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ATOMS, All elements are composed of atoms that are indivisible and…
ATOMS
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Models of Atom
Atomic Theories
Democritus (400 BC) – the theory he made was lacked experimental support and it is not based on scientific method. He described the atom as billiard ball because he believes that atom is a solid ball that could not be break into smaller pieces.
John Dalton (1800) – he builds the idea of Democritus about the atoms. He also proposed a 5 atomic theory, that is stated below:
Joseph John Thomson (1897) – he discovered the electron that is first called corpuscles, with the help of experimenting with the cathode ray tubes. He states that in the cathode rays are negatively charged. Furthermore, he also studied the positively charged particles in the neon gas. This give him hint that the atoms are not the smallest things that exist, and it can still be further divided. Thomson suggested a “plum pudding model”, suggesting that electrons are tiny negative charges attached to a positively charged medium. In addition, Thomson added that negatively charged electrons would "balance" the positively charged medium such that all atoms would be neutrally charged.
Ernest Rutherford - Through several experiments from 1909 to 1911, Ernest Rutherford identified the nucleus of atoms. His discovery came by mistake and as an utter surprise. His experiment consisted of shooting alpha particles on a very thin layer of gold foil. Alpha particles were made up of two protons and two neutrons. The idea of the experiment was to determine how far the alpha particles had deflected from their original path when they passed through the gold foil. As the alpha particles are positively charged and the electrons are negatively charged, the electrons were supposed to slightly modify the trajectory of the alpha particles.
Neil Bohr - A Danish physicist and Rutherford student, Bohr created a new model of the atom that somehow resembled the Solar System. He was the first to discover that electrons are moving in different orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of the element.
The Bohr model is summarized as follows:
Erwin Schrödinger (1926) – an Austrian physicist who developed an atomic model called quantum mechanics model of the atoms and this model predicts the possible location of electrons. He also calculated the likelihood of finding an electron in certain position using a mathematical equation.
James Chadwick (1932) – an English physicist that confirmed of the existence of neutrons. The experiment he made was similar with what Walter Bothe and Herbert Becker conducted, where beryllium was bombarded with alpha particles and this was generated with unknown radiation. While his conducted experiment was subjected with numerous substances and elements to the radiation. After that he concluded that the radiation was composed of the neutral particles that had the same amount of mass as protons that he called neutrons.
The Atomic Number
- Henry Moseley – he is the one who observed the properties of x-rays from about a dozen consecutive elements in the periodic table. He developed that the wavelength of x-rays can be shorter when the atomic weight increased.
The discovery of radiation by Marie and Pierre Curie paved the way for an accurate picture of the atomic structure. Some components have been found to emit particles, which can move through matter in a similar way to x-rays. The Curies published clear evidence supporting the existence of a new element – radium. After the death of her husband Pierre, Marie Curie set up a world-class laboratory to honor her late husband and became the first woman professor at the Sorbonne.
Structures of Atom
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- The protons and neutrons can be found in the central part of the atom that is called nucleus.
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- Electrons have a very small negligible mass and can be found in orbitals or electron shells.
- The collective term for neutrons and protons is called nucleons.
Parts of Subatomic Particles:
- Atomic mass (A)–the mass of the nucleus, measured in amu
- Atomic number (Z)–the number of protons inside the nucleus
References:
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De Borja, R.S. (2016). Chemistry for Senior High School. Mandaluyong City. Books Atbp. Publishing Corp.
Nucum, Z. T. (2017). General Chemistry 1. Quezon City: C & E Publishing, Inc.
Wilbraham, A.C., Staley, D.D., Matta, M.S., & Waterman, E.L. (2010). Chemistry. Boston: Pearson.
Zumdahl, S.S. & Zumdahl, S.A. (2018). Chemistry (10th ed.). Boston, MA, USA: Cengage Learning.
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All elements are composed of atoms that are indivisible and indestructible.
Atoms that have the same elements are exactly alike.
Atoms that have different elements are different.
The compounds can be formed when the atoms of different elements were combined in a fixed proportion.
A chemical reaction can be involving in rearrangement of atoms when there will be no change in the atoms themselves.
Electrons occupy only certain orbits around the nucleus. Those orbits are stable and are called “stationary orbits”.
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Each orbit has an energy associated with it. The orbit nearest the nucleus has an energy of E1, the next orbit is E2, and so on.
Energy is absorbed when an electron jumps from a lower orbit to a higher one and energy is emitted when an electron falls from a higher orbit to a lower one.
The energy and frequency of light emitted or absorbed can be calculated by using the difference between the two orbital energies.
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