CEM 141 Final Exam Questions & Answers Solved 100% Correct!!

Why are alpha particles deflected by the nucleus? - Answer-Because both the alpha particles and the nucleus are positively charged and so the alpha particle is repelled. Is this statement (Dalton's Theory) true or false and why? "All atoms of an element are identical and have the same mass and properties." - Answer-False. Atoms of the same element can have different numbers of neutrons. What is the evidence that electrons are subatomic particles? - Answer-The nature of the electron is independent of the material from which it emerges. Example of a theory (explains) - Answer-The properties of matter can be EXPLAINED by understanding that matter is composed of atoms that interact and move in various predictable ways. Why is the boiling point of iodine higher than that of bromine? - Answer-Because iodine has a larger more polarizable electron cloud. The electrostatic attraction between the iodine molecules requires more energy to overcome. When bromine melts, what is happening? - Answer-Attractive forces between molecules are overcome. When oxygen freezes, what is happening with the forces and energy changes during this process? - Answer-New LDFs are formed. Energy is released to the surroundings. Energy is transferred via collisions. Where would two atoms of He be most stable on a PE curve? - Answer-The PE well, where the attractive and repulsive forces are equal and the system is most stable. For a pencil sitting on a desk, what forces are acting upon the pencil? - Answer-Both gravitational and electrostatic. If the PE increases as two particles approach, what are they most likely? - Answer-Two protons (positively charged/same charge).How do atoms know that temperature is increasing? - Answer-Thermal energy is transferred upon collision with other atoms. What two atoms would have the greatest gravitational forces? Two 10g separated by 10 meters. Or, one 100g and one 1g separated by 5 meters? m1m2/r^2 - Answer-100g and 1g separated by 5 meters. (100)(1)/(25) = 4 In the solid state, atoms of xenon are held together by.. - Answer-London Dispersion Forces ONLY because Xenon is a noble gas that cannot bond together. What does a lower PE well mean? What does a further right position on the PE graph mean? - Answer-More energy needed to break interactions. Longer bond. What is true about the PE minimum for the approach of two atoms? - Answer-The depth of the well tells you how much energy is required to break an interaction. In breaking a single chemical bond.. - Answer-Energy is RELEASED. As two atoms approach each other why does the PE decrease? - Answer-Because there is an attractive force between the two atoms. What does not have atoms in it? - Answer-Light and heat. What subatomic particle was discovered last? - Answer-The neutron because it has no charge and is therefore difficult to detect. Can you have an atom of a compound? - Answer-NEVER.What does atomic radius do from left to right across a row on the Periodic Table? - Answer-Decreases because the relative attraction between the protons and the outer electrons increases. What is the relationship between the energy and frequency? - Answer-Positive linear. As energy increases, the frequency increases. Why do we use an energy level diagram rather than the Bohr model of the atom to describe electron behavior in atoms? - Answer-Energy level diagrams describe electron behavior of all elements and the Bohr model only describes hydrogen. Energy level diagrams do not imply distance from the nucleus but the Bohr model does. Will an electron be emitted below a substances minimum frequency? - Answer-NEVER. Which way does the arrow point for absorption? For emission? What colors correspond with larger/shorter arrows? - Answer-UP for absorption. DOWN for emission. Blue for higher energy, and red for lower energy. What is the electron configuration of a nitride ion N3-? - Answer-1s2 2s2 2p6 At the present time, is the number of atoms in the universe increasing or decreasing? - AnswerDecreasing because of nuclear fusion in the stars. U-235 is most likely to spontaneously undergo...? - Answer-Nuclear fission because it has a large # of protons int he nucleus and the p-p repulsion makes it unstable. Break apart produces lighter more stable elements. Can you determine properties of products based off of reactants. - Answer-No. Properties are emergent.Is Cl- or K+ bigger and why? - Answer-Cl- because it has the same # of electrons as K+ but fewer protons, so the attraction between the electrons and nucleus are weaker. What happens to ionization energy across the Periodic Table? - Answer-Increases across the periodic table because the electrons are more strongly attracted to the nucleus. Why do two hydrogen atoms interact through covalent bonds and He does not? - Answer-Hydrogen has more electrons in the bonding orbitals than the anti-bonding orbitals, whereas Helium has the same number in both. Does F2 or Br2 have the higher boiling point? - Answer-Br2 because it has stronger LDFs than F2 and therefore takes more energy to overcome the LDFs when Br2 boils. Why don't metals shine in the dark? - Answer-Metals shine because they absorb and re-emit photons. There are no photons to absorb in the dark. Why does graphite conduct electricity while diamond does not? - Answer-Some of the valence electrons in graphite, but not in diamond, are delocalized in the pi molecular orbitals that extend across the entire network, so electrons can move freely in these orbitals. According to the Valence Bond Theory, what types of orbitals does carbon use for bonding in diamond? - Answer-The sp3 hybridized orbitals that form upon mixing s and p orbitals. What types of geometries can cancel out to become nonpolar? - Answer-Linear and trigonal planar because they are all the same distance away from one another and if they are all pulled away, the inner atom stays in place and is nonpolar. The molecule CH2Cl2 is.. - Answer-always polar! Which is likely to have the highest melting point? MgF2 MgBr2NaBr - Answer-MgF2 because the magnitude of the charges on the ions is the greatest and the radii of the ions is the smallest. What is the hybridization of the sulfur in SO3? - Answer-sp2. What is the formal charge on the sulfur in SO3? - Answer-+2. What is the formula for the compound formed between aluminum and chlorine? - Answer-Al+3Cl-1 Which one would have the highest melting point? Substances with purely LDFs or substances with hydrogen bonding? - Answer-Substances with hydrogen bonding because those IMFs are harder to break. Would Ar, CH4, or N2 be moving fastest on average? - Answer-Ar because it is the lightest mass of the three. In a system composed of two different molecules, one light and one heavy. At the same temperature, which molecule has a lower kinetic energy? T=KE - Answer-Both are the same. On a humid day, water in the air condenses on the outside of a cold cup. The condensation of the water is.. - Answer-Exothermic and thermal energy is transferred from the system to the surroundings. From a gas to a liquid, energy is being released as IMFs are being created. When sweat evaporates from your skin you feel cooler. What process is responsible for this? - AnswerEnergy transfers from your skin to the water and the energy makes the molecules vibrate more strongly, and intermolecular forces between the water molecules are overcome and the water evaporates. Two substances are in a pot, one heats up more with the same amount of thermal energy added, which one has the higher specific heat? - Answer-The one that is cooler after the thermal energy has been added.