Bohrs Model Of Atom

Bohr’s Model of atom

Postulates of Bohr’s Model of atom:

1. An atom consists of positive charge (nucleus) and electrons are revolving around it in a circular orbit.

2. Electrons revolving in these orbits which have fixed value of energy hence these orbits are called as stationary states or energy levels.

3. Energy of different states can be calculated by :

En=21.8*10-19 Z2/n2 j/atom or 13.6 z2/n2 ev/atom or 1312 kJ/mole

4. Radii of stationary states can be calculated as r=ao n2/z where ao=52.1 pm.

5. Velocity of electron is given by the expression:

V= vo z/n where vo=2.18*108 cm/sec

6. As electrons can have discreet or fixed values of energy and not have their own values of energy they can be express by saying that energy of electron is quantised.

7. Like energy, angular momentum of electron is also have definite value and given as mvr= nh/2( pie) n lambda=(2pie) r

And lambda=h/p

From this we can get the value of mvr = nh/2 pie

8. When an electron in an atom are revolving in orbit without any loosing or gaining energy than atom is said to be in normal state or in ground state.

9. When an electron is emitting or absorbing energy than it means they are jumping from one level to another level which is subjected to high temperature and said to be in excited state.

Negative energy:

When an electron is at infinity there is no force of attraction and energy is taken as zero but when it comes closer to nucleus energy being released and hence it becomes negative.

Thermodynamics Theory

Thermodynamics

Thermodynamics can be represented as thermal + dynamics which mean heat and motion.

Define: it is a branch of science which deals with various forms of energy and tells about following things:

1. Extent of reaction

2. Reactions feasibility

3. Can tell about initial and final state of the system.

4. Can tell about the various properties like temperature, pressure and volume.

Some basic terms related to thermodynamics

System And Surroundings:

A part of the universe which is under investigation termed as system and the universe excluding system is termed as surroundings.

Types of System

A system which can exchange matter as well as energy.

Closed system:

A system which can exchange matter energy but not matter.

Isolated system:

A system which can neither exchange matter nor energy.

Thermodynamic Equilibrium: When pressure and temperature does not change w.r.t time and said to be attained equilibrium.

Thermodynamic Process:

1. Isothermal: It is a process in which temperature constant.

2. Isobaric: It’s a process in which pressure remains constant.

3. Isochoric: It’s a process in which volume remains constant.

4.Adiabatic: q=0

Pictures of J.J THOMSON electron discovery | Cathode ray tube diagram

J.J THOMSON TUBE | WILLIAM CROOKES TUBE

CATHODE RAY TUBE EXPERIMENT DIAGRAM

Tyre Car Puzles| Rickshaw puzzles | Five Fans Puzzles

Tyre Car Puzles| Rickshaw puzzles | Five Fans Puzzles

1. 1. There is a car owner who is standing very far from the market and a thief comes to that place & steals nut and bolt of one tyre and car owner doesn’t have any spare nut and bolt .Now tell me how he can reach home?

(Note: Car has four tyres)

1. 2. There is a rickshaw having three tyres and one tyre can travel only for 1 km and rickshaw puller have one more tyre in spare. Now, tell me the maximum distance travelled by rickshaw?

2. 3. In a house, we have five fans having same speed and their switches are outside the room. Now, How can you identify which switch belongs to which fan?

How can we see atom |STM| Scanning Tunneling Microscopy

How can we see atom ?

For the last 200 years we are talking about atoms but no body has seen this atom because there is no technology to see this atom until this technology came in to the existence i.e STM

Atom can be seen by using STM (Scanning tunneling microscopy).

A scanning tunneling microscope (STM) is a powerful instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer (at IBM Zürich), the Nobel Prize in Physics in 1986.^[1][2] For an STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution.^[3] With this resolution, individual atoms within materials are routinely imaged and manipulated. The STM can be used not only in ultra high vacuum but also in air, water, and various other liquid or gas ambients, and at temperatures ranging from near zero kelvin to a few hundred degrees Celsius.^[4]

The STM is based on the concept of quantum tunneling. When a conducting tip is brought very near to the surface to be examined, a bias (voltage difference) applied between the two can allow electrons to tunnel through the vacuum between them. The resulting tunneling current is a function of tip position, applied voltage, and the local density of states (LDOS) of the sample.^[4] Information is acquired by monitoring the current as the tip's position scans across the surface, and is usually displayed in image form. STM can be a challenging technique, as it requires extremely clean and stable surfaces, sharp tips, excellent vibration control, and sophisticated electronics.

source:http://en.wikipedia.org/wiki/Scanning_tunneling_microscope