Chapter 5 Review

Chapter 5 Review

5.1

o Early Models of the Atom

o Democritus

 Greek teacher who lived in the 4th century B.C.

 Was the first to suggest the existence of particles, atoms

 Believed these structures were indivisible and indestructible.

 His ideas were not useful in explaining chemical behavior.

• Lacked experimental support

o John Dalton

 The modern process of discovery regarding atoms began with him.

 Was an English school teacher

 Unlike Democritus, Dalton performed experiments to test and correct his atomic theory.

 Dalton’s atomic theory

• All elements are composed of tiny invisible particles called atoms

• Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

• Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds

• Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

 Much of Daltons theory is accepted today

• Except we now know atoms are divisible and can be broken down into even smaller, more fundamental particles.

o Atom

 The smallest particle of an element that retains the properties of that element.

 Scanning tunneling microscopes provide a visual image of individual atoms.

5.2

Three kinds of subatomic particles

o Elections

o Negatively charged subatomic particles.

o Electrons were discovered by J.J Thompson

o Thompson performed an experiment that resulted with a cathode ray, a glowing beam formed between the electrodes

o Thompson discovered the beam attracted to positive metal plates and repealed negative plates

o He proposed that the cathode ray is a stream of tiny negatively charged particles moving at high speeds.( electrons)

o He concluded electrons must be parties of the atoms of all elements

o E. Goldstein