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Why will the energy well on PE graph be deeper for H vs He?
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Why does He not go as far left on a PE graph vs H when two atoms are coming together?
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CHEM 141 Chapter 3 &
Exam Study Guide for CHEM 141 exam at MSU
| Question | Answer |
|---|---|
| Why will the energy well on PE graph be deeper for H vs He? | It is deeper for H because when two H atoms interact they form a covalent bond which is much stronger than an LDF and requires a lot more energy to break. He atoms do not form covalent bonds, only LDF's. |
| Why does He not go as far left on a PE graph vs H when two atoms are coming together? | He has a larger radius and that means there will be a larger distance between the nuclei and the LDF's that He form will not pull the atoms as closely together as H's covalent bonds. |
| If the strong nuclear force did not exist what would be the consequences? | Only H would exist. |
| What is the strong nuclear force? | It is what holds neutrons and protons (which would normally repel each other) together in the nuclei. |
| What neutral atom has 5 valence electrons and 7 neutrons? | Nitrogen |
| How many protons and neutrons does U-235 have? | 92 protons and 143 neutrons, 92 is the atomic number of U. |
| What causes the release of energy when propane burns in oxygen? | Making bonds in CO2 and H20 releases energy. |
| What forces will atoms of a lower melting/boiling point likely overcome? | LDF's |
| Are elements with low melting/boiling points usually non-metals? | Yes |
| What forces will atoms of high melting/boiling points likely overcome? | Depends on the element but metallic or covalent bonds. |
| What do element forms with high melting/boiling points look like? | Extended network solids that are held together by metallic bonds or covalent bonds. |
| What do element forms with low melting/boiling points look like? | Discrete atoms or small molecules with LDF's between them. |
| Why is N a gas at room temperature and C is a solid? | N molecules interact with each other through LDF's caused by the momentary fluctuating dipoles. C atoms form localized, strong interactions between the atoms (covalent bonds). Takes more energy to break bonds than LDF's. |
| What were the 1st elements to form almost immediately after the Big Bang? | H, He, and Li |
| What happened between the forming of H, He, and Li and the formation of stars? | The universe cooled and subatomic particles began to stick together due to attractive forces which led to the formation of stars. |
| How were all other atoms in the universe formed? | All other atoms were formed from fusions of H, He, and Li inside of stars. |
| Do fusions occur naturally on earth? | No, only in stars. |
| What evidence supports the Big Bang Theory? | The Doppler effect, computer models along the red shift, and CMBR. |
| What is the Doppler effect? | The increase/decrease in the frequency of sound, light, or other waves as the source and observer move towards/away from each other. |
| What are computer models along the red shift? | The red shift is caused by objects that move away from the observer and causes lower wavelengths which correlate with red. |
| What is CMBR? | CMBR stand for cosmic microwave background radiation and can be defined as filling all space; a remnant that provides an important source of data on the primordial universe, the background space between stars and galaxies is almost completely dark. |
| What is nuclear fusion? | Two tiny nuclei combine. |
| What is nuclear fission? | The nuclei breaks apart. |
| What is nuclear radioactive decay? | An unstable nucleus becomes more stable. |
| What is a chemical reaction? | The rearrangement of valence electrons, but the element is unchanged. |
| What is a nuclear reaction? | A change to the nucleus which as a result changes the element. |
| What is the process of fusion in terms of potential energy and forces? | Fusion occurs at high temperatures inside stars, two nuclei come closer together and electrostatic forces repel like charges so the PE increases, then the nuclei are close enough and strong nuclear forces attract the nuclei, PE decreases, the nuclei fuse. |
| What is the difference between microscopic and macroscopic properties? | Microscopic properties are determined by the element and the macroscopic properties are dependent on the atoms that make up the macroscopic objects (like higher ionization energy means a higher boiling/melting point). |
| What are the force and energy changes that occur when two atoms approach each other and form a bond? | As two atoms approach each other PE increases and attractive forces. A third atom is required to transfer energy to one of the two atoms in the system to them to move and increase in energy. |
| What determines whether a bond interaction is stable and how does it relate to temperature? | We have to see what bonds or IMFs are present and all bonds and IMFs can be broken with a certain temperature increase. |
| What do molecular diagrams show? | They show if an atom forms a bond by showing the antibonding levels and bonding levels of interacting atoms. |
| How can you complete and interpret a molecular orbital diagram given a blank diagram for a diatomic molecule? | Count the electrons of each and add them together and correctly put them in the right energy levels. The lower energy levels fill up first (anti-bonding require more energy so electrons settle less easily with them). |
| How do metals bond? | Metals bond through metallic bonding and form in structures. |
| What makes metals malleable? | Molecular orbitals form and the layers of structures form a sea of electrons in layers on top of each other than can easily slide across each other, which also makes them conductive. |
