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Atomic History Democritus Dalton JJ Thomson Rutherford Chadwick Bohr Matter is composed of empty space in which atoms move Elements consist of atoms and compounds are collection of atoms “Plum pudding model” : Atoms contain negative particles called electrons Alpha particles, positive charge with a mass 7500x of electron. Proved the pp model was wrong. Nucleus center ( +) and tiny electrons moved in space around it. Found neutrons(slightly more massive than a proton. Electrons are in circular paths depending on their energy levels Atomic History De Broglie Shrodinger Millikan Moseley electrons move in waves rather than straight circular paths Wave Mechanical Model or Quantum Mechanical Model. Furthered De Broglie’s idea of waves by stating that electrons are in clouds but in certain energy region Oil drop experiment: discovered that atoms had positive and negative charges and that they equal each other Helped to arrange atoms in the periodic table. Atoms were arranged in increasing atomic number using wavelengths and xrays Atoms, Isotopes and Ions How do atoms of different elements differ? The Modern View of Atomic Structure What are the particles that make up an atom and how do they differ from one 02m14an1 another? proton mass = 1 charge = +1 neutron mass = 1 charge = 0 electron mass = “0” charge = -1 02m14an1.mov.lnk atoms have equal numbers of protons and electrons so they are electrically neutral 1/1840 Atomic Number Atomic number Number of protons in an atom Identifies the element 6 C Carbon 12.01115 Atomic Number Use the Periodic Table to complete the following. 1. 2. What element has the atomic number 18? What element has 35 protons? How are atoms of one element different from those of another element? They have different numbers of these subatomic particles. Atomic Number Chemical Symbol Element Name Average Atomic Mass 1 H Hydrogen 1.00797 Isotopes Isotopes How do we distinguish between atoms? Do all atoms of an element have the same composition? Heavy Water and Water Ice Cube in water atom_parts.exe.lnk Isotopes Isotopes What implication does this have for the masses of atoms? nuclear_particles.exe.lnk Average atomic mass Isotopes differ only in the number of Neutrons Difference is shown by their mass numbers Notation: superscript for mass number, which is the sum of the number of protons and neutrons Notation: subscript for atomic number, which is the number of protons (and electrons) Nuclear Nuclear Particles Particles How many of each particle are in these atoms? 76 Br 78 Br 80 Br 35 35 35 14 N 7 15 N 7 18 O 8 17 O 8 16 O 8 15 O 8 Ions When an atom loses or gains electrons and acquires a net electrical charge. Gain electrons – negative ion - anion Lose electrons – positive ion - cation Mg Mg2+ Ions Charge of ion = # of protons - # of electrons How many protons, neutrons and electrons does 4120Ca2+ have? How many protons, neutrons and electrons does 7835Br - have? Classwork Atomic and Isotopic Symbols 10 min How do we know what makes up an atom? What What do do atoms atoms look look like? like? See the electron microscope image of the molecular art drawn with CO molecules. See the image of graphite. Are these images proof of atoms? How do we see atoms? benzene nickel Surface Surface Imaging Imaging What can we learn about atoms from video generated by electron microscopy? Ex. What do you know about silver? Silver surface.MOV Silicon surface.MOV Cathode Ray Tubes Why does the beam bend? Gold Gold Foil Foil Experiment Experiment Examine the diagram of Rutherford’s alpha ray experiment. What is the implication of this experiment? atomic Au foil.MOV Gold Foil Exp.MOV Line Spectra 700 650 600 550 500 450 400 350 Observation of unique line spectra led to Quantum Theory E=hν Fourth Third Second First Nucleus Where all of this has lead to Bohr Model – did some good things but it is not the whole truth. Some Some Questions Questions Color arises from electrons shifting from one orbital to another of different energy Na excitation.MOV Ground state and excited state What shift would give rise to emission of light? to absorption of light? absorb_emit.exe How do fireworks emit light? Demo Sr, K, Li, Cu, Na Where all of this has lead to Quantum Model What is the Quantum Mechanical Model? It predicts quantized energy levels for electrons, like the Bohr model. What is the Quantum