Lecture 2 (9/11/2006) – Crystal Chemistry Part 1: Atoms, Elements, and Ions

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What is Crystal Chemistry? study of the atomic structure, physical properties, and chemical composition of crystalline material study of the atomic structure, physical properties, and chemical composition of crystalline material basically inorganic chemistry of solids basically inorganic chemistry of solids the structure and chemical properties of the atom and elements are at the core of crystal chemistry the structure and chemical properties of the atom and elements are at the core of crystal chemistry there are only a handful of elements that make up most of the rock-forming minerals of the earth there are only a handful of elements that make up most of the rock-forming minerals of the earth

Fe – 86% S – 10% Ni – 4% Chemical Layers of the Earth SiO2 – 45% MgO – 37% FeO – 8% Al2O3 – 4% CaO – 3% others – 3%

Composition of the Earth’s Crust

Average composition of the Earth’s Crust (by weight, elements, and volume)

The Atom The Bohr Model The Schrodinger Model Nucleus - contains most of the weight (mass) of the atom - composed of positively charge particles (protons) and neutrally charged particles (neutrons) Electron Shell - insignificant mass - occupies space around the nucleus defining atomic radius - controls chemical bonding behavior of atoms

Elements and Isotopes Elements are defined by the number of protons in the nucleus (atomic number). Elements are defined by the number of protons in the nucleus (atomic number). In a stable element (non-ionized), the number of electrons is equal to the number of protons In a stable element (non-ionized), the number of electrons is equal to the number of protons Isotopes of a particular element are defined by the total number of neutrons in addition to the number of protons in the nucleus (isotopic number). Isotopes of a particular element are defined by the total number of neutrons in addition to the number of protons in the nucleus (isotopic number). Various elements can have multiple (2-38) stable isotopes, some of which are unstable (radioactive) Various elements can have multiple (2-38) stable isotopes, some of which are unstable (radioactive) Isotopes of a particular element have the same chemical properties, but different masses. Isotopes of a particular element have the same chemical properties, but different masses.

Isotopes of Titanium (Z=22) IsotopeIsotope Half-life Spin Parity Decay Mode(s) or AbundanceHalf-lifeSpinParityDecay Mode(s)Abundance 38Ti 38Ti 0+ 39Ti 39Ti 26 ms(3/2+) EC=100, ECP+EC2P ~ 14 40Ti 40Ti 50 ms0+ EC+B+=100 41Ti 41Ti 80 ms3/2+ EC+B+=100, ECP ~ Ti 42Ti 199 ms0+ EC+B+=100 43Ti 43Ti 509 ms7/2- EC+B+=100 44Ti 44Ti 63 y0+ EC=100 45Ti 45Ti m7/2- EC+B+=100 46Ti 46Ti stable0+ Abundance= Ti 47Ti stable5/2- Abundance= Ti 48Ti stable0+ Abundance= Ti 49Ti stable7/2- Abundance= Ti 50Ti stable0+ Abundance= Ti 51Ti 5.76 m3/2- B-=100 52Ti 52Ti 1.7 m0+ B-=100 53Ti 53Ti 32.7 s(3/2)- B-=100 54Ti 54Ti 0+ 55Ti 55Ti 320 ms(3/2-) B-=100 56Ti 56Ti 160 ms0+ B-=100, B-N=0.06 sys 57Ti 57Ti 180 ms(5/2-) B-=100, B-N=0.04 sys 58Ti 58Ti 0+ 59Ti 59Ti (5/2-) B-=? 60Ti 60Ti 0+ B-=? 61Ti 61Ti (1/2-) B-=?, B-N=?Source: R.B. Firestone UC-Berkeley

Properties of Electrons Occur in discrete (quantized) energy levels or orbitals around the nucleus Occur in discrete (quantized) energy levels or orbitals around the nucleus Behave as particles with wave-like properties Behave as particles with wave-like properties Position of an electron in space around the nucleus is a probability function defined by 4 quantum numbers Position of an electron in space around the nucleus is a probability function defined by 4 quantum numbers n – principle quantum number (= 1, 2, 3, 4...) defines the energy level of the primary electron shell l – azimuthal quantum number (= n -1) defines the type and number of electron subshells (s, p, d, f,...) m – magnetic quantum number (= +l to -l ) defines orientation and number of orbitals in each subshell s – spin quantum number (= +1/2 or -1/2) defines direction of spin of the electron in each orbital

Electron Shells, Subshells, and Orbitals

Filling up the Orbitals Controlled by the energy of the orbitals

Structure of the Periodic Table # of Electrons in Outermost Shell Noble Gases Anions Transition Metals Primary Shell being filled

Ions, Ionization Potential, and Valence States Cations – elements prone to give up one or more electrons from their outer shells; typically a metal element Anions – elements prone to accept one or more electrons to their outer shells; always a non-metal element Ionization Potential – measure of the energy necessary to strip an element of its outermost electron Electronegativity – measure strength with which a nucleus attracts electrons to its outer shell Valence State (or oxidation state) – the common ionic configuration(s) of a particular element determined by how many electrons are typically stripped or added to an ion

1 st Ionization Potential Electronegativity Elements with a single outer s orbital electron Anions Cations

Valence States of Ions common to Rock-forming Minerals Cations – generally relates to column in the periodic table; most transition metals have a +2 valence state for transition metals, relates to having two electrons in outer Anions – relates electrons needed to completely fill outer shell Anionic Groups – tightly bound ionic complexes with net negative charge Anionic Groups – tightly bound ionic complexes with net negative charge Transition Metals

Next Lecture Crystal Chemistry II Crystal Chemistry IIBonding Atomic and Ionic Radii Read p Read p