Estructura atomica y enlace

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CHAPTER

2
Atomic Structure And Bonding
2-1

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Structure of Atoms
ATOM
Basic Unit of an Element Diameter : 10 –10 m. Neutrally Charged

Nucleus
Diameter : 10 m Accounts for almost all mass Positive Charge
–14

Electron Cloud
Mass : 9.109 x 10 –28 g Charge : -1.602 x 10 –9 C Accounts forall volume

Proton
Mass : 1.673 x 10 –24 g Charge : 1.602 x 10 –19 C 2-2

Neutron
Mass : 1.675 x 10 –24 g Neutral Charge

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Atomic Number and Atomic Mass
• • • Atomic Number = Number of Protons in the nucleus Unique to an element
Example :- Hydrogen = 1, Uranium = 92

Relative atomic mass = Massin grams of 6.203 x 1023 ( Avagadro Number) Atoms.
Example :- Carbon has 6 Protons and 6 Neutrons. Atomic Mass = 12.

One Atomic Mass unit is 1/12th of mass of carbon atom. • One gram mole = Gram atomic mass of an element. •
Example :-

One gram Mole of Carbon
2-3

12 Grams Of Carbon

6.023 x 1023 Carbon Atoms

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Periodic Table

Source: Davis, M. and Davis, R., Fundamentals of Chemical Reaction Engineering, McGraw-Hill, 2003.

2-4

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Example Problem
• A 100 gram alloy of nickel and copper consists of 75 wt% Cu and 25 wt% Ni. What are percentage of Cu and Ni Atoms in this alloy?Given:- 75g Cu Atomic Weight 63.54 25g Ni Atomic Weight 58.69
75 g

• Number of gram moles of Cu = • Number of gram moles of Ni =

= 1 .1803 mol

63 .54 g/mol

25 g

= 0 .4260 mol

58 .69 g/mol 1.1803 • Atomic Percentage of Cu = (1.1803+ 0.4260) ×100 = 73.5%

• Atomic Percentage of Ni =
2-5

0 . 4260 × 100 = 25 . 5 % (1 . 1803 + 0 . 4260 )

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Electron Structure of Atoms


• • •

Electron rotates at definite energy levels. Energy is absorbed to move to higher energy level. Energy is emitted during transition to lower level. Energy change due to transition = ∆E = hc
h=Planks Constant Absorb Energy (Photon) Emit Energy (Photon) = 6.63 x 10-34 J.s c= Speed of light λ = Wavelengthof light

λ

Energy levels
2-6

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Energy in Hydrogen Atom
• • Hydrogen atom has one proton and one electron Energy of hydrogen atoms for different energy levels is 13 .6 given by (n=1,2…..) principal quantum E = − 2 ev numbers n • Example:- If an electron undergoes transition from n=3 state to n=2state, the energy of photon emitted is ∆E = − 13 .6

• Energy required to completely remove an electron from hydrogen atom is known as ionization energy

3

2



13 .6

2

2

= 1 .89 ev

2-7

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Quantum Numbers of Electrons of Atoms Principal Quantum Number (n)
• Represents mainenergy levels. • Range 1 to 7. • Larger the ‘n’ higher the energy.
n=1 n=2 n=3 n=2 n=1 p Orbital (l=1)

Subsidiary Quantum Number l • Represents sub energy
levels (orbital). • Range 0…n-1. • Represented by letters s,p,d and f.
s orbital (l=0)

2-8

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Quantum Numbers of Electrons of Atoms (Cont..)Magnetic Quantum Number ml.
• Represents spatial orientation of single atomic orbital. • Permissible values are –l to +l. • Example:- if l=1, ml = -1,0,+1. I.e. 2l+1 allowed values. • No effect on energy. • • • •

Electron spin quantum number ms.
Specifies two directions of electron spin. Directions are clockwise or anticlockwise. Values are +1/2 or –1/2. Two electrons on same orbital have...
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