Ch. 2: Atomic Structure & Periodic Table of Elements
alpha particle
-A helium-4 nucleus (⁴₂He) -Has a positive charge of +2
Positron Emission
-a proton is converted to a neutron because there are too many protons but too few neutrons -a positron is emitted (a positively charged particle with the same mass as an electron) by a proton, which turns into a neutron -atomic number decreases by 1, and mass number stays the same
James Chadwick
-discovered neutron -Beryllium, when bombarded by alpha particles, emitted a very energetic stream of radiation. Like gamma rays, these rays were extremely penetrating and since they were not deflected upon passing through a magnetic field, neutral. However, unlike gamma rays, these rays did not discharge charged electroscopes (the photoelectric effect). When a beam of this radiation hit a substance rich in protons, for example paraffin, protons were knocked loose which could be easily detected by a Geiger counter.
What are transition elements?
-elements involved in the filling of the d sublevel with electrons after 2 electrons in the s sublevel of the next principal energy level (AKA transitional metals) -4s and 3d sublevels are very close in energy and there is therefore the possibility of some or all 3 d electrons being involved in chemical bonding
Robert Millikan
-measured charge on electron 1. oil drops sprayed into chamber & during became randomly charged by gaining/ losing electrons 2. charged oil drop (electric field adjusted so negatively charged drop will move slowly upward in front of grid in telescope) 3. known: rate of drop rising, strength of field & mass of droplet -mass of electron: 9.11 * 10⁻²⁸
What is the ratio of Carbon-12 to Carbon 14?
same in the atmosphere as in a living organism because of the constant interchange of materials
Mass Spectrometry
separates isotopes of same element based on mass differences -intensity of photographic plate indicates amount of each isotope ionizes atoms and molecules with a high-energy electron beam and then deflects the ions through a magnetic field based on the mass-to-charge ratio of the ion, m/z. -mass spectrum of a sample shows relative abundance of each ion on the y-axis and m/z along the x-axis.
Angular momentum
shape of orbital (s, p, d, f) Formula: L = n-1 (0, 1...)
Why does the atomic radius of an element decrease from left to right on the periodic table?
since the number of valence electrons increases from left to right, the nuclear charge of the element increases because the added protons pulls the electrons more tightly around the nucleus and balances the repulsion between the added electrons and the other electrons
nuclear fission reactions
splitting of a heavy nucleus into 2 or more lighter nuclei Example: U-235 is bombarded with slow neutrons to produce Ba-139 and, Kr-94, or other isotopes and 3 fast neutrons. ²³⁴₉₂U + ¹₀n → ¹³⁹₅₆Ba + ⁹⁴₃₆Kr + 3¹₀n + Energy
Why do atomic radii increase down a period?
the increase in the outer principal energy level leads to the electrons being less tightly held by the nucleus do to the increased distance from the nucleus as well as charge and electron shielding by the core electrons
What element is the most electropositive on the periodic table?
Francium (Fr)
ground state
Lowest energy state of an atom.
atomic spectra chart
Lyman Series (ultraviolet): emissions (consisting of ultraviolet radiations) that occur when an electron goes from level higher down to ground state) Balmer Series (visible) Paschen Series (infrared) -wavelength increases and magnitude of eV decreases from Lyman to Paschen Series -photons can fall energy levels individually or all at once -electrons can absorb all of the photon or none of it, none of it being when energy falls between allowed energy levels (photon will pass right through it)
quantized energy levels with quantum/ wave mechanics
Max Plank quantum theory of light: light has both particle/ wave-like properties Louis de Broglie: if Plank's statement true, particles can also have particle and wavelike characteristics (electrons behave similarly to waves of electromagnetic radiation) -proved with electrons producing different diffraction patterns (property associated with waves when passed through narrow holes)
Niels Bohr
atom = positively charge nucleus & negatively charged electrons in specific spherical orbits (shells, energy levels) around concentrically Formula for principle energy level vs. maximum number of electrons: e⁻=2n²
Isotopes
atoms of the same element with different masses -Hydrogen: 1) Protium = ¹H (most abundant) ¹ 2) Deuterium = ²H (2nd) ¹ 3) Tritium = ³H (3rd in nature, radioactive, artificial) ¹
Period Law
certain properties of elements occur periodically when arranged by atomic number.
