Base Units

Physical Quantities	SI Unit	Symbol
Length	meter	m
Mass	kilogram	kg
Time	second	s
electric current	ampere	A
Thermodynamic temperature	kelvin	K
Intensity of light	candela	cd
Amount of substance	mole	mol

Physical Quantities, Base and Derived Quantities

Physical Quantities:-

All those quantities in term of which laws of physics can be described and whose measurement is necessary to understand and problem, are call end physical quantities.

CATEGORIES OR TYPES OF Physical Quantities:-

Base Quantities:-

 Base quantities are those quantities which cannot be defined in term of other physical quantities.

Examples:-

• Length
• Mass
• Time

Derived Quantities:-

 Derived Quantities are those whose definitions are expressed in term of other physical quantities (Base Quantities)

Examples:-

• Velocity
• Acceleration
• Force

Kinetic Molecular Theory (KTG) (introduction and Explanation)

Kinetic Molecular Theory:-physical theory that explains the behavior of gases on the basis of the following assumptions: 

(1) Any gas is composed of a very large number of very tiny particles called molecules.

(2) The molecules are very far apart compared to their sizes, so that they can be considered as points.

(3) The molecules exert no forces on one another except during rare collisions, and these collisions are perfectly elastic, i.e., they take place within a negligible span of time and in accordance with the laws of mechanics. 

A gas corresponding to these assumptions is called an ideal gas . as the temperature of a real gas is lowered, or its pressure is raised, its behavior no longer resembles that of an ideal gas because one or more of the assumptions of the theory is no longer valid. The analysis of the behavior of an ideal gas according to the laws of mechanics leads to the general gas law, or ideal gas law: The product of the pressure and volume of an ideal gas is directly proportional to its absolute temperature, or PV = kT (see gas laws). Boyle's law, Charles's law, and Gay-Lussac's law, which are special cases of the general gas law, may also be easily derived. The theory further shows that the absolute temperature is directly proportional to the average kinetic energy of the molecules, thus providing an interpretation of the nature of temperature in general in terms of the detailed structure of matter (see temperature; Kelvin temperature scale). Pressure is seen to be the result of large numbers of collisions between the molecules and the walls of the container in which the gas is held. See thermodynamics.

Dipole Moment (introduction and Explanation):-

Introduction:-
Dipole moment (µ) is the measure of net molecular polarity, which is the magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges.

µ= Q X r

Dipole moments tell us about the charge separation in a molecule. The larger the difference in electronegativities of bonded atoms, the larger the dipole moment. For example, NaCl has the highest dipole moment because it has an ionic bond

EXPLANATION:-

For example, in CH3Cl molecule, chlorine is more electronegative than carbon, thus attracting the electrons in the C—Cl bond toward itself . As a result, chlorine is slightly negative and carbon is slightly positive in C—Cl bond. Since one end of C-Cl is positive and the other end is negative, it is described as a polar bond. To indicate the increased in electron density, the dipole is represented by an arrow with a cross at one end. The cross end of the arrow represents the positive end and the point of the arrow represents the negative end of the dipole.


The vector will point from plus to minus charge and run parallel with the bond between 2 atoms. The symbol δ indicates the partial charge of an individual atom. In addition, the direction of vector implies the physical movement of electrons to an atom that has more electronegativity when 2 atoms are separated by a distance of r. In other words, the electrons will spend more time around atom that has larger electronegativity.

Table 1: Dipole Moments of Some Compounds

Compound Dipole Moment (Debyes)
NaCl 9.0 (measured in the gas phase)
CH3Cl 1.87
H2O         1.85
NH3         1.47
CO2         0
CCl4 0

Polar molecules and Dipole-Dipole Interaction
A polar molecule is a molecule where one end has a positive electrical charge and the other end has a negative charge due to the arrangement or geometry of its atoms. Because polar molecules have a positive and negative charge ends, the positive charge end of a molecule will attract to the negative end of adjacent molecule with the same or different kind of molecule. The attraction beween two polar molecules is called dipole-dipole interaction. The attraction between two dipoles create a very strong intermolecular force, which have great influence in the evaporation of liquid and condensation of gas.

