Sainavle

NEET Foundation Notes For Physics Chapter 1 Motion Rate of Change of Velocity

Acceleration

In our daily life, the velocity of a moving object tends to vary a lot either in magnitude or in direction. We express this change in another physical quantity called acceleration. Acceleration is the rate of change of velocity with time, i.e., change in velocity per unit time. Numerically, it is expressed as:

\(\text { Acceleration }=\frac{\text { change in velocity }}{\text { time interval }}=v-\frac{u}{t}\)

For example, the direction of acceleration is along the direction of change in velocity of the body. Acceleration is vector quantity which can be negative, positive or zero depending on the change in the velocity. The direction of acceleration is along the direction of changes in velocity of the body.

Read and Learn More: NEET Foundation Notes

Retardation

Negative acceleration or retardation is the decrease in velocity per second. For retardation, the direction of the velocity is opposite to the direction of the acceleration.

Let us understand these with the following example.

Example

Let an object move in a straight line in the same direction with an initial velocity of u. After some time t, its velocity u becomes v.

So, change in velocity = v – u

Time interval = t

\(\text { Acceleration }=\frac{\text { change in velocity }}{\text { time interval }}\)

Therefore, Acceleration a = \(\frac{v-u}{t}\)

a t = v – u

v = u + a t

a = acceleration, if v > u, a is positive

a = retardation, if v < u, a is negative

Unit

\(\text { Unit of acceleration }=\frac{\text { Unit of velocity }}{\text { Unit of time }}\)

SI unit of acceleration = \(\frac{\mathrm{m} / \mathrm{s}}{\mathrm{s}}=\mathrm{ms}^{-2}\)

CGS. unit of acceleration = cm^-2

Uniform Acceleration

The uniform acceleration is one when equal changes in velocity take place in equal intervals of time.

Example: Free fall of a ball, which shows the motion of a body under gravity.

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

Variable Acceleration

If change in velocity is not same in the same intervals of time, it is called variable acceleration. For example, car moving in a crowded market.

Whenever the magnitude of velocity decreases, the rate of change of velocity is referred as retardation or deceleration. It is not necessary that the rate of change of velocity, i.e., the acceleration is always constant. In situation where the rate of change of velocity of a body in motion is not constant, the body is said to be moving with non-uniform acceleration or variable acceleration.

Acceleration due to Gravity

When an object falls freely, the acceleration produced in the body due to earth’s gravitational attraction is called acceleration due to gravity. It is donated by the letter g.

g = 9.8 m/s² (downward)

(~ 10 m/s², downward)

Due to gravitational force, all objects are accelerated towards the earth. This uniform acceleration towards the earth, irrespective of the mass is known as acceleration due to gravity and is denoted by ‘g’.

Equations of Uniform Accelerated Motion

Relation among velocity, distance, time, and acceleration is called equations of motion. There are three equation of motion for bodies moving with uniform acceleration.

First Equation of Motion:

v = u + at (1)

Second Equation of Motion:

s = \(u t+\frac{1}{2} a t^2\) (2)

Third Equation of Motion:

v² = u² + 2as (3)

Here,

v = final velocity of body

u = initial velocity of body

a = acceleration

t = time take by body

s = distance travelled by body in time t.

Average Velocity in Uniform Acceleration Motion

If a body move ‘s’ distance in ‘t’ time interval. Then,

\(\text { Average velocity }=\frac{\text { displacement }}{\text { time }}\)

=\(\frac{s}{t}\)

= \(\frac{u t+\frac{1}{2} a t^2}{t}\)

= \(u t+\frac{1}{2} a t\)

= \(u t+\frac{1}{2}(v-u)\)

= \(u+\frac{v}{2}-\frac{u}{2}\)

= \(\frac{u}{2}+\frac{v}{2}=\frac{u+v}{2}\)

Here ‘a’ is uniform acceleration of body.

NEET Foundation Chemistry Notes For  Chapter 4 Structure Of Atom Isotopes

Isotopes are the atoms having same number of protons, but different numbers of neutrons, i.e., they have different atomic weights. Isotopes are different forms of a single element. Till now, there are 275 isotopes of the 81 stable elements and over 800 radioactive isotopes have been discovered which are both natural and synthetic. Every element which is present on the periodic table has multiple isotope forms.

The chemical properties of isotopes of a single element are nearly identical. Except the isotopes of hydrogen, as the number of neutrons has a significant effect on the size of the hydrogen nucleus. Physical properties of isotopes are different from each other, as it depends on mass.

Read and Learn More: NEET Foundation Notes

So, Isotopes have same atomic number but different mass number and occur due to the presence of different number of neutrons in elements which have a same atomic number as mass number is the sum of the number of neutrons and protons. Not all elements have isotopes.

