Dalton's Atomic Theory and Subatomic Particles

Dalton's Atomic Theory

• The word "atom" originates from the Greek word "atomos," meaning uncuttable or indivisible.
• Dalton stated that atoms are the smallest particles of matter and are indivisible.
• Dalton faced challenges when presenting his atomic theory at the Royal Society of London.

Subatomic Particles

• JJ Thomson, Rutherford, and Chadwick disproved Dalton's theory by discovering that atoms are divisible.
• They discovered electrons, protons, and neutrons, which are the fundamental subatomic particles.
• "Fundamental" means present in every element's atom.
• Subatomic particles like bosons and mesons also exist within atoms.

Discovery of the Electron

• JJ Thomson discovered the electron using the cathode ray tube or discharge tube experiment.
• Scientists like William Crookes and Michael Faraday also worked with discharge tubes.

Discharge Tube (Cathode Ray Tube) Components:

• Glass tube
• Two metal electrodes (cathode and anode)
• Battery connecting electrodes
• Vacuum pump reduces pressure inside the tube
• Gas: such as hydrogen, oxygen, or nitrogen
• Initially, Thomson observed nothing with high voltage alone.
• Only when the pressure was lowered to 10^-2 to 10^-4 atm and applied high voltage (10,000V) resulted in a glow.
• The glow appeared to travel from the cathode to the anode.
• Thomson theorized that the rays contained negatively charged particles moving towards the positively charged anode.

Explanation of Cathode Ray Production

• Applying high voltage to a gas (e.g., hydrogen) causes dissociation of H2 molecules into individual H atoms.
• Further increasing voltage breaks electrostatic forces between the nucleus and electrons.
• Electrons are ejected from the atom, creating positive hydrogen ions.
• The ejected negative ions (electrons) are attracted to the anode, creating the observed rays.

Cathode Rays

• The negative charge is transported from the cathode towards the anode.
• The rays are originating from the electron emitted after ionization of a gas in the tube.
• The phenomenon of negative rays appearing from the cathode leads to the name "cathode rays".
• A high vacuum results in increased speed and thus increased rate of extraction of electron due to atomic collisions.

J.J. Thomson Confirmation

• The glass tube was modified with a perforated anode, that is, an anode with holes in it
• A fluorescent screen was added behind the anode to check if the rays travel through the anode
• The screen produced bright spots when struck by the rays, confirming the presence of negatively charged particles.
• Johnstone Stoney named these negative charge particles "electrons".

Properties of Cathode Rays

• Cathode rays do not emanate from the cathode.
• Cathode rays are produced in the space between the cathode and anode.
• Cathode rays travel in straight lines if there is no magnetic or electric field, and this can be proved by creating a shadow of an object put in between
• The rays deviate in electric and magnetic fields, bending towards the positive plate.
• Cathode rays can rotate a paddle wheel placed in their path
• Kinetic energy to do work, thereby verifying that cathode rays are a stream of particles.

Nature of Cathode Rays

• Specific charge (e/m ratio): the ratio of the electron’s charge to its mass.
• The specific charge remains constant irrespective of electrode material and the contained gas.
• Electron: a fundamental subatomic particle.
• Regardless of gas (hydrogen, oxygen, or nitrogen), a consistent e/m ratio is observed due to its fundamental nature amongst various atomic substances.
• Thomson determined the value to be approximately 1.76 x 10^11 Coulombs per kilogram (C/kg)

Charge and Mass of an Electron

• Robert Millikan determined the charge of an electron using the oil drop experiment giving a charge of -1.6 x 10^-19 Coulombs.
• With the charge and specific charge known, the mass of an electron could be calculated using the equation: m = e / (e/m).
• Mass of an electron is calculated using the results of Thomson and Millikan experiment, and is approximately 9.1 x 10^-31 kg.

Discovery of Anode Rays or Canal Rays

• Goldstein conducted experiments to find rays coming from anode as well, since ionization produces positive charges too.
• He used a perforated cathode for the generation of these rays.
• The rays interacted with Zinc Sulfide screen to produce fluorescence and bright spots.
• The experiment showed that the rays consisted of positively charged particles.

