AP Chem Unit 4- Atomic Structure & Periodicity

atomic radius

• increases left & down

• period explanation- increasing Z_eff

  • greater coulombic attraction=smaller radius

  • orbitals become tighter

  • more mass but smaller volume

• group explanation- adding energy levels/orbitals of electrons

  • distance between valence elctrons & nucleus increases

ionic radius

• radius of element’s most common ion

• metals generally lose electrons, losing an entire orbital, decreasing radius, increasing Z_eff

• nonmetals generally gain electrons, filling valence shell, increasing radius, increasing electron repulsion

• large jump in energy needed as ion goes from losing to gaining electrons (metals→nonmetals)

electronegativity

• increases up & right

• smaller atomic radii=larger electronegativity

• period explaination- increasing Z_eff

  • greater coulombic attraction pulls all eletrons closer, including those shared in a bond

  • increasing pull & electronegativity

• group explaination- adding energy levels/orbitals of electrons

  • valence electrons at greater distance from nucleus

  • far-away electrons have weaker coulombic attractions to nuclei

  • decreasing pull & electronegativity

ionization energy

• increasing up & right

• energy needed to remove one electron from atom

  • X→X⁺+e^-

  • unless told otherwise, assume you are looking at 1st I.E. (energy required to remove first outermost electron)

  • higher I.E., stronger an atom holds onto electrons, lower I.E., more likely atom gives up electrons

• period explaination- increasing Z_eff

  • greater coulombic attraction pulls electrons closer

  • harder to remove

• group explaination- adding energy levels/orbitals of electrons

  • valence electrons at greater distance from nucleus 

  • far-away electrons have weaker coulombic attractiosn to nuclei

  • easier to remove

• on graphs, large jumps in I.E. occur when core electrons are removed (successive ionization energies)

• on tables, look for the big jump

electron affinity

• increases up & right

• energy released when one electron is added to an atom, forming an attraction

  • X+e^-—>X^-

  • generally negative values (greater E.A., smaller value)

  • greater E.A. (larger negative #), easier to add electron

• period explaination- increasing Z_eff

  • greater coulombic attraction leads to greater attraction for additional electrons

• group explaination- adding energy levels/orbitals of electrons

  • valence electrons at greater distance from nucleus

  • far-away electrons have weaker coulombic attractions to nuclei

  • more difficult to add

  • exothermic energy decreases as per. table progresses downward

coulombic attraction

• electrons repel each other

• electrons & nucleus attract each other

• forces dissipate w/ increasing distance

relationship between distance & force of attraction

inverse- distance increases, force of attraction decreases

relationship between number of protons in nucleus & force of attraction on electron

direct- # of protons increases, force of attraction increases

true/false- attractive force of nucleus is not divided up among electrons in atom, each electron gets approximately the full attractive force of nucleus (minus repulsive effects of other electrons)

true

effective nuclear charge (Z_eff)

net positive charge experienced by an electron in a multi-electron atom

Z_eff equation

atomic # - (all electrons-valence electrons)

spectroscopy

• using interaction between light & electrons to determine info about atomic/molecular structure

microwave spectroscopy

• interact w/ dipoles of polar molecules, causing molecules to spin

• looks at rotation of bonds/molecules, giving info about shape/location of bonds

infrared spectroscopy

• molecule switches from one vibrational state to another, causing a specific amount of energy to be absorbed/released

• measures wavelengths energy is absorbed at & determines types of bonds/functional groups present (single, double, triple)

ultraviolet-visible spectroscopy

• excites valence electrons, causing them to jump to higher energy levels

• only certain wavelengths of light will be absorbed as electrons in atoms/molecules have quantized states; other wavelengths bounce off to create certain color

• identify or determine concentration of substances

• will need to be interpreted

photoelectron spectroscopy (PES)

• x-rays that remove any electron (core, valence)

• particular wavelength needed to remove each electron tells the number of electrons in each shell & its coulombic attraction

group 1

alkali metals

group 2

alkaline earth metals

groups 3-12

transition metals

Al, Ga, In, Sn, Ti, Pb, Bi, Po

other metals/post-transition metals

B, Si, Ge, As, Sb, Te

metalloids/semi-metals

C, N, O, P, S, Se

other nonmetals (cannot hydrogen bond)

group 17

halogens

group 18

noble gases