Kaplan Gen Chem Chapter 1: Atomic Structure

Protons and neutrons are found in the nucleus of an

atom

• protons have a mass of 1 amu

• in neutral atom, num of protons=num of electrons

What is the atomic number?

• number of protons found in an atom of that element

• all atoms of a given element have the same atomic number, but don’t nec have the same mass

What is the mass number?

• sum of protons and neutrons in the atom’s nucleus

• neutron’s mass slightly larger than proton’s mass

• given element can have variable amt of neutrons, so atoms of same element can have same atomic num, but not nec same mass num

What are isotopes?

• atoms of the same element with varying mass numbers

• differ in num of neutrons

• name of element followed by mass number like for ex carbon-12

What are electrons?

• move through the space surrounding the nucleus

• mass smaller than proton

What are valence electrons?

• these are electrons farther from nuc with strongest interactions to surrounding environment and weakest with nuc

• they are more likely to bond with other atoms bc they have the least electrostatic pull from their own nuc

• determine reactivity of an atom

• electrons move around nuc at varying distances→closer to nuc means lower energy levels→lower electron shells

Give the protons, neutrons, and electrons for nickel 58 atom and nickel 60 +2 cation.

• nickel 58: protons→28, neutrons→30, electrons→28

• nickel 60 +2 : protons→28, neutrons→32, electrons→26

What is the difference between atomic mass and atomic weight?

• atomic mass/mass num varies from one isotope to another

• atomic weight is constant for a given element; weight displayed on periodic table(avg of diff isotopes)

The atomic mass of an atom in amu is nearly equal to its

• mass number

What are the 3 isotopes of hydrogen called?

• protrium: 1 proton, 1 amu

• deuterium: 1 proton, 1 neutron, 2 amu

• tritrium: 1 proton, 2 neutrons, 3 amu

Half life is a marker of

• stability; longer lasting isotopes are more abundant

What is a mole?

• number of things equal to Avogadro’s number NA= 6.02 × 10 ^ 23

• the atomic weight of C is 12 amu→avg C atom has a mass of 12 amu and 6.02 × 10 ^ 23 C atoms have a combined mass of 12 g

What is the Planck relation equation?

• energy as electromagnetic radiation from matter comes in bundles called quanta

• energy of a quantum or E= hf

• h is Planck’s constant, 6.626 × 10 ^-34 J x S

• f is frequency of radiation

In the Bohr model, what is the angular momentum of an electron orbiting a H nucleus ?

• L= nh/ 2pi

• n→principal quantum num

• h→planck’s constant

What is the energy of an electron?

• E= - R H/ n²

• RH→Rydberg unit of energy, 2.18 × 10^-18 J/electron

• neg sign means electron in any of its quantized states in the atom will have an attractive force toward the proton

• equation is saying energy of an electron inc/becomes less neg the farther out from the nuc it is(increases n)

What is ground state of an atom? excited state?

• state of lowest energy, in which all electrons in lowest possible orbitals

• state where at least 1 electron has moved to a subshell of higher than normal energy

What happens when electrons in ground state transition?

• excited to higher energy levels by heat or other energy forms

• lifetime of excited state is temporary, so will return to ground state→results in emission of energy in photons E=hf

• as electrons go from lower to higher energy level, they absorb light, have higher potential, get excited, and become distant from nuc

• the electromagnetic energy of these photons are calculated using E=hc/wavelength

• h→Planck’s constant

• c→speed of light, 3.00 × 10^8 m/s

What is a line spectrum?

• each line on an emission spectrum corresponds to a specific electron transition

• bc each element can have its electrons excited to a diff set of energy levels, each have a unique atomic emission spectrum

What is the Lyman, Balmer, and Paschen series?

• Lyman: ground of H emission lines corresponding to transitions from energy levels n greater than or equal to 2 to n=1; includes larger energy transitions from Balmer; shorter photon wavelengths in the UV region of the EM spectrum

• Balmer: n greater than or equal to 3 to n=2; includes 4 wavelengths in the visible region

• Paschen: n greater than or equal to 4 to n=3

What is the energy of electron transition formula?

