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DATCrusher Chem Videos > Chemistry Video 16 > Flashcards

Chemistry Video 16 Flashcards

1
Q

Nuclear reactions

A

The nucleus emits or absorbs particles and the identity of the atom changes

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2
Q

Nuclide symbol

A

Element symbol, atomic number in bottom left and mass number at top left

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3
Q

Protium

A

Isotope of hydrogen. 1 proton, mass number of 1

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4
Q

Deuterium

A

Isotope of hydrogen. 1 proton, 1 neutron, mass number of 2

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5
Q

Tritium

A

Isotope of hydrogen. 1 proton, 2 neutrons, mass number of 3

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6
Q

Atomic structure

A

Dense nucleus. Protons repel via electromagnetic force. Nucleons attract via the strong nuclear force, which makes the nucleus stable. But some nuclei are unstable.

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7
Q

Graph examining neutron to proton ratio for all stable isotopes

A

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.

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8
Q

Magic numbers

A

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.

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9
Q

Double magic

A

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.

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10
Q

Nuclear binding energy

A

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.

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11
Q

Mass defect

A

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

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12
Q

Weak nuclear force

A

Mediates nuclear decay.

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13
Q

Fundamental forces

A

Electromagnetic force, strong nuclear force, weak nuclear force

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14
Q

Strong nuclear force

A

Binds nucleons together in the nucleus

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15
Q

Nuclear decay

A

Caused by nuclear instability. Nuclear reaction in which the nucleus will try to do something in order to become more stable.

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16
Q

Alpha particle

A

2 protons, 2 neutrons. 4 amu. High energy helium nucleus.

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17
Q

Beta particle

A

High energy electrons. Mass number is 0. Atomic number is -1.

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18
Q

Positron

A

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.

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19
Q

Gamma ray

A

Particle of light or electromagnetic radiation known as a photon. Very high energy electromagnetic radiation. Mass number is 0. Atomic number is 0.

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20
Q

Particles involved in nuclear reactions

A

alpha particle, beta particle, positron, proton, neutron, gamma ray

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21
Q

Alpha decay

A

Alpha particle ejected. Occurs if the nucleus is too large to be stable. The strong nuclear force is less than the electromagnetic force.

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22
Q

Beta decay (beta minus decay)

A

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

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23
Q

Positron emission (beta plus decay)

A

Positron emitted. Occurs because a proton is being converted to a neutron. This is favourable if the neutron to proton ratio is too low.

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24
Q

Electron capture

A

Absorbing an electron. Proton is changed into neutron. This is favourable if the neutron to proton ratio is too low. X-ray emitted

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25
Q

Gamma emission

A

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.

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26
Q

Balancing nuclear reactions

A

Both the mass numbers and atomic numbers need to add up to the same value on both sides of the reaction

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27
Q

Half-life

A

The amount of time for a sample of radioactive nuclei to be reduced to half the original amount

28
Q

Radiometric dating

A

Used to determine the age of particular objects i.e. fossils.

29
Q

Carbon-14

A

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).

30
Q

Uranium-238

A

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.

31
Q

Nuclear fission

A

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

32
Q

Nuclear fission of uranium

A

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.

33
Q

Fissile material

A

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.

34
Q

Sub-critical mass

A

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

35
Q

Critical mass

A

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

36
Q

Atomic bombs

A

Created using nuclear fission chain reactions. Contained several pounds of fissionable material, such as U-235.

37
Q

Nuclear fusion

A

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.

38
Q

Temperature needed for nuclear fusion

A

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.

39
Q

Most common type of fusion reaction produces

A

helium

40
Q

Coordination compounds

A

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

41
Q

Coordinate covalent bond

A

In coordination compounds. Both electrons come from the ligand (Lewis base) and are being donated to the metal centre.

42
Q

Coordination sphere

A

Place square brackets around the complex and place any formal charge exhibited by the complex in the upper right hand corner.

43
Q

Coordination number

A

The number of donor atoms bound to the central atom in the complex

44
Q

Monodentate ligands

A

Interact with the central atom through one atom

45
Q

Bidentate ligands

A

Interact with the central atom through two atoms. The coordination number is double the number of ligands.

46
Q

Polydentate ligands AKA chelating ligands

A

Interact with the central atom through many atoms.

47
Q

Octahedral

A

Coordination number of 6. Bond angle of 90 degrees

48
Q

Tetrahedral

A

Coordination number of 4

49
Q

Square planar

A

Coordination number of 4

50
Q

Tetrahedral vs square planar

A

Geometry determined by crystal field theory, number of d electrons in the valence shell for the central metal atom

51
Q

Pentagonal bipyramid

A

Coordination number of 7

52
Q

Square antiprism

A

Coordination number of 8

53
Q

Dodecahedron

A

Coordination number of 8

54
Q

Naming coordination compounds

A
  1. If the coordination compound is ionic, name the cation first, and then name the anion
  2. 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.
  3. 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.
  4. 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.
55
Q

Structural isomers

A

Molecules with the same molecular formula but different connectivity

56
Q

Stereoisomers

A

Same molecular formula and connectivity but arranged differently in space

57
Q

Optical isomers

A

Molecules are mirror images of each other.

58
Q

Chiral compound

A

Compound with 2 optical isomers, where each one is an enantiomer. These compounds are optically active, meaning that it will rotate plane-polarized light

59
Q

Crystal Field Theory

A

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

60
Q

eg and t2g in octahedral shape

A

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)

61
Q

Crystal field splitting energy

A

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

62
Q

Weak-field ligands in complex

A

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

63
Q

Pairing energy

A

The repulsion between paired electrons

64
Q

Strong-field ligands in complex

A

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

65
Q

Tetrahedral

A

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

66
Q

Neutron emission

A

Rare decay. Neutron emitted from nucleus. Results in atomic mass decrease by 1 amu but atomic number remains the same

67
Q

Radioactive decay follows which order of kinetics?

A

First order kinetics

DATCrusher Chem Videos (17 decks)

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