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Introduction to Atoms

Introduction to Atoms. Preview. Section 1 Development of the Atomic Theory Section 2 The Atom. Concept Mapping. Section 1 Development of the Atomic Theory. Bellringer.

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Introduction to Atoms

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  1. Introduction to Atoms Preview Section 1 Development of the Atomic Theory Section 2 The Atom Concept Mapping

  2. Section1 Development of the Atomic Theory Bellringer The following is a quote by Democritus (c. 460–c. 370 bce). Paraphrase this quote in your own words in your science journal. “Color exists by convention, sweet by convention, bitter by convention; in reality nothing exists but atoms and the void.” What do you know about Democritus? And why are his thoughts important?

  3. Section1 Development of the Atomic Theory Objectives • Describesome of the experiments that led to the current atomic theory. • Compare the different models of the atom. • Explain how the atomic theory has changed as scientists have discovered new information about the atom.

  4. Section1 Development of the Atomic Theory The Beginning of the Atomic Theory • What Is an Element?Around 440 BCE, a Greek philosopher named Democritus thought that you would eventually end up with a particle that could not be cut. He called this particle an atom. • From Aristotle to Modern ScienceAristotle, another Greek philosopher, disagreed with Democritus’s ideas. He believed that you would never end up with a particle that could not be cut.

  5. Section1 Development of the Atomic Theory The Beginning of the Atomic Theory, continued • From Aristotle to Modern ScienceDemocritus was right, though: Matter is made of particles, which we call atoms. • An atom is the smallest unit of an element that maintains the chemical properties of that element.

  6. Section1 Development of the Atomic Theory Dalton’s Atomic Theory Based on Experiments • Dalton’s TheoryJohn Dalton published his atomic theory in 1803. His theory stated that all substances are made of atoms. • Atoms are small particles that cannot be created, divided, or destroyed. • Atoms of the same element are exactly alike, and atoms of different elements are different. Atoms join with other atoms to make new substances.

  7. Section1 Development of the Atomic Theory Dalton’s Atomic Theory Based on Experiments, continued • Not Quite Correct The atomic theory was then changed to describe the atom more correctly.

  8. Section1 Development of the Atomic Theory Thomson’s Discovery of Electrons • Negatively Charged ParticlesThomson experimented with a cathode-ray tube like the one shown on the next slide. He discovered negatively charged particles that are now known as electrons. • Like Plums in PuddingAfter learning that atoms contain electrons, Thomson proposed a new model of the atom. Thomson thought that electrons were mixed throughout an atom, like plums in a pudding.

  9. Section1 Development of the Atomic Theory

  10. Section1 Development of the Atomic Theory Rutherford’s Atomic “Shooting Gallery” • Negatively Charged ParticlesIn 1909, Ernest Rutherford aimed a beam of small, positively charged particles at a thin sheet of gold foil. The next slide shows his experiment. • Surprising ResultsRutherford expected the particles to pass right through the gold in a straight line. To Rutherford’s great surprise, some of the particles were deflected.

  11. Section1 Development of the Atomic Theory

  12. Section1 Development of the Atomic Theory Where Are the Electrons? • Far from the NucleusRutherford proposed that in the center of the atom is a tiny, positively charged part called the nucleus. • Bohr’s Electron LevelsIn 1913, Niels Bohr proposed that electrons move around the nucleus in certain paths, or energy levels.

  13. Section1 Development of the Atomic Theory Where Are the Electrons?, continued • The Modern Atomic TheoryAccording to the current theory, there are regions inside the atom where electrons are likely to found. These regions are called electron clouds.

  14. Section1 Development of the Atomic Theory Comparing Models of the Atom Click below to watch the Visual Concept. Visual Concept

  15. Section2 The Atom Bellringer Answer the following question:An atom is the smallest particle into which an element can be divided and still be that element. Now that scientists have learned that an atom is made up of even smaller particles, is this definition still accurate? Explain your answer in yourscience journal.

  16. Section2 The Atom Objectives • Describe the size of an atom. • Namethe parts of an atom. • Describe the relationship between numbers of protons and neutrons and atomic number. • State how isotopes differ. • Calculate atomic masses. • Describe the forces within an atom.

  17. Section2 The Atom How Small Is an Atom? • Three One-Hundred-Millionths of a Centimeter! Scientists know that aluminum is made of average-sized atoms. An aluminum atom has a diameter of about 0.00000003 cm.

  18. Section2 The Atom What Is an Atom Made Of? • The NucleusProtons are positively charged particles in the nucleus. Neutrons are the particles of the nucleus that have no electrical charge. • Outside the Nucleus Electrons are the negatively charged particles in atoms. Electrons are found around the nucleus within electron clouds. All the structures of the atom can be seen on the next slide.

  19. Section2 The Atom

  20. Section2 The Atom How Do Atoms of Different Elements Differ? • Starting SimplyThe hydrogen atom has one proton and one electron. • Now for Some NeutronsThe helium atom has two protons, two neutrons, and two electrons.

  21. Section2 The Atom How Do Atoms of Different Elements Differ? • Building Bigger AtomsFor bigger atoms, simply add protons, neutrons, and electrons. • Protons and Atomic NumberThe number of protons in the nucleus of an atom is the atomic number of that atom. All atoms of an element have the same atomic number.

  22. Section2 The Atom Isotopes • Isotopesare atoms that have the same number of protons but have different numbers of neutrons.

  23. Section2 The Atom Isotopes, continued • Properties of IsotopesAn unstable atom is an atom with a nucleus that will change over time. This type of isotope is radioactive. • Telling Isotopes ApartYou can identify each isotope of an element by its mass number. The mass number is the sum of the protons and neutrons in an atom.

  24. Section2 The Atom Isotopes, continued

  25. Section2 The Atom Isotopes, continued • Naming IsotopesTo identify a specific isotope of an element, write the name of the element followed by a hyphen and the mass number of the isotope. • Calculating the Mass of an ElementThe atomic mass of an element is the weighted average of the masses of all the naturally occurring isotopes of that element.

  26. Section2 The Atom

  27. Section2 The Atom Forces in Atoms • Four Basic ForcesFour basic forces are at work everywhere, even within the atom. These forces are gravitational force, electromagnetic force, strong force, and weak force. • These forces work together to give an atom its structure and properties.

  28. Section2 The Atom

  29. Introduction to Atoms Concept Mapping Use the terms below to complete the concept map on the next slide. a nucleus atoms mass number electrons isotopes atomic number protons

  30. Introduction to Atoms

  31. Introduction to Atoms

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