Properties of Anode Rays or Canal Rays

• Anode rays are produces in the space between the cathode and anode.
• Anode rays travel in straight lines.
• They are deflected by electric and magnetic field toward the negative plate, which indicates its particles are positive charge in nature

Nature of Anode Rays or Canal Rays

• Anode ray specific charge, the e/m ratio depends on the gas inside the tube, unlike the cathode ray particles of electrons.
• The positive charge will vary based on the gas, since its nature depends on the gas.

Proton Discovery

• The e/m ratio is maximum when Hydrogen gas is used as a gas in the tube.
• Hydrogen molecules dissociate in a discharge tube into single H atoms.
• During hydrogen ionization, H+ is produced, and mass charge ratio is minimal, thus H+ has the maximum charge.
• Rutherford discovered proton while verifying anode rays after goldstein produced it.
• A charge of +1.6 x 10^-19 Coulombs, equivalent to but opposite in sign to the electron charge.
• A mass of 1.67 x 10^-27 kg, significantly more massive than electrons.

Discovery of Neutron

• Alpha Particle: Helium 2+ or a helium nucleus without electrons.
• Chadwick discovered the neutron by bombarding a thin sheet of Beryllium with alpha particles.
• Neutral particles with approximately 1 AMU mass were produced.
• He proposed that Beryllium-9 reacts with alpha particles to form Carbon atoms and neutrons.
• Neutrons have no charge.
• Neutrons have a mass of 1.674 x 10^-27 kg, slightly higher than that of protons.

Atomic Representation

• Elements: symbolized with atomic number (Z) as subscript and mass number (A) as superscript.
• Atomic Number (Z): number of protons in the nucleus.

Atomic Structure Examples

For Carbon-13 (C-13):

• Atomic number (Z): 6
• Mass number (A): 13
• Number of protons: 6
• Number of neutrons: A - Z = 13 - 6 = 7 For Oxygen-16 (O-16):
• Atomic number (Z): 8
• Mass number (A): 16
• Number of protons: 8
• Number of neutrons: A - Z = 16 - 8 = 8

Isotopes

• Isotopes are same element atoms with equal numbers of protons but differ in the amount of neutrons (different mass numbers)
• Protium: 1 proton, 0 neutron, 1 AMU mass
• Deuterium: 1 proton, 1 neutron, 2 AMU mass
• Tritium: 1 proton, 2 neutrons, 3 AMU mass

Isobars

• These are different atoms that have the same mass number but different atomic numbers.
• An example of this is is carbon-14 and nitrogen-14
• Carbon-14 has 6 protons and has 8 neutrons
• Nitrogen-14 has 7 protons and has 7 neutrons
• Nuclear number the mass number is 14 for both nitrogen-14 and carbon-14

Thomson Model of the Atom

• JJ Thompson created first model of atom, an atomic structure that suggested that an electron could occur randomly throughout the atom.
• It said that the model was like a watermellon where the atom itself was the read part.
• Atom with a uniform positive charge distribution.
• Proposed that electrons were embedded in the atomic sphere
• Suggested that electrons arranged with negative charge in sphere with atoms.
• Atoms and electrons cancel each other out such that the mass is as a whole neutral.
• This model failed, because the distribution could not be proven and negative and positive charges should stick with each other.

Rutherford's Gold Foil Experiment

• Rutherford performed gold file experience to add more insight into atomic structure, observing the scattering of alpha particles beamed at a thin gold foil
• The expectation was for a tiny amount deflection.
• Few of the particles went theough directly unscattered, some small anngle scattering and small bit large angle scattering occuredd.
• This was significant, because it gave more data that Thompsons was wrong.

Rutherford Model of Electron Distribution

• Most of the atom is empty space due to no deflection of most alpha rays indicating electrons do not have structure.
• Positive center is found at atom center where mass and positive charge are in atom, is very densely packaged with most charge, and called nucleus
• Nucleus causes scattering through strong repulsion to alpha positive rays passing by it.
• Rutherford gave more specific model, that said atom has two parts:
• Negative- charged electrons are moving in orbial motion around nucleus.
• Electrostatic and centriptal forces balance each other out, and are the forces are the ones that help the charge to be at the radius and not fall in the electron.
• Electrons can never fall into the atom becuase the balance of attraction.
• Electrons cannot approach at the place and always stay in position.
• The size is measured by the atom having a very minimal area that is 10 to -15 that.
• Atom is mostly space though the mass of nuvlues and electrons. This meant the size can be big as well.

