Bohr’s And Rutherford’s Atomic Model

Presented By : Lorain Maria

ManojIX - A

How are atoms studied?

• Atoms are the building blocks of matter

• Atoms are too small in size to study easily

• Size of Earth : soda can = soda can : atom

Who studied the atom?

• Studied by many scientists for centuries:– Democritus (400 BC) – phrase “atomos”– Rutherford (1911) – nucleus (gold foil

experiment)– Moseley (1913) – X-rays to find atomic #– *Bohr (1913) – planetary model of the atom– *Schrödinger (1923) – electron cloud model

What they knew then…• By the late 1800’s scientists

had a working model of the atom.

• Dalton proposed that the atom was a sold sphere

• JJ Thomson (remember him?) came up with another model…mmm, plum pudding

Born: 7 October 1885(1885-10-07) Copenhagen, Denmark

Died: November 18, 1962 (aged 77) Copenhagen, Denmark

Nationality: Denmark

Fields: Physics

Known for: Copenhagen interpretation Complementarity Bohr model Bohr effect Sommerfeld-Bohr theory BKS theory Bohr-Einstein debates

Notable awards: Nobel Prize in Physics (1922)

I’m an electron!

I’m a proton!I’m a neutron!

I was walking along and I saw these two.

I was telling jokes to the neutron.The proton and I were having fun.

They looked so happy there together.

I was p o s i t i v e l y charged!I couldn’t have amassed more happiness.

The proton looked happy, so I wandered closer.

I could see the electron coming near.The who? Huh?

They were HUGE next to me!

The electron was so cute!Like a speck of dust, or something…

I didn’t want to seem obvious, so I kept walking.

Around and around the electron goes.Hey electron, you’re making the proton dizzy.

The proton seems so happy with the neutron.

I’m having fun, but I still notice the electron.It won’t bother me if the electron hangs around.

I guess I’ll just wander around out here.

I’m happy hanging out here.The center is cool, but sometimes it can be a “Bohr”.

Electrons circle around the nucleus of an atom.

Protons are a main part of the nucleus of an atom.Neutrons also hang out in the nucleus of an atom.

Electrons have a negative charge. Protons have a positive charge. +Neutrons have no charge. 0

Electrons are little and have a mass of almost zero.

Protons are big and have a mass of one.Neutrons are also big and have a mass of one.

Born August 30, 1871)Brightwater, New Zealand

Died October 19, 1937 (aged 66)Cambridge, England

Nationality British

Fields Physics

Known for Father of nuclear physicsRutherford modelRutherford scatteringRutherford backscattering spectroscopyDiscovery of protonRutherford (unit)Coined the term 'artificial disintegration'

Rutherford and Thomson

• Rutherford was a scientist who also explored radiation.

• He discovered three kinds of radiation and decided that different particles were causing each kind:

1. Alpha2. Beta3. Gamma

Probing the atom…again!• 1909 – Rutherford designs an

experiment where he fires radioactivity through gold foil to see what happens…

So What did Rutherford find out?

1) The nucleus is so small that the odds are overwhelmingly in favor of a given alpha particle motoring right on through the gold foil as if nothing were there. It turns out that the atom is a very empty place, indeed!

2) Some alphas, by pure random chance,

will pass near some gold atom nuclei

during their passage through the foil and

will be slightly deflected.

3) A very, very few alphas, by pure, random

chance, will hit a nucleus almost head-on.

The alpha, traveling at 10% the speed of

light, penetrates the atom and gets very

close to the nucleus.

However, the repulsion between the alpha

and the atom nucleus is so great that the

atom flings the alpha back out, and it does

so in a hyperbolic path. Depending on

various factors, this occasionally results in

the alpha being turned around 90° or more.

The very heavy nucleus recoils a bit from the

impact, but essentially goes nowhere.

InferringRutherford inferred the nucleus of the atom like

so...How could the foil repel the dense, strongly

positive alpha particles?Well…the atoms must possess something

that is very dense and very positiveBut … these things must be very small

because most of the particles get through the foil.

So… the atoms must have a large area that is mostly empty.

Technology break…

• Nucleur medicine uses radiation as its main tool–X-rays

–Therapy – to kill cancer cells

–Radioactive injections to look inside the body and trace pathways.

But what about the Neutron?But what about the Neutron?

• Rutherford calculated that GOLD must have 79 protons in its nucleus.

• BUT…he also calculated that GOLD must have a mass of around double that.

• Where is the missing mass???????• Negative charge is already accounted for• Positive charge is already accounted for• Must be something neutral – ah the Neutron!