Progression of Atomic model

Revisions on Dalton's theory (what he wasn't right about)

1 atoms are composed of subatomic particles 2 not all the atoms of a specific element have the same mass 3 atoms, under special circumstances, can be decomposed.

Dalton theory of Atoms (proposed in the early 1800's,)

1. Elements are composed of minute, indivisible particles called atoms. 2. Atoms of the same element are alike in mass and size. 3. Atoms of different elements have different masses and sizes. 4. Chemical compounds are formed by the union of two or more atoms of different elements. 5. Atoms combine to form compounds in simple numerical ratios, such as one to one, one to two, two to three, and so on. 6. Atoms of two elements may combine in different ratios to form more than one compound.

Summery of Early atomic theories

1. Democritus - he said that atoms are the smallest types of matter, and that there are different types of atoms for everything. 2. Dalton - Said that atoms are indivisible, indestructible, and that chemical reactions were a rearrangement of atoms. 3. Thompson - Created the plum pudding model, discovered the electron. 4. Rutherford - Matter mostly empty space, discovered proton/neutron. 5. Bohr - Electrons in atoms only have certain energy levels they stay on. Principle Energy Levels are energy levels denoted by the quantum number "n" Bohr's model was only for hydrogen

Niels Bohr

His research led him to believe that electrons exist in specific regions at various distances from the nucleus.Bohr theorized that electrons have several possible energies corresponding to several possible orbits at different distances from the nucleus. Therefore, an electron has to be in one specific energy level; it cannot exist between energy levels. In other words, the energy of the electron is said to be quantized.

Bohr's line spectrum of hydrogen experiment

Atom's emit light at specific wave lengths and that each element has its unique set of wavelengths. Bohr applied this knowledge to come up with his model of how atoms behave and are structured.

J. J. Thomson Cathode ray tube

A stream of electrons passes between electrodes. The fast-moving particles excite the gas inside the tube, creating a greenish glow between the electrodes. J. J. Thomson demonstrated in 1897 that cathode rays (1) travel in straight lines, (2) are negative in charge, (3) are deflected by electric and magnetic fields, (4) produce sharp shadows, and (5) are capable of moving a small paddle wheel. This was the experimental discovery of the fundamental unit of charge—the electron.

Progression of the model of atom

Democritus (Ancient Greece) - he said that atoms are the smallest types of matter, and that there are different types of atoms for everything. Dalton- Elements are composed of minute, indivisible particles called atoms. Thomson-Atoms were divisible and consisted of negative particles imbedded in a positively charged environment. Rutherford- That there is a dense positively charged nucleus with negatively charged electrons surrounding it. Also surprisingly the atom consist mostly of empty space. British Physicist James Chadwick discovered the neutron. The existence of neutrons explained why atoms weighed more than there total mass of protons and electrons. Niels Bohr Niels Bohr revised Rutherford's model by suggesting thatThe electrons were confined into clearly defined orbits. They could jump between these orbits, but could not freely spiral inward or outward in intermediate states. An electron must absorb or emit specific amounts of energy for transition between these fixed orbits. Bohr's theory Depicts the atom as small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with attraction provided by electrostatic forces rather than gravity. Robert Sanderson Mulliken atomic orbital- is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.[1] This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus. The term may also refer to the physical region or space where the electron can be calculated to be present, as defined by the particular mathematical form of the orbital.

J. J. Thomson

English physicist was able to show experimentally the existence of the electron. He proved his theory using the cathode ray tube. He demonstrated that cathode rays were negatively charged

Rutherford's Gold foil experiment

In experiments performed in 1911, he directed a stream of positively charged helium ions (alpha particles) at a very thin sheet of gold foil (about 1000 atoms thick). These particles for most part went through sheet but some were deflected and some bounced back. The behavior of the alpha particles was experimental evidence that Rutherford concluded that the atom consisted of a small, dense, positively charged nucleus in the center of the atom with negatively charged electrons surrounding it. (a) The nucleus of the atom contains most of the mass since only a collision with a very dense, massive object would cause an alpha particle to be deflected backwards towards the source. (b) The positive alpha particles were deflected from their initial flight trajectory indicating that the nucleus of the atom is also positively charged. (c) Most alpha particles pass through the gold foil undeflected leading to the conclusion that the atom is mostly empty space.

Problem with Bohr model

It only works with hydrogen. The Bohr model treats the electron as if it were a miniature planet, with definite radius and momentum. This is in direct violation of the uncertainty principle which dictates that position and momentum cannot be simultaneously determined

Ernest Rutherford

The alpha-particle scattering experiments of Rutherford established that the atom contains a dense, positively charged nucleus and established the nuclear nature of atoms.

Thomson model of the atom

Thomson asserted that atoms are not indivisible but are composed of smaller parts; they contain both positively and negatively charged particles—protons as well as electrons. His model of the atom which he likened to plum pudding. The negative electrons represented the raisins in the pudding and the dough contained the positive charge. Neutrons were NOT part of Thomson model.

Democritus (about 470-370 b.c.)

Thought that all forms of matter were composed of tiny indivisible particles, which he called atoms, derived from the Greek word atomos, meaning "indivisible." He held that atoms were in constant motion and that they combined with one another in various ways. (Dalton was influenced by this idea)