Drawbacks of Rutherford Model

• Maximum could not explain the stability of positive charge.
• In realtiy with electron moving around nuvlues, should be a loss charge in the electromagnetic charge.

Electromagentic Wave Theory

• When charge gets emitted, must lose charge or emit it to become in contact to electro magnetic radiotions.
• Wuth maximum could never expalin why stable, this is because theory, said that the electrons cannot accelerate.
• There are some electromagentic waves, there is an area of electric, also magentic.

Wave Characteristics

• Waves transport electric, in which electric and magnetic waves are always perpedicular, and go in same direction.

Electromagentic Waves

• These waves do not require medium and are used by sun and light, and travel at speed of light, or 3 x e8.

Wave Parameters

• Crest is the very top peak of the wave and the trough is the very bottom low wave, the lenghth in between can be the wave lenghth, which is measured in meters by standard. However, other forms such as mm amd nm, picometers, used as length measurements

Wave Number

• Wave number is the cycles per cm, and thus wave number is one the divided between 1/wl.
• When wave moves for one cm, it is 1/wl

Frequency

• The number of a wave cycles per second, and has a unit of time inverse, and an inverse of the time with the speed of light, cycle rate per second.
• Hz is measure of frequency, and is standard SI Unit for frequency

Time Period

• The amount of time it takes for the wave cycle to be completed, and always is with one wave, so you can find all with it.

Wave velocity

• Is 3 x 10 to the 8. Wave length is inverse from the speed of light. Cycle rate and wavelength relatioship

Relationship of Wavelength and Frequency

• We can measure properties with the formula c= v * wl, which also help explain some phenomens.

The Electomagentic Spectrum

• EM is when energy and light travel in wave.
• It goes from lowerest, most harmless to more intense
• These EM Waves can be measured with a Spectrum, as it is a way to arrange, and the arragement can be by increasing frequency or wave length.
• For longer wavelengths, more cycles.
• Rahul's mother is Vguses expensive golds coins helps remember with acronym
• Has Radio, microo, infared, visiblee area, ultra, expensive aka x ray, gold aka gamma, coins, and others can all be found EM specturm.
• Long to short is lower wavelength at read end, to violrt on the short side with the wave length of violet and light.
• Short wavelength means that its a higher frequency, and lower means greater frequency, and color can also give you great insight in the light cycle.

Failure of the Wave Theory

• EM is one of the forms of light, in EM EM and it has been proven that light also be partical with the EM theory, and that the EM waves have partical behavior as well
• Photoelectric effect Black body of the specturm all prove the partical nature, inclouding Planks quantum theory, which expalin nature, energy and radation is not contiouns.

The Planks Equation

• There are photons which is energy in partiacl way, and has units of quatham called plank, carried by each EM wave

Explanation of Planks Equations

• The energy of the photo is direclty proportion to frequency, and as such E is propoortion to frequency.
• When take proprition away constant h needs to be multipied, with h called planks constant, with a value of 6.6 is the 10 to -34, and Units Johes divided by second.

More Planks Theory

• Considers what happens to the energy with light when it has lots of photons.
• The energy and quatham, one two, with units called photons with multiple, and as such can say that mutlple photons energy equals to multiplue * h
• In order to account for total energy, the number of photons need to be accounted for, with the total and n number of photons = number of photons x energy/planks

Electromeagentic Probelm

• Need to show what wave number is and frequency, when the light is 4 10 to the 7.

Wave Length Calculations

• Convert units: 4 10 to the 7 to e_nanomaters to mmConvert units is
• Nanomoaters * amount equals to that many nummbers.
• 4 to 7 is nm = 4 *100/m which is the conversion.
• 4x ee 9 m conversion as each nm is 1 e 9 scale down
• Thus, get 205

Calculations of Freq

• Calculate freqq: is very easy to calculate as is given by planacks. Now that number is given c is lamba, now solve.

Photo Electricity - Hertz

• When a metal surface surface is shone with radiation of certain frequency, a photoelectric effect occurs, and emissions of radiation must occur before electromagentic reaction.

