ap chem unit 1

Atomic Structure and Properties

• Periodic Table

  • Alkali metals, alkaline earth metals, transition metals, halogens, noble gases

  • Mass number = Protons + Neutrons

  • Isotopes - atoms of an element with different numbers of neutrons

  • Average atomic mass from weighted average of isotope mass and relative abundance (frequency)

• Moles

  • PV = nRT

  • Avogadro’s number 6.022*10^23

  • AT STP (1 atm, 273K), 22.4 L/mol

  • Molarity M = moles/L

  • Percent composition - divide the mass of each element/compound by the total molar mass of the substance

  • Empirical formula is simplest ratio, molecular formula is actual formula for substance

• Energy

  • Electron potential energy increases with distance from nucleus

  • Electron energy is quantized - can only exist at specific energy levels at specific intervals, not in between

  • Coulomb’s law: F = kq1q2/(r^2) where F is electrostatic force

  • Atoms absorb energy in the form of electromagnetic radiation as electrons jump to higher energy levels; when electrons drop levels (closer), atoms give off energy

• Photoelectron spectroscopy

  • energy measured in electronvolts (eV)

  • Incoming radiation energy = binding energy + kinetic energy of the ejected electron

  • Electrons that are further away from nucleus require less energy to eject, thus will move faster

  • Photoelectron spectrum

    • Each section of peaks represents a different energy level (1, 2, 3, etc.)

    • Subshells within each energy level (shape of space electron can be found in orbiting nucleus) are represented by the peaks (1s, 2s, 2p, etc.)

    • s(2) - first subshell, p(6) - second subshell

    • Height of peaks determines number of electrons in subshell (ex. Peak of p subshell in energy level 2 will be 3x that of s subshell)

• Electron configuration

  • Electron configuration - spdf - shorthand with noble gas first

  • Configuration rules

    • Aufbau principle - electrons fill lowest energy subshells available first

    • Pauli exclusion principle - 2 electrons in same orbital cannot have same spin

    • Hund’s rule - Electrons occupy empty subshells first

  • Zn +2, Ag +1, Al +3, Cd +2, most other transition metal charges vary

• Periodic trends

  • Electrons are more attracted if they are closer to the nucleus, or if there are more protons

  • Electrons are repelled by other electrons - if there are electrons b/w the valence electrons and nucleus, the e- will be less attracted (shielding)

  • Completed shells are very stable, completed subshells are also stable; atoms will add/subtract valence electrons to complete their shell

  • INCREASING: atomic radius down left; ionization energy up right; electronegativity up right

    • Ionization energy - energy required to remove an electron from an atom

    • Electronegativity - how strongly the nucleus of an atom attracts electrons of other atoms in a bond

    • Electron affinity - energy change that occurs when an electron is added to an atom in the gas state (usually exothermic - energy is released)