John Dolton chemistry

Introduction
John Dalton law was proposed by John Dalton in the year 1801. According to this law at a particular temperature, the total pressure of a mixture of two or more non-interacting gases is equal to the sum of partial pressures of the individual gases.
This law can be mathematically written as:
P_total = P₁ + P₂ + P₃ + ...
Here P₁, P₂, P₃ are the partial pressures of each component in the mixture.

John Daltons Atomic Theory, Laws of multiple proportions, Dalton’s law of partial pressure and for Daltanism.  Dalton concluded that evaporated water exists in air as an independent gas in the course of his studies.  Dalton found that evaporation might be viewed as a mixing of water particles with air particles. He performed a series of experiments on mixtures of gases to determine what effect properties of the individual gases had on the properties of the mixture as a whole and he was the first to associate the ancient idea of atoms with stoichiometry.  Dalton came to know the vital theoretical connection between atomic weights and weight relations in chemical reactions. The core concepts of Dalton’s theory are foundations of modern physical science.


                   John Dolton

Assumptions of John Dolton chemistry

All matter consists of tiny particles
Atoms are indestructible and unchangeable: According to this assumption of John Dalton atoms of an element cannot be created, destroyed, broken into smaller parts or transformed into atoms of another element. So he stated that atoms cannot be created, destroyed or transformed into other atoms in a chemical change.

Elements are characterized by the mass of their atoms: According to this assumption atoms of different elements have different weights.

When elements react their atoms combine in simple, whole number ratios:  In this postulate Dolton explained that compounds contained characteristic atom-to-atom ratios in this postulate he effectively explained the law of definite proportions.

When elements react, their atoms sometimes combine in more than one simple, whole-number ratio:  According to this postulate why the weight ratios of nitrogen to oxygen in various nitrogen oxides were themselves simple multiples of each other.

Atoms in compounds according to John Dalton Chemistry

The law of fixed composition

Conservation of matter and energy

Introduction
The conservation of matter and energy means that the total amount of energy and the total amount of matter is always constant in a given closed, isolated system. In other words, neither energy nor mass can be created or destroyed in any physical or chemical process.

Formation of the law of conservation of matter and energy

Until the discovery of mass - energy equivalence by Albert Einstein in 1905, conservation of matter and conservation of energy were two different conservation laws. Conservation of matter implied that matter can neither be created nor destroyed, and conservation of energy implied that energy can neither be created nor destroyed. The two were not related to each other in any  aspect except that they were both conversations laws.
But, as physics and science increased its parameters with the advance of technology,nuclear reactions were discovered, and it was discovered that in nuclear fusion and fission reactions, the total mass of reactants does not equal to the total mass of the products obtained. For example, in the following nuclear fusion reaction,
4H → 2He,
There is a difference between the mass of the reactants, that is, four atoms of Hydrogen, and the mass of the products, that is, one atom of Helium. This difference can be clearly depicted by the following diagram:-



The difference in the mass could not be explained by any laws, and furthermore, it was a direct failure of the law of conservation of mass. Huge amount of energy was produced in the above reaction, and this "creation" of energy and in was certainly a setback to the law of conservation of energy. But in 1905, Albert Einstein pointed out that in the chemical reactions like above, the difference in mass of the reactants and products is balanced by the release of energy, that is, some mass of the reactants was converted into energy, and since matter and energy are the same thing, conversion of matter into energy cannot be regarded as the creation of energy. He also gave the formula to calculate the amount of energy produced as follows:-
`e = mc^2` .

Conservation of Matter and Energy : Albert Einstein

Albert Einstein pointed out that matter and energy are the same thing, and matter can be converted to energy. Thus, if energy is being "produced" in a nuclear reaction, although the total calculated amount of energy is increasing, but since the calculated amount of mass is decreasing, and matter and energy are the same thing, therefore the total energy of the system can be regarded as constant.
Thus, the law of conservation of energy and the law of conservation of matter were combined, to form the law of conservation of matter and energy. Note that the term "The Law of Conservation of Energy" implies the law of conservation of matter and energy.

Conservation of Mechanical energy

Introduction :
Conservation of mechanical energy states that the whole mechanical power (sum of kinetic energy+ potential energy) of a structure remains stable provided the forces acting on the body are conservative. The standard of conservation of mechanical energy states, the whole mechanical energy of a conservation system leftovers constant.

