TBR Chemistry Ch. 2

Procedure of Mass Spectrometer

1. Particle is ionized using high-energy electron impact or incident electromagnetic radiation. Ionized particle accelerates to cathode plate. Particle velocity is adjustable. 2. Particles passes through double filter to ensure a uniform perpendicular beam. 3. Particle leaves the accelerating region and enters a perpendicular magnetic field (into the page) where it is deflected in a counterclockwise, radial fashion by the magnetic force. 4. Radius is ascertained from the strike point against a collision detector. Mass-to-charge ratio is calculated from radius.

Number of electrons in shell

2(n)² where n is the principle quantum number

Chalcogens

6th column of periodic table Metalloids and non-metals.Tellurium and polonium are metalloids, the rest are non-metals. Valence shell: ns²np⁴ Characteristics: Form covalent bonds with non-metals. Neutral elements. Oxidizing agens because they gain two electrons to become a -2 anion with a filled octet. Reactivity decreases as you descend the column becasue the first and second electron affinities are not as great. Often insoluble, but varies. Oxygen exist as O₂ and selenium/sulfur exist as Se₈ and S₈

Halogens

7th column of the periodic table Valence shell: ns²np⁵. Characteristics: Form covalent molecules with non-metals and ionic compounds with metals. Neutral elements. They are strong oxidizing agents because they readily gain an electron to become a -1 anion. Reactivity decreases as you descend the column because the electron affinity is not as great. Often soluble although it varies. All exist as diatomic X₂

Mass Spectrometry

A mass spectrometer is designed to measure the charge-to-mass ratio for a charged particle. This is done by sending a particle into a perpendicular magnetic field and observing the degree to which it curves. Variables: radius of curvature, mass, initial velocity, magnitude of charge, and strength of magnetic field

Common uses of EM radiation

AM: cheap radio communication FM: expensive radio communication Microwave: satellite, cell phones, radar, heating water Infrared: line-of-sight com, molecular ID, heat Visible: Vision, fiber optic communication Ultraviolet: Bond-breaking, exciting electrons X-ray: nucleus detection, core e ionizaiton Gamma: nuclear excitation, world destruction

Procedure and Apparatus of Millikan experiment

After the charged oil drops pass through the plate of a capacitor, it eneters a region where a uniform electric field exists, applying a force that drops the falling due to gravity. 1. The falling oil rop gains a charge by either losing or engulfing an electron as it falls. The electric field strength is adjustable, so that the oil droplet can be suspended. 2. If the particle is suspended (or falls at a constant velocity), then he net force is zero so mg=-qE. Since we know E, m, and g, we can solve for q.

Lyman series

All transitions in hydrogen atoms down to n=1. Photons emitted are in the UV region of EM spectrum.

Rutherford Experiment procedure and apparatus

An incident beam is focused and aimed at a thin slice of gold metal, thin enough so that the beam can penetrate and pass through the gold foil. Gold was chosen due to its large nucleus and light is able to pass through it more easily than other metals. X-rays or alpha particles pass through the foil and strike a photographic plate or luminescing screen. The particles that are deflected by the gold sample results in parts of the luminescing screen never illuminating

Photoelectric effect

An incident photon causes the release of an electron. In other words, a compound can be ionized with a photon, as long as the photon has energy greater than the ionization limit of the material. The energy required to remove an electron from the surface of the solid material is referred to as the work function, phi h∨ = phi + 1/2 mv² = energy to eject electron + kinetic energy of ejected electron As the energy of the incident photon increases, the kinetic energy of the discharged electron increases hv = hv₀ + KE (of the electron) v₀ is the threshold frequency. Corresponds to the photon equal in energy to the ionizing energy. Any photon with a frequency less than the threshold frequency does not have enough energy to ionize the material, so no electron is ejected

Periodic Trend: Size

As you descend a family in the periodic table, the valence shell increases, so the distance of the valence electron from the nucleus of the atom increases

Diamagnetic

Atom with all electrons paired. Diamagnetic compounds are not susceptible to magnetic fields. If a magnetic field is applied to a diamagnetic species, half of the electron spins align with the field, forcing the other half to align against the field. Cannot have magnetism induced.

Paramagnetic

Atom with unpaired electrons Referred to as radicals. An unpaired electron is susceptible to magnetic fields. If an external magnetic field is applied to a paramagnetic species, the electron spins align with the field. Paramagnetic species can have magnetism induced into them.

