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ATOMIC THEORYBY: Chesca Alba, Celine Bengzon, Rea Del Rio, Aitana Morales and Paula Santos

+Democritus Atom

Democritus is an Ancient Greek philosopher born in Abdera, Thrace, Greece

He was said to be the first step toward the current atomic theory.

Hypothesized that all matter is composed of tiny indestructible units, called atoms.

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His atomic theory contradicted the idea that matter can be infinitely divided.

According to him, atoms cannot be divided forever.  

In the long run, the object will become so small and invisible that you cannot divide it any further.

He said that these indivisible invisible particles are ATOMS. The word atom means not to be cut or indivisible.

+TAKE NOTE!

He DID NOT MAKE THE ATOMIC THEORY. He just EXPANDED it.

He learned this from the founder of the atomic theory, Leucippus.

+John Dalton

English chemist, meteorologist and physicist. He is best known for his pioneering work in the development of modern atomic theory.

+ Dalton’s atomic theory stated that elements

consisted of tiny particles called atoms. He said

that the reason an element is pure is because

all atoms of an element were identical and that

in particular they had the same mass. He also

said that the reason elements differed from one

another was that atoms of each element were

different from one another; in particular, they

had different masses. He also said that

compounds consisted of atoms of different

elements combined together.

+ 5 POINTS of Dalton’s Theory

All matter consists of tiny particles called atoms. These are indivisible and indestructible.

All atoms of a given element are identical in mass and properties.

The atoms of a given element are different from those of any other element; the atoms of different elements can be distinguished from one another by their respective relative atomic weights.

+Compounds are formed by a combination of two or more different kinds of atoms.Compounds are pure substances. They can’t be separated into elements by phase changes because the atoms of different elements are bonded to one another and are not easily separated from one another.

A chemical reaction results to rearrangement of atoms.

+Joseph John “JJ”

Thomson

•Born on December 18

•British physicist

•Discovered of electron

•Discovered of isotopes

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•Invented the mass spectrometer

•Proposed first waveguide

•Proposed the Plum pudding model

•Awarded the 1906 Nobel Prize in Physics

+PLUM PUDDING MODEL

•Also known as the “Chocolate Chip Cookie or Blueberry Muffin Model.”

•Atom is composed of electrons surrounded by a soup of positive charge to balance the electron’s negative charge, like negatively-charged “plums” surrounded by positively-charged “pudding”.

+•Sometimes visualized as having a cloud of

positive charge, a striking contrast to the most recent atomic model, which describes the positive nucleus to be surrounded by an electron cloud.

•Electrons were free to rotate within the cloud of positive substance.

•These orbits were stabilized in the model by the fact that when an electron moved farther from the center of the positive cloud, it felt a larger net positive inward force, because there was more material of opposite charge, inside its orbit.

+Ernest Rutherford

•Born on August 30

•New Zealand chemist and physicist

•Father of nuclear physics

•Discovered that atoms have their positive charge concentrated in a very small nucleus.

•Rutherford Model

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•Gold Foil Experiment

•Discoverer of proton

•Awarded Nobel Prize in Chemistry in 1908

•Widely credited as splitting the atom in 1917

•Leading the first experiment to “split the nucleus”

+ Gold Foil Experiment

•Also called “Geiger–Marsden experiment or Rutherford experiment”

•An experiment to examine the structure of the atom performed by Hans Geiger and Ernest Marsden in 1909

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•The unexpected results of the experiment demonstrated for the first time the existence of the atomic nucleus, leading to the downfall of the plum pudding model of the atom, and the development of the Rutherford (or planetary) model.

+A beam of alpha particles, generated by the

radioactive decay of radium, was directed normally onto a sheet of very thin gold foil. The gold foil was surrounded by a circular sheet of zinc sulfide (ZnS) which was used as a detector: the ZnS sheet would light up when hit with alpha particles. Under the prevailing plum pudding model, the alpha particles should all have been deflected by, at most, a few degrees; measuring the pattern of scattered particles was expected to provide information about the distribution of charge within the atom. However they observed that a very small percentage of particles were deflected through angles much larger than 90 degrees.

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Large amount of the atom’s charge and mass is instead concentrated into a very physically small, giving it a very high electric field.

Outside of this “central charge”, he proposed that the atom was mostly empty space.

+EUGEN GOLDSTEIN

•German Physicist

•Early investigator of discharge tubes

•Discoverer of anode rays

•Credited with the discovery of proton

+ Julius Plücker

• investigated the light emitted in discharge tubes and the influence of magnetic fields on the glow.

