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If the composite is designed and fabricated correctly, it combines the strength of the reinforcement with the toughness of the matrix to achieve a combination of desirable properties not available in any single conventional material. Some composites also offer the advantage of being tailorable so that properties, such as strength and stiffness, can easily be changed by changing amount or orientation of the reinforcement material. The downside is that such composites are often more expensive than conventional materials.
Section 2.3. The atomic bonding in Matter.
It should be clear that all matter is made of atoms. From the periodic table, it can be seen that there are only about 100 different kinds of atoms in the entire Universe. These same 100 atoms form thousands of different substances ranging from the air we breathe to the metal used to support tall buildings. Metals behave differently than ceramics, and ceramics behave differently than polymers. The properties of matter depend on which atoms are used and how they are bonded together.
There are 4 kinds of atomic bonding:
i.Metallic Bonding.
ii.Covalent Bonding.
iii.Ionic Bonding.
iv.Van-der-Waal Bonding.
All chemical bonds involve electrons. Atoms will stay close together if they have a shared interest in one or more electrons. Atoms are at their most stable and chemically inert form when they have no partially-filled electron shells such as Inert Gases /Noble Gases/Rare Gases such as He,Ne, Ar, Kr, Xe and Rn . These are odourless, colorless, monoatomic gases with very little reactivity hence they are called Inert Gases.
In Table 2.2 and Table 2.3. the salient parameters and the electronic shell configurations of the Noble Gases are given.
Table 2.2. The salient parameters of Noble Gases
| Gas | B.P(K) | M.P.(K) | Z* | Atomic radius(pm) | IonizationEnergy(eV) |
|---|---|---|---|---|---|
| He | 4.4Below 4.4K He exhibitssuperluidity | 0.95Solid He found in the Core of Jupiter.It Behaves like metal | 2 | 31 | 24.8 |
| Ne | 27.3 | 24.7 | 10 | 38 | 21.5 |
| Ar | 87.4 | 83.6 | 18 | 71 | 16 |
| Kr | 121.5 | 115.8 | 36 | 88 | 14 |
| Xe | 166.6 | 161.7 | 54 | 108 | 12 |
| Rn | 211.5 | 202.2 | 86 | 120 | 11 |
*Z = Atomic Number.
Table 2.3. Shell Structure of Inert Gas Atoms.
| Gas | Z | K-Shell(n=1) | L-Shell(n=2) | M-Shell(n=3) | N-Shell(n=4) | O-Shell(n=5) | P-Shell(n=6) |
|---|---|---|---|---|---|---|---|
| He | 2 | 1s 2 | |||||
| Ne | 10 | 1s 2 | 2s 2 ,2p 6 | ||||
| Ar | 18 | 1s 2 | 2s 2 ,2p 6 | 3s 2 ,3p 6 | |||
| Kr | 36 | 1s 2 | 2s 2 ,2p 6 | 3s 2 ,3p 6 ,3d 10 | 4s 2 ,4p 6 | ||
| Xe | 54 | 1s 2 | 2s 2 ,2p 6 | 3s 2 ,3p 6 ,3d 10 | 4s 2 ,4p 6 ,4d 10 | 5s 2 ,5p 6 | |
| Rn | 86 | 1s 2 | 2s 2 ,2p 6 | 3s 2 ,3p 6 ,3d 10 | 4s 2 ,4p 6 ,4d 10 ,4f 14 | 5s 2 ,5p 6 ,5d 10 | 6s 2 ,6p 6 |
Table 2.4. Simplified Shell Structure of Inert Gas Atoms.
| Gas | Z | ||||
|---|---|---|---|---|---|
| He | 2 | 1s 2 | |||
| Ne | 10 | He | 2s 2 ,2p 6 | ||
| Ar | 18 | Ne | 3s 2 ,3p 6 | ||
| Kr | 36 | Ar | 3d 10 | 4s 2 ,4p 6 | |
| Xe | 54 | Kr | 4d 10 | 5s 2 ,5p 6 | |
| Rn | 86 | Xe | 4f 14 | 5d 10 | 6s 2 ,6p 6 |
K, L, M, N, O and P-Shell are major Shells corresponding to the Principal Quantum Number n = 1,2,3,4,5 and 6.
Within each Shell there are Sub-Shells s, p, d and f.
Here we will briefly discuss the Periodic Table.
Principal Quantum Number: n → gives the energy quantization as well as the complete ONE period of elements.
Azimuthial Quantum Number: l → gives the orbital angular momentum quantization.
Magnetic Quantum Number: m → lħ , ( l -1)ħ……0,…….-( l -1)ħ, - lħ . This gives the orientation quantization. When a magnetic field B external is applied in Z-axis, Orbital Angular Momentum L will align so as to give an Integral Projection of l ħ on Z-axis as shown in Figure 2.2.
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