Periodic trend: atomic size

Atomic size decreases (distance from center of nucleus to exterior of the valence electron cloud) as we go up and right

Isotopes

Atoms of the same element that contain a different number of neutrons but the same number of protons within their nuclei. Isotopes are chemically similar but have different atomic masses. Used as markers and tags in chemical labeling experiments and nuclear magnetic spectroscopy. Common isotopes are deuterium, tritium, carbon-13, carbon-14, phosophorous -32, and iodine 121. Can be monitored by radioactive decay or NMR

Results and Conclusions of the rutherford Experiment

Because most particles passed through the gold foil, it is concluded that the atom is made up predominantly of empty space. Atoms are composed of a nucleus holding the mass. Disproved the diffuse particle model (plum pudding model). Found that the mass of gold is not evenly distributed in the gold foil but rather in dense nuclei, creating a lattice structure.

Atomic Model

Bohr model shows that electrons occupy specific circular orbits about the nucleus and thus the electrons have specific energy levels associated with each orbit. Electrons can exist only in specific orbits (electronic shells), so each energy level of an atom is quantized More energy is required to carry out trasitions when the electron is nearest to the nucleus. Energy must be absorbed by the atom for an electron to elevate to a higher energy level.

Isotopes to know

Carbon-12: most abundant isotope of carbon Carbon-13: NMR Carbon-14: carbon dating Hydrogen-1: most abundant isotope of hydrogen Hydrogen-2: Used in proton NMR solvents Hydrogen-3: radio-labeling experiments Uranium-235: nuclear fission Uranium-238: most abundant isotope of uranium

General rule about cation and anion size

Cations are smaller than neutral atoms because the loss of electrons allows the atom to compact more tightly, given the diminished repulsion associated with the missing electrons. Anions are larger than neutral atoms because the gain of electrons causes the atom to expand, given the enhanced repulsion associated with the additional electrons

Results of Millikan experiment

Charge of an electron has a fixed numerical value that is the same for all electron. Value for this fundamental unit of charge is 1.6 x 10^-19 C.

Emitted color

Color is emitted from a source that radiates visible photons. This can happen when an electron relaxes from an excited state to a lower level. If you can see it in the dark, then it is emitted. Ex. are tv screens, fireworks, glow in the dark ink

Periodic Families (Groups)

Columns in the periodic table contain elements that have the same valence electron count and thus show similar chemical reactivity.

Fluorescence

Conversion of ultraviolet light into visible light. A material with a semi-stable excited state can absorb an ultraviolet photon, relax a slight amount giving off infrared photons, and then relax completely back to its original state. The visible photon emitted is of slightly less energy than the ultraviolet photon absorbed, because of the small energy loss when the infrared photon was lost.

First order decay equation

Ct = C₀e^-(kt)

Thomson experiment

Demonstrated the existence of opposite charges in an atom and that charge is a fixed quantity. Thomson deflected a stream of charged particles (electrons) using an external electric field (the plates of a capacitor). Because the stream of particles bent in a uniform fashion, Thomson concluded that there was a consistent charge-to-mass ratio for the particles

Angular momentum (l)

Describes the orbital in which the electron resides. Must be less than the value of n. Can be positive or 0.

Magnetic (m(l))

Describes the orientation of the orbital about a plane or axis. Can be any value in the range from negative l to positive l, including 0

Spin (m(s))

Describes the rotation of the electron about its axis. Can be either positive or negative one-half

Principle (n)

Describes the shell in which the electron resides. Can be any integer greater than 0

Rutherford Experiment

Determined that atoms have dense nuclei with nearly all of the atomic mass centrally concentrated. Metals have uniformly spaced atoms in their microscopic composition.

Atomic Radius

Distance from the center of the nucleus to the edge of the valence could of electrons. Measured in picometers. Radius of an atom decreases as the periodic table ascends because the number of electronic shells decreases. The radius decreases as period in the periodic table is scanned from left to right because the effective nuclear charge increases. Exception: helium is larger than hydrogen. This is due to shielding of the two neutron in the helium nucleus and the electron repulsion experienced by electrons in the first quantum level

Hydrogen Energy Levels

E = -2.17 x 10⁻¹⁸ (Z²/n²) Energy levels are defined as being negative relative to a free electron. If the electron is in the n=infinity energy level, then E =0 and the electron is free Ionization of hydrogen from its ground state ( n =1) is 1312 kJ/mole. Because of the squarig of principle energy level, the ionization of an electron in hydrogen from the n = 2 level is 1/4 of that value (328 kJ/mole). Transition from n=2 to n=1 is the difference, 984 kJ/mol

