Chemistry The structure of the atom. The Atomic Theory: • All matter is made of atoms, which are particles too small to be seen. • Each element has its own kind of atom. The evolution of the atomic Theory: 1. Dalton 2. Rutherford’s gold foil experiment 3. BohrAllmodels matter is composed of atoms 4. Quantum Mechanics Atoms cannot be made or destroyed All atoms of the same element are identical Different elements have different types of atoms Chemical reactions occur when atoms are rearranged Compounds are formed from atoms of the different elements coming together. Sub Atomic Particles Subatomic Charge Particle Proton Mass (Amu) Where it is Atomic mass located in an atom units + 1 Inside the nucleus Neutron 0 1 Inside the nucleus Electron - Basically 0 Orbiting outside the nucleus The Modern Theory of Atomic Structure: • Atomic number: The number of protons in the nucleus of an atom of that element. – Gives the number of electrons in a neutral element. – Gives the order of elements on the periodic table – If an atom gains or loses a proton it not only changes its atomic number, it also becomes a new element. The Modern Theory of Atomic Structure: • Mass number: is the total number of protons and neutrons in the nucleus of an atom • How do we find the number of Neutrons? (mass number) - (atomic number) =# of neutrons Bohr’s Model of Electrons: • Suggested that electrons move around the nucleus of an atom in orbits or shells. • Each orbit is a certain distance from the nucleus and contains a definite number of electrons. • The orbits are filled in a routine way: – First orbit: 2 electrons – Second orbit: 8 electrons – Third orbit: 8 electrons Bohr model of Nitrogen: • Check your periodic table for Nitrogen -3 7 N Nitrogen 14.0 Bohr model for Magnesium: Bohr Model for Argon Isotopes • • Atoms of the same element that have different numbers of neutrons Two ways to recognize isotopes: 1. Isotope Name: Chemical name – mass # – Example: Carbon -11, Carbon -12, Carbon -13 2. Isotope Symbol: • Example: Mass number X atomic number Chemical Symbol of element Isotopes: • The Isotope symbol makes it easy to find the number of neutrons Atomic mass: • The weighted average of the mass an element’s naturally occurring isotopes. • A “weighted average” means you take into account the % of each isotope that is present in an ordinary sample of the element. Example: A particular sample of carbon has 10% carbon-11, 80% carbon-12, and 10% carbon-13. Calculate the atomic number of this sample of carbon.