“Atoms are said to be the very tiny particles of any matter that cannot be divided any more after a certain stage “ for example : Take a chair and keep on doing its pieces , a stage will come when there will small particle left that particle can be said to be an atom.
According to todays chemistry I know that atom has 3 types of particles and they are :1. Electron2. Proton3. Neutron
Particle Charge Symbol Location on the in atom particleElectron -1 unit e- Outside the nucleusProton +1 unit p+ In the nucleusNeutron No n0 In the charge nucleus
As we make it from the name that I must be talking about the mass of the atom taken. The mass is nothing but the sum of electrons Protons & neutrons . But actually mass no. can be finded through just doubling the atomic no. of the given atom if the atomic no. is even .If the atomic no. is odd then just double the atomic no. and add 1 to the answer .
Atomic no. is denoted with ‘X’ , mass no with ‘A’ and atomic no. with say ‘Z’.Atomic no. is written in downward and mass no. is written in upward form. Therefore :Mass no. = A X= symbol of elementAtomic no.=z
Now if we know the atomic no. then we can find both of the proton & electron. Because the no. of protons and electrons are directly proportional to the atomic no. for example :We take sodium . The atomic no. of Sodium (Na) is 11 therefore the :-Atomic no. = no. of Protons = no. of Electrons
There is very easy and simple way to find neutrons as we had earlier taken sodium (Na) so the formulae for finding neutrons is :- Mass no. – Atomic no. = no. of neutrons
Eugene Goldstein noted streams of positively charged particles in cathode rays in 1886. Particles move in opposite direction of cathode rays. Called “Canal Rays” because they passed through holes (channels or canals) drilled through the negative electrode.
Canal rays must be positive. Goldstein postulated the existence of a positive fundamental particle called the “proton”.
Thomson’s Experiment And Discovery of Electrons - Voltage source + Passing an electric current makes a beam appear to move from the negative to the positive end.
Thomson’s Experiment Voltage source + - By adding an electric field he found that the moving pieces were negative.
The electron was discovered in1897 by Thomson. He imagined theatom as a “raisin pudding” withelectrons stuck in a cake of positivecharge.
Plum Pudding Model, 1896 Thought an atom was like plum pudding Dough was cloud Raisins were electrons Didn’t know about neutrons at this time
English physicist Ernest Rutherford (1911) Shot alpha particles at fluorescent screen. When an alpha particle hits a fluorescent screen, it glows.
He thought the mass wasevenly distributed in the atom
Since someparticles weredeflected atlarge angles,Thomson’smodel couldnot be correct.
How Rutherfordexplained results….. Atom is mostly empty space. Small dense, positive piece at center is (NUCLEUS)
In 1912, Rutherford discovered the nucleus by doing scattering experiments. He concluded the atom was mostly empty space, with a large dense body at the center, and electrons which orbited the nucleus like planets orbit the Sun.
The model created by Rutherford hadstill some serious discordance.According to the classic science, electronmoving around the nucleus should emitan electromagnetic wave. Electronshould than move not by the circle buthelical and finally collide with thenucleus. But atom is stable.
Rutherford also realized that thenucleus must contain both neutral andpositively charged particles. Theneutron was then discovered in 1932 byChadwick.
Similar to Rutherford’s model Thought atom was mostly empty space Neils Bohr, 1913 Nucleus in center is dense, positively charge Electrons revolve around the nucleus.
Following Rutherford’s planetarymodel of the atom, it wasrealized that the attractionbetween the electrons and theprotons should make the atomunstableBohr proposed a model in whichthe electrons would stablyoccupy fixed orbits, as long asthese orbits had specialquantized locations
Parts of an AtomEach element has a different number of protonsin its nucleus Protons have positive charge p Change the number of protons change elements This is called nuclear physicsThe element also has the same number ofelectrons Electrons have negative charge e Change the number of electrons ionize the element This is called chemistrySome elements also have neutrons Neutrons have no charge n They are in the nuclei of atoms