Chapter 3 Atoms Atoms and Elements; Isotopes and Ions; Minerals...

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Chapter 3

Atoms and Elements; Isotopes and Ions;Minerals and Rocks

A Review of Chemistry:What geochemistry tells us

Clicker 1

Chemistry Background?

A. No HS or College ChemistryB. High School ChemistryC. 1 semester College ChemistryD. 2+ semesters College Chemistry

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

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 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 naturalelements range from 1 (hydrogen) to 92 for uranium.

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Atomic Number• 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)

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.

Chemistry• 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 ValenceCharge Denoted by Superscript

• Cations• H+1

• Na+1

• Mg+2

• Al+3

• Si+4

• Anions• F-1

• O-2

• S-2

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Chemical Compounds

• Elements occur in integer ratios to maintain charge balance

• H2 hydrogen gas• H2O 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 ofelectrons 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.

Chemical Compounds

• Elements occur in integer ratios to maintain charge balance

• H2

• H2O• 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 precedingsuperscripts.

• 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 (mass number)– 2H, 3H, 14C, 16O, 18O, 90Sr, 137Cs, 235U

• Molecules and compounds are denoted with subscripts– H2, O2, SiO2, CaCO3, Mg2SiO4

Atomic Weight• 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

Nucleosynthesis• 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.

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.

1mm

Chondrule

Earth differentiated into core and mantle.

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Minerals:Learning Goals

• 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 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

Ice H2O

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

• Quartz (SiO2)• Pyrite (FeS2)• Calcite (CaCO3)• Gold (Au)• Silver (Ag)• Copper (Cu)• Diamond (C)• Graphite (C)

• 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

Occurrence: Evaporites, Salt Domes

Uses: Table salt, De-icing, Nuclear waste host rock?

Halite NaCl (Salt)

Calcite CaCO3

Ice H2O

Quartz SiO2

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• Hardness (Mohs Scale)• Luster• Color• Shape• Density

Some Non-Mineral Solids

• Obsidian (Glass)• Opal (Amorphous)• Coal (Amorphous)• Wood (Organic)• Amber (Organic)

Which of these is not a mineral?

• A. Gold• B. Diamond• C. Obsidian• D. Graphite• E. Quartz

Which of these is not a mineral?

• A. Gold• B. Diamond• C.Obsidian• D. Graphite• E. Quartz

Polymorphs• 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 ofMinerals

A Rock is an Aggregate of Minerals• 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 MantleLithosphere and Asthenosphere

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.

Depositional Environments

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A Rock is an Aggregate of Minerals• 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.

A.IgneousB.MetamorphicC.Sedimentary



Black Rock


Red Rock


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Atoms & Elements Terms• Proton• Neutron• Electron• Atomic weight• Atomic number• Mass Number• Cation• Anion• Valence

• Isotope• Fusion• Fission• Chondrule

Mineral & Rock Terms• Mineral• Crystal• Hardness• Luster• Habit• Density• Isomorph• Polymorph

Assignment

•Grotzinger Chapter 4

•Igneous Rocks

•Homework # 4

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

Chapter 3 Atoms Atoms and Elements; Isotopes and Ions; Minerals...

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