For example, Since water are polar molecules, the interaction between water molecules are so strong that it takes a lot of energy to break the bond between the water molecules. Therefore, the boiling point of polar substances are higher than those of nonpolar substance due to stronger intermolecular force among polar molecules.

Polar molecules and Ions Interaction
When a polar molecule is mixed with ion, the positive charge end of the polar molecule will be attracted to the negative charge called anion on the ion. Also, the positive charge called cation on the ion will be attracted to the negative charge end of the polar molecule. This ion-dipole interaction is stronger than the dipole-dipole interaction between polar molecules, but is weaker than the ion-ion interaction.

Since ions and polar molecule have positive and negative charge, we can use Coulomb's law to evaluate the force attraction between them



q1, q2 are the charges on atoms
ke is the proportionality constant
r is the distance between 2 separated charges..

Determination of Relative Atomic Masses of isotopes by Mass Spectrometry

Mass Spectrometer:-
 it is am instrument which is used to determine the exact masses of different isotopes of an element.
How to Measure the masses with Spectrometer:-
     Mass spectrometry works by ionizing chemical compounds to generate charged molecules or molecule fragments and measuring their mass-to-charge ratios.In a typical MS procedure a sample, which may be solid, liquid, or gas, is ionized. The ions are separated according to their mass-to-charge ratio.The ions are detected by a mechanism capable of detecting charged particles. The signal is processed into the spectra (singular spectrum) of the relative abundance of ions as a function of the mass-to-charge ratio. The atoms or molecules can be identified by correlating known masses by the identified masses or through a characteristic fragmentation pattern.
A mass spectrometer consists of three components: ion source, mass analyzer, and detector.The ionizer converts some portion of the sample into ions. There is a wide variety of ionization techniques, depending on the phase (solid, liquid, gas) of the sample, and the efficiency of various ionization mechanisms for the target species in question. An extraction system which removes ions from the sample and gives them a trajectory which allows the mass analyser to sorts the ions by mass-to-charge. The detector, which measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present. Some detectors also give spatial information, e.g. a multichannel plate.
Mass spectrometry has both qualitative and quantitative uses. These include identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation. Other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry (the chemistry of ions and neutrals in a vacuum). MS is now in very common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds.

Spectroscopy (Introduction and explanation):-

INTRODUCTION:-
Spectroscopy  is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is often represented by a spectrum, a plot of the response of interest as a function of wavelength or frequency.
One of the central concepts in spectroscopy is a resonance and its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency. This plot is one type of spectrum, with the peak often referred to as a spectral line, and most spectral lines have a similar appearance.
EXPLANATION:-
In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon. The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy  of a photon is related to its frequency  by  where  is Planck's constant, and so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can also excite resonant interactions.

Spectra of atoms and molecules often consist of a series of spectral lines, each one representing a resonance between two different quantum states. The explanation of these series, and the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first successfully explained by the Rutherford-Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can also overlap and appear to be a single transition if the density of energy states is high enough.

Concept Of Atom

The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons (except in the case of hydrogen-1, which is the only stable nuclide with no neutrons). The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain bound to each other by chemical bonds based on the same force, forming a molecule. An atom containing an equal number of protons and electrons is electrically neutral, otherwise it is positively or negatively charged and is known as an ion. An atom is classified according to the number of protons and neutrons in its nucleus: the number of protons determines the chemical element, and the number of neutrons determines the isotope of the element.

Chemical atoms, which in science now carry the simple name of "atom," are minuscule objects with diameters of a few tenths of a nanometer and tiny masses proportional to the volume implied by these dimensions. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.94% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass. Each element has at least one isotope with an unstable nucleus that can undergo radioactive decay. This can result in a transmutation that changes the number of protons or neutrons in a nucleus. Electrons that are bound to atoms possess a set of stable energy levels, or orbitals, and can undergo transitions between them by absorbing or emitting photons that match the energy differences between the levels. The electrons determine the chemical properties of an element, and strongly influence an atom's magnetic properties. The principles of quantum mechanics have been successfully used to model the observed properties of the atom.

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