Atoms and Elements. Chemical Composition of the Earth s Crust Crystallinity. Chemical Activity Ions. The Silicon-Oxygen Tetrahedron

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1 Atoms and Elements Chemical Activity Ions Chemical Composition of the Earth s Crust Crystallinity The Silicon-Oxygen Tetrahedron

2 Minerals Crystalline Solids Natural and Inorganic Substances Definite Chemical Composition The Important Minerals

3 Rocks versus Minerals Granite rock type Rock: an aggregate of one or more minerals; in this case there are three minerals present. Feldspar: NaAlSi 3 O 8 - KAlSi 3 O 8 Quartz: SiO 2 Biotite: KMg 3 AlSi 3 O 10 (OH) 2 - KFe 3 AlSi 3 O 10 (OH) 2

4 Mineral Structures and Atoms 1 angstrom = meters Mineral: A naturally occurring inorganic element or compound having orderly internal structure and characteristic chemical composition, crystal form, and physical properties. From: Plummer et al.

5 Atomic Structure and the Composition of Matter The atom is a basic building block of minerals. Matter is a special form of energy; it has mass and occupies space. Neither matter nor energy may be created or destroyed - they may only be converted from one form to the other. Energy is the ability to do work and it occurs in a number of forms, including: Potential; Kinetic; Electrical; Heat; Chemical; Nuclear Radiant (the only form in which there is an absence of matter) Atoms are the smallest division of matter that retain the characteristics of the elements.

6 Elements and the Periodic Table Approximately 300 different kinds of atoms that are capable of independent, prolonged existence. These are called nuclides. If nuclides are grouped by chemical characteristics, about 100 sets result and these are referred to as elements. The modern Periodic Table was devised in 1869 by Julius Meyer and Dmitri Mendeleev. It organizes the elements into groups and families with similar chemical and physical properties.

7 Periods Groups or Families Periodic Table

8 Crustal Abundance Crustal volume:<1% of Earth Mantle volume: 83% of Earth Core volume: 16% of Earth Crustal mass:<1% of Earth Mantle mass: 68% of Earth Core mass: 31% of Earth What element is most abundant for the entire Earth?

9 Atomic Particles: Basics Atoms are composed of electrons and two large nuclear particles called protons and neutrons. Protons and neutrons are approximately equal in mass and are ~1800 times more massive than the electron. Both nuclear particles are composed of quarks, smaller fundamental particles. Protons have unit positive charge (+1), while electrons have unit negative charge (-1). Neutrons carry no charge. Atoms are electrically neutral and thus the number of electrons must equal the number of protons.

10 Basic Terminology Atomic number (Z): The atomic number represents the number of unit positive charges on the nucleus and is equal to the number of protons within the nucleus, since each proton carries unit positive charge. In electrically neutral atoms, it also represents the number of electrons, which carry unit negative charge. Mass number (A): The mass number is equal to the total number of nucleons, which is the sum of the number of protons and neutrons. A does not equal the total mass of the atom; rather, it represents a whole number approximation of the mass, as expressed in amu. The number of neutrons is simply defined as the A - Z.

11 Isotopes and Isobars A specific type of atom is designated by using its chemical symbol, which is an abbreviation of its name in German, Latin, or English, with the A, the mass number, placed in the upper left and Z, the atomic number, placed in the lower left corner. For example, 23 Na 11, has a mass number of 23 and an atomic number of 11. Isotopes are atoms of the same element that differ in mass. For example, 87 Sr and 86 Sr or 238 U and 235 U. Isotopes have similar chemical characteristics and are studied using a mass spectrograph or spectrometer. Most elements have at least two naturally occurring isotopes. Isobars are nuclides that have the same mass number but different atomic numbers. For example, 36 S and 36 Ar are isobars; they both contain a total of 36 nucleons (protons plus neutrons), but the sulfur isotope has 16 protons and 20 neutrons, while the argon isotope has 18 protons and 18 neutrons. Isobars do not have similar chemical characteristics!

