Rules for filling orbitals There are three rules for filling orbitals. • Aufbau Principle: Electrons always fill the lowest energy levels first. • Electrons start at the bottom and work their way up. • This also implies that electrons fill orbitalsthe same way every time. • Pauli Exclusion Principle: No two electrons with the same energy characteristics can occupy an orbital at the same time. • One electron must be spin up and the other electron must be spin down. • Hund’s Rule: When filling multipleorbitals of the same sublevel (p, d, and f), electrons half-fill the sublevel first before pairing electrons.
Order for Filling Orbitals • 7s 7p 7d 7f • 6s 6p 6d 6f • 5s 5p 5d 5f • 4s 4p 4d 4f • 3s 3p 3d • 2s 2p • 1s
Connections to the Periodic Table • The first two columns of the periodic table are the s-block. • The last six columns of the periodic table are the p-block. • The middle ten columns of the periodic table are the d-block. Remember that d-block elements fill one energy level late! After 3p is filled, 4s is filled, then 3d is filled, and then 4p is filled. • The bottom two rows of the periodic table are the f-block. Remember that f-block elements fill two energy levels late! After 5p is filled, 6s is filled, then 4f is filled, then 5d is filled, then 6p is filled.
The Equation Triangle • Rule #1 – Write the equation so that it has no division lines. • Rule #2 – What is on the left side of the equal sign goes on the top of the triangle. • Rule #3 – What is on the right side goes on the bottom of the triangle.
Pure Substance: has characteristic physical & chemical properties that can be used to identify it & has a CONSTANT COMPOSITION • Element: • Made up of ONE kind of atom (one element from the periodic table of the elements!) • Cannot be broken down any further • EX: Carbon (C), Nitrogen (N), Oxygen(O), Sodium (Na) • Compound: • TWO or more atoms chemically combined (molecule) • Can be chemically broken down into individual atoms (cannot be physically separated) • Definite **ratio of elements** in the compound • EX: Water (H2O), Salt (NaCl), sugar (C6H12O6)
Mixture:Made up of TWO or more substances (the proportions of the ingredients can vary) that can be physically separated • Homogeneous Mixture: • Substances are mixed EVENLY throughout • Looks the “same” • EX: Sugar Water, Salt Water, Kool-aid • Heterogeneous Mixture: • Substances are NOT evenly distributed • Looks “different” throughout • EX: Concrete, Dirt, Pond Water, chocolate chip cookie
Know the 5 common shapes How to Determine Molecular Shape • 1. Draw the Lewis Diagram. • 2. Tally up # of bonding regions and lone pairs on central atom. • double/triple bonds = ONE bonding region • 3. Shape is determined by the # of bonding regions and lone pairs.
CO2 1. LINEAR (180°) 2 bonding regions 0 lone pairs
BF3 2. TRIGONAL PLANAR (120°) 3 bonding regions 0 lone pairs Exception to the octet rule! – 6 valence electrons!
NO2-1 3. BENT (<120°) 2 bonding regions 1 lone pair BENT <120°
CH4 4. TETRAHEDRAL (109.5°) 4 bonding regions 0 lone pairs
NH3 5. TRIGONAL PYRAMIDAL (107°) 3 bonding regions 1 lone pair
H2O 6. BENT (104.5°) 2 bonding regions 2 lone pairs
What are the properties of light? • By 1900 there was enough experimental evidence to convince scientists that light consists of waves. • The amplitude of a wave is the wave’s height from zero to the crest. • The wavelength, represented by , is the distance between the crests. • The frequency, represented by , is the number of wave cycles to pass a given point per unit time.
The Electromagnetic Spectrum • The product of frequency and wavelength equals a constant (c), the speed of light. c = • The wavelength and frequency of light are inversely proportional to each other. • As the wavelength of light increases, the frequency decreases.
Electromagnetic Radiation According to the wave model, light consists of electromagnetic waves. • Electromagnetic radiation includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays. • All electromagnetic waves travel in a vacuum at a speed of2.998 108 m/s.
The Visible Spectrum The sun and incandescent light bulbs emit white light, which consists of light with a continuous range of wavelengths and frequencies. • The wavelength and frequency of each color of light are characteristic of that color. • When sunlight passes through a prism, the different wavelengths separate into a spectrumof colors. • Red has the longest wavelength and the lowest frequency in the visible spectrum.
