AP Chem (Unit 1): Atomic Structure

nucleus

a small, positively charged core that has protons (+) and neutrons (0)

mass number

protons + neutrons (always a whole number)

atomic mass

the average mass of all isotopes

isotope notation

A - mass number, Z - Atomic number (A,Z)

isotopes

have the same number of protons, but different numbers of neutrons (neutrons have no effect on Chemistry)

amu

atomic mass units (g)

mass spectrometry

compares the masses of isotopes

How to find the amu of an isotope

AV mass = (isotope mass x %)+ (isotope mass x %) —> AVERAGE MASS FOUND ON PERIODIC TABLE

AV mass = (34.969x0.7578) + (36.996×0.2422)

35.45 amu → the element is chlorine

absorption of light

electrons become excited, jump energy levels, no light

emission of light

electrons go back to ground state, releases light as ELECTROMAGNETIC RADIATION

light

characterized by wavelength and frequency

frequency

how many wavelengths pass a certain wavelength per second (nu, v, s^-1, s/1, Hz)

cycle

movement of crest and trough

wavelength

the distance between two corresponding points on consecutive waves

electromagnetic radiation

energy traveling through space (c=wavelength*frequency)

1 m

10^9 nm

10^-9 m

1 nm

Spacing of E lvls

N=1 and n=2 has the biggest gap, and it gets smaller as you move up

Lyman series

electrons end at n=1, large E gap = ultraviolet radiation

Balmer series

electrons end on n=2 (visible light)

concentric degenerate energy levels

the data that the spectrum of a hydrogen produced led to the more refined model of ever increasing of ever increasing energy levels with ever decreasing gaps of E between them

Cathode Ray Tube

JJ Thompson created a negatively charged particle beam through a tube full of air; vacuumed air out and electors were left = DISCOVERED ELECTRONS

Gold Foil Experiment

Ernest Rutherford shot alpha particles at a thin gold sheet, the gold’s nucleus repelled alpha particles = MASSIVE, DENSE, POSITIVELY CHARGED NUCLEUS (+ solar system model, most of the atom is empty space)

alpha particles

radioactive, positively charged, 2p+ and 2n (helium nucleus)

Discovery of the Neutron

James Chadwick shot alpha particles at Be, Br, Li (rays get released through the atoms) something was shot out (neutral). Then, he put parafin on he rays and the protons flew out = NEUTRONS ARE NEUTRALLY CHARGED IN THE NUCLEUS AND HAVE THE SAME MASS OF PROTONS

electrons closest to the nucleus are…

Harder to pull off

ionization energy

the energy required to remove an electron and make a cation

high potential energy

valence electrons, easier to remove, lower ionization energy

low potential energy

electrons closest to the nucleus, harder to remove, high ionization energy

Einstein's Photoelectric Effect

if you put the right amount of energy (light) on a metal, you should be able to knock off the atoms

electrostatic attraction (repulsion)

opposites attract, likes repell

Coulomb's Law

Force of Attraction (FoA): the closer opposite charges are to each other, the greater the Foa, bigger charges = stronger force

photoelectron spectroscopy (PES)

high energy photons remove electrons from any shell, not just outer (KE of e- determined and frequency of electrons is determined)

How is Ionization Energy (IE) calculated?

IE = hv - KE

when there is a larger nuclear charge…

the element has a higher ionization energy

shielding effect

repulsion from the inner electrons (successive shells are larger than the previous shells, spend more time farther from the nucleus)

Zeff

charge experienced by an electron, decreases as shielding increases (more E lvls)

atomic radius trend

decreases as protons increase and energy levels stay the same, increases as energy levels are added (shielding is constant across a period)

cation radius

MUCH smaller than the radius of the atom the came from (remove an entire energy level, decreases left to right

anion radius

anion radius is slightly bigger than the atom the came form (increases in electron repulsion), decreases left to right, first anion radius increases dramatically bc of repulsion

first ionization energy

the minimum amount of energy necessary to remove the least tightly held electron form an atom or ion in the gas phase (decreases as energy levels are added, generally increases when nucleus is bigger, except for p sub shell)

Why does every element have a sudden increase in ionization energy?

the electron configuration drops an energy level, and the radius shrinks more than other ionizations

Why is second ionization energy greater than the first?

every electron costs more than the one before it, its harder to take an electron form a more positive space!

electron affinity

the energy change that occurs when an electron is added to a gaseous atom to form a negative ion, energy comes in (THE CLOSER AN ELECTRON CAN GET TO THE NUCLEUS, THE MORE ENERGY)

if the EA value is negative

it is exothermic, releases energy because it is more energy efficient to accept an electron

if the EA value is positive…

it is endothermic, it takes more energy to accept the electon

electron affinity trend

decreases as energy levels increase, electron affinity increases as atomic number increases (group 2 - e- goes to the p sub shell, group 8 - extra electron goes to a new energy level, oxygen)

electronegativity

al elements ability to attract electrons in a chemical bond

electronegativity trend

increases as protons increase in the same energy level and decreases as as energy levels are added (inc. as atomic radius dec.)