Chapter 4. Models of the Atom

Review - Rounding  Round 399 to one sig fig. Chapter 4: Models of the Atom Hopefully you said 400 not 4. What is wrong with 4??? The zeroes ARE important, they are place holders. 400 and 4 are NOT the same! If you had $400 in the bank but they said you had only $4 you’d be pissed off! Round 2389 to 2 sig fig and then to 1 sig fig 4.1 Dalton’s Atomic Theory 1. An element is made of tiny, indestructible particles called atoms. (Not quite true – why?) Dalton’s Atomic Theory 2. All atoms of an element are identical and have the same properties. (Not quite true – why?) Dalton’s Atomic Theory 3. Atoms of different elements combine to form compounds. + Dalton’s Atomic Theory 4. Compounds contain atoms in small whole number ratios. e.g. Each H2O molecule consists of one O and two H atoms, not ½ atoms or ¾ atoms. 1 Dalton’s Atomic Theory 4.2 Thomson Cathode Ray Experiment 5. Atoms of 2 or more elements can combine to form different compounds. e.g. C and O may form CO or CO2 Thompson “Plum Pudding Model” http://highered.mcgrawhill.com/sites/0072512644/student_view0/cha pter2/animations_center.html# 4.3 Rutherford’s Scattering Experiment http://www.mhhe.com/physsci/chemistry/animations/chang_2 e/rutherfords_experiment.swf • Atom is + charged - - + • e-’s are distributed throughout atoms like raisins in plum pudding - Explanation of Scattering Nuclear Model 1) The atom is mostly empty space with electrons moving around. 2) Each atom has a small, dense nucleus with the Protons & Neutrons. 2 - Rutherford’s Model Subatomic Particles atom (~10-8 cm diameter) + nucleus (~10-13 cm diameter) - Think about it: If the nucleus is the size of a small marble, then the atom is the size of Cardinal’s stadium! 4.4 Atomic Notation Atomic Number • Every atom of an element has the same number of protons. • The number of protons defines an element. • Carbon atoms ALWAYS have 6 protons. • If we change the number of protons, we change the element. Mass Number Mass number = # protons + # neutrons So how do we calculate the number of neutrons? Isotopes Isotopes of an element have the same atomic number (# p+), but a different mass number (# no). Ex: carbon-12, carbon-13 and carbon-14 # neutrons = mass - # protons How many protons do the above have? Neutrons? 3 Isotopes Ex. 1: Write the atomic notation for potassium-40. How many neutrons are there? Isotopes Ex. 2: Write the atomic notation for bromine-81. How many neutrons are there? ______________ _________________ InIsotopes an atom  Number of protons (+) = number of electrons (-)  Atoms are neutral in charge. 4.5 Atomic Mass Masses of atoms are so small that we define the atomic mass unit (amu) •Mass of proton & neutron  1 amu. •Mass of electron is basically zero amu •Atomic Mass in the Periodic Table is the weighted average of all atoms for that element in the world, so that is why it is NOT a whole number. Atomic Mass Main natural isotopes of carbon: carbon-12 (98.89%) carbon-13 (1.11%) The atomic mass reported for carbon (12.01 amu) is closer to carbon-12 since it is most abundant isotope for C. (There is a ton more C-12 than C-13.) Atomic Mass Example: Use the Periodic Table to determine the most abundant isotope: a. lithium-6 or lithium-7 b. chlorine-35 or chlorine-37 4 4.6 Wave Nature of Light Wave Nature of Light  As wavelength , the frequency , and the Wavelength () is the distance between peaks energy  Frequency () is the number of wave cycles per second. (like a beat) Wave Nature of Light Wave Nature of Light Radiant Spectrum: Which wave has higher energy? Lower frequency? 4.7 Quantum Concept In 1900, Max Planck proposed the controversial idea that energy was emitted in small bundles called quanta. 4.7 Quantum Concept Ball loses potential energy continuously as it rolls down a ramp. Ball loses potential energy in quantized amounts as it bounces down a stairway. A particle of light energy is called a photon. 5 4.8 Bohr Model of the Atom 4.8 Bohr Model Neils Bohr proposed that ~1913 electrons orbit around the nucleus, occupying orbits with distinct energy levels. Electrons are quantized! Bohr Model of the Atom  The electrons orbit around the nucleus kind of like planets orbit around the sun but in 3D.  These orbits are called energy levels or shells.  Each orbit has a specific radius and energy, so it is a certain distance from the nucleus. Bohr Model of the Atom When the light from a heated element passes through a prism, a series of narrow lines is seen. These lines are the emission line spectrum. The orbit closest to the nucleus is lowest in energy; the energy increases with distance from the nucleus. Proven by line spectra. Bohr Model of the Atom Each element produces a different emission line spectrum and therefore its own unique color and set of lines that serve as atomic fingerprints. Bohr Model of the Atom Each element has it’s own energy levels that are unique. 6 Bohr Model of the Atom Bohr theory explains 4 lines in H2 spectra. 4.9 Energy Levels/Sublevels Each energy level can be subdivided into sublevels. Electrons gain energy from heat or electricity and jump to a higher energy level. These “excited” electrons ultimately lose energy and drop to lower energy levels, which causes light to be emitted. Levels: 1-7 Sublevels: s, p, d, and f. 4.9 Energy Levels/Sublevels 4.9 Energy Levels/Sublevels Each level has “n” sublevels: 1st level has 1 Sublevel 2nd level has 2 Sublevels 3rd level has 3 Sublevels 4th level has 4 Sublevels 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f This is depicted on next slide. 4.9 Energy Levels/Sublevels 4.10 Electron Configurations Orbitals are regions in space where there is a high probability of finding an electron. One orbital can hold a maximum of 2 electrons.  s has 1 orbital (2 electrons)  p has 3 orbitals (6 electrons)  d has 5 orbitals (10 electrons)  f has 7 orbitals (14 electrons) (Orbitals are boxes on next slide) 7 Electron Configurations Shorthand description of electrons by sublevel.  Sublevels are filled in order of increasing Writing Electron Configurations 1. How many electrons does the element have? energy. 2. Fill in sublevels to reach that number. 1s < 2s < 2p < 3s < 3p < 4s  You will do configurations for the 1st 20 3. Use superscripts to show the number of elements.  Note the 3d sublevel is higher in energy than the 4s which is why we fill 4s first Ex: C has 6 e-’s; 1s22s22p2 e-'s in each sublevel. Writing Electron Configurations Na O Ca Cl 4.11 s Orbitals 1s 2s p Orbitals 3s s orbitals are the only orbitals that are spherical. The letter of the orbital tells us the shape. No matter what level or shape, ALL orbitals can only hold 2 electrons. 8 d Orbitals – Just for fun! Ch. 4 Self Test, p. 129  Try # 1-4, 6-7, 9, 12, 13-14, 16-18  Answers in Appendix J  Try to answer first, then check your answer!  Also work the problems in the online NOTES and worksheets. 9