Quiz 4

Describe and explain the evidence that supports the Big Bang Theory.

red shift, computer models, and Cosmic Microwave Background Radiation

What determines whether a bond or interaction is stable? Explain how temperature influences the stability of bonds and interactions.

A bond will form there are 2 electrons in a bonding molecular orbital. (these 2 electrons make up one bond). However, if there are also 2 electrons in an antibonding, this cancels out the stabilization from 2 electrons in bonding orbital and, therefore, no bonds are formed. Draw picture

Describe the bonding in metals. Explain on the atomic/molecular level why metals are malleable (you can make them into different shapes), ductile (you can draw them out into wires), shiny, and conduct electricity.

A photon is absorbed promoting movement to higher energy level, it immediately moves back down emitting a photon making metal shiny. Electrons are free flowing allowing metal to conduct electricity. Since atoms can move with respect to one another metals are ductile.

Explain the force and energy changes that occur when two atoms approach each other and form a bond. Explain why a third body (another atom or molecule) is (almost always) needed to form a stable bond. (Think back to what we learned in Chapter 1).

As two atoms approach, the potential energy decreases until they are close enough to form a bond, in which the potential energy increases.A third atom is needed to take some of that energy away so it doesn't break the atoms apart

Explain why the atomic radius decreases across the row on the periodic table. What causes a heavier atom (with more subatomic particles) to be smaller in size than a lighter atom?

As you read across the periodic table from left to right, the number of protons and electrons increases. The valence electrons are shielded from the full charge of the nucleus by the core electrons. However because the number of core electrons stays the same, the effective nuclear charge (ENC) also increases across the row. This means that the valence electrons of Chlorine experience a greater attractive force (due to greater ENC) than those of Sodium. This results in the electrons of Chlorine being held more closely and thus accounts for the atomic radius being smaller.

Describe chain of events that led from big bang to atoms that make up your body.

At first, no protons, neutrons or atoms (too hot). After a microsecond, quarks and gluons were able to form stable structures and protons and neutrons appeared. The temperature dropped more to allow some protons and neutrons to stick and stay together. After a billion years, things began to heat up again. As clumps of mostly hydrogen became more dense, atoms collided with one another. At the same time, gravitational attraction caused matter to condense and draw in more hydrogen. Atoms began to undergo nuclear fusion, thus stars were created. As star's inner temperature heats up enough energy is available to produce other fusion reactions. Further collapse of the star's core increases temperature, and carbon's nuclei could fuse, leading to new types of nuclei.

Differentiate between properties of atoms, nano-particles, and larger macroscale materials. Explain why is it that atoms don't have macroscopic properties like melting point, boiling point, and color, while macroscopic materials do (and can be identified by them).

Atoms: single unit, and on their own they can't have things like a melting point because those properties depend on interactions or bonding, which then create emergent properties like melting point.Nanoparticles: Super small, so intermolecular forces are more important (between).This focuses more on the spatial arrangement of molecules in a solid, gas, etc. Macroscale: Larger objects that have properties like melting point and color, and can be easily identified because of that

Why are metals shiny?

Because they absorb photons and re-emit them.

What factors affect the size of an atom?

Both the force of attraction between the protons in the nucleus and the surrounding electrons, and the repulsion between electrons play a role. Ultimately it is a balance between these forces that determines the size of the atom.

Predict, draw models (pictures), and explain why relative melting points and boiling points for substances that exist as molecules (like H2O) differ from those that exist as continuous extended networks (like diamond or metals).

Discrete: exist as molecules (diatomic, H2) or individual atoms (monoatomic, He). Held together by LDFs and sometimes no bond so easier to break down, therefore a low melting pointContinuous Extended Network: (Li, Be, C, B) can form ensembles of atoms, so have more bonds that are stronger *(covalent) and therefore harder to break, which gives higher melting point

Describe the bonding in diamond and graphite in terms of the hybrid orbital model (valence bond theory). Explain how the macroscopic properties of diamond and graphite (appearance, melting point, strength, electricity conductance, etc.) can be explained in terms of the kind of bonding that occurs in these networks.

For graphite the sp2 orbitals will overalap end to end making sigma bonds and the left over P orbitals overlap side to side to make Pi bonds.For Bonding in Diamond atomic orbitals 'hybridized' to form bonding orbitals that then combine with orbitals from other atom to form a bond. Tetrahedral geometry bonding hybridized atomic orbitals (sp3) overlap to give strong directed bonds. Macroscopic properties :Hard- 3D network of strong bonds, you would have to break bonds to disrupt a crystal. High mp/bp- same reasonDoesn't conduct electricity : electrons are located in bonds between atoms- not free to roam. There is a large band gap between the bonding and antibonding orbitals.Translucent- light passes through or is reflected. To absorb light an electron must be promoted to a higher energy level. There is a large "band gap" between the bonding and antibonding orbitals.Graphite properties explained-Conducts electricity: bc electrons can move freely over the entire sheet within its delocalized Pi MOs.-Shiny: because it can absorb and emit photons of many wavelengths (just metals)-slippery: sheets can slide over each other- only "held together" by LDFs.

If a reaction occurs between a compound that has a lemon smell and one that has a rose smell, what will the product smell like?

It is impossible to predict the smell of a product because the properties of new substances depend on its molecular structure. The properties are emergent.

Compare and contrast the molecular orbital bond model and the valence bond model. What are the similarities? What are the differences?

Molecular orbital-each orbital holds max 2 electrons-electrons in bonding orbital stabilize system-electrons delocalize-electrons in antibonding less stable-atomic orbitals combine to equalValence Bond-atomic orbitals overlap to form bond-stronger bond greater overlap-Each bond made up of 2 electrons

Does one molecule of water have a boiling point? Why?

No, because the boiling point is the temperature at which the particles change from liquid to gas. If there is only one particle the words liquid and gas are meaningless.

What do you think happens to the atomic radius when an electron is removed from a neutral atom (for example when Na forms Na+)? Explain your answer in terms of the forces and interactions that govern the size of the atom.

The atomic radius will decrease. For any atom, removing an electron will result in a decrease in the amount of repulsive force between electrons. This allows the electrons to be drawn closer to the nucleus and the atomic radius to decrease.

What do you think happens to the atomic radius when an electron is added to a neutral atom (for example if Cl added an electron to form Cl-)? Explain your answer in terms of the forces and interactions that govern the size of the atom.

The atomic radius will increase. For both Cl and Cl - the ENC is the same. Therefore, the valence electrons will experience the same amount of attractive force. However by adding an electron, the amount of repulsive force increases. With more repulsive force, the electrons will have to move further away from the nucleus to maintain the balance between attractive and repulsive forces. Therefore, the atomic radius will increase.

Why is energy required to remove an electron from an atom? Explain your answer in terms of the forces and interactions involved in this process.

The electrons are attracted to the nucleus of the atom by the electrostatic force between the positively charged protons and the negative electrons. Therefore, to remove the electron, that attractive force must be overcome via the addition of energy.