Chemistry: Quantum Mechanical Model of the Atom
Orbitals, quantum numbers, and electron configurations
Chemistry: Quantum Mechanical Model of the Atom
Orbitals, quantum numbers, and electron configurations
Chemistry - Grade 9-12
- 1
Describe how the quantum mechanical model of the atom is different from the Bohr model of the atom.
Focus on the difference between a fixed path and a probability region.
The Bohr model places electrons in fixed circular paths around the nucleus, while the quantum mechanical model describes electrons as existing in orbitals, which are regions of high probability where an electron may be found. - 2
In the quantum mechanical model, what is an orbital?
An orbital is a three-dimensional region around the nucleus where there is a high probability of finding an electron. - 3
Explain why the word probability is important when describing the location of an electron.
Think about why an electron cloud is not drawn as a simple circle.
Probability is important because the exact position of an electron cannot be known at all times. The quantum mechanical model predicts where an electron is most likely to be found. - 4
Identify the four types of atomic orbitals commonly used in high school chemistry and give the maximum number of electrons each sublevel can hold.
The common sublevels are s, p, d, and f. The s sublevel holds 2 electrons, the p sublevel holds 6 electrons, the d sublevel holds 10 electrons, and the f sublevel holds 14 electrons. - 5
A student says, "An electron in a 3p orbital is in the third main energy level." Explain whether the student is correct.
In an orbital label such as 3p, the number tells the main energy level.
The student is correct because the number 3 in 3p represents the principal energy level, also called the main energy level. - 6
For the orbital label 4d, identify the principal energy level and the sublevel.
In the label 4d, the principal energy level is 4 and the sublevel is d. - 7
Complete the electron configuration for carbon, which has 6 electrons.
Fill lower-energy orbitals before higher-energy orbitals.
The electron configuration for carbon is 1s^2 2s^2 2p^2. This accounts for all 6 electrons. - 8
Write the electron configuration for sodium, which has 11 electrons.
The electron configuration for sodium is 1s^2 2s^2 2p^6 3s^1. This shows that sodium has one electron in the 3s orbital. - 9
Use the Aufbau principle to explain why the 4s sublevel is filled before the 3d sublevel in many electron configurations.
Aufbau means building up from lower energy to higher energy.
The Aufbau principle states that electrons fill the lowest available energy orbitals first. In many atoms, the 4s sublevel is lower in energy than the 3d sublevel, so 4s fills first. - 10
State Hund's rule and apply it to the three 2p orbitals when carbon has two electrons in 2p.
Hund's rule says that electrons occupy equal-energy orbitals one at a time with the same spin before pairing. For carbon, the two 2p electrons go into two separate 2p orbitals before pairing in one orbital. - 11
State the Pauli exclusion principle and explain what it means for one orbital.
Think about the arrows used in orbital box diagrams.
The Pauli exclusion principle states that an orbital can hold at most two electrons, and those two electrons must have opposite spins. - 12
An orbital box diagram shows one box with two arrows both pointing up. Explain what is wrong with this diagram.
The diagram is incorrect because two electrons in the same orbital must have opposite spins. The arrows should point in opposite directions. - 13
Explain how an atomic emission spectrum provides evidence that electrons have quantized energy levels.
Specific lines in a spectrum mean specific energy changes.
An atomic emission spectrum shows only specific colors or wavelengths of light. This means electrons can only lose certain amounts of energy as they move from higher energy levels to lower energy levels, so their energy levels are quantized. - 14
A photon has an energy of 3.20 x 10^-19 joules. Use E = hν, with h = 6.63 x 10^-34 J·s, to calculate the frequency of the photon.
Rearrange E = hν to solve for frequency.
The frequency is found using ν = E ÷ h. ν = (3.20 x 10^-19 J) ÷ (6.63 x 10^-34 J·s) = 4.83 x 10^14 Hz. - 15
Explain why the quantum mechanical model is more useful than the Bohr model for describing atoms with many electrons.
The quantum mechanical model is more useful because it describes electrons in orbitals with different shapes and energies, and it accounts for electron behavior in atoms with more than one electron. The Bohr model works best as a simple model for hydrogen but does not accurately describe many-electron atoms.