Material Science : Chapter 2 Notes

Chapter 2

Properties of solid metals depend on geometrical atomic arrangements and also the interactions that exist among constituent atoms or molecule.

Charge	Weight	Charge Equivalent
Electron	9.11 x  kg	1.602 x  C
Proton	1.67 x  kg	-1.602 x  C
Neutron	1.67 x  kg	0

Isotope – elements that have two or more different atomic masses.

A = Z + N

Atomic Mass = (# of protons) + (# of neutrons)

                A – atomic mass. The sum of the masses of protons and electrons within the nucleus

                Z – atomic number. Number of Protons in nucleus. Ranges from 1 (Hydrogen) to 92 (Uranium). For neutral atom, #                 of proton = # of electrons

                N – neutrons;

1amu/atom = 1 molecule = 1g/mol

Isotopes – elements that has uniform # of protons but differs in # of neutrons.

Atomic Weight – corresponding average weight of the natural occurring isotopes.

Quantum Mechanics is set of principle and law that govern system of atomic and subatomic entities.

“Electrons are permitted to have only specific values of energy”

Quantum Numbers – size, shape, spatial orientation.

Quantum Number	Shell Designation	Subshells	Number of States	Number of Electrons
				Per subshell	Per Shell
1	K	S	1	2	2
2	L	S	1	2	8
		p	6	6
3	M	S	1	2	18
		P	3	6
		D	5	10
4	N	S	1	2	32
		P	3	6
		D	5	10
		F	7	14

Electron States- values of energy that are permitted for electrons.

Pauli Exclusion Principle states that each electron state can hold no more than two electrons, which must have opposite spins. S – 2, P – 6, D – 10, F – 14

                Ground state – when all lowest possible energies is occupied.

                Electron Configuration represents the manner in which these states are occupied.

                Valence Electrons are those occupy the outermost shell.

Periodic Table

Elements are classified according to electron configuration and increasing atomic #, in seven horizontal rows called periods

1A

O

2A

3A

4A

5A

6A

7A

3B

4B

5B

6B

7B

8

8

8

IB

2B

O – inert gas, filled electron shell, stable.

7A (halogens), 6A – one or two electron deficient

1A (Alkali), 2A (Alkaline) – one or two excess electron

3B-2B –transition metal, partially filled d electron state

3A-5A – has character between metal and nonmetal.

Electronegative – right hand side of the PT. (donate electron to become positively charged ion)

Electropositive- left hand side of the PT. (Accept electron to become negatively charged  ion)

Bonding Energies

                Fn = Fa + Fr                                         0 = Fa + Fr                                           En = Ea + Er

Primary Interatomic Bonds

1.       Ionic Bonding (donates electrons to nonmetallic) – occurs between metallic and nonmetallic elements.

                % ionic character = ( 1 – exp [-0.25 (Xa – Xb)^2 ]) x 100; Xa, Xb – electronegativity of the elements

2.       Covalent Bonding (sharing electrons) – occurs on nonmetals

                               

3.       Metallic Bond – occurs on metals and alloys

                Ea = -A / r

                Eb = B / r^n ; n=8

                A= k (z1 e)(z2 e);              e=1.602 x10^-19 c,           k=9x10^

Secondary Bonding / Van der Waals Bonding – occurs only when three bonding are present.

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