The Scientists of the Atomic Theory

Period 1

John Dalton(1766-1844)

Dalton

• An English chemist, meteorologist, and physicist, from England.

• He was a teacher & public lecturer.

• Began his village school at the age of 12.

Dalton’s atomic theory

• In the early 1800’s Dalton came up with his theory of the atom.

• He stated that elements are made up of atoms. The reason an element is whole is because all atoms of an element are the exact same.

• Different atoms have different mass• Compound have different atoms of

different elements combined together.

Atom Model1803

Theory

• matter is composed of atoms• Atoms cannot be made or destroyed • All atoms of the same element are identical • Different elements have different types of atoms • Chemical reactions occur when atoms are

rearranged • Compounds are formed from atoms of the

constituent elements

Errors he made

He made a mistake in assuming that the simplest compound of two elements must be binary. He formed atoms of each element in a 1:1 ratio.

His system of atomic weights was not very accurate either.

• Some of Dalton's original atomic theory are now known to be wrong, but the basic concepts

- chemical reactions can be explained by the union and separation of atoms is what laid more foundation of basic physics.

J.J. ThomsonJ.J. Thomson

Period 1Period 1

J.J. ThomsonJ.J. Thomson

When The Discovery OccurredWhen The Discovery Occurred

Discovered the electron in 1897Discovered the electron in 1897

How The Discoveries were made…How The Discoveries were made…

Thomson built a cathode ray tube ending in a pair of metal Thomson built a cathode ray tube ending in a pair of metal cylinders with a slit in them. These cylinders were in turn cylinders with a slit in them. These cylinders were in turn connected to an electrometer. He wanted to see if, by bending the connected to an electrometer. He wanted to see if, by bending the rays with a magnet, he could separate the charge from the rays. rays with a magnet, he could separate the charge from the rays. He found that when the rays entered the slit in the cylinders, the He found that when the rays entered the slit in the cylinders, the electrometer measured a large amount of negative charge, but it electrometer measured a large amount of negative charge, but it didn’t register much electric charge if the rays were bent so they didn’t register much electric charge if the rays were bent so they would not enter the slit. Thomson discovered that the negative would not enter the slit. Thomson discovered that the negative charge could not be separated from the rays (by the application of charge could not be separated from the rays (by the application of magnetism), and that the rays could be deflected by an electric magnetism), and that the rays could be deflected by an electric field. He concluded that these rays, rather than being waves, were field. He concluded that these rays, rather than being waves, were composed of negatively charged particles.composed of negatively charged particles.

In 1904, Thomson suggested a model of the atom as a sphere of In 1904, Thomson suggested a model of the atom as a sphere of positive matter in which electrons are positioned by an electron positive matter in which electrons are positioned by an electron fieldfield

The ModelThe Model

In this model, the atom is composed In this model, the atom is composed of electrons surrounded by a soup of of electrons surrounded by a soup of positive charge to balance the positive charge to balance the electron's negative charge, like electron's negative charge, like plums surrounded by pudding.plums surrounded by pudding.

Summary of his discoveriesSummary of his discoveries

His experiments led to the fact that His experiments led to the fact that in 1897 that atoms were made of in 1897 that atoms were made of negatively charged particles that are negatively charged particles that are now known as electronsnow known as electrons

Additional InfoAdditional Info

J.J. Thomson won the Hughes Metal J.J. Thomson won the Hughes Metal for his discovery of the electron.for his discovery of the electron.

He also won the Noble Peace Prize in He also won the Noble Peace Prize in Physics LaureatePhysics Laureate

Credited for the discovery of the Credited for the discovery of the electron and the isotopeelectron and the isotope

Thomson called electrons corpuscles, Thomson called electrons corpuscles, the name electron came from G. J. the name electron came from G. J. Stoney.Stoney.

Ernest RutherfordErnest RutherfordKnown as the “Father of nuclear physics” Known as the “Father of nuclear physics”

Rutherford’s ExperimentRutherford’s Experiment

Rutherford took a radioactive substance put it in a Rutherford took a radioactive substance put it in a lead box and placed a thin piece of gold foil in the lead box and placed a thin piece of gold foil in the middle of a detecting screen. middle of a detecting screen.

When Rutherford was performing his experiment he When Rutherford was performing his experiment he saw that many particles went through the screen; but saw that many particles went through the screen; but some of the particles would bounce back (hitting the some of the particles would bounce back (hitting the nucleus), not going straight through the screen. nucleus), not going straight through the screen.

Rutherford performed his experiment in 1911Rutherford performed his experiment in 1911

Rutherford’s ExperimentRutherford’s Experiment

Concluding Concluding

Rutherford determined that because most of Rutherford determined that because most of the particles went through the atom, it was the particles went through the atom, it was made of a “hollow space.”made of a “hollow space.”

Concluding that atom was an “empty space” Concluding that atom was an “empty space” but there was a + charged nucleus in the atom.but there was a + charged nucleus in the atom.

““Planetary Model”Planetary Model”

Niels BohrNiels Bohr

Makeda Smith Chemistry I 10.23.07Makeda Smith Chemistry I 10.23.07

Bohr’s Atomic DiscoveryBohr’s Atomic Discovery

Niels Bohr discovered the quantum model which is explained the Niels Bohr discovered the quantum model which is explained the theory that electrons were found in energy levels (orbits) around the theory that electrons were found in energy levels (orbits) around the atom’s nucleus.atom’s nucleus.

Bohr made this discovery in the year 1913 and is said to have won a Bohr made this discovery in the year 1913 and is said to have won a Nobel Prize in 1922.Nobel Prize in 1922.

Bohr also suggested: that the electrons don’t continuously lose Bohr also suggested: that the electrons don’t continuously lose energy as they travel; they can only gain and lose energy by energy as they travel; they can only gain and lose energy by jumping from one allowed orbit to the next; and atoms don’t radiate.jumping from one allowed orbit to the next; and atoms don’t radiate.

- This picture is of Bohr in Einstein discussing the atomic model.

Quantum ModelQuantum Model

The quantum model basically shows that the atom’s electron are in orbits (or energy levels) around the nucleus of the atom.

How was this discovery found?!How was this discovery found?!

Bohr actually used Ernest Rutherford’s Bohr actually used Ernest Rutherford’s Gold Foil experiment. He then Gold Foil experiment. He then discovered that Rutherford’s idea had discovered that Rutherford’s idea had few problems.few problems.

Other InformationOther Information

In 1911 Niels Bohr followed experimental In 1911 Niels Bohr followed experimental work going on under the supervision of Sir work going on under the supervision of Sir JJ Thomson. JJ Thomson.