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Essay questions – Chemistry Exams

Explain the trends in ionization energy as they relate to the trends in atomic radii.
Answer should:
Define ionization energy: the amount of energy needed to remove one electron (valence electron) from an atom.
State and explain period trends for atomic radii: moving from left to right across a period, atomic radii decreases; reason: as you move from element to element within a period, 1 proton and 1 electron are added. Since the electrons have a natural attraction for the nucleus, the added proton causes the electrons to be even more attracted. Therefore, they pull in closer, making the radius smaller.
State and explain group trends for atomic radii: Atomic radii increases as you move down a group; reason: as you move down a group, more energy levels are added/ greater shielding effect.
State and explain period trends for ionization energy: As you move from left to right across a period, ionization energy increases; reason: as atomic radius decreases more energy is required to remove electrons.
State and explain group trends for ionization energy: For main group elements, ionization energy decreases as you move down a group; reason: since valence electrons are further, they are easier to remove.
Explain Ernest Rutherford’s most famous experiment pertaining to atomic structure.
Your answer should:
Describe what the experiment consisted of (what did he do?): Gold-foil experiment- shot positively charged particles at a piece of extremely thin gold foil. He thought the particles would pass through, which most of them did. Some, however, were slightly deflected, and a few even bounced back.
What the results were (what did he observe?): He thought the particles would pass through, which most of them did. Some, however, were slightly deflected, and a few even bounced back.
What the effects were on atomic theory (what did it tell about atomic structure?): proposed nuclear atomic theory- tiny nucleus; atom is mostly empty space, densely-packed nucleus, nucleus contained positively-charged protons, most of an atom’s mass is contained in nucleus.
Name and state the 3 rules that describe the filling of orbitals according to quantum theory.
Include:
The name of each rule or principle:
1. Aufbau Principle: says that electrons will occupy the orbital with the lowest energy first.
2. Hund’s Rule: says that for orbitals of equal energy (within a subshell), one electron will go into each orbital before any pair up. All “first” electrons will have the same spin (and the same spin quantum number.)
3. Pauli Exclusion Principle: says that if 2 electrons occupy the same orbital, they must have opposite spins. Another way of stating this is that no 2 electrons in the same atom may have the same four quantum numbers. The last one (spin) will always be different.
A complete statement of what each rule or principle says: ^
An ex. of an element that has a “deviant” config., along with an explanation of the reasons for the deviant config.: Ex: Cr
1. expected config.-[Ar] 4s^2 3d^4
2. Actual config. – [Ar] 4s^1 3d^5
Reason: sometimes an atom may become more stable by moving an electron from one orbital to another. This causes it to have a different electron config. from what the “rules” predict.

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