Chemistry Video 16 Flashcards
Nuclear reactions
The nucleus emits or absorbs particles and the identity of the atom changes
Nuclide symbol
Element symbol, atomic number in bottom left and mass number at top left
Protium
Isotope of hydrogen. 1 proton, mass number of 1
Deuterium
Isotope of hydrogen. 1 proton, 1 neutron, mass number of 2
Tritium
Isotope of hydrogen. 1 proton, 2 neutrons, mass number of 3
Atomic structure
Dense nucleus. Protons repel via electromagnetic force. Nucleons attract via the strong nuclear force, which makes the nucleus stable. But some nuclei are unstable.
Graph examining neutron to proton ratio for all stable isotopes
Number of neutrons on y-axis and number of protons on x-axis. All stable isotopes represented by a dot. Band of stability is where number of neutrons = number of protons, which is a linear region containing all stable isotopes. Graph shows a preference for nature to use nuclei that, at low mass, show a 1:1 ratio of neutron and protons. As the nucleus gets bigger, there is preference for ratio of 1.5:1 for neutrons:protons. This is because as more protons are added to the nucleus, the repulsion between protons gets greater. Thus, more neutrons are needed to diffuse the repulsion from the increased amount of protons. It is also preferred for protons and neutrons to be both present in even numbers.
Magic numbers
If a nucleus has a number of protons or neutrons equal to 2, 8, 20, 28, 50, 82 or 126, it will be very stable.
Double magic
Both the number of neutrons and the number of protons are equal to 2, 8, 20, 28, 50, 82 or 126, making it even more stable than just having 1 magic number.
Nuclear binding energy
The energy needed to disassemble the nucleus of an atom into its components
Plots the binding energy per nucleon against the mass number; The average force holding every particle inside a particular nucleus. The maximum binding energy per nucleon occurs at 56 atomic mass units. Thus, iron-56 is the most stable nucleus in the universe because it has the maximum binding energy per nucleon.
Mass defect
Fusing nuclei will cause the loss of a tiny bit of mass. A fraction of the mass of each nucleon is converted directly to energy and released during a fusion. The mass of a nucleus is always slightly less than the mass of its constituent nucleons. Represented by equation: deltaE = (deltam)*(c)^2, where deltaE is the energy released upon fusion, deltam is the change in mass or the mass defect and c is the speed of light. The greater the mass defect, the greater the nucleat binding energy
Weak nuclear force
Mediates nuclear decay.
Fundamental forces
Electromagnetic force, strong nuclear force, weak nuclear force
Strong nuclear force
Binds nucleons together in the nucleus
Nuclear decay
Caused by nuclear instability. Nuclear reaction in which the nucleus will try to do something in order to become more stable.
Alpha particle
2 protons, 2 neutrons. 4 amu. High energy helium nucleus.
Beta particle
High energy electrons. Mass number is 0. Atomic number is -1.
Positron
Antimatter particles of the electron. Particles with the same mass as an electron but with 1 unit of positive charge. Mass number is 0. Atomic number is +1.
Gamma ray
Particle of light or electromagnetic radiation known as a photon. Very high energy electromagnetic radiation. Mass number is 0. Atomic number is 0.
Particles involved in nuclear reactions
alpha particle, beta particle, positron, proton, neutron, gamma ray
Alpha decay
Alpha particle ejected. Occurs if the nucleus is too large to be stable. The strong nuclear force is less than the electromagnetic force.
Beta decay (beta minus decay)
Emits an electron. Occurs because a neutron is being converted to a proton. The electron ejected (beta particle) is not one of the electrons that is surrounding the nucleus and is called negatron. This is favourable if the neutron to proton ratio is too high
Positron emission (beta plus decay)
Positron emitted. Occurs because a proton is being converted to a neutron. This is favourable if the neutron to proton ratio is too low.