Sample problem: Calculating the wavelength of light Use the speed of light to calculate the wavelength of yellow light emitted by a sodium lamp if the frequency of the radiation is 5.09 1014 Hz(5.09 1014 s–1). (contd.)
Sample problem: Calculating the wavelength of light 1. Analyze List the knowns and the unknown.Use the equation c = to solve for the unknown wavelength. Knowns frequency () = 5.09 1014/s c = 2.998 108 m/s Unknown wavelength () = ? m (contd.)
Sample problem: Calculating the wavelength of light 2.Calculate Solve for the the unknown. Write the expression that relates the frequency and the wavelength of light. c = Rearrange the equation to solve for . Substitute the known values for and c into the equation and solve. (contd.)
Sample problem: Calculating the wavelength of light 3. EvaluateDoes the result make sense? The magnitude of the frequency is much larger than the numerical value of the speed of light, so the answer should be much lessthan 1.
The quantization of energy • Planck showed mathematically that the amount of radiant energy (E) of a single quantum absorbed or emitted by a body is proportional to the frequency of radiation (). E orE = h • The constant (h), which has a value of 6.626 10–34 J · s is called Planck’s constant. • The energy of a quantum equals h.
Sample problem: Calculating the energy of a photon Use Planck’s constant to calculate the energy of a photon of microwave radiation with a frequency of 3.20 1011/s. (contd.)
Sample problem: Calculating the energy of a photon AnalyzeList the knowns and the unknown.Use the equation E = h to calculate the energy of the photon. Knowns frequency () = 3.20 1011/s h = 6.626 10–34 J · s Unknown energy (E) = ? J (contd.)
Sample problem: Calculating the energy of a photon 2. CalculateSolve for the unknown. Write the expression that relates the energy of a photon of radiation and the frequency of the radiation. E=hv Substitute the known values for and h into the equation and solve. E = (6.626 10–34 J · s) (3.20 1011/s) = 2.12 10–22 J (contd.)
Sample problem: Calculating the energy of a photon 3. Evaluate Does the result make sense? Individual photons have very small energies, so the answer seems reasonable.
Valence Electrons • Valence electrons are the number of electrons in the outermost energy level. • All elements within a group have the same number of valence electrons • These electrons are available to be lost, gained, or shared in the formation of chemical compounds. • Found in the s and p orbitals of the highest energy level. • Often located in incompletely filled energy levels.
How do I find the number of Valence Electrons? • To find the number of valence electrons, underline the largest number as often as it occurs and add the superscripts. • Example: Cl – 1s2, 2s2, 2p6, 3s2, 3p5– 7 valence electrons • Example: Mg - 1s2, 2s2, 2p6, 3s2– 2 valence electrons • Example: Kr – 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6– 8 valence electrons • Example: U – 1s2, 2s2, 2p6, 3s2, 3p6, 4s2, 3d10, 4p6, 5s2, 4d10, 5p6, 6s2, 4f14, 5d10, 6p6, 7s2, 5f4 – 2 valence electrons
Shortcut to finding Valence Electrons! Group 1 1 valence electronGroup 2 2 valence electronsGroup 13 3 valence electronsGroup 14 4 valence electronsGroup 15 5 valence electronsGroup 16 6 valence electronsGroup 17 7 valence electronsGroup 18 8 valence electrons
WARNING • there is no shortcut for finding valence electrons for transition or inner-transition metals • The number of valence electrons for elements from Groups 3-12 can have different values based on the conditions of chemical reactions. This is also true for a small number of the metals in Groups 13-16
Reactivity of groups • Elements in the same group/family have the same number of valence electrons. • If you’ll remember from last class, elements in the same group have the similar physical and chemical properties; they react the same way (think alkali metal demo). This has to do with the number of valence electrons!
Oxidation Numbers Remember that all atoms want to have a full outermost energy level of 8?.....
Oxidation Numbers • The electrical charge resulting from atoms gaining or losing electrons to fill their outermost s and porbitals. • All uncombined elements have an oxidation number of zero (0) • Metals lose electrons and have (+) oxidation numbers; nonmetals gain electrons and have (–) oxidation numbers • All Noble Gases have an oxidation number of zero (0).
Ions • Ion – a charged particle or molecule created through the loss or gain of valence electrons • Cation – positively charged particle or molecule created through the loss of valence electrons as a result of ionization • Anion – negatively charged particle or molecule created through the gain of valence electrons as a result of electronegativity
Summary: periodic trends 15. Explain Periodic TrendsIn general, how can the periodic trends exhibited by the elements be explained?