Materials T1 - Atomic Structure

4 Classes of Materials

Metal, ceramic, polymer, composite

Isotopes

Atoms of same element with different number of neutrons

Atomic Weight

Weighted average of atomic masses of the atom’s naturally occuring isotopes

Bohr Atomic Model

Electrons revolve around nucleus in discrete orbitals, position defined by 1 quantum number

Wave-Mechanic Model

Electrons have wave and particle properties and are in orbits defined by probability, position defined by 4 quantum numbers

Principle Shell

n, energy shell level

Subshells, l

s, p, d, f

2

Number of e- in s subshell

6

Number of e- in p subshell

10

Number of e- in d subshell

14

Number of e- in f subshell

Magnetic

m_l, defines no. of energy state from -l to +l

Spin

m_s, defines electron orientation (+1/2, -1/2)

Valence Electrons

Electrons in outer-most shell

Group

Columns, same no. of valence electrons

Period

Rows, same no. of electron shells

Total Interatomic Force

F_Net = F_Attractive + F_Repulsive

Energy Required for Atom Separation

E_Net = E_Attractive + E_Repulsive

Higher Bonding Energy

Higher melting temperature

Ionic Bonds

Electron tranfer between atoms with dissimilar electronegativity, between metals and nonmetals

Covalent Bonds

Electron sharing between atoms with similar electronegativity, between nonmetals

Metallic Bonds

Free electrons in crystalline metal structure adhere positively charged ions, between metals

Mixed Bonds

Colvalent and ionic bonding, greater electronegativity difference means more ionic

Secondary Bonding

Interactions between dipoles

Fluctuating Dipole Interaction

Instantaneous secondary bond caused by unequal distribution of electrons

Permanent Dipole Interaction

Permanent secondary bond between polar molecules

Hydrogen Bonding

Occurs between covalent-bonded hydrogen with fluorine, oxygen or nitrogen

Atomic Radius

Largest at bottom left of table, smallest at top right of table

Ionisation Energy, Electron Affinity, Electronegativity

Greatest at top right of table, lowest at bottom left of table

Crystalline

An orderly array of atoms that have a repeating unit

Amorphous

Non-crystalline

Unit Cell

Smallest repetitive entity in crystal

Lattice Parametres

Size and shape of unit cell

Simple Cubic

Coordination Number = 6

Body Centred Cubic

Coordination Number = 8

Face Centred Cubic

Coordination Number = 12

Hexagonal Close Packed

Coordination Number = 12

Tetragonal

Orthorhombic

Monoclinic

Triclinic

Rhombohedral (Trigonal)

Hexagonal

Isotropic

Material properties are same in all directions

Anisotropipc

Material properties are dependent on direction

Vacancy

Point defect where atom is missing, common in metals

Self Interstitial

Point deffect where atom is inserted into interstitial space between structure

Edge Dislocation

Line defect where edge terminates, causes dislocation line

Screw Dislocation

Line defect where upper front region is shifted one atomic distance to right

Grain Boundaries

Plane defect, regions between crystals

Halogens

Group 17

Noble Gas (nonreactive)

Group 18

Transition Metals

Groups 3-12

Alkali Metals (highly reactive)

Group 1

Halogen (missing one e-)

Periodic group of 1𝑠²2𝑠²2𝑝⁵

Noble Gas (full outer shell)

Periodic group of 1𝑠²2𝑠²2𝑝⁶3𝑠²3𝑝⁶

Transition Metal (partially filled d shell)

Periodic group of 1𝑠²2𝑠²2𝑝⁶3𝑠²3𝑝⁶4𝑠²3𝑑⁸

Alkali Metal (one extra e-)

Periodic group of 1𝑠²2𝑠¹