| Why are metals shiny? | Loose electrons come into contact with light and from the energy begin to vibrate and shine reflected light. |
| Why do diamond and graphite form hybrid orbitals? | C atoms don't naturally form at the angles necessary for the atomic structures to exist so hybridization is necessary for the structures of diamond and graphite. |
| How can the macroscopic properties of diamond vs graphite be explained? | The strong bonds of diamond cause it to have a non existent melting point, be translucent, and localized atoms cause it to be unconducive. Graphite's structure cause it to be more brittle. |
| What are some tips for drawing Lewis structures? | Always count the valence electrons, the periodic table shows which atoms form what number of bonds, C atoms always form 4 bonds, H always form 1. |
| What does a space filling model look like? | It looks like a ball and stick model but the atoms are blown up like balloons until they’re filling all available space between the atoms. |
| What does a ball and stick model look like? | Atoms are illustrated as balls and are connected by sticks. |
| What does a perspective formula model look like? | Atoms are represented by their atomic letters and connected by lines, dashed lines (farther away), and wedged lines (coming towards). |
| What does a Lewis structure look like? | Atoms are represented by their atomic letters and are connected by lines. |
| How can you distinguish between structural isomers and alternative representations of the same molecule? | Structural isomers differ in structural orientation while alternative representations are differences in certain structures like a double bond rotating. |
| Why is the rotation of sigma bonds easier to do than pi bonds? | Sigma bonds are end to end bonds while pi are side to side, if a side to side bond is rotated it will break, if an end to end bond is rotated it will not break. |
| How can you use the Lewis structure and VSEPR to deduce the number of electron centers? | Draw the Lewis structure and count the number of electron centers around the central atom, each lone pair counts as 1 and each bond counts as 1 (regardless if its a single, double, or triple bond). |
| How do the number of electron centers tell the shape of geometry? | 2 centers= linear, 3=trigonal planar, 4=tetrahedral, 5=trigonal bipyramidal, 6=octahedral. |
| How can the number of electron centers determine the hybridization? | Every electron center needs a hybrid orbital, so by counting the number of electron centers we can determine the hybridization (sp=2 centers, sp2=3, sp3=4, sp3d=5, sp3d2=6). |
| What is an isomer? | When a compound has the same formula but different arrangements of atoms. |
| How is molecular shape determined from numbers of electron centers, geometry, and hybridization? | If there are no lone pairs, geometry=shape. If not, the atoms will repel each other and equal amount that determines the geometry (lone pairs don't determine shape in any way). |
| How can we use drawings of electron shape to describe its electronegativity? | We can draw the shapes of the Lewis structures and then the vectors pointing toward the partial negative atoms. The correct directions from the shape will tell us if the charges cancel out or add on top of each other, determining if the electron is polar. |
| What are trends of polarity of the periodic table? | Electronegativity is weakest on the left side and strongest on the right. F has the strongest electronegativity, and H has the same electronegativity as C. |
| If a molecule is NON-polar, what IMF(s) does it have? | LDFs only. |
| If a molecule is POLAR, what IMF(s) does it have? | LDFs and dipole-dipole. |
| If a molecule is polar and has an H atom bonded to F, O, or N with a lone pair, what IMF(s) does it have? | H-bonding, dipole-dipole, and LDFs. |
| Why do metals form positive ions? | Because they are very electropositive and their valence electrons are very loosely bonded to them. |
| Why do nonmetals form negative ions? | Because they have more electrons than protons which makes them electronegative. |
| How can you predict the charge on single atom ions? | Check if the atom is a nonmetal or a metal. |
| How can the structure of a molecule be used to predict the melting/boiling point? | More bonds or stronger and more IMFs will lead to a higher melting/boiling point. |
| How can the structure of a molecule be used to predict the conductivity? | Conduction is found in metallic bonding when sheets of bonded molecules slide across each other creating a sea of electrons between them. |
| How can the structure of a molecule be used to predict the hardness? | Structures that are more secure and unable to shift around (e.g. hexagon) are stronger. |
| How can you predict and/or rank the relative melting/boiling points in terms of forces and energy? | Stronger forces have need more energy to break them, check the IMFs and/or bonds of the molecule and determine the strengths of the forces present. |
| What are the differences in melting and boiling points in terms of energy and forces? | Melting points are lower temperatures and only break bonds/forces between molecules while boiling points break bonds/forces within molecules and require a higher temperature. |
| Why do nuclear reactions release large amounts of energy? | Part of the mass of the reactants is converted into energy. |
| What is the explanation for why metals are ductile? | When the nuclei move relative to one and other, the valence electrons act as a glue holding them together. |
| Why is N more electronegative than P? | The bonding electrons are closer to the nucleus. |
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