Mechanical Model? It does not describe the exact path that electrons take around the nucleus of an atom, but is concerned with the probability of an electron being in a certain place. Nucleus Orbitals Areas where an electron can be found Can have up to two electrons Fuzzy boundaries → “Electron Cloud” The Closed Sphere Model For convenience Shows where the electron is 90% of the time The Heisenberg Uncertainty Principle You can never know exactly where an electron is if you know how exactly fast it is moving. You can never know exactly how fast an electron is moving if you know exactly where it is. The Atom is a Scientific Model With the scanning tunneling microscope we can see atoms, but we still cannot see their internal structure. Scientific models are created by experiments, but are often modified. There may be flaws in the current model. THE END Flame Test What can you see? Why does it have different colors? Line Spectra 700 650 600 550 500 450 400 350 Observation of unique line spectra led to Quantum Theory E=hν Fourth Third Second First Nucleus Bohr's Bohr's Model Model Model of electrons in fixed orbits to explain quantization Transitions between orbits emits or absorbs light 07m07an1 07m07an1.mov.lnk Figure 6.14 Today we use aspects of line spectrum to identify elements, compounds and mixtures? UV-Vis Spectrometer Distances and types of stars Blood test- carbon monoxide poisoning Mobile weapons detectors Chlorophyll How we determine these energy levels Orbital Diagrams and Electron Configurations n = Principle quantum number Describes the energy level the electron occupies n=4 n=3 n=2 n=1 Valence Shell The number of electrons in the outer most energy level. Example: Lithium Li has 1 electron in valence shell Electron Dot Structure Shows the number of valence electrons of the element in a dot structure. Octet rule: 8 electrons is the maximum allowed electrons in a valence shell! Mg Li O Ne Practice Create a Bohr model, valence electrons?, Electron Dot diagram of each: Nitrogen Calcium Argon Orbital Energy Levels Shape of orbital designated by the letters s, p, d, f, g Excited states Ground state Shapes Shapes of of Orbitals Orbitals Shape of orbital designated by the letters s, p, d, f, g Orbitals have different shapes Describe the motion of an electron in an orbital. Combination of electron microscopy and x-ray diffraction produced image of orbitals Sets Sets of of Orbitals Orbitals (Subshells) (Subshells) Depending on the type of orbital, we find that they occur in sets differing in their orientation in space s - set of 1 p - set of 3 d - set of 5 f - set of 7 Orbitals.exe.lnk Sizes of orbitals Size depends on the value of n Orbitals with the same n are about the same size Shape Orbital Diagram Hydrogen Chlorine Electron Electron Configurations Configurations of of Some Atoms Some Atoms The The first ten elements 1s1 1s2 1s2 2s1 1s2 2s2 1s2 2s2 2p1 1s2 2s2 2p2 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p5 1s2 2s2 2p6 Shorthand Shorthand Notation Notation for for Orbitals Orbitals Combinations of first two quantum numbers; number of orbital types equals the shell number (n). 1s 2s, 2p 3s, 3p, 3d 4s, 4p, 4d, 4f 5s, 5p, 5d, 5f, (5g) 6s, 6p, 6d, 6f, (6g, 6h) Aufbau Principle Aufbau Principle: start with the nucleus and empty orbitals, then “build” up the electron configuration using orbitals of increasing energy Aufbau.exe Electron Electron Configurations Configurations Electron Spin and Pauli Exclusion Principle: Only two electrons can occupy a single orbital and they must have opposite spins Electron Configurations Hund's Rule: When filling a subshell, such as the set of 3 p orbitals, place 1 electron in each before pairing up electrons in a single orbital Electron Configurations Arrangement of electrons in the orbitals is called the electron configuration of the atom The ground state configuration can be predicted, using the Aufbau Principle, the Pauli Exclusion Principle, and Hund’s Rule. Electron configurations Filling _ rules.exe How do we know what the filling order is? What chemistry tool might we rely on? Electron Electron Configurations Configurations and and the the Periodic Periodic Table Table Valence electron configurations repeat down a group aufbau.exe.lnk Ground state electron configurations Example: Li atomic number = 3 nucleus has 3 protons neutral atom has 3 electrons 2 electrons in 1s orbital, 