nuclear fusion reaction
combination of very light nuclei to make a heavier nucleus -extremely high temperatures and pressures are required to overcome the repulsive forces of 2 nuclei -only achieved in H bombs -Example of 2 deuterium atoms combining: ²₁H + ²₁H → ⁴₂H + Energy -Example of tritium and hydrogen combining: ³₁H + ¹₁H → ⁴₂H + Energy (much greater than the energy released during chemical reactions; comes from a fractional amount of mass converted into energy)
transmutation
conversion of an element to a new element (produced artificially by bombarding the nuclei of the substance with particles from a cylotron or other particle acclerator)
radioactive dating
determination of the ages of substances containing bits of organic material Example: If Carbon-14 has a half-life of 5700 years, then if wood contained 5g of Carbon-14 and it now only has 2.5g, it has an age of 5700 years.
Henry Mosely
determined atomic numbers of elements through x-rays
How are spectra formed?
dispersion of light by prism/ diffraction grating in spectroscope -diffraction grating: splits light into colors so it can be measured separately -since only certain E jumps available in each type of atom, each element has unique spectra composed of lines of specific corresponding wavelength -Lyman invisible to naked eye, while Balmer are violet blue green -Frequency increases from red to purple, while wavelength decreases from red to purple -black space is photons that aren't allowed -absorption spectrum = emission spectrum -all photon absorption is negative -energy levels get closer as less negative (more positive leads to no longer bound to atom)
Gamma radiation
electromagnetic radiation identical with light, high energy -problem it is changing: too much energy in nucleus -often accompanies other types of radioactive properties 1. No charge. 2. beta particles and gamma rays are usually emitted together, as after a beta particle is emitted, a gamma ray follows 3. arrangement in the nucleus is unknown. 4. same velocity as visible light. 5. range is unspecified. 6. Shielding needed: around 13 cm of Pb 7. Interactions: weak of itself; gives energy to electrons, which then perform the ionization.
Bohr Model
electron can only exist in certain energy levels without an energy change BUT when electron changes state, must absorb the exact amount of energy that will bring it up from the initial to the state. formula: change in energy(∆E electron) = Efinal - Einitial -emits energy when excited to ground & vice versa
Aufbau Principle
electron occupies the lowest energy orbital that can receive it
first ionization energy
energy supplied to 1 outer electron to remove it from its atom -succeeding electrons are more difficult to remove due to an imbalance between the positive nuclear charge and the remaining electrons
Scintillation counter
fluorescent screen (e.g. ZnS) will show electrons in the presence of electrons and x-rays. If the screen is viewed with a magnifying eyepiece, small flashes of light, called scintillations, will be observed. By observing the scintillations, one not only can detect the presence of alpha particles, but also can actually count them.
metalloids
have certain characteristics of metals and nonmetals, such as tending to form amphoteric oxides.
Pauli Exclusion Principle
in a given atom no two electrons have have the same set of four quantum numbers
Heisenburg Uncertainty Principle
it's impossible to know both precise location and velocity (momentum) of subatomic particles (electron) at the same time -with Erwin Shrodinger for electrons bound to orbitals similar to a standing wave --develop wave mechanical model of atom with solution of orbitals (3D regions around nucleus where electrons might be)
Magnetic quantum number
mL, number of spatial orientations of orbitals -s = 1 space-oriented orbital (0) -p = 3 space-oriented orbital (-1, 0, 1) -d = 5 (-2, -1, 0, 1, 2) -f = 7 (-3, -2, -1, 0, 1, 2, 3)
atomic radii
measured distance between 2 nuclei in a solid state/ 2
Spin quantum number
ms, spin of electron (positive or negative spin) with each orbital filled by 2 opposite spinning electrons
Principle Quantum Number
n, average distance of orbital from the nucleus with 1 being closest to the nucleus and the lowest energy
Components of Atomic Structure (in order of mass)
neutrons = ¹n ₀ protons = ¹H ¹ electrons = ⁰e ⁻¹
probability function
orbital describes the likelihood that an electron will be found in a particular location
subshell
orbitals of the same shape in a given energy shell comprise a _______.
