Atomic evolution timeline (Ethan Bortmess, Ciara Bucci, Ben Elsenheimer, Nathaniel Spauling, and Alaina Strickler)
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335
Aristotle and Democritus (335 B.C.)
Aristotle denies Democritus' ideas and gives his own, believing in only four elements of water, earth, fire, and air. He believed everything was made of different combinations of these four things, and caused Democritus' ideas to be ignored for almost 2000 years -
400
Democritus' theory (400 B.C.)
Democritus theorized the following: 1) All matter consists of invisible particles called atoms. 2) Atoms are indestructible. 3) Atoms are solid but invisible. 4) Atoms are homogeneous. 5) Atoms differ in size, shape, mass, position, and arrangement. Solids are made of small, pointy atoms. Liquids are made of large, round atoms. Oils are made of very fine, small atoms that can easily slip past each other. -
Protium
Hydrogen has no neutrons and its mass number is 1 -
Dalton's postulates
Dalton postulated the following through his research on atoms. 1)all matter consists of indivisible particles called atoms. 2) Atoms of the same elements are similar in shape and mass, but differ from the atoms of other elements. 3) Atoms can not be created nor destroyed. 4) Atoms of different elements may combine with each other in a fixed, simple, whole number ratios to form compound atoms. 5) Atoms of same element can combine in more than one ratio to form two or more compounds -
Dalton's atomic model
Dalton's atomic model was a simple ball shape, as the subatomic particles have not yet been discovered. -
Thomson's experiment
Thomson deducted that cathode rays exhibited a simgle charge- to- mass ratio e m and must be composed of a single type of negatively charged particle, which he called "corpuscles." After further experiments on how cathode rays penetrate gases, Thomson hypothesized that "we have in the cathode rays matter in a new state this matter being the substance from which all the chemical elements are built up." Thomson might be described as "the man who first split the atom," and to a great extent, he ma -
Thomson's experiment (part 2)
atom," and to great extent, he made atom psychics a modern science. JJ Thomson discovered the first subatomic particle which we call the electron -
Plum pudding diagram
Thomson also proposed the plum pudding model, in which areas of positive charge are interrupted by negative particles -
Subatomic particles are discovered
Ernest Rutherford discovered them. A subatomic particle is a unit of matter or energy that's the fundamental makeup of all matter. According in modern atomic theory, an atom has a nucleus, which is its center, or core. The nucleus contains subatomic particles: protons and neutrons. Protons are positively-charged particles. Neutrons are neutral particles. Surrounding the nucleus is a cloud of very small subatomic particles, called electrons. Electrons are negatively-charged particles. -
Max Planck
The photoelectric effect could not be rationalized based on existing theories of light. Planck postulated that the energy of light is propotional to the frequency, and the constant that relates them is known as Planck's constant (h). His work lead to Einstein's determining that light exists in discrete photons. Planck's Quantum Theory is E=hf, which calculates the energy of the element. -
Albert Einstein (part 1)
The photoelectric effect is the observation that many metals emit electrons when light shines upon them. Electrons emitted in this manner can be called photoelectrons. The phenomenon is commonly studied in electronic physics, as well as in fields of chemistry or electrochemistry. instead of corresponding with the predicitions made, electrons are only dislodged by the impingement of photons when these photons reach or exceed a threshold frequency. Einstein proposed the beam was not a wave -
Einstein (part 2)
Below the threshold, no electrons were emitted from the metal regardless of the light intensity is low. Light was a discrete collection of photons and he viewd Planck's work for help to his conclusion. -
The Geiger- Marsden experiments
The Geiger- Marsden experiments (also called the Rutherford gold foil experiment0 were a landmark series of experiments by which scientists discovered that every atoms has a nucleus where its positive charge and most of its mass are concentrated. -
Robert Milikan (1908- 1917)
Robert Millikan measured the charge on an electron with the oil drop apparatus. He was able to show that the charge on a drop was always an intergral multiple of a small, but finite value. Combining his value he obtained for the charge on a single electron with the charge to mass ratio for the electron confirms that the mass of an electron is at least 1000 times smaller than the lightest atom -
Nuclear model diagram
Ernest was working with JJ Thomson, but through his gold foil experiment, helt felt his data was incompatible with the plum pudding model, so he devised the nuclear model of the atom -
Niel Bohrs
The '"planetary model" of the atom illustrates the adjacent figure. In this model, neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus. this is not drawn to scale and as far as we can tell, electrons are point particles without a physical extent -
Atomic Spectra
When atoms are excited they emit light of certain wavelengths which correspond to be different colors. The emitted light can be observed as a series of colored lines with dark spaces in between. Lyman series are all in a ultraviolet band (n'=10). Balmer Series are historically referred to as "H-alpha", "H-beta", and "H- gamma" and 4 lines are truly visible. (n'=2). Paschen Series overlaps with the Brackett series and shortest line has a wavelength that falls among this series. (n'=3) -
Ladder analogy
Bohr proposed that electrons do not radiate energy as they orbit the nucleus, but exist in states of constant energy which he called stationary states. This means the electrons orbit at a fixed distances from the nucleus. The ladder analogy arises because no techinque can measure distances at all ranges encounteered in astronomy. Each rung of the ladder provides information that can be used to determine the distance at the next higher rung. -
Louis de Broglie (1924-1928)
He developed his revolutionary theory of electron waves, which he has published. Experiments had indicated that the electron must move around a nucleus and that, for reasons then obscure, there are restrictions on its motion. A wave confined within boundaries imposed by the nuclear charge would be restricted in shape and in motion -
Erwin Schrodinger
He took the Bohr atom model one step further. He used mathematical equations to determine the position of the electron. This known as the quantum mechanical model, which does not define the exact path but predicts the odds of the location of the electron. Where the cloud is most dense, the probablity of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense are of the cloud. -
Werner Heisenberg
He states that the more precisely the position of some particle is determined , the less precisely its momentum can be known and vice versa. The uncertainty principle states that it is not possible to measure both the momentum and position of a particle simultaneously -
Orbitals
Orbitasl are the regions of space which electrons are most likely to be found. Since an electron can theoretically occupy all spcae, it is impossible to draw an orbital. At the first energy level, the only orbital available is the 1s orbital. At the second level, there are also orbitals called 2p in addition to 2s orbitals. In addition to s and p orbitals, there are two other sets of orbitals which become available atr higher energy levels. At the third level, there is a set of 5 d-orbitals -
James Chadwick
James Chadwick conducted experiments that proved the existence of particles devoid of electrical charge, or neutrons. In constrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forges present in the nuclei of heavy atoms, this new tool in atomic disintegration needs not overcome any electrical barrier and is capable of splitting the nuclei -
Deutrium
It is an isotope of Hydrogen that has one neutron and its mass number is 2 (has one electron to balance the charge of the proton) -
Tritium
It is an isotope of Hydrogen that has 2 neutrons and has the mass number of 3 (has one electron to balance the charge of the proton)
