Lecture 3.  Orders of magnitude
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Lecture 3. Orders of magnitude From planets to atoms. Example of coordination number. SiO 2 CN Si = 4. Atomic and ionic radii In picometers (pm). How big is an atom? ~100 picometers (pm) or ~1 Angstrom. Lengthscales in nature span more than 27 orders of magnitude.

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Lecture 3. Orders of magnitude From planets to atoms

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Lecture 3. Orders of magnitude

From planets to atoms


Example of coordination number

SiO2

CNSi = 4


Atomic and ionic radii

In picometers (pm)


How big is an atom?

~100 picometers (pm) or ~1 Angstrom


Lengthscales in nature span more than 27 orders of magnitude

Diameter of Milky Way Galaxy100 kilo-lightyears

Distance to Neptune from Earth4.3 x 109 km

Radius of Sun7 x 105 km

Radius of Earth6.37 x 103 km

Thickness of Earth’s continental crust3.2 x 101 km

Depth of oceans4 km

Deepest hole drilled into the Earth10 km

Tallest building on Earth1.3km

Length of a soccer field109.7m

Diameter of soccer ball0.22 m

Dimensions of soccer goal2.44 by 7.135 m

Size of an ant1 mm

Size of an atom0.1 nm

1 lightyear = 9.46 x 1015 m


Orders of magnitude

1,250,000

is

1.25 x 106

or 1.25 billion

Numbers can be converted to scientific notation

The base 10 logarithm (or log10) gives you the order of magnitude of that number

For example…

log10(1,250,000) = log10(1.25 x 106)

= log10(1.25) + log10(106)

= log10(1.25) + 6

Since log10(1) = 0, we say that 1,250,000 is on the order of 1 million (106)


Metric system units

[LENGTH]

km

m

cm

mm

μm

nm

pm

kg

g

mg

μg

ng

pg

=103 m

=100 m

=10-2 m

=10-3 m

=10-6 m

=10-9 m

=10-12 m

=103 g

=100 g

=10-3 g

=10-6 g

=10-9 g

=10-12 g

[MASS]

Do not confuse metric units with miles, inches, or pounds.


Rough diamonds

Kimberly diamond mine in S Africa

Diamond mine NWT, Canada


Gypsum CaSO4(H2O)2

Gypsum crystals from a Lead mine in Mexico


Z = Proton Number

N = number of neutrons

A = Atomic Mass Number

= Z + N

An element is defined by its proton number

Number of protons and electrons dictates chemical behavior of atom


Electronegativity

Tendency for an atom to attract an electron in a molecule


Chemical bonding

Similar electronegativity

Contrasting electronegativity

Covalent bonds tend to be stronger than ionic bonds


Al

1.41

Ca

1.54

?

2.9

Ni

1.8

Fe

32.1

O

30.1

Si

15.1

Mg

13.9

BULK EARTH


Majority of earth materials are made up of silicates

Silicates are mineral compounds that have silica tetrahedra as their basic building blocks, e.gSiO4-4

Si-O bond is dominantly covalent


Quartz

SiO2

Silica tetrahedra are linked at all apices

Fully polymerized

One of the most common minerals in the continents


[SiO4]4- Independent tetrahedraNesosilicates

Olivine

Mg2SiO4

(aka peridot)

Abundant mantle mineral

Garnet

(Mg,Ca,Fe)3Al2Si3O12

Common crustal mineral


Nesosilicates: independent SiO4tetrahedra

OLIVINE

SiO4tetrahedra are not linked to each other

-separated by Mg2+cations that are ionically bonded to O2- apices of the silica tetrahedra

Olivine (100) view blue = M1 yellow = M2

http://www.whitman.edu/geology/winter/


Peridotite

An olivine-rich rock that makes up much of the mantle


n[SiO3]2-n = 3, 4, 6 Cyclosilicates

Examples: benitoiteBaTi[Si3O9]

axiniteCa3Al2BO3[Si4O12]OH

beryl Be3Al2[Si6O18]

tourmaline CaMg3Al6(BO3)3(Si6O18(OH)4

Beryl with charge transfer = aquamarine

Beryl with Cr = Emerald

tourmaline

http://www.whitman.edu/geology/winter/


PYROXENES

Spodumene

(kunzite)

LiSiO3

[SiO3]2- single chains

pyroxenes pyroxenoids

Dark green mineral in peridotite

Diopside

CaMgSi2O6

Common mineral in the mantle


Amphiboles

Hornblende

(Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2

[ [Si4O11]4- Double tetrahedra

amphiboles

One of the common “black” minerals in granitoids


Phyllosilicates

Micas and clays

[Si2O5]2- Sheets of tetrahedra Phyllosilicates

micas talc clay minerals serpentine

http://www.whitman.edu/geology/winter/


Biotite

K(Mg,Fe)3(AlSi3O10)(F,OH)2

Common “black” mineral in granitoids

Differs from hornblende in being flaky and sheet-like


Tectosilicates

Feldspars and quartz

low-quartz

[SiO2] 3-D frameworks of tetrahedra: fully polymerized Tectosilicates

quartz and the silica minerals feldspars feldspathoids zeolites

http://www.whitman.edu/geology/winter/


FELDSPARS

Plagioclase

CaAlSSi2O8

Orthoclase

(K,Na)AlSi3O8

Common minerals in granitic rocks

The precursor of clays used in ceramics


What did we learn today

  • Concepts of orders of magnitude

  • Chemical Bonding

  • Basic minerals on Earth

Next lecture – physical properties of rocks and minerals


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