Atomic Structure A brief look at the history of the atom.

The Greeks 5 th Century B.C., time of ?? 5 th Century B.C., time of ?? Socrates  Plato  Aristotle Socrates  Plato  Aristotle Aristotle, the father of “Natural Philosophy”. Aristotle, the father of “Natural Philosophy”. Believed everything was composed of 4 elements. Believed everything was composed of 4 elements. Earth  water  air  fire Earth  water  air  fire

Democritus of Abdera Democritus considered himself quite a speaker! Began the discussion of the possible existence of ATOMS! ATOM: from the Greek meaning “cannot be cut”. But, he had no empirical evidence, so for centuries people believed Aristotle.

Democritus' Ideas Matter is composed of empty space through which atoms move. Matter is composed of empty space through which atoms move. Atoms are solid, homogeneous, indestructible, and indivisible. Atoms are solid, homogeneous, indestructible, and indivisible. Diff. kinds of atoms have different sizes and shapes Diff. kinds of atoms have different sizes and shapes The differing properties of matter are due to the size, shape, and movement of atoms. The differing properties of matter are due to the size, shape, and movement of atoms. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves. Apparent changes in matter result from changes in the groupings of atoms and not from changes in the atoms themselves.

The Aristotelian Approach to Knowledge The scientific method is still another 2000 yrs. away. The scientific method is still another 2000 yrs. away. They believed one should separate the mind from the body (emotions) in order to understand anything. Attaining knowledge by pure reason, or Rationalism. They believed one should separate the mind from the body (emotions) in order to understand anything. Attaining knowledge by pure reason, or Rationalism. What’s the purpose of knowledge?? What’s the purpose of knowledge?? To lead you to the truth. To lead you to the truth.

The Empirical Approach Come to knowledge by relying on our senses... the beginning of experimentation. Come to knowledge by relying on our senses... the beginning of experimentation. So, compare Rationalism to Empiricism. So, compare Rationalism to Empiricism. What’s better?? What’s better?? Rational – problems with our reason. Plato’s Academy. Rational – problems with our reason. Plato’s Academy. Empirical – problems with trusting our senses. Empirical – problems with trusting our senses.

The integration of Church and Science !! Aristotle’s explanation of the heavenly motions focused on the Earth as the center: Geocentrism. Aristotle’s explanation of the heavenly motions focused on the Earth as the center: Geocentrism. The Holy Church liked this idea and incorporated it into its Doctrine. The Holy Church liked this idea and incorporated it into its Doctrine. It took almost 2000 years and the courage of Aristarchus, Copernicus, Kepler, Galileo and finally Newton to supplant Geocentrism with the correct explanation of Heliocentrism (Sun centered). It took almost 2000 years and the courage of Aristarchus, Copernicus, Kepler, Galileo and finally Newton to supplant Geocentrism with the correct explanation of Heliocentrism (Sun centered). Copernicus Galileo

5 th Cent. B.C. to 1600’s & Newton Not much happened in Science. Not much happened in Science. Dark Ages  Middle Ages  Renaissance, and things started to move again. Dark Ages  Middle Ages  Renaissance, and things started to move again. The Alchemists – tried to turn base metals into Gold! Discovered many of the early elements on the P. Table. The Alchemists – tried to turn base metals into Gold! Discovered many of the early elements on the P. Table. Newton invents the flux, or Calculus. He, too, believed in Alchemy and the elixir vitae. Thought just as a transformation from base metal to pure gold was possible, an individual could be transformed into a better person, too.

John Dalton – 19 th Century The atom lives !! The atom lives !! The first theory of atoms that could be tested and used to explain chemical reactions. The first theory of atoms that could be tested and used to explain chemical reactions. He took Lavosier’s conservation of Mass and Proust’s law of definite proportions and came up with His model of the Atom He took Lavosier’s conservation of Mass and Proust’s law of definite proportions and came up with His model of the Atom

What is the purpose of a Model? Dalton’s Model of the Atom – p. 89. Dalton’s Model of the Atom – p Each element is made of tiny particles called atoms. 2. Atoms of the same element are identical, having similar properties. 3. Atoms cannot be divided any further. 4. Different atoms combine in whole number ratios to create compounds. 5. Chemical reactions are due to atoms separating, combining or rearranging.

But, what does the changing?? As technology got better, more about the atom was discovered, and the Model changes. As technology got better, more about the atom was discovered, and the Model changes. Invention of the Cathode Ray Tube – p. 92. Invention of the Cathode Ray Tube – p. 92. J. Thomson discovers the Electron in 1890s. J. Thomson discovers the Electron in 1890s. Protons soon afterwards. Protons soon afterwards. J. Chadwick discovers the Neutron in J. Chadwick discovers the Neutron in Result? The table atop page 97. Result? The table atop page 97.

Subatomic Particles Dalton’s 3 rd tenant is proven wrong. Protons: p+positive charge Protons: p+positive charge Electrons: e - negative charge Electrons: e - negative charge Neutrons: n o neutral charge Neutrons: n o neutral charge But where in the Atom are these particles found??? But where in the Atom are these particles found???

Protons Positive charge Defines the element Located in the nucleus

Neutron No electrical charge About the same size as a proton Located in the nucleus

Electron Negative charge Makes up the volume of the atom Located outside the nucleus in the energy levels and sublevels Is involved in most chemical reactions

Fundamental Principle in Charges! (physicists knew there were 2 types of charges). Like charges repel: + and + will repel. Like charges repel: + and + will repel. So will two negatives ( - ). Unlike charges will attract !! Unlike charges will attract !! + and - and lookout!

Where are these Subatomic particles Found ?? Dalton – didn’t have a clue. Dalton – didn’t have a clue. Thomson – electrons stuck inside the atom, not moving, like raisins in pudding. Became the “Plum Pudding” model. Thomson – electrons stuck inside the atom, not moving, like raisins in pudding. Became the “Plum Pudding” model. What about the protons and neutrons?? What about the protons and neutrons?? Look to the famous Experiment by Ernest Rutherford – p. 95. Look to the famous Experiment by Ernest Rutherford – p. 95. Transparency. Transparency.

Rutherford’s Model Gives us the existence of the Nucleus! Gives us the existence of the Nucleus! Electrons are still stuck like raisins, but that will change, soon. Electrons are still stuck like raisins, but that will change, soon. The atom is mostly space: the nucleus is 1/10,000 the volume of an atom. The atom is mostly space: the nucleus is 1/10,000 the volume of an atom.

So, answer these.... If opposite charges attract, why don’t the electrons fall into the Nucleus? If opposite charges attract, why don’t the electrons fall into the Nucleus? Why don’t all atoms merge together? Why don’t all atoms merge together? How does e-e repulsion allow you to leave when the bell rings????? How does e-e repulsion allow you to leave when the bell rings????? It’s all about chemistry. It’s all about chemistry.

Ch. 4 H.W ,58,60,64,66 and ,58,60,64,66 and 67.