Download Chemistry primer Atom = the smallest unit of an element Element

Chemistry primer
Atom = the smallest unit of an element
Element determined by the number of protons in the nucleus
E- is an electron, P+ is a proton, N is a neutron
Carbon atom
Electron cloud
Nucleus
Carbon has 6
electrons…
…and a nucleus
of 6 protons
…
…and 6 neutro ns.
Electron (–)
Proton ( +)
Neutron
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Atoms have the same number of e- and P+
Ion: in an ion the number of e- is not equal to the number of P+
Charge = number of P+ minus number of eAtomic weight is equal to the number of protons plus the number of neutrons
Atomic number si equal to the number protons
Atomic number determines the identity of the atom or ion. In other words
atomic number determines which element the ion or atom is.
Columns indicate ionic charge
Columns indicate number of e- in outer shell
Row indicates number of electron shells
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The charge of an ion determines which
elements (and how many ions) will
combine together.
The size of the ion determines how the
ions are arranged
Chemical Bonds
• Covalent Bonds: ions share electrons
• Ionic Bonds: One ion takes electron from
the other ion and a weaker electrical
attraction hold ions together
• Metalic Bond: free electron sharing across
many ions
• Van Der Wal Bond: a weak electronic
attraction between polarized regions of
chemical compounds.
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Salt
Ionic bond one
ion takes away
the other ions
electron
Diamond
Covalent bond sharing of electrons
Van Der Wal Bond
C
C
+
C
C
C
+
-
C
+
C
C
Carbon nucleus
This is a + polarized area
Due to the presence of protons
C
C
+
C
C
+
C
-
C
C
Covalent bond this is a negatively
polarized area due to the
presence of electrons
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Mineral: an inorganic, naturally occurring, crystalline solid with a
narrowly defined chemical formula
Crystalline: an ordered repeating pattern within a crystal structure
Crystal is the outward expression of this crystalline structure
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Physical Properties of mineral related to crystalline structure and
composition
(the more reliable ones for mineral identification)
Hardness: Resistance to scratching. Greater hardness due to: strong
bonds, tight structure, small ions
Cleavage: Planes of weakness along which a mineral breaks. Reflect
crystalline structure, Cleavage occurs along planes of weakness between
atoms. Week bond have better cleavage.
Density: Mass of mineral divided by volume. This is related to chemical
formula, (size of ion and atomic weight) and tightness of packing (crystalline
structure and bond type)
Crystal habit: This is the shape of the crystal, It reflects internal structure.
This is reliable but seldom found and can be confused with cleavage.
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Cleavage
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Crystal Habit
Crystals rarely have room to grow
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Physical Properties of mineral related to crystalline structure and composit ion
(The less reliable ones for mineral identification)
Luster: How the mineral reflects light.
Streak: Color in power form. This is more reliable than color due to uniformit y
of grains.
Color: Determined by the composition (chemical formula) but it can also be
affected by impurities. This is why color is a poor mineral identifier.
Fracture: How a mineral breaks across cleavage planes. Related to strength
and arrangement of bonds
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Color
Color can be unreliable due to impurit ies
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Streak is more reliable
Ionic compounds certain combinations of ions occur in many minerals with
other elements
Silicate (SiO 4) contains one silicon and four oxygen which leaves a -4 ionic
charge for this compound.
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Carbonate
Quartz
structure
Silicate ion ( SiO44–)
The silicate
ion forms
tetrahedra.
Quartz is
a silicate
polymor ph.
Oxygen io ns
(O2–)
Silicon io n
(Si4+)
Tetrahedra can arra nge i n other ways.
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Mineral
Chemical fo rmula
Cleavage planes
and numbe r of
cleavage directions
1 plane
O livine
( Mg, Fe) 2SiO 4
Pyroxene
( Mg, Fe) SiO 3
Amphibole
Ca2( Mg, Fe) 5Si 8O 22( O H ) 2
Micas
Muscovite:
KAl2( Al Si3O 1 0) ( O H ) 2
2 planes at 90°
Silicate
structu re
Specimen
I solated
tetra hedra
Single chains
2 planes at 60°
and 120°
Double chains
1 plane
Sheets
2 planes at 90°
Three-di mensional
framewo rk
Biotite:
K( Mg, Fe) 3AlSi 3O 10( O H ) 2
Feldspars
O rthoclase feldspar :
KAlSi 3O 8
Plagioclase feldspar:
( Ca, N a) AlSi3O 8
Silicate layer
Alu minu m
hydroxide layer
“Sandwich”
Alu minu m a tom
Silicate layer
Potass iu m ion s
Cleavage
occu rs
between
layers.
“Sandwich”
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