Download Atoms, Molecules and Minerals

Atoms, Molecules
and Minerals
Matter
• Atoms
– The smallest unit of an element that
retain its properties
• Molecules - a small orderly group of atoms
that possess specific properties - H2O
– Small nucleus surrounded by a cloud of
electrons
– The nucleus contains protons and
neutrons
The Nucleus
• Protons
– Positive electrical charge
– Mass equal to 1 atomic unit
• 1 atomic unit = 1.66 * 10-24g
– The number of protons in the nucleus
determines the atomic number
Atomic number defines the element!
The Nucleus
• Neutrons
– Electrically neutral - no charge
– Mass of 1 atomic unit
– The number of neutrons + protons equals
the atomic mass
– The number of neutrons in the nucleus of
a given element may vary producing
isotopes (stable or unstable, i.e.
radioactive)
Isotopes
• Number of protons constant in a given
atom
• Number of neutrons vary
• Atomic mass varies
• Isotopes may be stable or radioactive
12 protons and neutrons
C
6 protons
stable
13
C
6
stable
14
C
6
Unstable, i.e.,
radioactive
Electrons
• Electrons form clouds around nucleus
– Negative electrical charge
– Mass is much much less than 1
• Not a significant contribution to the mass of the
atom
– Electrons = protons in electrically neutral
atom
– Variations in the number of electrons
produce ions
Ions
• Atoms may gain or lose electrons
– „Want‟ to achieve noble gas electron
structure
– Loss of electrons makes a positively
charged ion - cation
– Gaining electrons makes a negatively
charged ion - anion
– Oppositely charged ions may attract one
another
Bonding
• Atoms are stable when their outmost
electron shell is filled
– Electron structure like a noble gas
– Atoms lose, gain or share electrons to
achieve a noble gas structure
– The outmost electrons are referred to as
the valence electrons. They are the most
important factor in determining the
chemistry of the element.
Where are the
electrons in an
atom?
In particular, where are the
valence (outer shell) electrons
in an atom?
Schrodinger Wave Equation
In 1926 Schrodinger wrote a wave equation (Y) that
describes the location and other properties of electrons
surrounding the nucleus of an atom.
Four quantum numbers uniquely specify the position and
characteristics of an electron in an atom
Schrodinger Wave Equation
Y = f(n, l, ml, ms)
principal quantum number n
n = 1, 2, 3, 4, ….
Determines the distance of electron from the nucleus
n=1
n=2
n=3
Where 90% of the
e- density is found
for the 1s orbital
e- density (1s orbital) falls off rapidly
as distance from nucleus increases
7.6
Schrodinger Wave Equation
Y = f(n, l, ml, ms)
angular momentum quantum number l
l=0
l=1
l=2
l=3
s orbital
p orbital
d orbital
f orbital
The angular momentum quantum number determines the
shape of the “volume” of space that the e- occupies
7.6
l = 0 (s orbitals)
l = 1 (p orbitals)
7.6
l = 2 (d orbitals)
7.6
• The magnetic quantum number ml relates to the
orientation of the region the electron is most likely in. It
takes integer values between –l and +l:
ml = -l, -l+1,…, 0,…, +l-1, +l.
• The spin quantum number ms does not relate to where an
electron is likely to be found in space. It refers to
the orientation of the electron’s magnetic field. It takes
values
ms = +1/2 and -1/2,
sometimes called “up” and “down”.
This is the source of magnetism!
Energy of orbitals in a single electron atom
Energy only depends on principal quantum number n
n=3
n=2
En = -RH
(
1
n2
)
n=1
7.7
Energy of orbitals in a multi-electron atom
Energy depends on n and l
n=3 l = 2
n=3 l = 1
n=3 l = 0
n=2 l = 0
n=2 l = 1
n=1 l = 0
7.7
“Fill up” electrons in lowest energy orbitals (Aufbau principle)
? ?
Li
Be
B 6534electrons
C
electrons
electrons
BBe
Li1s21s
2s222s
2p12 1
H
He12electron
electrons
He
H 1s
1s12
7.7
The most stable arrangement of electrons in
subshells is the one with the greatest number of
parallel spins (Hund’s rule).