Proof of Conservation of Mechanical energy

Suppose a particle of mass m moves from position x₁ to another position x₂ under the action of conservation force. As a result its velocity changes from v₁ to v₂. By work-energy theorem, we have

If V₁ and V₂ are the potential energies at positions x₁ and x₂, we have

If effort done by a conservative force is positive, the kinetic energy of body increases and potential energy of body decrease to stay total mechanical energy conserved.

Example of Freely Falling Body

Gravitational force is conservation force. When a body of mass m, initially at rest at height H, above the ground, falls under gravity, then its total mechanical energy remains constant.

At heighest point A:
The body is at rest, therefore kinetic energy,

Potential energy, V=mgh
Total mechanical energy at A=K+V=0+mgH=mgH

At point B:
Let the body reach at intermediate point B at distance x below point.

Potential energy=mg(H-x)

At point C:
Let C be the point on the ground. If v_C is the velocity at point C, then relation
V²=u²+2gs gives v²_C =0 +2gH=2gH
Kinetic energy,

Potential energy = 0
Total mechanical energy at C=mgH=0=mgH
Thus it is clear that for a freely falling body, the total mechanical energy remains constant.

Example of Mass-Spring System in Conservation of Mechanical Energy

Consider a spring-block system located on a horizontal frictionless table. Mass of block is M and force stable of spring is K. when mass is in position A, spring is in its usual length. So that elastic PE of spring is zero. When mass is taken to position B, the spring is stretched by an amount x₀, so elastic potential energy of spring (= (1/2 )kx₀²) and kinetic energy in this position = zero.

Torque Equation of a D.C Motor

Introduction:
The turning or twisting force about an axis is called torque. Consider a wheel of radius R meters acted upon by a circumferential force F Newton’s .Basically the torque is developed in the armature and hence, gross torque produced is denoted as T_a. The mechanical power developed in the armature is transmitted to the load through the shaft of the motor.

Torque Equation of a D.C Motor

Let us see about examples of torque,
The wheel is rotating at a speed of N r.p.m
Then angular speed of the wheel is,



So, work done in one revolution is,
W  =   F * distance travelled in one revolution
      =   F * 2π R Joules
P   =   Power developed = Work done/ Time



P  = T *ω      Watts
T = Torque   in  N  - m
ω = Angular speed in rad / sec.

let T_a be the gross torque developed by the armature of the motor in examples of torque. It is also called armature torque. The gross mechanical power developed in the armature is E_b I_a, as seen from the power equation. So if speed of the motor is N r.p.m. then,
Power in armature = Armature torque * ω



But E_b in a motor is given by,


This is the examples torque equation of a d.c motor.

Example of torque

Let us see about examples of torque,
A 4 pole d.c motor takes a 50 A armature current. The armature has lap connected 480 conductors. The flux per pole is 20 mWb. Calculate the gross torque developed by the armature of the motor.
Solution:

Types of torque in the motor

In examples of torque,the mechanical power developed in the armature is transmitted to the load through the shaft of the motor. It is impossible to transmit the entire power developed by the armature to load.This is because while transmitting the power through the shaft, there is a power loss due to the friction, windage and the iron loss. the torque required to overcome these losses is called lost torque.

Diffraction patterns

A method is described which assigns indices to a set of single-crystal reflections recorded by the rotation-oscillation technique using a fixed X-ray wavelength. It is assumed that the space group and approximate unit-cell parameters are known. The unknown crystal orientation is determined directly from the observed diffraction pattern of one or several oscillation data records. A local indexing procedure is described which tolerates large initial errors in the parameters controlling the diffraction pattern. These parameters are refined subsequently, thereby satisfying the constraints imposed by the space-group symmetry.

Diffraction bending of waves around the edge of an obstacle. When light strikes an opaque body, for instance, a shadow forms on the side of the body that is shielded from the light source. Ordinarily light travels in straight lines through a uniform, transparent medium, but those light waves that just pass the edges of the opaque body are bent, or deflected. This diffraction produces a fuzzy border region between the shadow area and the lighted area. Upon close examination it can be seen that this border region is actually a series of alternate dark and light lines extending both slightly into the shadow area and slightly into the lighted area. If the observer looks for these patterns, he will find that they are not always sharp. However a sharp pattern can be produced if a single, distant light source, or a point light source, is used to cast a shadow behind an opaque body.
The radiation diffraction pattern for amorphous materials requires special analysis for information on atomic groupings. Powdered crystalline material may also give diffuse patterns requiring this type of analysis. Absence of a sharp diffraction pattern does not necessarily indicate absence of the material. Examples are given for chrysotile and powdered chrysotile.