Hund's Rule of Maximum Multiplicity
pairing will occur with the addition of 1 more electron to each orbital
Dimitri I. Mendeleev
proposed a table containing 17 columns and organized the groups according to their atomic weights and properties -if the atomic weight disagreed with the property, the property was prioritized
nuclear chain reaction
reaction in which an initial step leads to the succession of repeating steps that continue indefinitely -used in nuclear reactors and bombs
What are the characteristics of transitional metals?
1) They often form colored compounds. 2) They have variable oxidation states. 3) At least 1 of their compounds has an incomplete d electron shell. 4) Often good catalysts. 5) Silvery blue at room temperature (except for Au and Cu) 6) Solids at room temperature (except Hg) 7) Form complex ions. 8) Often para magnetic (i.e. attracted by external magnetic fields)
John Dalton atomic theory
1. All matter is composed of very small, discrete particles called atoms. 2. All atoms of an element are alike in weight and this weight is different from that of any other atom type. 3. Atoms cannot be subdivided, created, or destroyed. 4. Atoms in different numbers combine in simple, whole # ratios to form compounds. 5. In chemical reactions, atoms are separated, combined, or rearranged.
What are the 2 exceptions to the electron filling trend?
1. At atomic number 24 the half-filled AND filled sublevel are stable, making its electron configuration: ₂₄Cr= 1s²2s²2p⁶3s²3p⁶3d⁵4s¹ 2. At atomic level 29, the 3d becomes filled by taking the 4s electron. ₂₉Cu= 1s²2s²2p⁶3s²3p⁶3d¹⁰4s
Electron configuration rules
1. an element in d area of row n has outer electrons in the (n-1)d subshell 2. an element in f area of row n has outer electrons in the (n-2)f subshell
Ernest Rutherford gold foil experiment
1. found that alpha particles pass through foil with few deflections but some directly back toward source 2. atom mostly empty space between nucleus & electrons (reasoned that force = small space because little alpha particle deflected & positive charge) 3. nucleus volume very small compared to atom volume
How many electrons can an orbital hold?
2
radioactive
A material that has an unstable nuclei will decay spontaneously in order to lose the energy created by the unstable combination of protons and neutrons.
photographic plate
A plate dependent on the ionization of radioactive particles and rays that can be used to detect them. The fogging of a photographic emulsion led to the discovery of radioactivity. If this emulsion is viewed under a high-power microscope, it is seen that beta and gamma rays cause the silver bromide grains to develop in a scattered fashion.
Geiger counter
Any particle that will produce an ion gives rise to an avalanche of ions, so the type of particle cannot be identified. However, each individual particle can be detected. -used to detect and measure radioactive decay -The Geiger-Müller tube or G-M tube is the sensing element of the Geiger counter instrument used for the detection of ionizing radiation
What element is the most electronegative on the periodic table?
Fluorine (F)
How does an beta particle act in radioactive decay?
Ejected when a neutron decays into a proton and an electron, reducing neutron to proton ratio. -happens when too many neutrons, too few protons, so a neutron turns into a proton -the atomic number increases by 1, but the mass number remains constant. 1. High velocity, low energy. 2. Range is around 12 meters. 3. Shielding needed: stopped by 1 cm of aluminum Example: Protactium-234: radioactive nuclide that undergoes Beta emission. ²³⁴₉₁Pa→²³⁴₉₂U+⁰₋₁e
Beta particle
Fast electron with a negative charge of -1
How does the emission of a positron change the atomic number of an element?
