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Name ______________________ Period _______ Chapter 4: Atomic Structure Atomic Theories Greeks: Dalton’s Atomic Theory All elements are composed of _____________________indivisible particles called_____________. Atoms of the same element are_________________. Atoms of different elements are __________________. Atoms of different elements can _________________mix together or ___________________ combine. Chemical reactions occur when atoms are__________________, _________________, or _________________________. J.J. Thomson English physicist discovered electrons in 1897. Experimented with flow of electron current through gases. Electrodes connected to high energy electricity source. Positive side – _______________ Negative side- _______________ Cathode ray – glowing beam, which travels from the cathode to the anode. Thomson proposed that the cathode ray had a stream of small negatively charged particles. Plum Pudding Theory – Electrons are imbedded in a positive sphere. Robert A. Millikan American Calculated by 1916 that the electron had one unit of negative charge and mass is 1/1840 the mass of Hydrogen atom. Sir James Chadwick Subatomic particles with no charge –_____________ Mass is nearly equal to that of the _____________ Subatomic Particles Particle charge relat.mass mass Proton (p+) Neutron (n0) Electron (e-) Ernest Rutherford 1911 – Gold Foil Experiment Proposed that almost all of the ________ and all the _____________ charge are concentrated in a small region at the center of the atom called the_______________. Nucleus- the central core of the atom, composed of protons and neutrons. The Development of Atomic Models Dalton’s Atomic Model – Thomson’s Model – Rutherford’s Model – Positive dense tiny ______________ is surrounded by ________________ in empty space. Neils Bohr – 1913, Danish physicist Planetary Model Electrons have a fixed path. Erwin Schrodinger – 1926 Quantum Mechanical Model – the modern description of the electrons in the atoms comes from the mathematical solution to the Schrodinger equation. Electron Cloud (_________________________) Atom Atom – smallest part of an element that retains the _______________________ Atomic Theory – proposed by John Dalton. Elements are ____________________________ Compounds are _______________________________ Subatomic Particles ___________________ negatively charged particle, has almost no mass. ___________________ positively charged particle, relatively heavy. ___________________ particle with no charge, relatively heavy. mass of ______________ = mass of ______________ Structure of the Atom Nucleus Negatively charged electrons move around the nucleus. only _____________ electrons involved in forming chemical bonds. most of atom is__________ __________. Atomic Number Atoms are _________________ which means _________. Ions are ______________which means ___________________________________. Mass Number The approximate ________ of an atom of an______________. Mass # = Sum of the mass of __________particles Amu – 1 amu = 1/12 the mass of a Carbon atom with 6p+ & 6no # neutrons = Isotopes Atoms that have the same ____________________________but different______________________________. Therefore they have different____________ ________. Different isotopes of an ____________ are chemically__________. When you round the atomic mass on the Periodic Table, you get the mass # of the most _______________________________of the element. Isotopes are ___________ which means ____________. ONLY the number of ________________ changes. Example: He or may be written as He-4 Note: The number of protons never changes; it is the number of protons that determines what element an atom is. Atomic Mass Found on the Periodic Table It is the _____________ ______________ of the masses of all the naturally occurring isotopes of that element. _________________________________is the weighted average of the masses of all the isotopes of an element. ____________________________is the total number of protons and neutrons in one atom of an element. Calculation of average atomic mass. For Element “X” isotopes x – 10 x – 11 mass # 10 11 abundance 20% = .20 80% = .80 10X (10)(.20) = 2.0 11X (11)(.80) = 8.8 10.8 amu You Try Copper (Cu) For Copper isotopes Cu-63 Cu-65 mass # 63 65 abundance 69.1% 30.9%