If the diffraction pattern of the hyperbolic umbilical diffraction catastrophe is produced by an optical system of increasing aperture, it passes continuously from the two-dimensional system of Airy rings in the focal plane, made by a very small aperture, to the full three-dimensional pattern corresponding to infinite aperture. The paper studies this transition by examining the truncated diffraction integral and following the evolution of the wave dislocation lines (phase singularities) on which the pattern is based. The seed of the evolution from a two-dimensional to a three-dimensional pattern turns out to be already present asymptotically even for the smallest aperture: namely, a column of small dislocation rings very close to the axis that stream in procession towards the focal plane, and become dislocations lying in the Airy fringe surfaces that run parallel to the main fold caustic, only to disappear ultimately by retreat to infinity. The evolution into the final dislocation pattern takes place by a sequence of primitive local topological events, such as reconnection (hyperbolic interchange) and ring creation.

X Ray diffraction Analysis

Introduction
After the discovery of X-rays, scientist started working on the wave nature of these rays. To test the nature, X-rays have to produce interference and diffraction patterns. For diffraction to occur, the wavelength should be in the order of its slit width. But we know that X-ray have shorter wavelength and it is quite impossible to make such a slit / grating of smaller dimension. So the wave nature was studied in atomic level. Scientist by name Laue suggested that crystal can act like a space grating to observe diffraction. This experiment was later supported by Bragg’s equation.

X Ray diffraction Analysis : Bragg’s law

Consider a plane lattice crystal with inter planar distance d. Suppose a beam of X-rays of wavelength λ  is incident on the crystal at an angle θ , the beam will be reflected in all possible atomic planes. The path difference between any two reflected waves is equal to the integral multiple of wavelength. The ray P gets reflected from the surface while the ray Q has to under go some path difference. The extra distance traveled by the ray Q from the figure is
 (BC +CD). From the diagram either BC or CD is equal to d sin theta. So the path difference is
    d sin θ  + d sin θ  = n λ
    2 d sin θ  = n λ
 Here n is the order = 1,2, 3 …… .This is Braggs law

X Ray diffraction : Analysis of the Pattern

The crystal which is considered as the slit is placed in the Bragg spectrometer for investigation. X-rays are incident on the crystal at different angles and its corresponding ionization current is noted. The below is the plot of ionization current and incident angle
 
  At a certain values of the angle of incidence, the ionization current is increases abruptly or at peak value. Basing on the angle at maximum current, the planar distance can be calculated using Bragg’s law.

 When the angle increases i.e. order of the spectrum, the intensity of the X- rays decreases

Ionization current will never fall to zero.

Thus we can say the diffraction analysis of X-rays helped us to study the crystal structure.

Multiple slit diffraction

Introduction to diffraction:
                The wave nature of the light is further confirmed by the phenomenon of diffraction. The word diffraction is derived from the Latin word diffracts which means break to pieces. When the waves are encountering obstacles they bend round the edges of the obstacles if the dimensions of the obstacles are comparable to the wavelength of the waves. The bending of waves around the edges of an obstacle is called diffraction.

Diffraction

Diffraction in opening:
                The diffraction may be take place in single or multiple slits. Here we are going to see about the diffraction by considering the passage of waves through the opening. When the opening is large compared to the wave length the waves do not bend round the edges which is given as,
                                                                                 
             When the opening is small, the bending effect round the edges is noticeable. When the opening is very small the waves spread over the surface behind the opening. The opening appears to act as an independent source of waves which propagate in all direction behind the opening.

