Atoms, Molecules and Minerals
Atoms Matter The smallest unit of an element that retain its properties Molecules - a small orderly group of atoms that possess specific properties - H 2 O Small nucleus surrounded by a cloud of electrons The nucleus contains protons and neutrons
Protons The Nucleus Positive electrical charge Mass equal to 1 atomic unit 1 atomic unit = 1.66 * 10-24 g The number of protons in the nucleus determines the atomic number Atomic number defines the element!
Neutrons The Nucleus 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 13 14 C C C 6 protons 6 6 stable stable 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, m l, m s ) 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, m l, m s ) 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 m l relates to the orientation of the region the electron is most likely in. It takes integer values between l and +l: m l = -l, -l+1,, 0,, +l-1, +l.
The spin quantum number m s 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 m s = +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 1 E n = -R H ( ) n 2 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 = 0 n=2 l = 0 n=3 l = 1 n=2 l = 1 n=1 l = 0 7.7
Fill up electrons in lowest energy orbitals (Aufbau principle)?? Li Be B C 56 34 electrons B Be Li 1s 2 1s 2s 22 2s 2p 12 1 H He 12 electrons He H 1s 12 7.7
The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hund s rule). C O F Ne 96 78 10 electrons Ne N C O F 1s 2 2 2s 2 2 2p 52 34 6 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 Diamagnetic all electrons paired 2p 2p 7.8
Classification of the Elements 8.2
ns 1 Ground State Electron Configurations of the Elements d 1 d 5 ns 2 ns 2 np 1 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6 d 10 4f 5f 8.2
Electron Configurations of Cations and Anions Of Representative Elements Na [Ne]3s 1 Ca [Ar]4s 2 Al [Ne]3s 2 3p 1 Na + [Ne] Ca 2+ [Ar] Al 3+ [Ne] Atoms lose electrons so that cation has a noble-gas outer electron configuration. Atoms gain electrons so that anion has a noble-gas outer electron configuration. H 1s 1 F 1s 2 2s 2 2p 5 O 1s 2 2s 2 2p 4 N 1s 2 2s 2 2p 3 H - 1s 2 or [He] F - 1s 2 2s 2 2p 6 or [Ne] O 2-1s 2 2s 2 2p 6 or [Ne] N 3-1s 2 2s 2 2p 6 or [Ne] 8.2
+1 +2 Cations and Anions Of Representative Elements +3-3 -2-1 8.2
Ionic bonds Bonding 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 Ionic 0 < and <2 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
Solid States of Matter 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
Mineral The Nature of Minerals 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 CaCO 3?
Internal structure Minerals 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
Composition Minerals Chemical composition expressed as a chemical formula Composition ranges from simple to complex Native copper - Cu Biotite - K(Mg,Fe) 3 AlSi 3 O 10 (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/cm 3
Cleavage Physical Properties 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
Hardness Physical Properties 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
Color Physical Properties Most obvious property Not diagnostic for ID purposes Variations due to trace elements Streak Color of mineral powder Diagnostic property
Hematite Colors & Streak
Luster Physical Properties 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
Magnetism Physical Properties Characteristic of only a few minerals Iron bearing minerals Magnetite A very important property of rocks in geophysical investigations of the Earth
Stability ranges Mineral Stability 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
Fig 3.11 Stability Ranges for SiO 2
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 SiO 4-4
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 CO 3 Dolomite - CaMg(CO 3 ) 2 Evaporite Minerals (seawater evaporation) Gypsum - CaSO 4-2H 2 O 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