Chemical Formulas and Atomic Structure

Finding an empirical formula from percentages is a step-by-step process. First, treat the percentages as grams. Then convert these grams to moles by dividing by the element's molar mass. Find the smallest mole value and divide all values by it. If you get decimals, multiply everything by the smallest number that makes them whole.

When analyzing mixtures, you can determine the ratio of components by converting masses to moles. Divide the mass of each component by its molar mass to find moles. The ratio is simply the moles of component A divided by the moles of component B.

Atomic structure features negatively charged electrons orbiting a positively charged nucleus of protons and neutrons. The force between these charged particles follows Coulomb's law: F = q₁q₂/r². This explains why electrons stay in orbit rather than flying away.

Quick Tip: When working with electron configurations, think of it like filling apartment buildings - electrons fill the lowest "floors" (energy levels) first before moving to higher ones, and they prefer having their own "rooms" (orbitals) before sharing.

Electron configurations follow specific rules: the Aufbau Principle (electrons fill lowest energy subshells first), Hund's Rule (orbitals get one electron each before any doubling up), and electrons prefer the same spin direction initially. The effective nuclear charge (Zeff) felt by outer electrons equals the atomic number minus the number of shielding core electrons $Zeff = Z - S$.