24 - Model of the Atom (w/ Pedro Rivera Pomales!)
24. Model of the Atom (w/ Pedro Rivera Pomales!)
What scientists understand as the basic unit of a chemical element has been heavily scrutinized for over one hundred years. What are the fundamental components of an atom? What are elements? How did philosophy and science work together for the discovery of the atom? Let’s learn to be scientifically conversational.
General Learning Concepts
1) Background knowledge
a. Previous particle knowledge: We previously discussed some preliminary information about atoms in episode 6 ‘Batteries: Zap, but How?’. An atom a fundamental piece of matter. (Matter is anything that can be touched physically.) Everything in the universe (except energy) is made of matter, and, so, everything in the universe is made of atoms.
i. What is a proton? A particle. Protons reside in the nucleus of atoms, containing a positive charge. They are responsible for most of the mass along with neutrons. (Protons and neutrons are responsible for most of the atomic mass e.g in a 150 person 149 lbs, 15 oz are protons and neutrons while only 1 oz. is electrons.)
ii. What is an electron? A particle. Electrons reside in orbitals around the nucleus. They contain a negative charge.
b. What is the periodic table? A list of chemical elements organized so that scientists can quickly discern the properties of individual elements such as their mass, electron number, electron configuration and their unique chemical properties.
c. States of matter: For the sake of simplicity, we will concern ourselves with three main states of matter: Solids, liquids, and gases. Solids retain a fixed volume and shape (rigid) while liquids assume the shape of the occupied container (slides/moves but not compressible), and gases assume the shape and volume of the contain (compressible). These states of matter are made up of the microscopic particles that populate the periodic table.
2) What was understood before previous atomic models?
a. Philosophy and science: Previously (episode one) we have discussed how the Greek philosopher Democritus (400 BC) believed that matter was made of tiny particles that could not be further separated, named atoms from the Greek atomos (uncut, indivisible). He claimed these atoms had shape, mass, motion, but could not conventionally be defined by color or flavor. Still, while he did develop and systematize classical atomism, he had no scientifically backed evidence to use to “prove” his ideas. 
b. John Dalton: An English chemist who lived from 1766 – 1844. He is perhaps most famously remembered for his atomic model despite also doing careful studies of color blindness and working in meteorology (with accounts saying he kept daily weather records for 57 years). His interest in meteorology was the foundation of his interest in the nature of gases and the development of his atomic theory.
i. All matter is made of atoms. Atoms are indivisible and indestructible.
ii. All atoms of a given element are identical in mass and properties
iii. Atoms of different elements are different weights and different chemical properties
iv. Compounds are formed by a combination of two or more different kinds of atoms.
v. A chemical reaction is a rearrangement of atoms.
Despite this, Dalton did not understand that atoms had a nucleus, protons, or electrons. This is why Dalton’s model was called the billiard ball model – an indivisible spherical object.
c. Thomson Model: Jospeh John Thomson was born in 1856, died in 1940. Thomson is most well-known for his discovery of the electron in 1897. JJ Thomson’s “plum pudding” model integrated smaller particles (subatomic particles) called protons and electrons. In this model, the protons and electrons were homogeneously mixed through the atom. 
d. Rutherford Model: Ernest Rutherford was born in 1871 and died in 1937. Rutherford was a previous student of Thomson. He was further testing Thomson’s hypothesis by firing alpha particles through a very thin sheet of gold and seeing how the particles reacted. If the plum pudding model was to believed, all particles should pass through evenly. However, Rutherford found that occasionally a particle would “hit” something seemingly solid. His deduction was the atom had most of its mass (and positive charge) in a central nucleus. The electrons, he reasoned, must orbit the positive nucleus like planets around the sun. 
3) Current common atomic models
a. Bohr Model: Niels Bohr was born in Denmark in 1885 and died in 1962. Niels Bohr proposed another model of the atom, saying that electrons are arranged in circular orbits around the nucleus but occupy only certain orbitals. Each orbit had an energy associated with it, and moving from one energy level to the next emitted or absorbed energy. Therefore, there was more structure about the electrons that was understood by the Rutherford model. These energy levels (or set orbitals that electrons exist in) allowed for the development of the periodic table that we know today. 
b. Schrodinger model: Ewrin Schrodinger was born in Austria in 1887 and died in 1961. A famous physicist, Schrodinger was renowned for helping develop quantum theory (a theoretical framework that constructs models of subatomic particles). Schrodinger model is truly the Bohr model, but further refined. It is also called the quantum mechanical model of the atom and does not define the precise location of an electron but rather uses the odds of finding an electron in a particular location. 
4) Fun Tidbits
a. Nobel Prizes: JJ Thomson (1906 physics), Ernest Rutherford (1908 chemistry), Niels Bohr (1922 physics), and Erwin Schrodinger (1933 physics) all won the Nobel Prize. Additionally, James Chadwick won the prize in 1935 (physics) for discovering the neutron and had previously worked with Rutherford (who discovered the proton, who worked with Thomson who discovered the electron).    
b. Dalton’s teachings: Dalton reportedly taught that atoms of different elements had different masses before proving it through his research.
5) Solicited Questions
a. Where does the word nucleus come from? Somewhat to the nucleus of a cell (Eukaryotic, that contains a separate compartment to hold genetic material), the nucleus is a central and important part of an object forming the basis for its activity and growth. When originally discovered in 1911, Rutherford did not use this lexicon and instead called the density a “very small central body”.
b. What is an alpha particle? Composed of two protons and two neutrons that are tightly linked, alpha particles are emitted from some radionuclides (radioactive isotopes) during radioactive decay. Ernest Rutherford distinguished and named alpha rays in 1909. They’re capable of doing high biological damage.