Experiments of Photoeffect

• It starts with tube, with metal, circle around metal, with battery, meter measure flow.
• When radiation hits the metal, you see flow of electricity, an effect that is all on the surface, and affect last energy to remove the electromns.
• Electrons are called valence electrons, and have last show electron with the valence.
• The effect can only be taken when a minimal frequency hit.

More Details About Energy with Photo Effect

• Energy, is what helps to get photo electro to occur with radiation, and if it does this results in a light to react
• Energy needs to cross that threshold for effect to occur, so its more effective with light, and to put extra radiation to help the surfaace.
• The metal force between electrons to remove it, and electrons have to over come the electric force.

Potasium Effects

• Potastrum better is better, and Rubetium, other a better effects.

Observations about Light and How it Affects Electrons (Per Postulates about Light)

• No time to eject electrons when radiation hits, that when theelectrons are ejected
• Only certain frequencies can trigger the effect as there must be minimal frequency called the threshold

If frequency is below the threshold, the effect won't occur If equal, it occurs only to reach threshold If above, the effect will occur

• There must be some positive and Kinetic energy, that is dependent and is based on frequency, and intensity is not.
• Ainstien helped proved this.

More info about theory

• Photon can help the surface to act, and due to this a portion of the kinetic energy is converted back due to photon energy, to over come the surface force

More theory

• H frequency is the same as potential adding up.
• One has potential plus the kineti. This explains as it means, that each is relative to all the types.
• What happens to the photo effect not. There are thresholds and function with functions, and it won't occurs as energy cannot hit it, and to over come that threshold when this occurs is shown with calculations

Calculations

• Solve it as it goes

Example One:

• What number emition of light the effect of to occur to

1. 1st

• The the value the h to get, as h is 39 then other number from 1,2,3

Bohr - More Model

• Rutherford showed, that it will lose energy on that. Need some way to solve this.
• Bohr took this into consideration when he built the electron model with he following key properties

Bohr Model Properties

1. nucleus and central mass
2. revolve shell for electron to move

Then we have to look at shells the area where the electrons can move 1 is one, when can know to calculate the shell with nuvlues can, and number 1 is the only value that can be used to make this calculation 2 is 2 or L other areas where the elecrons can move 3 and so on until m. They also can calculate with states numbers and levels with calculations

Electrons not the same

• They dont emit energy.
• To move electrons must absorb the energy
• Electrons wants to move from Lower to Higher
• They must reject the frequency to

Electrons at a Low state

• Higher than n equals two and must reject what ever to
• To move electrons must reject a frequency
• Bohr frequency rule, is a formula were n equals constant 2 pi
• Mass and electron velocity make up momentum with there respective value depending on some values only.

More about the model

• It is limited and its applicated with single electron space with only hydrogen-like effects.

Other Bohr rules and functions

• Readis can help to see where each goes
• Always 05 29 as angtrons has constnat
• N is squared so is the orbit which squared
• Hydgrogen is one
• And Heliums is two, at all times with Bohr. The properties can also be calculated for the electrons

Notes Section on Calculations

• Always remember there were electron. N is which energy with the one
• Levels always move from low to high to move the cycle to continue it.
• Successive levels lower each.

The Ground Cycle

• Level will go to one, for first circle the first with highers the level It needs to first excite.

Drawbacks - Bohr Model

• BOHRR is with only sinngls and must help prove the numbers.
• All must happen in the magnetic state what happens to light and light is not considered at all, which a big area we do not what

Quantum Mechantical Model

• Model that considers electron movement is like a state with time,

1. where to go

• But since movement it can not be accurately determined, all that can determined is its relative position.
• The position is determined with established quantom values.

Details Chart Quantom

1. Princple: Can state all the values for electrons, with shells such as L,M,, which go from one way to all Orbitals: one way, but the total has

The Wave Details Quantom

• Wave details can provide information for calculations

Rules for the Wave Details

Need to see the different If goes wave is

• Is low or not which has
• High or to high
• If is high is determined through calculations with certain range limitations

Poly Exclusion

• Electrons can only spin in the up or the down direction to be able to move

Explore Dalton's atomic theory and its evolution. Learn about the discovery of subatomic particles like electrons, protons, and neutrons, which disproved Dalton's initial concept of indivisible atoms. Understand the significance of the discharge tube experiment in discovering electrons.