Atoms and Atomic Theory
Part 1: Summary
An atom is the tiniest indivisible particle making up every material. Atom is used to mean indivisible. Its size is very small, and the atom sizes differ from an element to another. Each atom contains a nucleus in its center, which is formed by protons (bits with positive charges) and neutrons (bits without any charge). Electrons appear in the space around the nucleus. Electrons are particles negatively charged with their number equal to protons (Education video, 2010). Thus, an atom is neutral. They can exist individually or in small groups of similar or dissimilar atoms called molecules. Elements are built by single atoms and compounds built by molecules.
Part 2
- As discussed above, an atom is the tiniest unit of a given element consisting of protons, electrons and neutrons. Helium is an atom consisting of two protons in its nucleus. Most of the Helium atoms contain two neutrons besides the protons. In a neutral state, Helium contains two electrons that orbit around the nucleus (Cosmos, 2020).
- True or False Statements
- False
- True
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- True
- An atom is made of protons with positive charges, electrons with negative charges, and also neutrons that lack any charge (Johnson, 2020). The number of protons and electrons is the same as the other, hence cancelling each other (positive and negative). Since neutrons are not charged, they play no part in atoms’ neutrality.
- In the table, the radius of atoms improves from tip to base in one group, and it reduces from left to right over one period. Thus, francium is the biggest because the orbitals causing the high value of principal quantum numbers are added, causing the atom size to increase.
Part 3: History of Atomic Theory
J.J. Thomson, a noble-prize winner in 1906, was a physicist who discovered electrons through his researches. Cheetham Hill is were Thomson was born in 1856. He got a scholarship to learn at Trinity College. In addition, he worked under Lord Rayleigh after graduation (Biography Newslater, 2014). He researched cathode ray and discovered electrons. In 1890, he married Rose, his student. He published thirteen books. In 1918, he left research and became Trinity College’s master. He died in 1940 and was buried in Westminster Abbey.
Before his discovery, concrete evidence had proved the existence of atoms. Experiments had shown that every chemical element consists of one atom that chemical reactions could not destroy. Element’s atomic masses could be estimated and clear difference between atoms and molecules made (Helmenstine, 2019).
Description of the Experiment
Thomson experimented using cathode rays, glowing light beams, which abide by electronic discharge in a tube of high-vacuum. With better equipment, Thomson determined the angles they deflected and found the ratio of electronic charge to mass of those particles. Also, he realized that the rate remained the same despite the gas used, which led to the deduction that the particles making up these gasses were omnipresent (Helmenstine, 2019). He ascertained that all elements are made of small particles, tinnier than atoms. Positively charged metal plates attracted these rays, but they repelled negatively charged metal plates meaning they rays were negatively charged. Initially, he called them corpuscles, the now called electrons.
The New Atomic Model
Thomson’s atomic model described the inner structure of an atom. He had discovered the negatively charged part of atoms, the electron (Helmenstine, 2019). He believed atoms are constant domains of matter positively charged with electrons implanted through the plum pudding model. The model was discarded following the Rutherford model, where electrons described orbits of small positive nucleus.
References
Biography Newslater. (2014). J.J. Thomson. Retrieved 14 July 2020, from https://www.biography.com/scientist/jj-thomson
Cosmos. (2020). Helium. Retrieved 14 July 2020, from https://astronomy.swin.edu.au/cosmos/H/Helium
Education video. (2010). what are Atoms? [Video]. Youtube. Retrieved from: https://www.youtube.com/watch?v=jZO6W-DEVLk&feature=youtu.be
Helmenstine, A. (2019). The History of Atomic Theory Led to Quantum Mechanics. Retrieved 14 July 2020, from https://www.thoughtco.com/history-of-atomic-theory-4129185
Johnson, L. (2020). Why is an Atom Electrically Neutral?. Retrieved 14 July 2020, from https://sciencing.com/why-is-an-atom-electrically-neutral-13710231.html