Multiple slit diffraction

Diffraction in multiple slit:
                  Here we are going to discuss about the diffraction at multiple slits. We have seen the narrow slit gives a diffraction pattern considering of a principal maximum flanked by secondary maxima of lower intensity. In case of the multiple slit, each slit produces the similar diffraction effects in the same direction and the observed pattern is crossed by a number of interferences fringes. The regions of first order, second order, etc. maxima contain equally spaced fringes but they will be progressively fainter.
                 The envelope of the intensity variation of the interference fringes is identical to that of the diffraction pattern due to a single slit. In general I_S is the intensity at a point due to interference of light from multiple slits and I_d is the intensity due to diffraction of a single slit, then the resultant intensity I is given by,
                                                                                    I = I_d `xx` I_S
                Hence if I_d=0 at any point, then I=0 at that point irrespective of the values of I_S. The intensity and sharpness of the principal maxima increase and those of the secondary maxima decrease.
                When the slits are large in number, bright narrow lines are visible on a dark background . The greater the number of slits and the closer they are the narrower and brighter are the lines on the screen. Bringing the slits closer results, of course, in an increase in the distance between the lines on the screen.

Laser diffraction

The first laser diffraction system designed by Malvern Instruments was first introduced in the 1970’s. Since then, the technique has been accepted across a wide range of applications as a means of obtaining rapid, robust particle size data. The pages below provide an introduction to how the technique works and how the results obtained compare to other methods of particle size analysis.

Tri-Laser Diffraction Technolology

The TRI-LASER Diffraction System developed by MICROTRAC allows light scattering measurements to be made from the forward low angle region to almost the entire angular spectrum (approximately zero to 160 degrees). It does so by a combination of three lasers and two detector arrays, all in fixed positions. The primary laser (onaxis) produces scatter from nearly on-axis to about 60 degrees, detected by a forward array and a high-angle array, both of which have logarithmic spacing of the detector segments. The second laser (off-axis) is positioned to produce scatter beyond the 60 degree level which is detected using the same detector arrays. The third laser (off-axis) is positioned to produce backscatter, again using the same detector arrays. This technique effectively multiplies the number of sensors that are available for detection of scattered light.

During a measurement cycle, Laser 1 is switched on while Lasers 2 and 3 remain inactivated. The sample to be measured scatters light in an angular pattern depending on the material size. The scattered light from Laser 1 is detected by the on axis, forward detector and the off axis, high angle detector. Laser 1 is then switched off and Laser 2 is activated. Laser 2 is directed at the sample at a different angle of incidence providing a different optical axis. Light scattered by the sample is detected by the same fixed detectors. Laser 2 is then switched off and Laser 3 is activated. Again the angle of incidence and optical axis is different. In this case the fixed detectors detect light that is back–scattered by the sample. The resultant scattered light information from all three lasers is combined to generate particle size distributions with unsurpassed resolution. Tri laser diffraction technology is proprietary and is patented by Microtrac.

Electron Diffraction

Electyron Diffraction refers to the wave nature of electrons. However, a from of technical or practical point of view, it may be regarded as a technique used to study matter by firing electrons at a sample and observing the resulting interference pattern. This phenomenon is commonly known as the wave particle duality, in which it states that the behavior of a particle of matter (in this case the incident electron) can be described by a wave. For this reason an electron can be regarded as a wave, like sound or water waves. This technique is similar to X-ray and neutron diffraction.

Electron diffraction is most frequently used in the solid state physics and chemistry to study the crystal structure of solids. Experiments are usually performed in the transmission electron microscope (TEM), or a scanning electron microscope (SEM) as electron back scatter diffraction. In these instruments electrons are accelerated by electrostatic potential in order to gain the desired energy and determine their wavelength before they interact with the sample to be studied.

Electron Diffraction in Materials Science

Electron diffraction is an very important technique for crystallographic characterization, a valuable complementary tool to powder and single crystal X-ray diffraction.

Applications include phase identification and precision determination of suitable structural details for crystals in the micrometer to nanometer size range.

Electron Diffraction with the PDF-4+ Database

• The PDF-4+ database can be used to generate two types of electron diffraction patterns for all PDF entries with atomic coordinates:
  1.   Transmission electron spot patterns
  2.   Electron back scattering patterns
• To illustrate electron diffraction pattern generation with the PDF-4+ database, Iron (Fe, face centered
• cubic (FCC), space group Fm-3m) will be used as an example.
• The PDF-4+ database cannot perform search-match procedures directly on digital electron diffraction patterns, they must first be indexed to obtain a d-spacing-intensity (d/I) list. Search-match procedures can then be performed using SIeve+.
• Electron diffraction patterns generated by the PDF-4+ database do not account for intensity variation due to either sample or instrumental effects.

