Atomic Models and Theories

It is known as one of the foundations of modern physical science

Atomic Theory of Matter

1.All matter is composed of extremely small, indivisible, indestructible particles called atoms. 2.All atoms of each element are exactly alike, but they differ from atoms of other elements. The atoms of different elements have different mass and other properties. 3.When atoms of different elements combine to form a compound, the constituents atoms are always present in the same fixed numerical ratio. 4.A chemical reaction involves a rearrangement of atoms. No atom is created nor destroyed.

Dalton`s Atomic Theory (The Solid Sphere Model)

He pictured atom as solid, indestructible sphere with a mass like a billiard ball

Dalton`s Atomic Theory (The Solid Sphere Model)

1.The gold atoms in the foil must be mostly empty space because most of the alpha particle were able to penetrate the foil. 2.An atom has a positive, central core called nucleus (which means "little nut" in Latin), where most of its mass is concentrated. The nucleus was so dense that the alpha particles would bounce off. 3.The negatively charged electron in the atom circulates around the nucleus. The electrons were so tiny and spread out at such great distances that the alpha particles would pass right through this area of the atom.

Ernest Rutherford (Nuclear Model of an Atom)

In 1911, him and his colleagues tested Thompson`s theory using a very thin sheet of gold foil. They focused on a stream of alpha particles, and they discovered that most of the particles passed through and few were deflected. Based on his observation, they disagreed with Thompson`s theory and they came up with the following conclusions:

Ernest Rutherford (Nuclear Model of an Atom)

He is an English physicist and chemist, proposed his Atomic Theory of Matter in 1803

John Dalton (1766-1844)

Atoms are solid spheres made up of a solid positive mass (or core) with tiny negative particles embedded in the positive core. His discovery showed that atoms were not indivisible but composed of subatomic particles that are electrically charged. He said that the negatively charged electrons were embedded in the positively charged mass, like the way raisins are embedded in

Joseph John Thomson (The Raisin Bun Model)

He was able to discover the negatively charged particle, called electron, using a piece of equipment called a cathode ray tube. Each end of the tube had an electrode.

Joseph John Thomson (The Raisin Bun Model)

a British physicist, discovered that Dalton`s atomic model is not accurate. He conducted an experiment using a vacuum tube.

Joseph John Thomson (The Raisin Bun Model)

He also described the way atoms emit radiation by proposing that, when an electron jumps from outer orbit to an inner one, it emits light. Later, other physicists expanded his theory into Quantum mechanics. This theory explains the structure and actions of complex atoms.

Neils Bohr (Planetary Model of an Atom)

Rutherford`s model had orbiting electrons moving around the massive nucleus of the atom. However, James Maxwell had already shown that a charged particle moving through an electromagnetic field would continuously radiate energy. This would eventually cause the atom to lose all its energy. In that case, the atom would no longer exists as an atom and matter would collapse. Rutherford was unable to explain how this would not occur in this model of an atom.

Neils Bohr (Planetary Model of an Atom)

a Danish physicist, saw a possible solution in the Quantum Theory proposed in 1900 by Max Planck. Planck, in his study of black body radiation, concluded that at least in some cases, energy would be emitted not in continuous waves, but in discrete packages that he called quanta.

Neils Bohr (Planetary Model of an Atom)

1.The introduction of elliptical orbits. 2.Allowance of an orbiting motion of the electrons; and 3.The consideration of relativistic mass effects.

Neils Bohr and Arnold Sommerfeld (Bohr-Sommerfeld Atomic Model)

Years have passed and further experiments have shown that _______ atom seemed too simple to describe the heavier elements. In fact, the spectral lines did not appear correct when a strong magnetic field influenced the atoms. _____________, a famous German theoretical physicist, expanded their studies to enhance Bohr`s model of an atom. He studied carefully the spectral lines of hydrogen. He noticed that a single line in the spectrum really consists of several lines close together. His solution was to assume that electrons moved in elliptical, rather than circular orbits.He introduced the concept of elliptical orbits.

Neils Bohr and Arnold Sommerfeld (Bohr-Sommerfeld Atomic Model)