AP Chemistry - Unit 1 Progress Check

Moles and Mass Calculations

• Number of moles calculated using mass of sample divided by molar mass (e.g., 5.0g of CaO ÷ 56 g/mol).
• For 21g of copper (Cu), molar mass is essential to find the number of Cu atoms via Avogadro's number.
• The compound with the highest molar mass in a sample of 1.0 mol is N2O5 due to the number of atoms in the molecules.

Atomic Mass and Isotopes

• Average atomic mass from isotopes can be estimated; for unknown elements around 91 amu based on relative abundances.
• Gadolinium (Gd) isotopes suggest an average atomic mass of around 157 amu based on spectrum data.
• A pure element's average atomic mass can be derived from its isotopes, yielding 186.3 amu in a specific example.

Experimental Procedures and Purity

• The purity of BaCl2 can be assessed by comparing moles of Ba in the precipitate with moles in the sample.
• The molar mass of unknown metallic element M can be determined by mass change before and after reaction with oxygen.
• Empirical formulas derived from ratios of moles of C and H can identify substances.

Analytical Techniques

• Mass percent composition aids in determining purity of NaCl, an intensive property.
• Molar masses of components X and Z in a chloride mixture are necessary to calculate mole percent.
• For gas mixtures, molar masses are crucial to find each gas's mole fraction.

Electron Configuration and Spectra

• Atom with electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ has zero unpaired electrons.
• The correct ground-state electron configuration of oxygen reflects eight total electrons.
• Magnesium, with atomic number 12, has a specific electron configuration sequence.

Photoelectron Spectra Insights

• The peak corresponding to 1s electrons is identified based on binding energy; it indicates strong nuclear attraction.
• Boron's photoelectron spectrum illustrates electron subshell occupancy matching its configuration.
• Carbon's spectrum demonstrates equal numbers of electrons across occupied subshells, consistent with its structure.

Atomic Radii Trends

• Increasing atomic radius in the nitrogen group explained by decreasing effective nuclear charge as elements descend the group.
• Potassium (K) has a greater atomic radius than bromine (Br) due to lower effective nuclear charge on valence electrons in K.

Ionization Energy and Atomic Behavior

• First ionization energy of K is lower than Ca due to less effective nuclear charge affecting electron attraction.
• Rubidium (Rb) loses electrons more easily than lithium (Li) because Rb's valence electron is further from its nucleus.
• Elements in the same periodic group, like Cs and Rb, react with oxygen in a fixed mole ratio due to similar valence electron configurations.

Ionic Charges and Reactions

• Aluminum typically has a +3 charge in ionic compounds due to its three valence electrons being easily removed.