12 Atomic Weight Atomic weight is the weighted average of the atomic masses of the naturally occurring isotopes. For example, a natural sample of the element chlorine contains a mixture of 75.53% 35 Cl and 24.47% 37 Cl. Thus the atomic weight is obtained by multiplying the mass of each isotope (in amu) times its fractional abundance: (34.97 amu) (36.95 amu) = amu

13 Atomic Models Bohr Model Electron shells Quantum Mechanics Orbitals Afbau Filling Order Quantum numbers and superposition of states

14 Bohr Atomic Model Oxygen Atom The Bohr model for the atom envisioned these electrons in stable orbits of specified radius and energy, where we could exactly pinpoint the position of any individual electron. Each energy level was permitted to have a specified number of electrons, and was called a shell. We know now that this simple view is not correct; it is impossible to exactly determine the position of an electron in space.

15 The Quantum Mechanical View Using the theory of quantum or wave mechanics we can calculate the probabilities of various electron configurations, and thus show that specified regions near the nucleus have higher probabilities for finding an electron than others. Each electron does, however, have a specific energy. Must solve wave equation for specific states! The combination of the energy and probability gives rise to the current understanding for electron distributions, which are referred to as electron orbitals; these orbitals are referred to as s (sharp), p (principal), d (diffuse), and f (fundamental). With increasing atomic number, each new element has an additional electron also added to it extra-nuclear cloud. From theory and experiment, we know that these electrons are added in a systematic fashion, with the lowest energy orbitals being filled first. This process is called aufbau filling (1s -> 2s -> 2p -> 3s -> 3p -> 4s - > 3d -> 4p -> 5s, ). Combine with Pauli exclusion principle to yield filling order.

16 Quantum Numbers n = 6; l = 4; m = 1 n = principal l = orbital (0 -> (n-1)) m l = magnetic (± l) m s = spin (±1/2) l = 0 -> s orbital = 1 -> p orbital = 2 -> d orbital = 3 -> f orbital From:

17 Animated Orbital Simulations Superposition of States 4, 3, 3 and 4, 1, 0 3, 2, 2 and 3, 1, -1 From:

18 Water, Ice and Snow Most important substance on Earth Essential for biological life as we know it Unique volumetric property Molecular symmetry and its relationship to crystal morphology Crystal growth and its effect on crystal morphology

19 Chemical Formula: H 2 O Water Atomic Structure

20 Snowflake Morphology Hexagonal Symmetry Oddly, ice is less dense than liquid water, hence it floats and lakes freeze from the top down! 1-5 mm From:

21 Snowflake Growth From:

22 LT-SEM Images of Snow Crystals

23 Compounds and Bonding Chemical compounds Ionic bonding NaCl as a type example Electron transfer and shell completion Covalent bonding Diamond - pure C example Electron sharing Silicon Tetrahedron Structure (strong sp 3 covalent bonds) Building block of silicate minerals

24 Chemical compound: Two or more elements joined together by a chemical bond. Most minerals are composed of at least two elements. Chemical Formula: NaCl Note Cubic Symmetry and Closest Packing Halite Atomic Structure

25 1s 2 1s 2 2s 2 2p 6 Outer Shell Filling

26 Ionic Bonding and Electron Exchange 11p e - = +1 1s 2 2s 2 2p 6 3s 1 +1e - 1s 2 2s 2 2p 6 3s 2 3p 5 17p e - = -1

27 Ionic Bonding:Electron Transfer Cations (+) are always smaller than the neutral atom; Anions (-) are always larger than the neutral atom.

28 Covalent Bonding: Electron Sharing Diamond Example - Pure Carbon in complex 3D network

29 Silicon Tetrahedron: SiO 4 (net -4 charge) 1.30 Å 1 angstrom = meters 0.34 Å

30 Silicate Mineral Structures I Silcon Tetrahedron: strong sp 3 hybrid covalent bonds - 50% ionic; 50% covalent character These structures are the basic building blocks of silicate minerals. Bridging Oxygen (BO) Silicate structures may be Characterized by the the number of BO s per Si. The higher the BØSi Ratio, the more complex and polymerized the structure.

31 Silicate Structures

32 Olivine Structure: (Mg,Fe) 2 SiO 4

33 Models of Chain Silicates: Pyroxenes

34 Positive ion Oxygen Silicon A B

35 Oxygen Silicon

36 Silicon

37 Oxygen Silicon

38 Positive ion +2 +2

39 Positive ion Oxygen Silicon +2 +2