+ Johann Wilhelm Hittorf (1869)

• studied discharge tubes with energy rays extending from a negative electrode, the cathode.

• rays produced a fluorescence when they hit a tube's glass walls, and when interrupted by a solid object they cast a shadow.

+1870's

•Goldstein had undertaken his own

investigations of discharge tubes, and

named the light emissions studied by

others kathodenstrahlen, or cathode rays.

+1886

• discharge tubes with a perforated cathode also emit a glow at the cathode end.

+Conclusion

• In addition to the already-known cathode rays, later recognized as electrons moving from the negatively-charged cathode toward the positively-charged anode, there is another ray that travels in the opposite direction.

+CANAL RAYS

• beams of positive ions that were observed in experiments these latter rays passed through the holes, or channels, in the cathode

• A "ray" is produced in the holes (canals) in the cathode and travels in a direction opposite to the "cathode rays," which are streams of electrons.

• positive rays (Kanalstrahlen)

+1907

•a study of how this "ray" was deflected in a magnetic field, revealed that the particles making up the ray were not all the same mass.

•The lightest ones, formed when there was some hydrogen gas in the tube, were calculated to be about 1837 times as massive as an electron. They were protons.

+PROTONS

• subatomic particle with an electric charge of +1 elementary charge

• found in the nucleus of each atom, along with neutrons, but is also stable by itself

+ JAMES CHADWICK

• English Nobel laureate in physics awarded for his discovery of the neutron.

• Hughes Medal of the Royal Society (1932)

• Nobel Prize for Physics (1935)

+1932

• Chadwick discovered a previously unknown particle in the atomic nucleus.

• particle became known as electron because of lack of electric charge

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• Unlike positively charged alpha particles (consist of two protons and two neutrons bound together into a particle identical to a helium nucleus), which are repelled by the electrical forces present in the nuclei of other atoms, neutrons do not need to overcome any Coulomb barrier and can therefore penetrate and split the nuclei of even the heaviest elements.

+NEUTRON

•subatomic particle with no net electric charge and a mass slightly larger than that of a proton

•usually found in atomic nuclei

- nuclei of most atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons

+ ATOMIC NUMBER AND ATOMIC MASS

• p- proton

• n- neutron

• z- atomic number

• a- atomic mass

+Atomic number

• the number of protons in the nucleus of an atom.

Ex:

H1 = Hydrogen has one proton

+Atomic Mass

• the sum of the proton and neutron of an atom

Proton + neutron = atomic mass

+ISOTOPE

•when atoms of the same element have different numbers of neutrons and/or protons.

+ How Isotopes Are Written

AXZ ; X = symbol of element

A = atomic mass

Z = atomic number

Isotopes of hydrogen:

No neutron : 1H1

One neutron = deuterium : 2H1

Two neutrons = tritium : 3H1

+IONS

•an atom, group of atoms, or a particle with a positive or negative charge.

Positive charges = cation ;more protons than electrons

Negative charges = anion ;more electrons than protons

+ Ionic Bonding / Ionization

• transfer of electrons

Monatomic- ions with one atom

Polyatomic- ions with more than one atom

Metal + metalloid = ionic bond

Metal+ nonmetal = ionic bond

+Review

• Neutrons are all identical to each other, just as protons are.

• Atoms of a particular element must have the same number of protons but can have different numbers of neutrons.

• When an atom does not have the same number of protons and neutrons, it is called an isotope.

• Ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.

+Bohr’s Model

also known as the planetary model

neutrons and protons are in the nucleus while the electrons are orbiting the nucleus

electrons are able to jump from one orbit to another

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A quantum mechanics - a mathematical theory that could describe the behavior of microscopic objects

only works for hydrogen

+Photons

always in motion

bundle of electromagnetic energy

cause of jumping electrons from one orbit to another

Absorbed=lower to higher

Light=higher to lower

+ Electron Cloud Model

1920

consists of a dense nucleus composed of protons and neutrons surrounded by electrons that exist in different clouds at the various energy levels.

Erwin Schrodinger and Werner Heisenburg developed probability functions to determine the regions or clouds in which electrons would most likely be found.

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QUESTIONS

+Question 1:

What do you call an atom that does not have the same number of protons and neutrons?

+Question 2:

It is an ion with more electrons than protons.

+Question 3

What are protons?

+Question 4

What are electrons?

+Question 5

What is the main idea of the atomic theory of Democritus?

+Question 6

Draw the “Plum Pudding” model.

+Question 7

+Question 8

+Question 9

+Question 10