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Atomic Structure. Chapter 4 Video 3. 4.1. Early Models of the Atom. Early Models of the Atom An atom is the smallest particle of an element that retains its identity in a chemical reaction. Philosophers and scientists have proposed many ideas on the structure of atoms. 4.1.
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Atomic Structure Chapter 4 Video 3
4.1 Early Models of the Atom • Early Models of the Atom • An atom is the smallest particle of an element that retains its identity in a chemical reaction. • Philosophers and scientists have proposed many ideas on the structure of atoms.
4.1 Early Models of the Atom • Democritus’s Atomic Philosophy • How did Democritus describe atoms? Democritus
4.1 Early Models of the Atom • Democritus believed that atoms were indivisible and indestructible. • Democritus’s ideas were limited because they didn’t explain chemical behavior and they lacked experimental support.
4.1 Early Models of the Atom • Dalton’s Atomic Theory • How did John Dalton further Democritus’s ideas on atoms?
4.1 Early Models of the Atom • By using experimental methods, Dalton transformed Democritus’s ideas on atoms into a scientific theory. • The result was Dalton’s atomic theory.
4.1 Early Models of the Atom All elements are composed of tiny indivisible particles called atoms.
4.1 Early Models of the Atom • Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
4.1 Early Models of the Atom • Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
4.1 Early Models of the Atom • Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element are never changed into atoms of another element in a chemical reaction.
Atoms are solid and indivisible Solid Ball- no Parts
4.1 Section Quiz • 4.1.
4.1 Section Quiz • 1. The ancient Greek philosopher credited with suggesting all matter is made of indivisible atoms is • Plato. • Aristotle. • Democritus. • Socrates.
4.1 Section Quiz • 2. Dalton's atomic theory improved earlier atomic theory by • teaching that all matter is composed of tiny particles called atoms. • theorizing that all atoms of the same element are identical. • using experimental methods to establish a scientific theory. • not relating atoms to chemical change.
4.2 Subatomic Particles • Subatomic Particles • What are three kinds of subatomic particles?
4.2 Subatomic Particles • Three kinds of subatomic particles are electrons, protons, and neutrons.
4.2 Subatomic Particles • Electrons • In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron. Electrons are negatively charged subatomic particles.
4.2 Subatomic Particles • Thomson performed experiments that involved passing electric current through gases at low pressure. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.
4.2 Subatomic Particles • Cathode Ray Tube
4.2 Subatomic Particles • A cathode ray is deflected by a magnet.
4.2 Subatomic Particles • A cathode ray is deflected by electrically charged plates.
4.2 Subatomic Particles • Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements.
4.2 Subatomic Particles • Protons and Neutrons • In 1886, Eugen Goldstein (1850–1930) observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles. • Such positively charged subatomic particles are called protons.
Robert A. Millikan (1868 – 1953) • Millikan used the experimental evidence of Thomson and carried out further experiments that resulted in the calculation of the mass of the electron. The mass of the electron is 1/1840 that of a hydrogen atom and the electron has a unit negative charge.
Eugene Goldstein (1850 – 1930) • Observed a cathode ray tube and found rays traveling in the opposite direction to the cathode rays. Such positively charged subatomic particles are called protons. Each proton has a mass about 1840 times that of an electron.
4.2 Subatomic Particles • In 1932, the English physicist James Chadwick (1891–1974) confirmed the existence of yet another subatomic particle: the neutron. • Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton.
4.2 Subatomic Particles • Table 4.1 summarizes the properties of electrons, protons, and neutrons.
4.2 The Atomic Nucleus • The Atomic Nucleus • How can you describe the structure of the nuclear atom?
4.2 The Atomic Nucleus • Ernest Rutherford’s Portrait
4.2 The Atomic Nucleus • Rutherford’s Gold-Foil Experiment • In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.
4.2 The Atomic Nucleus • Rutherford’s Gold-Foil Experiment
4.2 The Atomic Nucleus • Alpha particles scatter from the gold foil.
4.2 The Atomic Nucleus • Rutherford’s Gold-Foil Experiment
4.2 The Atomic Nucleus • The Rutherford Atomic Model • Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus. • The nucleus is the tiny central core of an atom and is composed of protons and neutrons.
4.2 The Atomic Nucleus • In the atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.
4.2 Section Quiz • 4.2.
4.2 Section Quiz • 1. Which of the following is NOT an example of a subatomic particle? • proton • molecule • electron • neutron
4.2 Section Quiz • 2. The nucleus of an atom consists of • electrons only. • protons only. • protons and neutrons. • electrons and neutrons.
4.2 Section Quiz • 3. Most of the volume of the atom is occupied by the • electrons. • neutrons. • protons and neutrons. • protons.
Neils Bohr (1885-1962) • Was a young Danish physicist and a student of Rutherford’s when he proposed that the electron is only found in specific circular paths, or orbits, around the nucleus. This model of the atom is similar to the solar system because the electrons orbit the nucleus like the planets orbit the sun. Each electron orbit in Bohr’s model has a fixed energy level.
Each energy level can hold a certain number of electrons. • Level one can only hold 2 e’s, • Level two holds 8 e’s, • Level 3 can hold a maximum of 18 e’s • Level four holds 32 e’s. The energy of the electrons increases as the levels increase. When electrons lose energy they go down a level and when electrons gain energy they go to a higher level.