C 968710
N
O
F
Ne
electrons
electrons
electrons
22s
222p
22p
52346
Ne
N
C
O
F 1s
1s222s
7.7
Order of orbitals (filling) in multi-electron atom
1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s
7.7
Outermost subshell being filled with electrons
7.8
Paramagnetic
unpaired electrons
2p
Diamagnetic
all electrons paired
2p
7.8
Classification of the Elements
8.2
ns2np6
ns2np5
ns2np4
ns2np3
ns2np2
ns2np1
d10
d5
d1
ns2
ns1
Ground State Electron Configurations of the Elements
4f
5f
8.2
Electron Configurations of Cations and Anions
Of Representative Elements
Na [Ne]3s1
Na+ [Ne]
Ca [Ar]4s2
Ca2+ [Ar]
Al [Ne]3s23p1
Al3+ [Ne]
Atoms gain electrons so
that anion has a noble-gas
outer electron
configuration.
Atoms lose electrons so that
cation has a noble-gas outer
electron configuration.
H 1s1
H- 1s2 or [He]
F 1s22s22p5
F- 1s22s22p6 or [Ne]
O 1s22s22p4
O2- 1s22s22p6 or [Ne]
N 1s22s22p3
N3- 1s22s22p6 or [Ne]
8.2
-1
-2
-3
+3
+2
+1
Cations and Anions Of Representative Elements
8.2
Bonding
• Ionic bonds
– Formed between ions of opposite charge
• Covalent bonds
– Atoms share electrons to achieve noble
gas structure
• Metallic bonds
– Outer electrons are mobile
• Electrical conductivity
Ionic Bonding
Periodic Table of the Elements
Covalent Bonding
9.5
Classification of bonds by difference in electronegativity
Difference
Bond Type
0
Covalent
2
0 < and <2
Ionic
Polar Covalent
Increasing difference in electronegativity
Covalent
share e-
Polar Covalent
partial transfer of e-
Ionic
transfer e-
9.5
8.3
Atomic Radii
8.3
Cation is always smaller than atom from
which it is formed.
Anion is always larger than atom from which
it is formed.
8.3
8.3
States of Matter
• Solid
– Crystalline - atoms bond together in a
regular orderly pattern
– Amorphous - atoms bonded together in a
random pattern
• Liquid - atoms or molecules tightly packed
but in random motion
• Gas - particles in random motion at high
speeds, separated by empty space
The Nature of Minerals
• Mineral
– A naturally occurring inorganic solid that
has an exact (or clearly defined range)
chemical composition with an orderly
internal arrangement of atoms generally
formed by inorganic processes.
Minerals
• Naturally occurring inorganic solid
– Must be solid
• Ice vs. water
– Must be formed by a natural process
• Natural vs. synthetic diamonds
– Must be an inorganic compound
• Coal is not a mineral
• What about biologic and nonbiologic CaCO3 ?
