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The Bohr Model Today’s Objectives To Be Able To (TBAT) find the number of protons and electrons for any given element TBAT calculate the number of neutrons for any element TBAT use the 4 Step Method for Calculations TBAT use the proper number of electrons in orbitals for each element TBAT identify the correct number of Valence Electrons for each element Electrons in Atoms We know from our previous day that atoms are a theoretical idea. Because they are theoretical, we cannot show them exactly as they are Instead we use models Models- a way of showing/picturing how something works. Based on a Theory Problems with the Rutherford Model Rutherford’s Model did not account for the fact that opposite charges attract His model did not explain why electrons did not crash into the protons in an atom Because refined. of this, the model needed to be Double Slit Experiment Discovered that electrons act as both waves and particles Due to the characteristics of waves, they had to exist at certain energy levels (distances) from the nucleus. Bohr Model: From Denmark Niels Bohr was a Danish Physicist In 1913 made a planetary model of the atom: Atoms have a nucleus in the middle Nucleus contains the ALL the mass Electrons exist around the nucleus at certain energy levels Bohr’s Planetary Model Nucleus in the middle Electrons ‘orbit’ (go around) the nucleus in orbitals Orbital – area that electrons are allowed to exist at. Electrons are at exact distances from the nucleus Looks like planets orbiting the Sun Rules of Bohr Diagrams 1st orbital – maximum of 2 electrons 2nd and 3rd orbital – maximum of 8 electrons Each energy level must have a full amount of electrons before they go in the next orbital Protons The nucleus contains protons and neutrons Protons = positively charge particles (p+) Give an atom its identity Each element has a different number of protons The Atomic Number is the number of protons 10 Neutrons Neutrons are found in the nucleus The provide stability to the nucleus Elements always have the same number of protons but can have different numbers of neutrons in their nucleus The same element, with different numbers of neutrons are called Isotopes Atomic Mass The atomic mass is the mass of an atom Since the mass comes from the nucleus, we only include the protons and neutrons Each proton and neutron have about the same mass so we call that mass an ATOMIC MASS UNIT 1 proton has a mass of 1 amu 1 neutron has a mass of 1 amu Calculating using the Atomic Mass Atomic Mass = protons + neutrons A.M. = p+ + n0 Eg. How many neutrons are in an atom of carbon-13 (carbon atom with a mass of 13amu?) Bohr Model Examples Aluminum Chlorine