AP Chemistry: Core Concepts

What is the trend for first ionization energy across a period from left to right, and why?

First ionization energy increases across a period because the effective nuclear charge increases, pulling electrons closer to the nucleus and making them harder to remove.

Explain why the atomic radius decreases as you move from left to right across a period.

The atomic radius decreases because the increasing number of protons increases the effective nuclear charge, which pulls the electron cloud tighter toward the nucleus.

Which intermolecular force is responsible for the unusually high boiling point of water compared to other group 16 hydrides?

Hydrogen bonding, which occurs when hydrogen is covalently bonded to highly electronegative atoms like N, O, or F.

Define the term 'limiting reactant' in a chemical reaction.

The limiting reactant is the substance that is completely consumed first in a reaction, thereby determining the maximum amount of product that can be formed.

What is the formula for calculating the percent yield of a chemical reaction?

Percent Yield = (Actual Yield / Theoretical Yield) x 100%.

According to the Brønsted-Lowry definition, what is a conjugate base?

A conjugate base is the species that remains after an acid has donated a proton (H+).

If a solution has a hydronium ion concentration [H3O+] of 1.0 x 10^-4 M, what is its pH?

The pH is 4.0, calculated using the formula pH = -log[H3O+].

What does a negative value for the change in enthalpy (ΔH < 0) indicate about a reaction?

A negative ΔH indicates an exothermic reaction, where heat is released from the system to the surroundings.

What is the concept of 'effective nuclear charge' (Zeff) and how does it affect valence electrons?

Zeff is the net positive charge experienced by valence electrons, calculated as the total nuclear charge minus the shielding effect of core electrons; higher Zeff increases the attraction to the nucleus.

Write the ground-state electron configuration for Copper (Cu, Z=29) and explain the anomaly.

[Ar] 4s1 3d10; this occurs because a full 3d subshell provides extra stability compared to a partially filled one.