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10/8/13 4.1 Defining the Atom > 4.1 Defining the Atom > Sizing up the Atom Chapter 4 Atomic Structure 4.1 Defining the Atom 4.2 Structure of the Nuclear Atom 4.3 Distinguishing Among Atoms If you grind a piece of copper into dust, each speck of red dust would still have the properties of copper. • If you could continue to make the dust particles smaller, you would eventually come upon a particle that could no longer be divided and still have the chemical properties of copper. • This final particle is an atom. 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Early Models of the Atom 2 4.1 Defining the Atom > Early Models of the Atom How do you study something that you cannot see it? • Atom • smallest particle of an element that has the properties of that element Early Models of the Atom How did the concept of the atom change from the time of Democritus to the time of John Dalton? 3 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Early Models of the Atom Democritus – Greek philosopher (460 BC –370 BC) – One of the first to suggest existence of atoms. – Reasoned that atoms were indivisible and indestructible 5 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. • Early philosophers and scientists could not see individual atoms • They still proposed ideas about the structure of atoms. 4 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Early Models of the Atom Democritus’s Atomic Philosophy • Democritus’s ideas did not explain chemical behavior www.nndb.com Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. • Lacked experimental support • Not based on the scientific method 6 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 1 10/8/13 4.1 Defining the Atom > Early Models of the Atom Dalton’s Atomic Theory • English chemist and school teacher • Used experimental methods, transformed Democritus’s ideas into a theory • Studied ratios in which elements combine in chemical reactions 7 Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. www.learner.org Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Early Models of the Atom 9 4.1 Defining the Atom > Early Models of the Atom 8 4.1 Defining the Atom > Early Models of the Atom Dalton’s Atomic Theory 2. Atoms of the same element are identical; but atoms of one element are different from those of another element. 3. Atoms of different elements can combine in simple whole-number ratios to form compounds. Atoms of element B Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Early Models of the Atom 10 4. Chemical reactions occur when atoms are separated, joined, or rearranged in different combinations. Atoms of one element are never changed into atoms of another element. Mixture of atoms of elements A and B Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Dalton’s Atomic Theory 11 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Dalton’s Atomic Theory Atoms of element A Atoms of element A CHEMISTRY & YOU How was John Dalton able to study atoms even though he couldn’t observe them directly? What evidence did he use to formulate his atomic theory? Compound made by chemically combining atoms of elements A and B Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 12 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 2 10/8/13 4.1 Defining the Atom > 4.1 Defining the Atom > Sizing up the Atom How was Democritus’s idea of the atom different from Dalton’s? 13 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > Sizing up the Atom Sizing up the Atom 14 4.1 Defining the Atom > Sizing up the Atom • Despite their small size, individual atoms are observable with scanning electron microscopes (SEM). Atoms are very small. • A pure copper coin the size of a penny contains about 2.4 x 1022 atoms. • In an SEM, a beam of e- is focused on the sample. • By comparison, Earth’s population is only about 7 x 109 people. • Electron microscopes are capable of much higher magnifications than regular light microscopes. • If you could line up 100,000,000 copper atoms side by side, they would produce a line only 1 cm long! 15 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 16 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 4.1 Defining the Atom > If an atom has a radius of 1 x 10-10 m, how many of these atoms must be lined up in a row to produce a line 1 m long? 1 x 1010 (10,000,000,000) atoms of radius 1 x 10-10 m would need to be lined up in a row to produce a line 1 m long. 17 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. 3