INTRODUCTION TO BOHR MODELS OBJECTIVE I can demonstrate the arrangement of sub-atomic particles and explain how these particles form elements. I can diagram the energy levels in an atom. Niels Bohr suggested that the electrons moved around the nucleus in circular paths or orbits. After more research, Schrödinger further stated that electrons do not have a specified path around the nucleus but reside in an electron cloud; no pattern lines exist. The electrons found orbiting in this area are organized into energy levels or shells. There are 7 energy levels in the electron cloud (we will only be looking at the first three levels). In order for electrons to move from one level to another, they must gain or lose energy. A quantum of energy is the amount of energy needed to move an electron from its current level to the next higher level. Each level has a maximum number of electrons that it can hold. The first orbit closest to the nucleus is called the first energy level, and it can hold a maximum of two electrons. You must fill this level before moving out to the next energy level. The second energy holds 8, the third energy level can hold up to eighteen electrons and the fourth energy level holds 32 electrons. The outermost energy level is referred to as the valence energy level. The atomic number (number of protons or number of electrons) of an element determines how many total electrons an element will have in its energy levels. The group number of the element determines how many valence electrons (electrons in the outermost shell) the element has. 1st Level – up to 2 electrons 2nd Level – up to 8 electrons 3rd Level – up to 18 electrons (8) 4th Level – up to 32 electrons Steps to Solving Bohr Diagrams… 1. Find the atomic number of the element on the periodic table. 2. Draw the nucleus of the atom and write the atomic number in the center. 3. Determine the number of electrons for the atom. 4. Fill the first energy level and move to the next if needed. Example : Lithium Example : Magnesium Atomic # _____________________ Mass # ______________________ Valence Electrons _____________ Atomic # _____________________ Mass # ______________________ Valence Electrons _____________