Slide 1 of 18 © Copyright Pearson Prentice Hall Defining the Atom > Atomic Structure Chapter 4 Video 3

Slide 2 of 18 © Copyright Pearson Prentice Hall Defining 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

© Copyright Pearson Prentice Hall Defining the Atom > Slide 3 of 18 Early Models of the Atom Democritus’s Atomic Philosophy How did Democritus describe atoms? Democritus 4.1

© Copyright Pearson Prentice Hall Slide 4 of 18 Defining the Atom > 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

Slide 5 of 18 © Copyright Pearson Prentice Hall Defining the Atom > Early Models of the Atom Dalton’s Atomic Theory How did John Dalton further Democritus’s ideas on atoms? 4.1

Slide 6 of 18 © Copyright Pearson Prentice Hall Defining the Atom > 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

© Copyright Pearson Prentice Hall Slide 7 of 18 Defining the Atom > Early Models of the Atom All elements are composed of tiny indivisible particles called atoms. 4.1

© Copyright Pearson Prentice Hall Slide 8 of 18 Defining the Atom > 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

© Copyright Pearson Prentice Hall Slide 9 of 18 Defining the Atom > 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

© Copyright Pearson Prentice Hall Slide 10 of 18 Defining the Atom > 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. 4.1

© Copyright Pearson Prentice Hall Slide 11 of 18 Defining the Atom > Atoms are solid and indivisible Solid Ball- no Parts

© Copyright Pearson Prentice Hall Slide 12 of 18 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 4.1 Section Quiz 4.1.

© Copyright Pearson Prentice Hall Slide 13 of Section Quiz 1. The ancient Greek philosopher credited with suggesting all matter is made of indivisible atoms is a.Plato. b.Aristotle. c.Democritus. d.Socrates.

© Copyright Pearson Prentice Hall Slide 14 of Section Quiz 2. Dalton's atomic theory improved earlier atomic theory by a.teaching that all matter is composed of tiny particles called atoms. b.theorizing that all atoms of the same element are identical. c.using experimental methods to establish a scientific theory. d.not relating atoms to chemical change.

© Copyright Pearson Prentice Hall Slide 15 of 18 Subatomic Particles What are three kinds of subatomic particles? 4.2

© Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Slide 16 of Subatomic Particles Three kinds of subatomic particles are electrons, protons, and neutrons.

Slide 17 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles Electrons In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron. Electrons are negatively charged subatomic particles. 4.2

Slide 18 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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

Slide 19 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles Cathode Ray Tube 4.2

Slide 20 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles A cathode ray is deflected by a magnet. 4.2

Slide 21 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles A cathode ray is deflected by electrically charged plates. 4.2

Slide 22 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements. 4.2

Slide 23 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom

Slide 24 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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. 4.2

Slide 25 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Plum Pudding Model

Slide 26 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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.

Slide 27 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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.

Slide 28 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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

Slide 29 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom Subatomic Particles Table 4.1 summarizes the properties of electrons, protons, and neutrons. 4.2

© Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Slide 30 of 25 The Atomic Nucleus How can you describe the structure of the nuclear atom? 4.2

Slide 31 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom The Atomic Nucleus Ernest Rutherford’s Portrait 4.2

Slide 32 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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

Slide 33 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom The Atomic Nucleus Rutherford’s Gold-Foil Experiment 4.2

Slide 34 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom The Atomic Nucleus Alpha particles scatter from the gold foil. 4.2

Slide 35 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom The Atomic Nucleus Rutherford’s Gold-Foil Experiment 4.2

Slide 36 of 25 © Copyright Pearson Prentice Hall > Structure of the Nuclear Atom 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

© Copyright Pearson Prentice Hall Structure of the Nuclear Atom > Slide 37 of 25 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

© Copyright Pearson Prentice Hall Slide 38 of 25 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 4.2 Section Quiz 4.2.

© Copyright Pearson Prentice Hall Slide 39 of Section Quiz 1. Which of the following is NOT an example of a subatomic particle? a.proton b.molecule c.electron d.neutron

© Copyright Pearson Prentice Hall Slide 40 of Section Quiz 2. The nucleus of an atom consists of a.electrons only. b.protons only. c.protons and neutrons. d.electrons and neutrons.

© Copyright Pearson Prentice Hall Slide 41 of Section Quiz 3. Most of the volume of the atom is occupied by the a.electrons. b.neutrons. c.protons and neutrons. d.protons.

© Copyright Pearson Prentice Hall Slide 42 of 25 Neils Bohr ( ) 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.

© Copyright Pearson Prentice Hall Slide 43 of 25

© Copyright Pearson Prentice Hall Slide 44 of 25

© Copyright Pearson Prentice Hall Slide 45 of 25 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.

END OF SHOW