1 electron in 2s orbital 2s 1s Different ways to show electron configuration Energy level diagram Box notation ↑↓ 1s 2s ↑ 2s 1s Spectroscopic notation Li 1s2 2s1 Read this “one s two” not “one s squared” Write the superscript 1. Don’t leave it blank Practice Electron configuration wksht Using the Periodic Table The last subshell in the electron configuration is one of these (row #) s (row # – 1) d (row #) p (row # – 2) f Electron configuration of O Atomic number of O = 8 so neutral atom has 8 e– Electron configuration of Co Atomic number of Co = 27 so neutral atom has 27 e– Simplifying electron configurations Build on the atom’s noble gas core ↑↓ ↑↓ ↑↓ ↑ Ar Co Co ↑↓ ↑↓ 1s 1s He 1s2 O 1s22s22p4 O [He]2s22p4 2s 2s 2p 1s22s22p63s23p6 1s22s22p63s23p64s23d7 [Ar]4s23d7 ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑↓ ↑ 2p 3s 3p 4s ↑ 3d ↑ ↑ Noble Gases Far right of the periodic table These elements are extremely unreactive or inert They rarely form compounds with other elements Noble Gas electron configurations What is the electron configurations for Neon Abbreviated way to write configurations Start with full outer shell then add on Br Ba Noble Gases Neon- emits brilliant light when stimulated by electricity – neon signs- 4th most abundant element in the universe. Helium- light non reactive gas- used balloonsinexpensive, plentiful and harmless Radon- radioactive gas- can cause cancercolorless, odorless emitted from for certain rocks underground Electron configuration of Sn Locate Sn on the periodic table Electron configuration of Sn Sn [Kr] The noble gas core is Kr Electron configuration of Sn Sn [Kr]5s2 The noble gas core is Kr From Kr, go 2 spaces across the s-block in the 5th row → 5s2 Electron configuration of Sn Sn [Kr]5s24d10 The noble gas core is Kr From Kr, go 2 spaces across the s-block in the 5th row → 5s2 Then go 10 spaces across the d-block on the 5th row → 4d10 note: n = row – 1 = 5 – 1 = 4 Electron configuration of Sn— done Sn [Kr]5s24d105p2 The noble gas core is Kr From Kr, go 2 spaces across the s-block in the 5th row → 5s2 Then go 10 spaces across the d-block on the 5th row → 4d10 note: n = row – 1 = 5 – 1 = 4 Finally go 2 spaces into the p-block on the 5th row → 5p2 Why are we doing all of this? Properties of atoms correlate with the number and energy of electrons Electron configurations are used to summarize the distribution of electrons among the various orbitals Practice Practice 3-3 Practice Write the complete electron configurations and noble gas shorthand #1-4 Practice Refer to a periodic table and write the electron configurations of these atoms. Write the configurations using shorthand notation. Zn I Cs 1. 2. The f-block is inserted into to the d-block Find the electron configuration of Au Locate Au on the periodic table Find the electron configuration of Au Au [Xe] The noble gas core is Xe Find the electron configuration of Au Au [Xe]6s2 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row → 6s2 Find the electron configuration of Au Au [Xe]6s24f14 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row → 6s2 Then detour to go 14 spaces across the f-block → 4f14 note: for the f-block, n = row – 2 = 6 – 2 = 4 Find the electron configuration of Au Au [Xe]6s24f145d9 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row → 6s2 Then detour to go 14 spaces across the f-block → 4f14 note: for the f-block, n = row – 2 = 6 – 2 = 4 Finally go 9 spaces into the d-block on the 6th row → 5d9 note: for the d-block, n = row – 1 = 6 – 1 = 5 Electron configuration of ions What is an ion? How many electrons does Cl1- have? How many electrons does Ca2+ have? What is the electron configuration for the chloride ion? What is the electron configuration for the calcium ion? What do you notice? Practice Draw the orbital diagram for sulfur. What ion does sulfur want to form and why? Draw the orbital diagram for Potassium. What ion does sulfur want to form and why? What does this mean Properties of atoms correlate with the number and energy of electrons Atoms like to have full outer shells. Why is this important Valence electrons Electrons in the outermost energy level Where all the action occurs Practice Whiteboard - Atomic Structure (continued) Team Write the electron configuration for silver. Write the noble gas configuration for silver. What element has the following electron configuration? 1s22s22p6 3s23p64s23d4