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Models of the Atom

Physical Science - Middle School

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Models of the Atom © Copyright NewPath Learning. All Rights Reserved. 94-4836 Visit www.newpathlearning.com for Online Learning Resources. Atomic Models Scientists use models to explain things that cannot be seen directly. The first model of the atom was proposed by the Greek philosopher, Democritus, who hypothesized that all matter was made of small particles, called atoms. Dalton’s Atomic Theory In the early 1800s, John Dalton conducted experiments on gases and hypothesized the following: 1) All matter is made of atoms and atoms are small particles that cannot be created, divided or destroyed. 2) All atoms of the same element are identical & different elements have different types of atoms. 3) Atoms combine with other atoms to form new substances. Thomson’s Model of the Atom In 1904, J.J. Thomson proposed a model of the atom as a solid sphere with equal numbers of positive and negative charges spread throughout, much as raisins might be embedded in the surface of a pudding. + Oxygen J.J. Thomson 1856-1940 negative particles - “corpuscles” are repelled by the magnet + + + + + + Thomson’s atomic model “plum pudding” equally distributed positive & negative particles “plum pudding” model Rutherford’s Model In 1911, Ernest Rutherford proposed a new model of the atom which consisted of a positively charged nucleus, containing most of the atomic mass of the atom, and negatively charged electrons orbiting around the nucleus like planets around the Sun. + highest energy level Niels Bohr 1885-1962 lowest energy level photon electron Quantum Mechanical model Erwin Schrödinger 1887-1961 dense areas - more likely to nd electrons probability plot of electron density + Bohr’s Model of the Atom In 1913, Niels Bohr proposed electrons move in stable, or stationary, orbits at fixed distances from the nucleus. Each orbit had an energy associated with it. The closest orbit had the lowest energy and the energy increased with the distance from the nucleus. If an electron moves between orbits, then energy in the form of light (or photons), is absorbed or emitted. Oxygen Ernest Rutherford 1871-1937 gold foil detecting screen alpha-particle emier alpha particles (+ charge) + + + + + + + + + + + + + + + + + + + + + + + + + + + Rutherford’s model atoms in gold foil most alpha particles pass through beam of alpha (+) particles + + + + + + proton quarks nucleus u u d The Modern Atomic Theory In 1926, Erwin Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the Quantum Mechanical model of the atom. This model can be represented as a nucleus surrounded by an electron cloud. The probability of finding the electron is greatest where the cloud is most dense and least likely in a less dense area of the cloud. In 1932, James Chadwick discovered the neutron, an uncharged particle contained in the nucleus. Through continued experimentation, more particles have been discovered in the atom. Quarks are believed to be even smaller units than protons and neutrons. In turn, quarks are made up of vibrating strings of energy. The search to find even smaller particles that make up an atom continues. John Dalton J.J. Thompson Niels Bohr Erwin Schrödinger nucleus

Pause and Review Match the scientist with their atomic model. Fill in the name of the scientist under each model. + + + + + + + + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. made of called Atoms have a positive nucleus surrounded by negative electrons. The nucleus contains neutral particles called neutrons. Atoms have negatively & positively char ged particles, evenly spread throughout. J.J. Thomson 1856-1940 Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 John Dalton 1766-1844 + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. Atoms have a positive nucleus surrounded by negative electrons. The nucleus contains neutral particles called neutrons. Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 + + + + + + + in Electrons move in an electron cloud around the nucleus. The nucleus contains neutral particles called neutrons. Schrödinger 1887-1961 James Chadwick 1891-1974 + + + + + + + + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. All matter is made of small particles called atoms. Atoms have a positive nucleus surrounded by negative electrons. The nucleus contains neutral particles called neutrons. Atoms have negatively & positively char ged particles, evenly spread throughout. J.J. Thomson 1856-1940 Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 John Dalton 1766-1844 + + + + + + + + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. All matter is made of small particles called atoms. Atoms have a positive nucleus surrounded by negative electrons. The nucleus contains neutral particles called neutrons. Atoms have negatively & positively char ged particles, evenly spread throughout. J.J. Thomson 1856-1940 Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 John Dalton 1766-1844 + + + + + + + + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. is made of particles called atoms. Atoms have a positive nucleus surrounded by negative electrons. The nucleus contains neutral particles called neutrons. Atoms have negatively & positively char ged particles, evenly spread throughout. J.J. Thomson 1856-1940 Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 John Dalton 1766-1844 + + + + + + + + + Electrons move in stable orbits around the nucleus. Electrons move in an electron cloud around the nucleus. have a positive surrounded negative electrons. The nucleus contains neutral particles called neutrons. Niels Bohr 1885-1962 Erwin Schrödinger 1887-1961 James Chadwick 1891-1974 Ernest Rutherford 1871-1937 Models of the Atom © Copyright NewPath Learning. All Rights Reserved. 94-4836 Visit www.newpathlearning.com for Online Learning Resources.

Models of the Atom

Physical Science - Middle School

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