Atoms and Elements. Atoms: Learning Goals. Chapter 3. Atoms and Elements; Isotopes and Ions; Minerals and Rocks. Clicker 1. Chemistry Background?

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 Chemistry B. High School Chemistry

C. 1 semester College Chemistry D. 2+ semesters College Chemistry

Atoms:

Learning Goals

•Atoms are composed of Protons, Neutrons andElectrons.

•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 andElectrons

–A proton has an electric charge of +1 and a rest mass of 1.67 x 10^-24gm.

–A neutron has a charge of 0 and a rest mass of 1.67 x 10^-24gm. (about the same as a proton).

–An electron has a charge of -1 and a rest mass of 9.11 x 10^-28gm. (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

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

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 Valence

Charge Denoted by Superscript

•Cations

•H⁺¹

•Na⁺¹

•Mg⁺²

•Al⁺³

•Si⁺⁴

• Anions

• F^-1

• O^-2

• S^-2

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 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^-, O^2-, 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 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.

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 fusionand 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.

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 H

O

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)

Hydrothermal Gold

Occurrence: Evaporites, Salt Domes

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

Halite NaCl (Salt)

Calcite CaCO ₃

Ice H

O

Quartz SiO

Quartz SiO

•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⁺.

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)

Rocks are Composed of Minerals

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 Mantle

Lithosphere 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

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.Igneous B.Metamorphic C.Sedimentary

A.Igneous B.Metamorphic C.Sedimentary

A.Igneous B.Metamorphic C.Sedimentary

Black Rock

A.Igneous B.Metamorphic C.Sedimentary

Red Rock

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

A.Igneous

B.Metamorphic

C.Sedimentary

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

Clicker Question

•The composition of the mantle is said to be:

–A. Ultramafic –B. Mafic

–C. Intermediate –D. Silicic –E. Sedimentary