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ATOMIC STRUCTURE Text Book Chapters 2, 4, 5 OBJECTIVES Matter is made up of particles whose properties determine the observable characteristics of matter and its reactivity. Use models to describe the structure of an atom Relate experimental evidence to models of the atom Determine the number of protons or electrons in an atom or ion when given one of these values Calculate the mass of an atom, the number of neutrons or the number of protons, given the other two values Distinguish between ground state and excited state electron configurations Identify an element by comparing its bright-line spectrum to given spectra Distinguish between valence and non-valence electrons given an electron configuration Draw a Lewis electron-dot structure of an atom Interpret and write isotopic notation Given an atomic mass, determine the most abundant isotope Calculate the atomic mass of an element, given the masses and ratios of naturally occurring isotopes Matter matters! Chemistry = the study of the _______________________________________ Matter = anything that has ________________________________________ Elements = substance that ___________________________________________ by a chemical change; the simplest form of a pure substance Example: Atoms = the _________________ particle of an element that retains its identity Molecule = a ___________ group of 2 or more atoms ______________ combined Example: Compounds = substances that contain ___________________________________ in a fixed proportion Example: Parts of the Atom Subatomic particles: Location Protons Neutrons Electrons Charge Mass Symbol Atomic number = number of ________________ in the nucleus. Specific to an element Mass number = sum of _________________________________ ((Note::::difference between atomic number and mass number is neutrons)) N # neutrons = mass number - atomic number ISOTOPES Differences Different number of ___________ (this will mean different _____!!) Similarities Same number of _____________ Same number of _____________ Examples of isotopes__________________________________________ Carbon–12 or 12C ____ Protons ____ Neutrons ____ Electrons Carbon–14 or 14C ____ Protons ____ Neutrons ____ Electrons BOTH ARE CARBON!!!! Reminder: Isotopes are atoms of the ______________________ that have different __________________________, and therefore have different _____________________. Complete the table: Hydrogen Isotope # of Protons Protium Deuterium Tritium # of Neutrons Mass Number Symbol AVERAGE ATOMIC MASS Atomic Mass = the _____________ of all the isotopes in a sample of that element Example: Look on the periodic table….what is the atomic mass of chlorine? _____ Chlorine has 2__________ that contribute to this atomic mass: _______________ Why is the average atomic mass not 36amu? _______________________________________________________________ General Formula: Average atomic mass = (percent/100) x (mass) + (percent/100) x (mass)…… Example: What is the average atomic mass of carbon if we are considering that 98.89% is carbon-12 and 1.108% is carbon-13? Isotope name Si-28 Si-29 Si-30 Isotope mass (amu) percentage 92.23% 4.67% 3.10% Find the average atomic mass of an atom of silicon. CALCULATING ELECTRONS 1. Neutral : An atom has _______________ charge. # protons = __________________ # electrons = _________________ Example: ___________ 2. Ion : An atom with either a ________________________ (cation) or a ________________________ (anion) # protons = __________________ # electrons = _________________________________ Example of a cation: ____________ Example of an anion: ____________ Calculate the number of electrons for the following: 1. Na 2. Na+1 3. Ca 4. Ca+2 5. O-2 6. O 7. Cl-1 HOW DID WE FIGURE ALL OF THIS OUT??? 2000 years ago Greeks thought matter was made up of particles of 4 elements: ________________, _______________, _______________, _______________, Democritus 460-370BC said atoms were indivisible and unchangeable (but no one listened to him) 1600’s Robert Boyle He identifies gold and silver as elements – so they were not made of fire, earth, air or water. 1700’s John Dalton Dalton said that the basic unit of matter is a particle called the ____________ This is the basis for modern atomic theory Dalton’s Atomic Theory 1. 2. 3. 4. 1897 J.J. Thomson Used a cathode ray to show atoms are made of smaller parts – including the ___________________ Plum Pudding Model – Atoms are neutral – so the electron (negative) and proton (positive) charges must be equal in magnitude 1909 Ernest Rutherford Gold Foil Experiment – shot ______________ at a piece of gold foil. Expected most to be deflected slightly, but saw that most passed through and some were deflected greatly (even bounced back!). So there must be a dense positive core (nucleus!!) Nucleus contains all positive charge and all the mass 1913 Neils Bohr Planetary Model – Electrons only existed at specific circular orbits, and they gain / lose energy when they shift from one energy level Energy had previously just been viewed as a wave, while matter was made up of particles. In the early 1900’s the WAVE MECHANICAL MODEL suggested a dual nature model of the atom. Same as the earlier models…. Most of the atom is ____________________, with small positively charged dense nucleus separated from electrons located outside The difference is that Electrons do not stay in definite fixed orbits – rather they are probably found in a region around the nucleus called an _________________ Picture of current model: ELECTRON CONFIGURATION How the __________ are distributed throughout an atom’s energy levels. While not contributing to its mass, this will determine an atom’s chemical properties. Valence Electrons = electrons in the ___________________ energy level Kernel = everything except the __________________ electrons Group =Vertical rows on the periodic table. Name 3 elements in the same group_____________________ ___________________________ = very similar chemical properties The group number can be used to determine the number of valence electrons Example: Group 1 = ___ valence electron Group ___ = 2 valence electrons Group 14 = 4 valence electrons Group 15 = ___ valence electrons Lewis Dot Diagrams Valence electrons are represented as dots around the element symbol. Na Cl Li Li1+ Ground State vs. Excited State Ground State = When electrons occupy the lowest possible energy levels. Maximum number of electrons allowed in each energy level is 2-8-18-32 When atoms are excited, energy is __________ Electrons jump to higher principal energy levels, which are higher _____________ Excited State = When __________ occupy ___________ energy levels before occupying ______________________________________________________ Ground State: Excited State: 2-8-1 2-7-2 Ground State: Excited State: 2-8 Ground State: Excited State: 2-8-1 Ground State: Excited State: 2-4-1 BRIGHT LINE SPECTRUM ___________ absorbs a specific amount of energy. Electron _________________________ energy level (__________________) Electron releases ______________ that was ____________ Electron returns back to the ______ energy level (__________________________) Bright Line Spectrum formed This energy released is at a specific wavelength and so can predictably be seen in the bright line spectrum for each element. NAME: _______________________________________ ATOMIC STRUCTURE BIG IDEAS FORMULAS REFERENCE TABLES Atom Atomic mass Atomic mass unit Atomic number Average atomic mass formula Bohr Bright line spectrum Cathode ray tube Dalton Dot diagrams Electron Electron configuration Element Excited state Gold foil experiment Ground state Ion Isotope Mass number Neutral Neutron Nucleus Orbital Planetary model Plum pudding model Proton Rutherford Thompson Valence electrons Wave-mechanical model (cloud model)