Atomic Structure Subatomic Particles: particles that are smaller than atoms, they are the atomic building blocks 1. Protons: positively charged particles, with a mass of 1amu 2. Neutrons: neutral particles with NO charge, with a mass of 1amu 3. Electrons: negatively charged particles, with negligible mass, 0amu Atomic Structure: there are two main regions of the atom 1. Nucleus: the center of the atom that contains all of the atom's mass, protons and neutrons are here. *sometimes protons and neutrons are called nucleons 2. Energy Levels: the region of space outside of the nucleus, electrons are here. Note: Electrons located in the outermost level (far from the nucleus) are known as valence electrons. Describing Atoms: Mass Number (Atomic Mass): the total number of protons and neutrons in an atom's nucleus Atomic Number: the number of protons in an atom, this identifies the type of element! • because the atom is neutral overall, there must be an equal number of protons and electrons Dalton's Atomic Theory: 1. All matter is composed of atoms, that cannot be broken down, created, or destroyed. 2. All atoms of the same element are identical. 3. Different elements have different types of atoms. 4. Chemical reactions occur when atoms are rearranged. 5. Compounds are composed of atoms of different elements combined in fixed proportions. (whole number ratios) J.J. Thomson's Cathode Ray Tube Experiment Cathode Ray Tube: a glass tube that encloses a vacuum and can be energized by electricity Observations: • A beam of very small particles travels from one end of the tube to the other when electrified. • The beam is bent by a magnetic field, it bends towards the positive pole and away from the negative pole. Conclusion: • The atom is composed of smaller particles known as Electrons! Rutherford's Gold Foil Experiment: Alpha Particles: • positively charged radiation emitted by Uranium Observations: 1. Most of the alpha particles passed straight through the foil. 2. Some alpha particles were deflected at great angles. Conclusions: 1. The atom is mostly empty space. 2. The atom contains a small, dense, positively charged nucleus. Bohr Model of the Atom principle energy levels: regions where electrons are located around the nucleus; levels become larger as the distance from the nucleus increases Ground State: all electrons are as close to the nucleus as possible (low energy, stable) Excited State: electrons occupy energy levels that are further from the nucleus (high energy, unstable) energy level 1 2 3 4 5 6 maximum # of electrons 2 8 18 32 50 72 Wave-Mechanical Model Electrons do NOT move around the nucleus in circular orbits. Rather, they travel in waves, which results in "cloudy" regions of space around the nucleus where electrons can be found. Lewis Dot Structure (Electron Dot Diagram): a diagram that shows the symbol of the element surrounded by dots that represent the valence electrons of an atom of that element orbital: a region of high probability of finding an electron, 2 electrons can occupy each orbital Isotopes: atoms of the same element, and therefore contain equal numbers of protons, with different numbers of neutrons, atoms of the same element with different masses • same # of protons (atomic number) • different # of neutrons Percent Abundance: a measurement of the amount of naturally occurring isotopes of an element.