Energy of an electron

E = 2π²mZ²e⁴/n²h² m = mass of e e = charge of electron h = plank's constant Z = nuclear charge n = electron energy level E = Energy E is proportional to Z²/n²

Effective Nuclear Charge (Nuclear Attraction)

Effective nuclear charge is the net charge exerted upon the valence electrons. Accounts for attraction to the nucleus, repulsion from the core electrons, and minimal repulsion from other valence electrons Zeff When approximating effective nuclear charge, nuclear charge is added to the core electron charge. (Number of protons minus number of core electrons)

Periodic Trend: Electron affinity

Electron affinity increases (the energetics associated with an atom gaining an electron) as we go up and right

Periodic Trend: Electronegativity

Electronegativity increases (the tendency to share an electron with another atom within a bond) as we go up and right.

Aufbau Principle

Electrons are added one by one to the shells, starting with the lowest energy level and then into sequentially increasing energy levels.

Electron spin pairing

Electrons fill orbitals in a pre-determined sequence, filling evenly into orbitals of equal energy with like spin before placing a second electron with opposite spin into each orbital. By convention, electrons are said to fill orbitals spin up first, then spin down. Spinning electrons create magnetic fields. Opposite spins produce opposite magnetic fields.

Electronic theory

Electrons orbit in distinct shells. Shells farther from the nucleus have a greater radius, thus a greater capacity to hold electrons

Paschen series

Emits photons in the infrared region of EM spectrum. n=3

First order decay

Exponential decay. The half-life is constant, regardless of concentration. As the concentration decreases, the duration of the half-life remains teh same

Alkali Metals

First column of periodic table. Hydrogen is also included in his group, but hydrogen also acts as a halogen in addition to an alkali metal. Valence shell: ns¹ n<1 Characteristics: Neutral elements. Strong reducing agents because they readily lose an electron to become a +1 cation (giving them a complete valence shell). Reacts with any element that has a slight electron affinity. Reactivity increases as you descend the column because it is easier to lose an s-electron from a shell that is further out. Cation form is soluble in water with almost any anion. Alkali metals react favorably with water to form the metal hydroxide and hydrogen gas. 2M + 2H₂O → 2MOH + H₂ The oxides they form are variable with the metal. Lithium forms an oxide Li₂O. Sodium forms a peroxide, Na₂O₂. Potassium, rubidium, and cesium form superoxides (KO₂). See page 106. Alkali metals are oxidized by halogens, nitrogen and hydrogen.

Millikan Oil Drop Experiment

Goal is to suspend a charged oil drop in an electric field. The oil drop is charged by either adding an electron to the oil drop or ionizing the oil drop. In order to add an electron, falling oil drops pass through a beam of electrons where some of the oil drops are penetrated at random by an electron. The charged oil drops fall through a pore in the upper plate of a capacitor, where it falls at a constant speed or is suspended. In this case, qE=-mg q proportional to -mg/E

Periodic Trend: Effective Nuclear Charge

Increases as you move left to right across a period in the periodic table ENC is the net charge exerted upon the outermost electrons. Takes into account attraction due to protons, shielding due to neutrons, and repulsion due to the core electrons. ENC Affects how tightly electrons are held, which affects ionization energy, electron affinity, atomic radius.

Brackett series

Involves photons in the low infrared and microwave regions n = 4

Periodic Trend: ionization energy

Ionization energy increases (energy required to remove the outermost electron) as we go up and right

Heisenberg's Uncertainty Principle

It is not possible simultaneously to identify a particle's position and velocity. ∆x∆mv ≥ h/4π

Noble Gases

Last column of the periodic table Generally non-reactive since they are inert gases Valence shell: ns²np⁶ Characteristics: Form no bonds and exist as monatomic atoms.Fluorine is more electronegative than either xenon or krypton

Zero order decay

Linear decay The half life is directly proportional to the concentration of the compound. As the concentration decreases, so does the duration of the half-life. The second half-life is half as long as the first half-life because the concentration change is half as large.

Probability vs distance from nucleus

Looks like a 1/x plot. As distance increases, probability decreases making a concave up curve.

Electronegativity

Measure of an atom's tendency to gain and retain an electron from a neighboring atom within a bond. Measured using Paulin's scale. Electronegativity of an atom increases as the periodic table is ascended because as the number of electronic shells decreases, the attraction to the nucleus increases. The electronegativity of an atom increases as the periodic table is scanned from left to right because the effective nuclear charge increases. Shows no exceptions in trend. When electronegativity of two atoms within a bond are close, the bond is covalent. If there is a difference greater than 2.0, then the bond is ionic.