Electron capture
Absorbing an electron. Proton is changed into neutron. This is favourable if the neutron to proton ratio is too low. X-ray emitted
Gamma emission
Occurs when nucleus is in excited state. It can decay to its ground state by emitting a gamma photon. Asterisk indicates an excited state. This is the only nuclear reaction where the parent nucleus does not become another element.
Balancing nuclear reactions
Both the mass numbers and atomic numbers need to add up to the same value on both sides of the reaction
Half-life
The amount of time for a sample of radioactive nuclei to be reduced to half the original amount
Radiometric dating
Used to determine the age of particular objects i.e. fossils.
Carbon-14
Accurate in dating objects that are up to 50,000 years old. Used in radiometric dating. Carbon is common in living things. Anything with carbon atoms will have a trace amount of carbon-14. Forms in the upper atmosphere when nitrogen-14 collides with neutrons from cosmic rays in space. Plants absorb CO2 and animals eat plants; thus, living organisms have the same ratio of carbon-12 to carbon-14 as found in the atmosphere. When an organism dies, the ratio of carbon-12 to carbon-14 is locked in place. Then, carbon-14 undergoes beta emission to become nitrogen-14 again, thus gradually decreasing the amount of carbon-14 in the dead organism. Carbon-14 half-life is 5,730 years. This technique is only reliable for the duration of 10 half-lives. But, we can use different nuclei that have different half-lives (i.e. potassium, argon, lead).
Uranium-238
Used to determine age of rocks. Half-life of 4.5 billion years. It undergoes a decay series to produce Pb-206. We can simply measure the ratio of U-238 to Pb-206 in a rock to get its age.
Nuclear fission
Large nuclei splitting into smaller nuclei. The smaller nuclei are more stable. Can be induced by bombardment of large nuclei with neutrons. This process generates large amounts of energy
Nuclear fission of uranium
Can decay in a number of different ways. Uranium becomes 2 different smaller atoms and a few (2-3) neutrons. One nucleus will have a mass between 85 and 105. The other nucleus will have a mass between 130 and 150. One mole of U-235 will release 1.8*10^10 kJ of energy during nuclear fission. The neutrons that result from this can further cause nuclear fission of nearby nuclei, causing a chain reaction.
Fissile material
Capable of undergoing chain reaction. i.e. U-235. There must be a minimum of fissionable material present in order for a chain reaction to be sustained.
Sub-critical mass
Having less than the minimum fissionable material present in order for a chain reaction to be sustained. Neutrons will leave the material instead of colliding with other nuclei
Critical mass
Having enough fissionable material present in order for a chain reaction until all nuclei have split. Depends on identity of substance, purity of the sample, external temperature and shape of the sample
Atomic bombs
Created using nuclear fission chain reactions. Contained several pounds of fissionable material, such as U-235.
Nuclear fusion
Even more energy than nuclear fission. Small nuclei fuse together to make a larger nucleus. The mass of the nuclei is converted to energy. 3.6*10^11 kJ energy per mole of Helium, which is 20 times more the energy of nuclear fission. Requires high temperatures for particles to fuse when they collide because the particles need to be accelerated. Occurs easily inside the sun.
Temperature needed for nuclear fusion
1.5*10^7 K or greater. At this temperature, matter cannot exist as atoms or molecules, the matter becomes plasma instead, which is a soup of subatomic particles.
Most common type of fusion reaction produces
helium
Coordination compounds
Involve transition metals. Central metal ion acts as a Lewis acid and some ligands act as Lewis Bases. The ligands can be atom, molecules or ions, but usually have a lone pair that can coordinate to the electron-deficient metal ion to form a coordinate covalent bond AKA dative bond. Geometry is determined by coordination number and identity of ligands
Coordinate covalent bond
In coordination compounds. Both electrons come from the ligand (Lewis base) and are being donated to the metal centre.
Coordination sphere
Place square brackets around the complex and place any formal charge exhibited by the complex in the upper right hand corner.
Coordination number
The number of donor atoms bound to the central atom in the complex
Monodentate ligands
Interact with the central atom through one atom
Bidentate ligands
Interact with the central atom through two atoms. The coordination number is double the number of ligands.
