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Periodic Trends - Honors Chemistry - Duke

Terms in this set (53)

Dmitri Mendeleev (1869)
Russian chemist that published the first periodic table based on atomic mass and properties
What are examples of two elements that do not follow the atomic mass trend?
Cobalt and nickel. Nickel has a higher atomic number than cobalt but a lower atomic mass
Henry Moseley (1911)
English scientist that created the periodic table arranged by atomic number (the number of protons)
What did Moseley realize about protons?
Moseley discovered that protons existed in the nucleus by looking at X-rays emitted from excited electrons and realizing that the pattern in emitted wavelengths could be explained by an increased nuclear charge as the experiment progressed through the elements on the periodic table.
Ductile
Able to be drawn into a wire
Malleable
Able to be hammered into sheets or flattened
Brittle
Able to be crushed into smaller pieces or a powder
Luster
The quality of giving off light, brightness, glitter
Dull
Not reflective, does not glitter
What are the properties of metals?
Ductile, good conductors, have metallic luster, malleable, solids (except mercury)
What are the properties of nonmetals?
Dull, gases or brittle solids, poor conductors
What are the properties of metalloids?
Semi-conductors, used in computer chips. They have properties of both metals and nonmetals.
What elements are liquid at room temperature?
Mercury (Hg) and Bromine (Br)
What elements are gases at room temperature?
Hydrogen (H), Nitrogen (N), Oxygen (O), Fluorine (F), Chlorine (Cl), and the noble gases
What elements are solids at room temperature?
All metals (except Hg), metalloids, Carbon (C), Phosphorus (P), Sulfur (S), Selenium (Se), Iodine (I)
Periods
The rows going left to right on the periodic table. They are numbered 1 to 7.
Groups/Families
The columns (top to bottom) numbered 1 to 18. Elements in the same group have the same number of valence electrons.
Alkali metals
- Group 1
- Have 1 valence electron
- Ion charge: +1
- Shiny, soft, highly reactive
Alkali earth metals
- Group 2
- Have 2 valence electrons
- Ion charge: +2
- Shiny, silvery white, somewhat reactive
Transition metals
- Group 3-12
- Number of valence electrons vaires
- Ion charge varies
- Paramagnetic, conducts electricity, solids, malleable, ductile, brightly colored compounds
Aluminum family
- Group 13
- Have 3 valence electrons
- Charge of ion: +3
Carbon family
- Group 14
- Have 4 valence electrons
- Do not usually form ions
Nitrogen family
- Group 15
- Have 5 valence electrons
- Charge of ion: -3
Oxygen family
- Group 16
- Have 6 valence electrons
- Charge of ion: -2
Halogens
- Group 17
- Have 7 valence electrons
- Charge of ion: -1
- Reacts with metals and produce salts. Dangerous and lethally toxic
Noble gases
- Group 18
- Have 8 valence electrons (Helium has 2)
- Do not usually form ions
- Gases, inert, highly unreactive
What are the seven elements that form diatomic molecules?
Hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, chlorine (H₂, O₂, F₂, Br₂, I₂, N₂, Cl₂)
What states are the diatomic molecules in at room temperature?
Everything is in gas form, except iodine, which is a solid and bromine, which is a liquid
Shielding
Outer electrons are shielded from the nucleus. Therefore they feel less attraction
Nuclear charge (Z)
The number of protons
Effective nuclear charge (Z sub eff)
Nuclear charge minus the effects of shielding
What is the general trend across a period?
Going across a period, there are more protons and therefore a higher effective nuclear charge as a result of less shielding
What is the general trend down a group?
Going down a group, there are more energy levels (n) and therefore a lower effective nuclear charge as the result of more shielding.
Atomic radius
The distance between the center of the atom to the farthest valence electron, measured in picometers (pm).
What is the trend with atomic radius?
The largest radii occur at the bottom left, while the smallest radii can be found at the top right
Why does atomic radius follow this trend?
Going right on the periodic table, elements gradually have more protons and a higher effective nuclear charge. Therefore, there is more attraction between the nucleus and the electrons, which shrinks the radius. Going down, elements gain more energy levels, and larger orbitals, so the radius increases.
Ionic radii
Cations (positive ions) have less electrons and therefore smaller radii.
Anions (negative ions) have more electrons and therefore larger radii.
Electronegativy
The ability to attract electrons in a chemical bond.
What is the trend with electronegativity?
Highest electronegativity occurs at the top left, while lowest occurs at the bottom right.
Why does electronegativity follow this trend?
Going right on the periodic table, elements have more protons and higher effective nuclear charge. There is more attraction, so electrons will be drawn in. Going left and down, elements have more energy levels and more shielding, so they are less likely to attract electrons.
What are the exceptions to the electronegativity trend?
Ignore helium, neon, and argon, because they rarely bond and thus do not usually interact with electrons.
Electron affinity
The energy change when an electron is added to an atom. This can represented with the equation X (in gas phase) + electron → X⁻¹
What is the trend with electron affinity?
Most energy is released for elements at the top right of the periodic table, and the least at the bottom left.
Why does electron affinity follow this trend?
Going right, elements will have more protons and electrons will have a stronger attraction to the nucleus. Thus, when the electron is added, the energy difference will be a lot. Going left and down, elements get more energy levels and thus more shielding. Valence electrons are much less attracted, so adding one will not create a lot of energy difference.
What are the exceptions with the electron affinity trend?
Noble gases have positive electron affinity, so energy is *required* to add an electron.
Ionization energy
The amount of energy required to remove the highest energy electron from an atom.
What is ionization energy measured in?
kilojoules/mole (kJ/mol).
1st ionization energy
Energy it takes to remove the 1st highest energy electron.
What is the trend with ionization energy?
Highest ionization energies towards the top right of the periodic table, lowest ionization energy towards the lower left.
Why does ionization energy follow this trend?
Going right, elements have more protons, so the attraction is greater and it is harder to remove electrons and requires more energy. Going down, elements have more energy levels and more shielding, so there is less attraction and therefore requires less energy to remove electrons.
What is the irregularity with boron and beryllium in terms of ionization energy?
Some elements do not follow the trend, such as beryllium and boron. The extra electron in the p orbital for boron fills a new orbital and is easier to remove than the s-orbital electrons in beryllium due to more shielding for boron's p-orbital electron.
What is the irregularity with nitrogen and oxygen in terms of ionization energy?
Nitrogen has three unpaired electrons in its p-orbitals, while oxygen has 2 unpaired electrons and 2 electrons that are paired with each other. It is easier to remove one electron from oxygen than nitrogen because the paired electrons are repelling each other (like charges repel).
How do you tell how many valence electrons an element has from its ionization energy?
If there is big difference between different ionization energies, then all the electrons before that difference are valence electrons. For example, if an element were to have ionization energies of 496 kJ/mol, 4562 kJ/mol, and 6912 kJ/mol, then we know it has one valence electron because the greatest difference is from the first ionization energy to the second. Since valence electrons are at the topmost energy level and are therefore easier to remove, that difference must mean the second ionization energy is removing an electron from an inner energy level.
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