The Big Bang
(a) Calculate the approximate age of the universe from the average value of the Hubble constant, \(H_{0}=20 \mathrm{~km} / \mathrm{s} \cdot \text { Mly }\). To do this, calculate the time it would take to travel 0.307 Mpc at a constant expansion rate of 20 km/s. (b) If somehow acceleration occurs, would the actual age of the universe be greater or less than that found here? Explain.
Text Transcription:
H_0=20 km/s times Mly
Wednesday, February 3, y Lecture 3 Valence Shell Review outermost shell = valence shell 1st 2 electrons 2nd 8 electrons 3rd 8 electrons An atom is most stable when its outer most shell is filled Ionic Bonds Ex: NaCL • Bonds are weak • Na gives up an electron to Cl and now has 11 protons and 10 electrons not electrically balanced anymore • Cl accepts an electron from Na and now has 17 protons and 18 electrons • Na has a full second shell and Cl has a full 3rd shell • NaCl falls apart in a solution because of the weak bond Cations positive charge Anions (electrolytes) negative charge 1 Wednesday, February 3, y Covalent Bonds Ex: CH4 (Methane) • Strong bonds • Do not fall apart in a solution • The 4 hydrogens each give up 1 electron to form electron pairs with the carbons outer shell • Both carbon and hydrogen now have their outer shell filled • Certain atom types have a stronger attraction than others Electronegativity O > N > C = H The greater the electronegativity = the greater the amount of electrons Polar v. Non-polar Polar • Covalent bonds that have electrons that are not shared equally • Molecules tend to be soluble in water • Hydrophilic Nonpolar (neutral) • Electron pairs are shared equally • Molecules are not soluble in water • Hydrophobic 2