Term Diffraction

Introduction
The term diffraction in the case of waves refers to their bending round the obstacles. When the obstacle is large compared to the wavelength no wave bends around the edges of the obstacle. When the size of the obstacle is small compared to the wavelength of the light waves bend round the edges of the obstacle. When the size of the obstacle is very very small the waves bend round it so that we find no practical effect on the wave. The diffraction phenomena is more predominant when the size of the obstacle is small and is comparable with the wavelength of the incident light.
                                  
 One of the examples of diffraction phenomena is that when a beam of light passes from a narrow slit it spreads out to certain extent in the geometrical shadow.
                                               
In the above figure an obstacle AB with a straight edge is place in the path of a light wave spreading from a narrow slit illuminated by a monochromatic light source. The straight edge A is parallel to the slit S. The geometric shadow of edge A on the screen C is not sharp. A small portion of the light bends around the edge A into the geometrical shadow below the point C. Intensity gradually decreases as we enter into the shadow below C. As we go above C, the intensity alternately increases and decreases; several bright and dark bands parallel to the edge are observed. These bands are called diffraction pattern. The width of these bands goes on decreasing as we go upwards and uniform illumination is observed farther away from C

Term Diffraction : Pattern

                        
    A very small circular disk of diameter AB obstructs the path of (rays) waves emerging from a point source S. The diffraction pattern is observed on the screen SC. If the light propagates in straight line there would be a shadow of diameter CD on the screen. If the distance between the disk AB and the screen CD is great enough, we find diffraction pattern consisting of alternating dark and bright rings with a bright circular spot at the centre at 'O'.

Term : Diffraction

The diffraction phenomena is observed when the condition l `~~` b² / 4`lambda`  is satisfied, where l is the distance between the object and the screen, b size of th object an d`lambda`  is the wavelength of light obstructed by the object. There is a little difference between the formation of interference and diffraction patterns, though superposition of waves is involved in both the cases. Interference is the result of superposition of light waves emitted by two or more number of separate coherent sources, where as diffraction is due to superposition of light wavelets originating from every point of a wavefront which act as infinitely small coherent sources. Diffraction effects are observed only when a portion of the wave front is obstructed by the obstacle.

Electron diffraction pattern

Electron diffraction refers to the wave nature of electrons. However, from a technical or practical point of view, it may be regarded as a technique used to study matter by firing electrons at a sample and observing the resulting interference pattern. This phenomenon is commonly known as the wave-particle duality, which states that the behavior of a particle of matter (in this case the incident electron) can be described by a wave. For this reason, an electron can be regarded as a wave much like sound or water waves. This technique is similar to X-ray and neutron diffraction.

Electron diffraction is most frequently used in solid state physics and chemistry to study the crystal structure of solids. Experiments are usually performed in a transmission electron microscope (TEM), or a scanning electron microscope (SEM) as electron backscatter diffraction. In these instruments, electrons are accelerated by an electrostatic potential in order to gain the desired energy and determine their wavelength before they interact with the sample to be studied.

Most electron diffraction is performed with high energy electrons whose wavelengths are orders of magnitude smaller than the interplanar spacings in most crystals. For example, for 100 keV electrons l < 3.7 x 10-12 m. Typical lattice parameters for crystals are around 0.3 nm.

Electrons are charged, light particles and their penetration into solids is very limited.LEED and RHEED are therefore considered to be surface science techniques, while transmission electron diffraction is limited to specimens less than 1 mm thick. Transmission electron diffraction is usually carried out in a transmission electron microscope (TEM).

Features of electron diffraction

There are three particularly important features of diffraction using high energy electrons:
(1) Since l is very small, Bragg angles are also small, so the Bragg Law can be simplified to:
    l = 2dqB
(2) The diameter of the Ewald sphere is very large compared to the size of the unit cell in the reciprocal lattice.
(3) Lenses are able to focus the diffraction pattern and to change the camera length, which is equivalent to moving the film in an x-ray experiment.

Total ionic equation

Ions are formed when electrons are either added or removed from the atoms. Chemical reactions are represented by simple molecular formulas. However the reactions actually take place by means of ions.
When reactions take place in aqueous medium that is, in presence of water, the atoms in the molecule either gain or lose electrons to form ions. These ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking place by means of ions. However when done so, it is called total ionic equation.

Introduction to Total ionic equation:

Following denotions are used while writing the ionic equation.
(l) in the subscript  means the compound is in its liquid state,
(s) in the subscript means solid state.
(g) in the subscript means gas state.
The ionic reactions are single or double displacement reactions and are possible only with electrolytes.

