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Chemistry 4.1 Slide 1 of 18 4.1 Defining the Atom The lab technician shown here is using a magnifying lens to examine a bacterial culture in a petri dish. When scientists cannot see the details of what they study, they try to obtain experimental data that help fill in the picture. Slide 2 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > 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. Slide 3 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Early Models of the Atom Democritus’s Atomic Philosophy How did Democritus describe atoms? Democritus Slide 4 of 18 © Copyright Pearson Prentice Hall 4.1 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. Slide 5 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Early Models of the Atom Dalton’s Atomic Theory How did John Dalton further Democritus’s ideas on atoms? Slide 6 of 18 © Copyright Pearson Prentice Hall 4.1 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. Slide 7 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Early Models of the Atom All elements are composed of tiny indivisible particles called atoms. Slide 8 of 18 © Copyright Pearson Prentice Hall 4.1 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. Slide 9 of 18 © Copyright Pearson Prentice Hall 4.1 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. Slide 10 of 18 © Copyright Pearson Prentice Hall 4.1 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. Slide 11 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Sizing up the Atom Sizing up the Atom What instruments are used to observe individual atoms? Slide 12 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Sizing up the Atom Despite their small size, individual atoms are observable with instruments such as scanning tunneling microscopes. Slide 13 of 18 © Copyright Pearson Prentice Hall 4.1 Defining the Atom > Sizing up the Atom Iron Atoms Seen Through a Scanning Tunneling Microscope Slide 14 of 18 © Copyright Pearson Prentice Hall