Electron Affinity

Measures the tendency of an element to gain an electron. Can be negative or positive, meaning that gaining an electron can be either exothermic or endothermic. Within a row, electron affinity correlates with atomic number, but there are some spikes in the trend. These deviations are attributed to the stability associated with a filled s-shell or p-shell. No trend for electron affinity is evident in the transition metals. In general, an element releases more energy upon gaining an electron as you move left to right. Drastic exceptions occur when there is half-filled stability or a s²-shell. Also, an element releases more energy upon gaining an electron as you ascend a column in the periodic table. This is because as the number of electron shells decreases, the new electron is closes to the nucleus, and thus the attraction to the nucleus increases.

Periodic trend of nuclear effective charge

Moving left to right, the nucleus of each succeeding atom adds a proton and the valence shell adds an electron. The effect of the extra valence electron is not as significant as the effect of the additional proton. s a result, the effective nuclear charge increases as the periodic table is scanned from left to right.

Pauli's exclusion principle

No two electrons can have the same set of quantum numbers (n, l, m(l), m(s))

Electron Density and orbitals

Orbitals are 3D pictorial representations of the region where an electron is likely to be found. Electrons are more likely to be found near the nucleus. 95% of the time the electron can be found within the boundaries of the orbital

Quantum numbers

Set of four numbers that uniquely describe an electron within an atom. Four factors: the shell, the orbital, the orientation of the orbital, and the alignment of the magnetic fieldresulting from the precessing electron No two electrons can have the same set of quantum numbers (Pauli exclusion) n, l, m(l), m(s)

General rule about nuclear capture and decay

Particles with mass less than 56 amu undergo fusion, while particles with mass greater than 56 amu undergo fission

Notes about periodic trends

Periodic trends as we move from left to right across a row of the periodic table (period) are attributed to increasing effective nuclear charge Periodic trends as we move up through a column of the periodic table (family) are attributed to decreasing valence shells

Reflected color and the color wheel

Produced when incident light strikes a surface and the surface absorbs certain frequencies, thus reflecting only a portion of the incident light to the eye. The reflected radiation appears as a color that is a combination of the reflected photons. The color we observe is the complementary color of the frequency that hade the highest intensity of absorption If you cant see it in the dark, then it is a reflected color. Ex. paint pigments, pen inks, and fabric dyes

Effect of increasing charge magnitude of a particle in mass spectrometer

Radius of curvature decreases since force of deflection increases

Effect of increasing mass or velocity of particle in mass spectrometer

Radius of curvature increases because the particle deflects less

P orbitals

Result from barbell-like distribution fo the electrons about the nucleus. Each p-orbital is oriented about a different axis. P-orbitals have one node at the nucleus that is part of a nodal plane between the two lobes.

D orbitals

Result from double barbell-like distribution of the electrons about the nucleus. Five different d-orbitals, each oriented differently. Have two nodal planes and electrons are not found at the nucleus. Dxz, Dxy, Dyz lobes lie between axes. Dx²-y² and Dz² lobes lie on the axis

S orbitals

Result from spherical distribution of electrons about the nucleus. Principle quantum number represents the energy level and the average distance from the nucleus

F orbitals

Result from triple barbell-liek distribution of the electrons about the nucleus. There are 7 different f-orbitals, each oriented about a different plane or axis. Electrons are not found at the nucleus. F-orbitals have three nodal planes.

Visible spectrum and colors

Runs from red (700 nm), orange, yellow, green, blue, through violet (400 nm) UV spectroscopy ranges from 20 nm to 400 nm

Alkaline earth metals

Second column of periodic table. Valence Shell: ns² Characteristics: Neutral elements. Strong reducing agents because they readily lose two electrons to become a +2 cation with a filled octet. Not as reactive as alkali metals. Will react with any element that has a high electron affinity. Reactivity increases as you descend the column because first and second ionization energies both decrease. Cation form is not as soluble in water as alkali metals. This is due to their +2 charge and smaller radius Alkaline earth metals, except beryllium, react favorably with water to form a metal hydroxide and hydrogen gas. M + 2H₂) → M(OH)₂ + H₂ All alkaline earth metals form oxides when oxidized by oxygen gas 2M + O₂ → 2MO Can also be oxidized by halogens, nitrogen, and hydrogen. See page 108

Difference between shells and orbitals

Shells represent energy levels an electron can occupy. Orbitals represent the region in which the electron is likely to be found

Exceptions in periodic trends

Some common deviations from these trends, like with electron affinity and ionization energy, occur due to half-filled stability and filled-shell stability. Ex. Nitrogen has a greater ionization energy than oxygen because upon ionization, nitrogen loses its half-filed p-shell. Oxygen gains half-filled stability upon being ionized.

