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The Structure of an Atom Chapter 3. Early Theories Greek Philosophers –4 Elements Earth Fire Wind Water –Democritus Atoms make up matter –Aristotle.

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Presentation on theme: "The Structure of an Atom Chapter 3. Early Theories Greek Philosophers –4 Elements Earth Fire Wind Water –Democritus Atoms make up matter –Aristotle."— Presentation transcript:

1 The Structure of an Atom Chapter 3

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3 Early Theories Greek Philosophers –4 Elements Earth Fire Wind Water –Democritus Atoms make up matter –Aristotle Refuted Democritus and atom’s existence forgotten

4 Deomcritus Atoms Differences in atoms

5 Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. All atoms of a given element are identical. Atoms cannot be created, divided into smaller particles, or destroyed. Different atoms combine in simple whole number ratios to form compounds. In a chemical reaction, atoms are separated, combined or rearranged.

6 Dalton’s Atomic Theory All matter is composed of extremely small particles called atoms. All atoms of a given element are identical. Atoms cannot be created, divided into smaller particles, or destroyed. (This part proven wrong) Different atoms combine in simple whole number ratios to form compounds. In a chemical reaction, atoms are separated, combined or rearranged.

7 Democritus Atoms Differences in atoms Dalton Atoms Sameness Created/destroyed Combination Rearrangement

8 The Atom The smallest particle of an element that retains the properties of the element Has three main parts that have not been discovered at this point.

9 Subatomic Particles and the Atom Cathode ray tube –Stream of charged particles (electrons). Robert Millikan –Oil drop experiment –Found the charge/mass ratio for an electron J. J. Thompson –Used cathode ray tube to prove existence of electron. –Then used a charge to mass ratio to find the mass, proving part of Dalton’s theory wrong –Proposed “Plum Pudding Model”

10 Democritus Atoms Differences in atoms Dalton Atoms Sameness Created/destroyed Combination Rearrangement Thompson Atoms composed of electrons

11 Ernest Rutherford Gold Foil experiment –Used to prove the existence of a positively charged core (Nucleus) The results were “like firing a large artillery shell at a sheet of paper and having the shell come back and hit you!”

12 Democritus Atoms Differences in atoms Dalton Atoms Sameness Created/destroyed Combination Rearragement Thompson Atoms composed of electrons Rutherford Positively Charged Nucleus

13 Subatomic Particles and the Atom Chadwick –Worked with Rutherford. –Noted there was energy in the nucleus, but wasn’t the protons. –Concluded that neutral particles must also exist in nucleus. Mosley –Assigned atomic number to atoms Bohr –Designed “Bohr Model” of the atom.

14 Deomcritus Atoms Differences in atoms Dalton Atoms Sameness Created/destroyed Combination Rearragement Thompson Atoms composed of electrons Rutherford Positively Charged Nucleus Chadwick Neutrons exist in Nucleus

15 Subatomic Particles and the Atom Three main particles: (see chart in Ch. 3) –Proton Positive In nucleus –Neutrons Neutral In nucleus –Electrons Negative Orbiting the nucleus (not inside)

16 Atomic Differences Atomic Number –Distinguishes one atom from another. –= #p + (& #e - for a neutral atom) Isotopes –Differ in mass number Mass # = #p + + #n o –Change is in # n o Atomic Mass Unit –Defined as 1/12 mass of a Carbon-12 atom p + = 1 amu n o = 1 amu e - = 0 amu

17 Atomic Differences Mass on the periodic table is based on the percent abundance of each isotope of that element. Therefore it is a decimal. Ex: Chlorine exist naturally as Cl-37 and Cl-35. Cl-37 is about 75% and Cl-35 is about 25%. So, (37 X.75) + (35 X.25) = 36.5 amu. See Ex problem on pg 103 for more ideas.

18 Questions? Ask now, or forever come in the morning for them!


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