited from air and water on
the surface
• Metamorphic
– Recrystallized from pre-existing
igneous or sedimentary rocks.
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
Red Rock
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A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
A.Igneous
B.Metamorphic
C.Sedimentary
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Assignment
• Grotzinger Chapter 4
• Igneous Rocks
• Homework # 4
Atoms & Elements Terms
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Proton
Neutron
Electron
Atomic weight
Atomic number
Mass Number
Cation
Anion
Valence
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Isotope
Fusion
Fission
Chondrule
Mineral & Rock Terms
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Mineral
Crystal
Hardness
Luster
Habit
Density
Isomorph
Polymorph
Clicker Question
• The term for any molten silicate
material on or below the Earth’s
surface is:
– A. Granite
– B. Basalt
– C. Magma
– D. Pegmatite
– E. Lava
Clicker Question
• The most abundant element in
the Earth is:
– A. Hydrogen
– B. Oxygen
– C. Magnesium
– D. Silicon
– E. Iron
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Clicker Question
• The composition of the mantle is
said to be:
– A. Ultramafic
– B. Mafic
– C. Intermediate
– D. Silicic
– E. Sedimentary
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