Properties & Behavior of Gases
What are two fundamental properties of gases that distinguish them from liquids and solids?
Gases do not have a definite volume
They are highly compressible
What is visible light?
The portion of the electromagnetic spectrum that can be perceived by the human eye.
What is an orbital?
A region of space around the nucleus where an electron is likely to be found.
What are valence electrons?
Outermost electrons that determine chemical properties and bonding behavior.
What is ionization energy?
Energy required to remove an electron from a gaseous atom.
State Boyle’s Law and describe what happens to pressure if volume decreases at constant temperature.
Boyle’s Law: P1V1 = P2V2 at constant n and T.
If volume decreases, pressure increases therefore they are inversely proportional.
How does wavelength relate to energy in the electromagnetic spectrum?
Shorter wavelength → higher frequency → higher energy.
Longer wavelength → lower frequency → lower energy.
How many orbitals are in a d subshell?
5 orbitals.
What happens to atomic radius across a period from left to right?
It decreases. Remember the trends in the periodic table !!!!!
How does ionization energy change across a period?
It increases from left to right. Remember the trends in the periodic table !!!!!
According to Charles’s Law, why does volume increase when temperature increases at constant pressure?
Higher temperature increases kinetic energy → particles move faster → collide more → container expands to maintain constant pressure.
What is the photoelectric effect?
Emission of electrons from a metal surface when light of sufficient threshold energy strikes it.
State the Pauli Exclusion Principle.
No two electrons in the same atom can have the same four quantum numbers.
Why do atoms get larger down a group?
Because the principal quantum number (n) increases, adding larger orbitals.
Why is the second ionization energy always greater than the first?
Because removing an electron from a positively charged ion requires more energy.
Explain Dalton’s Law of Partial Pressures and why gases in a mixture do not affect each other's pressure.
Total pressure equals the sum of individual partial pressures.
Gases do not attract or repel one another (ideal gas assumption).
How did Bohr explain atomic emission spectra?
Electrons occupy discrete energy levels.
When electrons fall from excited state to ground state, they emit light equal to the energy difference between levels.
Why do electrons remain unpaired in orbitals before pairing?
Because of Hund’s Rule.
Electrons within a given subshell remain as unpaired as possible.
If there are two or more unpaired electrons in a given subshell, they must occupy different orbitals and must have the same electronic spin.
Why are cations smaller than their neutral atoms?
Removing electrons increases nuclear attraction on remaining electrons, pulling them closer.
What does a negative electron affinity indicate?
Energy is released when an electron is added (exothermic process).
Why do real gases deviate from ideal behavior at high pressure and low temperature?
At high pressure → gas particles occupy significant volume
At low temperature → intermolecular forces become significant
Why is the Bohr model not the modern model of the atom?
Because electrons do not travel in fixed circular orbits; modern theory uses quantum mechanical orbitals based on Schrödinger’s equation.
Why do some elements have anomalous electron configurations?
Half-filled and fully filled subshells provide extra stability, causing deviations from predicted configurations.
For isoelectronic species Cl⁻, K⁺, and Ca²⁺, which is smallest and why?
Ca²⁺ is smallest because it has the most protons (strongest nuclear attraction) with the same number of electrons.
Cl⁻ = 17 protons, 18 electrons
K⁺ = 19 protons, 18 electrons
Ca²⁺ = 20 protons, 18 electrons
Why do noble gases generally have positive electron affinity values?
Noble gases already have full outer energy levels.
Adding an electron would require placing it in a higher-energy orbital, which requires energy (endothermic process), so their electron affinity is positive.