Total ionic equation: Illustration-I

Let us consider a reaction of iodine precipitation from bromine and sodium iodide.
Br2_(l) + 2 NaI_(aq) -----------> 2 NaBr_(aq) + I2_(s)
Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionic compound, would dissociate into ions in water, hence represented by (aq), same about sodium bromide too.
However the iodine molecule in the products is insoluble in water and hence shown as solid which precipitates.
To write the total ionic equation, write the ionic forms as
2NaI ------------>2 Na⁺_(aq) +2 I^-_(aq)
Br2--------------->2Br^-_(aq)
Also in the products,
2 NaBr_(aq)---------------> 2 Na⁺(aq) + 2 Br^-_(aq)
Thus the total ionic equation is written as
Br_2(l) + 2 Na⁺_(aq) +2 I^-_(aq) ----->  2 Na⁺(aq) + 2 Br^-_(aq) + I2(s).

Total ionic equation: Illustration-II

Consider another example of formation of silver chloride from silver nitrate
CaCl_2(aq) + 2AgNO_3(aq) Ca(NO₃)_2(aq) + 2AgCl_(s)

The dissociation would be
CaCl_2(aq)--------------> Ca²⁺_(aq) +2Cl⁻_(aq)
2AgNO_3(aq)-----------------> 2Ag⁺ _(aq)+ 2NO₃⁻_(aq)
    Thus the total ionic equation would be:

Ca²⁺_(aq) + 2Cl⁻ _(aq)+ 2Ag⁺_(aq) + 2NO₃⁻_(aq) Ca²⁺_(aq) + 2NO₃⁻ _(aq)+ 2AgCl_(s)

Writing net ionic equations

Ions are formed when electrons are either added or removed from the atoms. Chemical reactions are represented by  simple molecular formulas.  However the reactions  actually take place by means of ions.

When reactions take place in aqueous medium that is, in presence of water, the atoms in the molecule either gain or loose electrons to form ions.  these  ions then combine with other ions to form resultant products. Generally the reactions are not shown as taking by means of ions.However when done so,it is called total ionic equation.

Following denotions are used while writing the ionic equation.
(l) in the subscript  means the compound is in its liquid state,
(s) in the subscript means solid state.
(g) in the subscript means gas state.

Illustration of writing net ionic equations

2NaI _(aq) +Br2 _(aq)--------------->2NaBr _(aq) +I_2(s)
 (aq) Bromine exists as liquid at room temperature hence marked (l).
Sodium iodide being an ionically bonded compound,would dissociate into ions in water ,hence represented by (aq), Same about sodium bromide too. However the iodine molecule in the products is insoluble in water and hence shown as solid which precipitates.
To write the total ionic reaction,write the ionic forms,
2NaI ------------>2 Na⁺_(aq) +2 I^-_(aq)
Br2--------------->2Br^-_(aq)
Also in the products,
2 NaBr_(aq)---------------> 2 Na⁺(aq) + 2 Br^-_(aq)
Thus the total ionic reaction is written as
Br_2(l) + 2 Na⁺_(aq) +2 I^-_(aq) ----->  2 Na⁺(aq) + 2 Br^-_(aq) + I2(s),
But since some ions i.e.Na⁺(aq) are present on both sides,they can be said to have not taken part in the reaction and hence treated as spectator ions. So if we overlook these ions from both sides,

The net ionic reaction is :-
Br_2(l) + 2I-_(aq) -----> 2Br-_(aq) + I_2(s)
Br_2(l) + 2 Na⁺_(aq) +2 I^-_(aq) ----->  2 Na⁺(aq) + 2 Br^-_(aq) + I2(s)

Illustration II of writing net ionic equations

Consider another example of formation of silver chloride from silver nitrate
CaCl_2(aq) + 2AgNO_3(aq) Ca(NO₃)_2(aq) + 2AgCl_(s)
The dissociation would be
CaCl_2(aq)--------------> Ca²⁺_(aq) +2Cl⁻_(aq)#
2AgNO_3(aq)-----------------> 2Ag⁺ _(aq)+ 2NO₃⁻_(aq)
    Thus the total ionic equation would be:
Ca²⁺_(aq) + 2Cl⁻ _(aq)+ 2Ag⁺_(aq) + 2NO₃⁻_(aq) Ca²⁺_(aq) + 2NO₃⁻ _(aq)+ 2AgCl_(s)
The net ionic reaction is
Ca²⁺_(aq) + 2Cl⁻ _(aq)+ 2Ag⁺_(aq) + 2NO₃⁻_(aq) ---------> Ca²⁺_(aq) + 2NO₃⁻ _(aq)+ 2AgCl_(s)
2Cl⁻ _(aq)+ 2Ag⁺_{(aq)------------------>} 2AgCl_(s)

