The Atom Atomic Structure Nucleus Electron Cloud Nucleus Core of Atom Contains most of mass of atom 1 amu (atomic mass unit) 6 x 10 23 protons equal one gram Contains Proton Positive charge 1 amu Neutron No charge 1amu Electron Cloud Surrounds the small nucleus Contains mostly empty space Largest part of atom Contains very little (considered no) mass Electron Cloud & Energy Levels Energy levels Areas where electrons travel Closest to nucleus- least energy Electrons move between energy levels Electrons In electron cloud Have negative charge Have almost no mass- takes 1836 to equal 1 proton’s mass Number of protons and electrons are the same in an atom Electrons determine an elements chemical properties Atomic Number The number of protons in nucleus of atom The number of protons in the nucleus determines what element is Atomic number of an element never changes Atomic Mass The number of protons plus the number of neutrons in an atom Mass is an average of isotopes of an atom Element Key Isotopes Number of neutrons in atom can vary Number of protons is constant Carbon- 6 Protons 4, 6, 7, 8 neutrons Mass can vary from 10 to 14 Average is mass of 12- all others are isotopes Can get mass with decimal – but can’t get a partial proton or neutron! Sample Problems An elements has 35 protons and 47 neutrons; a second element has 34 protons and 47 neutrons. Are they isotopes or different elements? Different number of protons- different elements Sample Problems Element x has an atomic number of 40 and has 42 neutrons; Element y has 40 protons and 40 neutrons. Are they the isotopes or different elements? Same number of protons- Isotopes Bohr’s Diagrams Include nucleus with number of p and n Include electron cloud number of energy levels Shows number of electrons per energy level. Include examples in notes! .