The isotopes of hydrogen are protium (has one proton and no neutrons) and that of deuterium (has one proton and one neutron) and tritium (has one proton and two neutrons). The chemical properties of isotopes are same as they have same number of protons and hence same number of electrons.

To Indicate Isotopes

• List the mass number of an element after its name or element symbol.
  For example, an isotope with 6 protons and 6 neutrons is carbon-12 or C-12. An isotope with 6 protons and 7 neutrons is carbon-13 or C-13.
• The mass number may be given in the upper left side of an element symbol.
  For example, the isotopes of hydrogen may be written as: ¹₁H, ²₁H, ³₁H

Isotopes of hydrogen

Example: Carbon-12 and Carbon-14 are isotopes of carbon, one with 6 neutrons and one with 8 neutrons. Carbon-12 is a stable isotope, while carbon-14 is a radioactive isotope (radioisotope).

Radioactive Isotope

It has an unstable combination of protons and neutrons, and that is why they have an unstable nucleus. Because these are unstable, hence they undergo decay and emit alpha, beta and gamma rays. Radioactive isotopes can be useful in different industries, such as food, agriculture, archaeology and medicine.

Fractional Mass Number

The atomic masses of most elements are fractional as there may be a mixture of isotopes of different masses, so the fractional atomic masses arise because of this mixture.

\(\text { Average mass }=\frac{\text { total mass of all atoms }}{\text { number of atoms }}\)

Application of Isotopes

• The identification of primary and secondary food sources.
• Tracing nutrient and mineral uptake by plants and animals.
• Determining the relative importance of plants and microbes to greenhouse gas emissions from soil.
• Measuring environmental stressors by monitoring plant uptake of CO2 and/or water.
• Tracing the sources of catchments waters.
• Isotope of Uranium 23592Ur, is used in nuclear plants to generate electricity.
• The use of isotopes is very common in Isotopic Labelling. Unusual isotopes are used as tracers or markers in chemical reactions.
• Radiations of radioactive isotopes can be used for detecting various reactants, rates, and so on in chemistry.
• Isotopes are used in Radiometric Dating, similar to Radio Isotopic Labelling or Radiocarbon Dating to study chemical processes by using naturally occurring isotopic tracers.
• Isotopic substitution can be used to determine the mechanism of a reaction using Kinetic Isotope Effect.
• Isotopes exhibit different nuclear properties as they have varied numbers of neutrons. This also affects their physical properties.
• Spectroscopy uses many unique nuclear properties of specific isotopes. For example, Nuclear Magnetic Resonance (NMR) spectroscopy can be used only for isotopes with a nonzero nuclear spin. Isotopes commonly used for NMR spectroscopy are ¹₁H, ²₁D, ¹⁵₇N, ¹³₆C, and ³¹₁₅P.

Isobars

Term “isobars” for nuclides was suggested by Alfred Walter Stewart in 1918 and is derived from the Greek word isos, which means “equal” and baros, means “weight”

Isobars are atoms of different chemical elements having the same number of nucleons. Isobars has different atomic number but same mass number. Example of isobars are ³²₄₀S, ³⁴₄₀Cl, ¹⁸₄₀Ar, ¹⁹₄₀K, and ²⁰₄₀Ca. The nuclei of all these nuclides contain 40 nucleons but are varying in numbers of protons and neutrons.

So, Isobars are the atoms having same mass number but different atomic number. For example, the atomic number of carbon and nitrogen is 6 and 7 respectively.

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

Example:

Isotones

Isotones are the atoms that have the same neutron number but different number of proton. For example, ³⁶₁₆S, ³⁷₁₇Cl, ³⁸₁₈Ar, ³⁹₁₉K and ⁴⁰₂₀Ca are all isotones of 20 since they all contain 20 neutrons.

NEET Foundation Chemistry Notes For Chapter 3 Atoms And Molecules About Atom

An atom is the smallest unit of matter which has the chemical properties of the element. An atom has number of constituents which may vary according to the different elements. It means that atoms of different elements will be of different size.

The earlier thinkers considered atom to be the smallest reachable unit which cannot be broken down further. But, it is now a basic knowledge that atom can be broken into its constituents but these constituents do not have the chemical properties of the atom.

Read and Learn More: NEET Foundation Notes

Size of the Atom

The atom is the smallest unit of the element. It is now known that atoms of different elements vary not only in mass but also in size. But, there is still no consensus on the shape of the atom. But as a general rule the shape of an atom is considered to be spherical. That is why the radius of the atom is discussed. The size of atom is measured in nanometre.

The magnified image of the atoms on the surface of the elements can be seen with the new technique called scanning tunneling microscopy (STM).

As we know, atoms are made up of three particles: protons, neutrons and electrons. Protons and neutrons are heavier than electrons and reside in the center of the atom, which is called the nucleus. Electrons are extremely lightweight and exist in a cloud orbiting the nucleus. The electron cloud has a radius 10,000 times greater than the nucleus.