Naming ionic and molecular compounds

A chemical compound has a unique and defined chemical structure in which fixed ratios of atoms are held together in a defined spatial arrangement by chemical bonds. Basically there are two types of chemical compounds in chemistry, namely

Ionic compounds: Any substance which consists of two or more ionically-bonded atoms is called ionic compounds. A good example of an ionic compound is sodium chloride (table salt). In ionic compound, ions are held together in a lattice structure by ionic bonds. Positively charged ions are called cations and negatively charged ions are called as anions.


Molecular compounds: A molecule is the basic unit of a molecular compound. A molecule is defined as an object containing two or more atoms bonded together by covalent bonds. A molecule is the smallest particle of a compound which defines the properties of that compound. When a molecule is dissolved, it never dissociates.

naming ionic compounds

Ionic compounds dissolve in polar solvents which ionize, such as water and ionic liquids. They are also capable of dissolving in other polar solvents like alcohols, acetone and dimethyl sulfoxide. Ionic compounds do not tend to dissolve in non polar solvents.
According to International Union of Pure and Applied Chemistry IUPAC names of any ionic compound is written in two words. First name contains cation with oxidation number written in parentheses followed by the name of the anions. For example, the name of Fe₂ (so₄)₃  is written as iron(III) sulfate.

naming molecular compounds

We use chemical formula to describe the constituents of any chemical compound. Basically, there are three types of chemical formula namely, simple formula, graphic formula, and structural formula.

Simple formula:
In this formula, the elements are represented in symbolic form with subscripts to describe their ratio. Consider the simple formula of water which is H₂o. It shows the presence of two parts hydrogen and one part of oxygen.

Graphic formula:
In graphical formula, the element is represented in such a way to show the physical orientation of the constituent atoms to one another. The graphic formula of water is HOH. Water molecule has an atom of hydrogen to either side of an atom of oxygen.

Structural formula:
In structural formula, each and every atom is two dimensionally represented. The structural formula for water is given by H-O-H.

An example of a compound

An example of a compound is the common salt in pure form.
The molecular formula or the chemical formula of this compound is NaCl and it's a pure homogeneous compound.

The general physical appearance of this compound is :
it is white , crystalline in nature.The taste of this compound as we are all  familiar with:  it is salty.
The given compound is a salt and  is called sodium chloride.
This  chemical species is  called a compound, because of the following reasons:
It cant be separated into its constituent elements by any physical means and
the properties of this compound are totally different from the properties of its constituent elements.

why NaCl is a compound

     1) NaCl is a compound,because it is made up of Na and Cl atoms in a fixed ratio of 1:1
    2)   In the formation of the compound  NaCl, some amount of energy transformations took place and made this formation of NaCl.
      a permanent change ..... which means we cannot revert to the elemental state of Na and Cl from   NaCl  by any physical means.
      3)Example: the properties of Na and the properties of Cl are totally different than the properties of NaCl compound.

Other properties of a compound.

For example Na is a soft metal with grey colour and a metallic lustre and it is a solid , highly reactive  in presence of water( so its kept in kerosene always ), it can form an oxide as Na₂O.  when in presence of air and this oxide readily dissolves in water to form NaOH,....... but the salt has none of these properties.... the salt is crytalline , white in colour , dissolves readily in water but does  not form any base or alkali in water ,  is not so reactive in air or water  and has no metallic lustre.
The other element that forms NaCl is chlorine and that we know is a gas and is acidic ,,, it is also suffocating and acidic to moist  litmus.

Properties of compounds are thus not the same.....

But the salt is totally neutral and is not a gas but is a solid .In other words the compound has properties far different from the properties of any of the constituent elements.
 Further we cannot separate the constituent elements by any physical means.That is why we can differentiate between a compound and a mixture and study of compounds  becomes more interesting.