• E=hc/wavelength=Rh(1/ni² - 1/nf²)

• formula tells us the energy of the emitted photon corresponds to the diff in energy btwn higher energy initial state and lower energy final state

What is an absorption spectrum?

• exciting the electrons of a particular element results in energy absorption at specific wavelengths

• the wavelengths of absorption correspond to the wavelengths of emission bc the diff in energy btwn levels remains unchanged

What is the Heisenberg uncertainty principle?

• impossible to determine the momentum and position of an electron at the same time

What is the Pauli exclusion principle?

• no 2 electrons in a given atom can have the same set of 4 quantum numbers

• energy state: position and energy of an electron described by its quantum numbers

What is the principal quantum number n?

• can be any positive number; the larger the number→the higher the energy level and radius of the electron’s shell

• in each shell, it can hold up to 2n² electrons

• diff in energy btwn 2 shells dec as distance from nuc inc based on energy of electron transition formula

What is the azimuthal quantum number l?

• refers to shape and number of subshells within a given principal energy level n

• for any given value of n, the range of values for l is 0 to (n-1)

• in each subshell, it can hold up to 4l + 2 electrons

• the energies of the subshells inc with inc l value

What is spectroscopic notation?

• n is a number, and l is designated a letter

• l=0 subshell is s

• l=1 subshell is p

• l=2 is d

• l=3 is f

What is the magnetic quantum number ml?

• specifies the particular orbital within a subshell where electron most likely to be found

• each orbital can hold up to 2 electrons

• possible values for ml are btwn -l and +l including 0

• the shape of orbitals dependent on the subshell they are found

• s: spherical

• p: dumbbell

What is the spin quantum number ms?

• electron has 2 spin orientations +1/2 and -1/2

• whenever 2 electrons are in the same orbital, they must have opposite spins and are referred to as being paired

• electrons in diff orbitals with the same ms values are said to have parallel spins

What is electron configuration?

• first number denotes principal energy level, letter designates the subshell, and superscript gives the number of electrons in that subshell

• ex: 2p^4 means 2nd principal energy level in p subshell with 4 electrons

• can be shortened by placing the noble gas that precedes the element of interest in brackets

What is Aufbau principle?

• electrons fill from lower to higher energy subshells and each subshell will fill before electrons begin to enter the next one

Which will fill first, 5d or 6s subshell?

• use n+l rule

• 5d: n=5, l=2 → 7

• 6s: n=6, l=o → 6

• 6s has lower energy and will fill first

What is the shorthand notation for osmium?

• [Xe]6s² 4f^14 5d^6

How do you determine the electron configuration for cations?

• you start with the neutral atom, and remove electrons from the subshells with the highest value for n first

• if multiple subshells are tied for the highest n value, then electrons are removed from the subshell with the highest l value among these

What is the electron configuration for F? F-? Fe 3+

• F: [He]2s²2p^5

• F- : [He]2s²2p^6

• Fe3+ : [Ar]3d^5

What is Hund’s rule?

• within a given subshell, orbitals are filled such that there are a max number of half filled orbitals with parallel spins

• basis for this is electron repulsion: electrons in the same orbital tend to be closer to each other and thus repel each other more than electrons placed in diff orbitals

• half filled and fully filled orbitals have lower energies(higher stability) than other states

What are the exceptions to electron configuration?

• chromium should be [Ar]4s²3d^4 but is actually [Ar]4s^1 3d^5 due to extra stability from making 3d subshell half-filled

• copper is actually [Ar]4s^1 3d^10 bc a full d subshell outweighs the cost of moving an electron out of 4s subshell

What does paramagnetic and diamagnetic mean?

• paramagnetic: materials that have unpaired electrons that align with magnetic fields, attracting the material to a magnet; ex: metallic spheres closed enough to be induced by a magnet→are attracted to it→move toward it

• diamagnetic: materials that have all paired electrons, which can’t easily be realigned; they are repelled by magnets

For groups 1 and 2 in PT, which subshell electrons are valence?

• 1 and 2: only the highest s subshell electrons

• groups 13-18: highest s and p subshell electrons

• transition elements: those in the highest s and d subshells

• lanthanide and actinide: those in the highest s and f subshells

• all elements in period 3 starting with sodium and below may accept electrons into their d subshell, which allows them to hold more than 8e in their valence shell