It decreases it by 1.
How does electron capture change the atomic number of an element?
It decreases it by 1. -happens when too many protons and not enough neutrons (like positron decay) -a proton from the atom's nucleus pulls in an electron from an orbital, making a neutron and gamma ray
How does the emission of a beta particle change the atomic number of an element?
It increases it by 1.
How do you measure the covalent radius?
It is half of the distance between 2 covalently-bonded nucleii in a nonmetal
How does an alpha particle act in radioactive decay?
Its ejection reduces the atomic number by 2 and the atomic weight by 4 amu -happens when the nucleus is too heavy, so 2 protons & 2 neutrons just split off the nucleus 1. high energy, relative velocity 2. range is around 5 cm in the air 3. Shielding needed: stopped by the thickness of a sheet of paper, skin. 4. Example: Thorium-230 has an unstable nucleus and undergoes radioactive decay through alpha emission. The nuclear equation that describes this reaction is: ²³⁰Th → ⁴₂He + ²²⁶₈₈Ra ⁹⁰ In a decay reaction like this, the initial element (thorium-230) is called the parent nuclide and the resulting element (radium-226) is called the daughter nuclide.
spectroscope
an instrument that allows examination of spectra (distinct colored lines) from light emitted by energized atoms
What the relationship between atomic and ionic radius in NONMETALS, and why?
The ionic radius is GREATER THAN the atomic radius because nonmetals gain electrons to form negative ions, causing an increase in the inner electron repulsion.
What the relationship between atomic and ionic radius in METALS, and why?
The ionic radius is LESS THAN the atomic radius because metals lose electrons to form positive ions, causing the positive nuclear charge to pull the remaining electron closer.
excited state
any state higher than the ground state
What is electronegativity?
a number that measures the relative strength with which the atoms of an element attract valence electrons in a chemical bond -the electronegativity number is an arbitrary scale from 0-4 with a value of less than 2 indicating its status as a metal. -the LOWER the electroNEGATIVITY number, the MORE electroPOSITIVE the element is
valence of an atom
absolute number of electrons gained, lost, or borrowed (since all attempt to have full outer shell) Ex: ₁₇Cl = Nucleus )2)8)7 valence # = 1 since to complete outer shell, Cl needs to borrow 1 electron
Where are the most active metals located on the periodic table? Nonmetals?
active metals: lower left active nonmetals: upper right
core electrons
all electrons except for valence
Why do transition metals have variable oxidation states?
they have variable numbers of electron involved in bonding Ex: Manganese possible oxidation numbers: +2, +3, +4, +6, +7 3d sublevel electron use: 0, 1, 2, 4, 5
half-life
time required for half of the atoms in a radioactive nucleotide to decay (rate of radioactive decay of a substance) Example: radium (Ra) has a half life of 1590 years for the half nuclei and then it will take twice as long for the remainder to decay Ex 2: If start with 1000 g of a radioactive substance, and half-life = 1 year, then after 1 year there will be 500 grams of the original sample left. After another year there will be 250 grams left, etc.
J J Thompson electron discovery
used a cathode ray (evacuated tube connected to spark coil) -as voltage increased across tube→ beam became visible -beam deflected by both electrical and magnetic field, and therefore cathode rays are composed of electrons -also found ratio of electric charge of electron to mass
electron volt (eV)
used to measure photons, it is the amount of energy gained by the charge of a single electron moved across electric potential difference of 1 volt
How do you measure atomic radii?
using x-ray diffraction for metals
average atomic mass (AKA atomic weight)
weighted average of atomic masses of naturally occurring isotopes of element Ex: Cu = 69.17% Cu-63 (62.919598 amu) & 30.83% Cu-65 (64.927793 amu) = 63.55 amu
What do the x, y, and z subscripts indicate?
what planes the orbital is located in
photons
when energy is released in allowed values, it is released in this form of discrete radiant energy