Absorption (Excitation)

The gain of energy by an element or molecule, resulting in the excitation of an electron from a lower energy state to a higher energy state. The form of energy absorbed can vary

Beta decay

The electron may or may not be added to the electrical shell of the atom. If it is added, the atom remains neutral. If the electron escapes, the compound becomes a cation Equivalent to positron capture Beta capture and positron decay are equivalent.

Relationship between speed of light, frequency, wavelength of light and light energy.

The energy of a photon and its wavelength of light are inversely proportional E = h∨ = hc/λ

Ionization Energy

The energy required to remove the outer-most electron from the valence shell. Depends on the attraction of the electron to the nucleus, distance from the nucleus, the stability of the electron configuration. General trend is within a row, ionization energy increases as atomic number increases, but there are some exceptions due to half-filled stability As you ascend a column, ionization energy increases because as the number of electronic shells decreases, the proximity of the electron to the nucleus increases, thus the attraction to the nucleus increases. The easier it is to ionize an atom, the easier it is to oxidize that atom. This leads to a larger value for the oxidation potential

Emission (Relaxation)

The loss of energy by an element or molecule, resulting in the relaxation of an electron from a higher energy state to a lower energy state. The form of energy emitted can vary.

Balmer series

The only electron transition series in hydrogen that emits photons in the visible range n = 2

Half-life

The period of time required for 50% of the concentration of material to decay to a different form

Nuclear Capture

The process of particle gain by the nucleus that results in a different nucleus is referred to as nuclear decay Also called fusion

Nuclear Decay

The process of particle loss from the nucleus that results in a different nucleus Also called fission

Half-filled d-shell and filled d=shell stability

The result of a sigle electron being elevated from a lower energy level that is paired (usually s-orbital) to yield even distribution of electrons in the d-level. Examples are chromium and copper. Chromium: [Ar]4s¹3d⁵ rather than [Ar]4s²3d⁴ Copper: [Ar]4s¹3d¹⁰ rather than [Ar]4s²3d⁹

Electronic configuration

The shorthand notation for the electrons present in an atom and their energy levels. 1s, then 2s, then 2p, then 3s, then 3 p, then 4s, then 3d, then 4 p, then 5s, etc.

Frequency/wavelength of light required to excite an electron

UV to visible rance of electromagnetic radiation. So, electrons emit energy as light energy when moving to a lower orbital. The less energy emitted, the longer the wavelength of light that is emitted

Why absorption and emission levels are bands

Vibrational energy levels, rotational energy, and changes in electronic energy levels

average atomic mass

Weighted average of the masses of all of the isotopes, taking abundance into account

Excitation of an electron/absorption of energy

When energy is absorbed or released due to a change in electron energy level. Energy must be absorbed by the atom for an electron to elevate to a higher energy level. Energy is emitted when an electron drops from a higher energy level to the lowest energy level

Nuclear capture and decay

a heavy element undergoes a decay process to increase its nuclear stability. A light element undergoes a capture process when struck by a high-energy particle to increase its nuclear stability

quantization of energy transitions

absorption and emission of light by hydrogen occurs in distinct increments (or quantities) Hydrogen has distinct transitions between energy levels, so it has distinct energy levels

neutrino

an uncharged particle with the mass of an electron

beta particles

electrons

Hund's rules

electrons completely fill lower energy levels before starting to fill higher energy levels. In a degenerate set of orbitals, electrons singly occupy each orbital before a second electron pairs up within the same orbital.

Alpha particle

helium nucleus

Ground state electronic configurations

occur when the electrons occupy the orbitals in the exact predicted order, starting from least energetic and filling orbitals that are progressively of higher energy

Know the EM spectrum

page 113

Lifetime of an excited states

picosecond to nanosecond range

positron

positvely charged particle with mass of an electron

Radius of Curvature proportions

r is proportional to mv/qB

Transition Energy

∆E = E final - E initial ∆E = -2.178 x 10⁻¹⁸(1/n²final - 1/n²initial) λ = hc/∆E