Materials Engineering Lecture 1: Introduction; Atom; Periodic Table of elements.

What is material science? Material science investigates the correlation between the structure and properties of materials. Structure: Macro- Micro- Properties: Mechanical; Electrical; Thermal; Magnetic; Optical; Deteriorative

Classification of materials Metals: good heat and electric conductors, non-transparent, strong, flexible, lustrous. Ceramics: heat and electric insulators, hard but brittle, stable to high temperatures. Polymers: very flexible, typically light. Composites: combination of several materials. Semiconductors: special electromagnetic properties. Biomaterials: intended for use inside a living body.

Atom Atomic Force microscopic image of silicon crystal. 1Å = 10-10 m = 0.1 nm

Atom Atomic Force microscopic image of a single silicon atom.

Atom structure (Rutherford, 1911) Elementary particles: Proton Neutron Electron __________ Neutrino Meson Etc. Q=+1 m=1 Proton (p) nuclons Q=0 Neutron (n) Q= -1 m=0 Electron (ē, e-) electron [m] = a.m.u. (atomic mass unit) = 1.66053886 × 10-27 kg [Q] = 1ē = 1.60217646 × 10-19 C Np = Nē => Q (atom) = 0

Calculation of elementary particles composition Atomic mass ≈ 24 a.m.u. Atomic number = 12 ____________________________ Atomic number = N(p) = N(ē) Atomic mass = N(p) + N(n) N(p) = 12 N(ē) = 12 N(n) = 12

Quantum model of electron in atom Electron is a special physical object having both corpuscular and wave properties. In the quantum model electron is best described by mathematical formalism as complex wave function ψ. ψ∙ψ* = probability density. Probability density can be visualized as the electron cloud. The most dense region of the electron cloud is referred to as orbital.

Schroedinger equation Mathematically a wave function is a solution of the Schroedinger equation (for a single electron in 3D space): Solutions are functions of 3 numbers called quantum numbers

Quantum numbers n (main quantum number) = 1, 2, 3, 4, 5, 6, 7, … determines the distance from the nucleus; l (orbital quantum number) = 0… (n-1) determines the shape of an orbital; designated as s, p, d, f etc. m (azimuthal quantum number) = -l…0…+l determines the spatial orientation of the orbital; s (spin quantum number) = ± ½;

Electron orbitals

Orbitals and electron levels n = 1 (1st level) => l = 0 (s-orbital), m = 0 (only one orbital), s = ± ½ (two electrons). n = 2 (2nd level) => l = 0, 1 (s- and p-orbitals) For s-orbital m = 0 => one orbital; For p-orbital m = -1, 0, +1 => three orbitals. 2ē on each orbital => eight ē totally. n=3 (3rd level) => l = 0, 1, 2 (s-, p- and d-orbitals) For s- and p-orbitals all is as before For d-orbitals m = -2, -1, 0, +1, +2 => five orbitals 2ē on each orbital => eighteen ē totally. n = 4 (4th level) => l = 0, 1, 2, 3 (s-, p-, d- and f-orbitals) For s-, p- and d-orbitals all is as before For f-orbitals m = -3, -2, -1, 0, +1, +2, +3 => seven orbitals 2ē on each orbital => thirty two ē totally.

Periodic Law Mendeleev (1869), Mayer (1870): The physical and chemical properties of the elements recur in a systematic manner with increasing atomic number.

Modern understanding of the Periodic Table Closed electron outer shell is stable (2ē for the 1st row or 8ē for the other rows). Each element tends to have a stable outer shell. Metals have 1-4 outer electrons and are ready to give up “extra” electrons. Non-metals have 1-4 missing electrons and tend to receive them to form a stable shell. The outer shell of light atoms is close to the nucleus; that is why these elements are more “non-metallic”. The outer shell of heavy atoms is far from the nucleus; that is why these elements are more “metallic”.

Examples: H (number 1, mass 1)

Examples: He (number 2, mass 4)

Examples: Li (number 3, mass 7)

Examples: B (number 5, mass 11)

Examples: Na (number 11, mass 23)

Musts of this lecture What is material science? Classification of materials. Atomic structure (nucleus, nucleons, electrons). Electron structure (orbital, level). Periodic table (row, group). Metal and non-metal character.