Revision : Empirical formula and structure of atom

Day 2
19.5.20
Good Morning Students,
we will be revising the concept of empirical formula and molecular formula. and we would also be revising the concepts of stucture of atom through google meet and blogs.

Learning outcomes :
student will be able to

• Recall the method for calculating empirical and molecular formula.
• Apply formula
• Revise the theories of quantum mechanical model of atom.

Empirical Formula And Molecular formula

An empirical formula represents the simplest whole number ratio of various atoms present in a compound.

Molecular formula shows the exact number of different types of atoms present in a molecule of a compound.

steps

Calculation of Empirical formula :

Step 1:- Conversion of mass per cent to grams.

Step 2:- Convert into number moles of each element

Step 3:- Divide the mole value obtained above by the smallest number

In case the ratios are not whole numbers, then they may be converted into whole number by multiplying by the suitable coefficient.

Step 4:- Write empirical formula by mentioning the numbers after writing the symbols of respective elements.

Calculation of Molecular Formula :

(a) Determine empirical formula mass

b) Divide Molar mass by empirical formula mass

n = (Molar mass/Empirical formula)

(c) Multiply empirical formula by n obtained above to get the molecular formula.

Characteristics of electromagnetic radiations:

• Wavelength: It may be defined as the distance between two neighbouring crests or troughs of wave. It is denoted by λ.

• Frequency (ν) (nu): It may be defined as the number of waves which pass through a particular point in one second.
• Velocity (v): It is defined as the distance travelled by a wave in one second. In vacuum all types of electromagnetic radiations travel with the same velocity which is 3 ×10 8m/sec. It is denoted by v.
• Wave number : Wave number is defined as the number of wavelengths per unit length.
  Velocity = frequency × wavelength, i.e, c = νλ 
•  Amplitude (a): It is the height of the crest or depth of the trough of a wave

  important formula 
1. Heisenberg’s uncertainty principle: 
$\Delta x.\Delta p>\frac{h}{4\pi }$ or $m\Delta x\cdot \Delta v\ge \frac{h}{4\pi }$ or $\Delta x.\Delta v\ge \frac{h}{4\pi m}$2. De-Broglie wavelength: $\lambda =\frac{h}{mc}=\frac{h}{p}\left(\text{for photon}\right)$

3. Wavelength of emitted photon: 
$\frac{1}{\lambda }=\overline{v}=R{Z}^2(\frac{1}{n_1^2}-\frac{1}{n_2^2})\; R\; =\; 1.096\; x\; 107 /m$4.  Planck’s Quantum Theory: 
 Energy of one photon $=hv=\frac{hc}{\lambda }$

$\frac{$ \left(n\right)=1,2,3,4\dots ..$}{$ \infty .$}$

5. Photoelectric Effect: 

$\text{hv}=h{v}_0+\frac{1}{2}{m}_e{v}^2$