Minerals
• Internal structure
– Repetitive geometric pattern of atoms
– Expressed in physical properties
• Interfacial angles
• Cleavage
• Revealed in X-ray diffraction
– Polymorph
• Minerals with the same chemical
composition but different internal structure
Polymorphs
Polymorphism
Minerals
• Composition
– Chemical composition expressed as a
chemical formula
– Composition ranges from simple to
complex
• Native copper - Cu
• Biotite - K(Mg,Fe)3AlSi3O10(OH)2
– Ionic substitution may occur causing
small variations in composition
Physical Properties
• Crystal faces & form
– Growth in unrestricted environment
– Form reflects symmetry of internal
structure
• Density
– Ratio of mass to volume
– Common rock-forming minerals range
from 2.6 to 3.4 grams/cm3
Physical Properties
• Cleavage
– Breakage along parallel planes of
weakness
– Related to internal structure -weaker
bonds
– May occur in 1 or more planes
– Fracture is uneven breakage - no natural
planes of weakness
Cleavage Planes
Physical Properties
• Hardness
– Resistance to abrasion
– Strength of atomic bonds holding solid
together
– Mohs hardness scale
• Arbitrary relative numbers assigned to 10
common minerals
• Scale is not linear
Physical Properties
• Color
– Most obvious property
– Not diagnostic for ID purposes
– Variations due to trace elements
• Streak
– Color of mineral powder
– Diagnostic property
Hematite Colors & Streak
Physical Properties
• Luster
– The appearance of reflected light
– Influenced by the type of bonding in the
mineral
– Metallic luster
• Shines like metal
– Non-metallic
• Widely ranging from bright to dull
Physical Properties
• Magnetism
– Characteristic of only a few minerals
• Iron bearing minerals
– Magnetite
– A very important property of rocks in
geophysical investigations of the Earth
Mineral Stability
• Stability ranges
– Range of pressure, temperature and
composition under which a mineral forms
– Stable
• Exists in equilibrium with its environment
– Metastable
• A mineral existing outside its stability range
Stability Ranges for SiO2
Fig 3.11
Growth & Destruction of Minerals
• Crystallization
– Addition of atoms to the crystal face
– Follows internal structure
– Faces may grow at different rates
– Ideal crystal forms are produced by
growth in unrestricted space
• In restricted space, crystals grow to fill the
space
Crystal Growth in a Confined Space
Growth & Destruction of Minerals
• Mineral destruction
– Melting
• Removal of atoms from crystal faces as
matter goes from solid to liquid
– Recrystallization
• Rearrangement of the internal structure of a
mineral by changing pressure and
temperature
• Solid state reaction
• Very common after lithification
Silicate Minerals
• Most common minerals on Earth
– Comprise 95% of the volume of the crust
– Approximately 75% of the Earth‟s mass
is made up of silicon and oxygen
– All silicate minerals are based on the
silica tetrahedron
• SiO4-4
Silica Tetrahedron
Silicate Minerals
• Silica tetrahedron may polymerize to
form a variety of geometric structures,
alone or in combination with other
cations
• Isolated tetrahedron
• Single chains
• Double chains
• 2-D sheet
• 3-D frameworks
Silicate Structures
Isolated
Single chain
Double chain
Sheet
Solid
Rock-Forming Minerals
• About 20 common minerals make up
most rocks
– Silicates dominate
– Quartz, Feldspars, Mica, Amphiboles,
Pyroxenes
– Carbonates are common
– Evaporite minerals
– Secondary minerals formed during
weathering
Felsic Minerals
• Silicate minerals rich in silicon and
aluminum
– Relatively low densities and low
crystallization temperatures
– Quartz
– Feldspars
• Potassium feldspar
• Plagioclase feldspar
– Mica - muscovite
Mafic Minerals
• Silicate minerals rich in iron and
magnesium
– Relatively high density and higher
crystallization temperatures
– Olivine
– Pyroxenes
– Amphiboles
– Mica - biotite
Clay Minerals
• Sheet silicates similar to mica
• Products of chemical weathering near
the Earth‟s surface
• Usually microscopic crystals
– Kaolinite
SEM photograph of clay minerals: authigenic chlorite flake
from the Watahomigi Formation in Andrus Canyon, Supai
Group, Grand Canyon; x 20,900. Figure 05-D, U.S.
Geological Survey Professional Paper 1173.
Nonsilicate Minerals
• Usually form at low temperatures
(reactions that occur at the surface of the E arth )
– Carbonates (biologic)
• Calcite - Ca CO3
• Dolomite - CaMg(CO3)2
– Evaporite Minerals (seawater evaporation)
• Gypsum - CaSO4-2H2O
• Halite - NaCl
– Oxides (rust and weathering)
• Hematite
Main points
– The number of protons in the nucleus of an atom
determines what the element is.
– The outer (valence) electrons are the primary
control of the chemistry of the element in that they
determine what reactions occur with other
elements
– There are predictable variations in size and charge
of ions and thus in the geometry of the minerals
that form from them.
Periodic Table of the Elements