Polydentate ligands AKA chelating ligands
Interact with the central atom through many atoms.
Octahedral
Coordination number of 6. Bond angle of 90 degrees
Tetrahedral
Coordination number of 4
Square planar
Coordination number of 4
Tetrahedral vs square planar
Geometry determined by crystal field theory, number of d electrons in the valence shell for the central metal atom
Pentagonal bipyramid
Coordination number of 7
Square antiprism
Coordination number of 8
Dodecahedron
Coordination number of 8
Naming coordination compounds
- If the coordination compound is ionic, name the cation first, and then name the anion
- Name the ligands first in alphabetical order. For neutral ligands, it is the normal name of the molecule (Exceptions are H2O named as aqua, NH3 named as ammine, CO named as carbonyl, NO named as nitrosyl). Anionic ligands will end in “O” i.e. fluoro, cyano.
- If the ligand appears more than once, it will have a prefix (di, tri, tetra). If the ligand already begins with di, tri, tetra, then these prefixes will be used instead: bis, tris, tetrakis.
- If the complex is a cation, list the metal by the name of its element followed by a roman numeral in parentheses to indicate its oxidation state. If the complex is neutral, it follows the same rules as cations. If the complex is an anion, add the suffix “-ate” to the metal.
Structural isomers
Molecules with the same molecular formula but different connectivity
Stereoisomers
Same molecular formula and connectivity but arranged differently in space
Optical isomers
Molecules are mirror images of each other.
Chiral compound
Compound with 2 optical isomers, where each one is an enantiomer. These compounds are optically active, meaning that it will rotate plane-polarized light
Crystal Field Theory
Metal ion and ligands can be treated as point charges. The spatial arrangements of the point charges will affect the energies of the d orbitals for the central metal atom. The ligands donate electron into these orbitals to form the bonds. This theory explains colours and magnetic behaviours. Ligands all have excess electron density and will donate electron density to the metal ion. The electron density repels existing electron density on the metal ion. Due to the repulsion, the energy of certain d orbitals will have their energies increase, and not in an equal manner
eg and t2g in octahedral shape
eg orbitals have higher energy because it points to direction of ligands; d(x^2-y^2) and d(z^2). t2g orbitals have lower energy and point in between the ligands; d(xy), d(xz), d(yz)
Crystal field splitting energy
The difference in energy between eg and t2g. The magnitude of the energy gap depends on whether the orbitals involved are 3d, 4d or 5d orbitals, oxidation state, coordination number and strength of ligands (the identiy of the ligands). From weak to strong-field ligands: I- < Br- < Cl- < F- < H2O < C2O4(2-) < NH3 < en < NO2(-) < CN (-). This energy results in emission of photons in the visible range, to produce colour
Weak-field ligands in complex
The crystal field splitting energy is small and not enough to overcome the pairing energy or the repulsion generated by doubling of electrons in an orbital. Electrons will spread out evenly; putting unpaired electrons in eg orbital before the t2g orbitals are completely full (in octahedral shape). These are called high-spin complexes
Pairing energy
The repulsion between paired electrons
Strong-field ligands in complex
The crystal field splitting energy is big. The system will be at a lower energy by doubling the electrons in the t2g orbitals (in octahedral shape). These are called low-spin complexes
Tetrahedral
Ligands tend to approach the d(xy), d(xz) and d(yz) orbitals, rather than the d(x^2-y^2) and d(z^2) orbitals. d(xy), d(xz) and d(yz) are higher energy orbitals and d(x^2-y^2) and d(z^2) orbitals are lower energy orbitals. Also, ligands do not approach the orbitals as directly, so the energy splitting will be of a lesser magnitude. Also tends to be high spin complexes
Neutron emission
Rare decay. Neutron emitted from nucleus. Results in atomic mass decrease by 1 amu but atomic number remains the same
Radioactive decay follows which order of kinetics?
First order kinetics
