1. Atomic Structure

2. What are Atoms? 4th century B.C. Greek philosopher Democritus stated the universe was made of invisible units called atoms.  (atom- “unable to be divided”) Believed movements in atoms caused changes observed in matter.

3. Late 1700’s  French Chemist, Antoine Lavoisier established the Law of Conservation of Matter.  Joseph Proust, later established the Law of Constant Composition (the compound always contains the same elements in the same proportions by mass.)

4.  In 1803 John Dalton purposed an atomic theory: Every element is made of tiny, unique particles called atoms that cannot be subdivided. Atoms of the same element are exactly alike. Atoms of different elements can join to form molecules. A chemical rxn is a rearrangement of atoms. Remember: an atom is the smallest part of an element that still has the element’s properties.

5. What’s in an Atom? We now know that atoms can be divided into many different subatomic particles. Nucleus- the center of the atom, very dense, contains protons and neutrons, has an overall positive (+) charge. Protons- positively (+) charged subatomic particle. Neutrons- neutral (not charged) subatomic particle. Electrons- negatively (-) charged subatomic particle that has very little mass. Creates a “cloud” that encircles the nucleus.  Atoms have no over all charge. They have an equal # of protons and electrons whose charges cancel.

6. Models of the Atom In 1913 Danish physicist, Niels Bohr, suggested that electrons move in set paths around the nucleus, depending on the energy of the electron, much like the planet around the sun. These paths defined the electron’s energy level. In order to move to a different path, the electron must gain or lose energy.

7. In 1925 Bohr’s model no longer explained all observations. A new model purposed that electrons did not orbit like planets around the sun… but instead behaved more like waves on a vibrating string, than a particle. Think about a moving fan.

8. Enter Heisenberg’s uncertainty principle: The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. --Heisenberg, uncertainty paper, 1927 Thus… there exist more of an “electron cloud” (where electrons are most likely to be found) around the nucleus.

9. Electron Orbital Electrons are found in orbitals within energy levels. The regions where electrons are found are called orbitals.

10. 4 Different Kinds of Orbitals There are 4 different kinds of orbitals:  The s orbital- has a spherical shape that surrounds the nucleus.  The p orbital- has a dumbbell- shape and can be oriented on the x-, y-, or z-axis.  The d & f orbitals are much more complex. The d having 5 possible orbitals and the f having 7.

11. Where do the Electrons GO? Although all these orbitals are different, each can only hold a max of 2 electrons.

12. Electron Shell Filling Electrons usually occupy the lowest energy levels available… thus you build from the s orbital up: s, p, d and f.  s having the lowest energy and f having the highest energy. Every atom has one or more valence electrons.  Valence electrons- electrons in the outer most energy level. http://intro.chem.okstate.edu/WorkshopFolder/Electronconfnew.html