An introduction to the evolution of the modern model of the atom

The following video covers some of the properties of an atom. Veritasium video on the atom - 1 We have now looked at many examples of the types of matter and materials that exist around us and we have investigated some of the ways that materials are classified. But what is it that makes up these materials? And what makes one material different from another?

An introduction to the evolution of the modern model of the atom

Atomism The idea that matter is made up of discrete units is a very old idea, appearing in many ancient cultures such as Greece and India. The word "atom" Greek: The first was the law of conservation of massclosely associated with the work of Antoine Lavoisierwhich states that the total mass in a chemical reaction remains constant that is, the reactants have the same mass as the products.

First established by the French chemist Joseph Louis Proust in[7] this law states that if a compound is broken down into its constituent chemical elements, then the masses of the constituents will always have the same proportions by weight, regardless of the quantity or source of the original substance.

An introduction to the evolution of the modern model of the atom

John Dalton studied and expanded upon this previous work and defended a new idea, later known as the law of multiple proportions: For example, Proust had studied tin oxides and found that there is one type of tin oxide that is Dalton noted from these percentages that g of tin will combine either with Dalton found several examples of such instances of integral multiple combining proportions, and asserted that the pattern was a general one.

Most importantly, he noted that an atomic theory of matter could elegantly explain this law, as well as Proust's law of definite proportions.

For example, in the case of Proust's tin oxides, one tin atom will combine with either one or two oxygen atoms to form either the first or the second oxide of tin. Indeed, carbon dioxide molecules CO2 are heavier and larger than nitrogen molecules N2.

Dalton proposed that each chemical element is composed of atoms of a single, unique type, and though they cannot be altered or destroyed by chemical means, they can combine to form more complex structures chemical compounds.

This marked the first truly scientific theory of the atom, since Dalton reached his conclusions by experimentation and examination of the results in an empirical fashion.

In Dalton orally presented his first list of relative atomic weights for a number of substances. This paper was published inbut he did not discuss there exactly how he obtained these figures. Dalton estimated the atomic weights according to the mass ratios in which they combined, with the hydrogen atom taken as unity.

However, Dalton did not conceive that with some elements atoms exist in molecules—e. He also mistakenly believed that the simplest compound between any two elements is always one atom of each so he thought water was HO, not H2O. For instance, in he believed that oxygen atoms were 5.

Adopting better data, in he concluded that the atomic weight of oxygen must actually be 7 rather than 5. Others at this time had already concluded that the oxygen atom must weigh 8 relative to hydrogen equals 1, if one assumes Dalton's formula for the water molecule HOor 16 if one assumes the modern water formula H2O.

Avogadro had proposed that equal volumes of any two gases, at equal temperature and pressure, contain equal numbers of molecules in other words, the mass of a gas's particles does not affect the volume that it occupies.

Thus, Avogadro was able to offer more accurate estimates of the atomic mass of oxygen and various other elements, and made a clear distinction between molecules and atoms. Brownian Motion Inthe British botanist Robert Brown observed that dust particles inside pollen grains floating in water constantly jiggled about for no apparent reason.

The JJ Thomson atomic theory

InAlbert Einstein theorized that this Brownian motion was caused by the water molecules continuously knocking the grains about, and developed a hypothetical mathematical model to describe it.

Discovery of subatomic particles Main articles: Electron and Plum pudding model The cathode rays blue were emitted from the cathode, sharpened to a beam by the slits, then deflected as they passed between the two electrified plates. Atoms were thought to be the smallest possible division of matter until when J.

Thomson discovered the electron through his work on cathode rays. When a voltage is applied across the electrodes, cathode rays are generated, creating a glowing patch where they strike the glass at the opposite end of the tube.

Through experimentation, Thomson discovered that the rays could be deflected by an electric field in addition to magnetic fieldswhich was already known. He concluded that these rays, rather than being a form of light, were composed of very light negatively charged particles he called " corpuscles " they would later be renamed electrons by other scientists.

He measured the mass-to-charge ratio and discovered it was times smaller than that of hydrogen, the smallest atom. These corpuscles were a particle unlike any other previously known. Thomson suggested that atoms were divisible, and that the corpuscles were their building blocks. Discovery of the nucleus Main article: Rutherford model The Geiger-Marsden experiment Left: Thomson's plum pudding model was disproved in by one of his former students, Ernest Rutherfordwho discovered that most of the mass and positive charge of an atom is concentrated in a very small fraction of its volume, which he assumed to be at the very center.

In the Geiger—Marsden experimentHans Geiger and Ernest Marsden colleagues of Rutherford working at his behest shot alpha particles at thin sheets of metal and measured their deflection through the use of a fluorescent screen.

To their astonishment, a small fraction of the alpha particles experienced heavy deflection. Rutherford concluded that the positive charge of the atom must be concentrated in a very tiny volume to produce an electric field sufficiently intense to deflect the alpha particles so strongly.

This led Rutherford to propose a planetary model in which a cloud of electrons surrounded a small, compact nucleus of positive charge.Introduction Periodicity Occurrence and Preparation of the Representative Metals Predict the paths taken by α particles that are fired at atoms with a Rutherford atom model structure.

Explain why you expect the α particles to take these paths. Evolution of Atomic Theory by Rice University is licensed under a Creative. Intro to Chemistry: Atoms & the Periodic Table Accelerated Science 8 Page Assignment Title Type of Assignment Date Due Grade Received Mercury: Mysterious and Deadly Article & Homework Questions Article/EDMODO 4 Notes: Introduction to the Modern Atom notes Identifying Sub-atomic Particles of Simple Bohr Model Diagrams.

Modern Knowledge of the Atom The evolution of the modern model of the atom and our general understanding of the atom progressed over several years through many, many experiments conducted in different countries by different people.

LESSON PLAN: Introducing the Atom structure of atoms by creating a physical model or illustrated depiction of an element when provided with number or protons, neutrons, electrons.

change or evolution of a system are critical elements of study. Introduction.

Basic properties

The following video covers some of the properties of an atom. Make a list of the key contributions to a model of the atom that each of these people made and then make a timeline of this information.

Try to get a feel for how it all eventually fit together . The main postulates of the JJ Thomson atomic theory along with a concise historical reference about its development.


which have laid the foundations of modern physics, such as we know it today. that at that time a great amount of physicists thought that cathode rays are immaterial. Moreover, the conventional model of an atom, which was.

History of the Atom