Protons and neutrons have approximately the same mass. However, one proton weighs more than 1,800 electrons. Atoms always have an equal number of protons and electrons, and the number of protons and neutrons is usually the same as well. Adding a proton to an atom makes a new element, while adding a neutron makes an isotope, or heavier version, of that atom.

Atomic Number and Atomic Mass

Protons exist in the nucleus of an atom and the number of protons of an atom constitutes the atomic number. Its symbol representation is done by ’z’. Similar atomic number is possessed by all atoms of an element. Elements are defined by the number of protons they possess. So the total number of protons present in the nucleus of an atom is called atomic number.

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

Example: For hydrogen, z = 1, because in hydrogen atom, only one proton is present in the nucleus. Similarly, for carbon, z = 6.

On observation of properties of the subatomic particles of an atom, it can be concluded that the mass of an atom is due to neutrons and protons. They are found in nucleus of the atom hence called nucleons. So, the mass of an atom resides in its nucleus. The amount of the total number of protons and neutrons present in the nucleus of an atom is called atomic mass.

Example: Mass of carbon is 12 u because it has 6 protons and 6 neutrons, 6 u + 6 u = 12 u. Similarly, the mass of aluminium is 27 u (13 protons + 14 neutrons).

Atomic masses of a few elements

Valency

Electrons exist in different orbits and the electrons present in the outermost orbit are known as valence electrons. The outmost shells can contain maximum of 8 electrons as per Bohr and Bury. It was noticed in an atom with completely filled outermost shell show little chemical activity meaning their combining capacity or valency is zero.

The only exception to this rule is helium. It has two electrons in its outermost shell. Except this all the inert elements have 8 electrons in the outermost orbit.

So, valency is a tendency in an atom to achieve the state of stability by achieving 8 electrons in its outermost shell by receiving, leaving or sharing of electrons from other atoms. It simply means that if an atom has 1 electron in its last orbit it will have a tendency to lose this electron for achieving stability. So it will have valency of

1. On the other hand if an atom has 6 electrons in its last orbit it should be easier for this atom to take 2 electrons for the other atom instead of leaving 6 electrons. So, the valency will be 2.

Example: CO₂ is made up of 1 carbon and 2 oxygen atoms. Valency of carbon is 4 while valency of oxygen is 2. So, to be stable 1 carbon atom will have to combine with 2 oxygen atoms to form 1 molecule of carbon dioxide.

John Dalton’s Atomic Theory

Basic theory about nature of matter was given by the British chemist, John Dalton. His theory was on the fundamentals of laws of chemical combination. His theory explained law of conservation of mass and the law of definite proportions extensively.

He gave his atomic theory in 1808 according to which all matter (element, compound or mixture) is made up of small particles called atoms. The postulates of Dalton’s atomic theory are:

Read and Learn More: NEET Foundation Notes

• Matter consists of very tiny particles called atoms.
• Atoms are of indivisible nature which cannot be created or destroyed in a chemical reaction.
• Mass and chemical properties of atoms of a given element are identical.
• Different element atoms have different masses and chemical properties.
• Compounds are formed by combining atoms in the ratio of small whole numbers.
• In a given compound, the relative number and kinds of atoms are constant.

Law of conservation of mass is related to Dalton’s fourth postulate. Every atom of an element has a definite mass. Rearrangement of atoms takes place in a chemical reaction. Thus after the reaction, mass of the product should remain the same. Law of definite proportions is explained in the fifth postulate.

A compound consists of matter having atoms of two or more elements in small whole number ratio. As the atoms have definite mass, the compound must have the elements in definite proportions by mass.

The Dalton’s atomic theory also predicted the new theories like law of multiple proportions  on the basis of his theory. The deduction of law of multiple proportions from atomic theory was important in convincing chemists of the validity of the theory.

Class 11 Physics	Class 12 Maths	Class 11 Chemistry
NEET Foundation	Class 12 Physics	NEET Physics

So, Dalton’s atomic theory explains states that:

• All matter is made of atoms. Atoms are indivisible and indestructible.
• All atoms of a given element are identical in mass and properties
• Compounds are formed by a combination of two or more different kinds of atoms.
• A chemical reaction is an arrangement of atoms.

Modern atomic theory is, of course, a little more involved than Dalton’s theory but the essence of Dalton’s theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions.

Many heretofore unexplained chemical phenomena were quickly explained by Dalton with his theory. Dalton’s theory quickly became the theoretical foundation in chemistry.

Symbols for every element were firstly used by Dalton in a particular way. His symbolization for an element defined a definite quantity of that element, i.e one atom of that element. Berzilius idea for the symbols of elements was to use one or two letters of the name of the element.

Initially the names of elements were derived from the name of the place where they were found for the first time.

Example: Copper was taken from Cyprus.

Some names were taken from specific colours.

Example: Gold was taken from the English word meaning yellow.