Molar Mass and Gas Densities. Gases Molar Mass and Gas Densities Density Has the units of mass per unit volume (n/V) has the units of moles/liter. If we know the molecular mass of the gas, we can convert this into grams/liter (mass/volume). The molar mass (M) is the number of grams in one mole of a substance. If we multiply both sides of the above equation by the molar mass: The left hand side is now the number of grams per unit volume, or the mass per unit volume (which is the density) Thus, the density (d) of a gas can be determined according to the following: Alternatively, if the density of the gas is known, the molar mass of a gas can be determined: Example: What is the density of carbon tetrachloride vapor at 714 torr and 125°C? The molar mass of CCl4 is 12.0 + (4*35.5) = 154 g/mol. 125°C in degrees Kelvin would be (273+125) = 398K. Caesar's Las Breath Of the molecules in Caesar's last gasp, how many of them are in the breath you just took? Given: 1.
N = PV/RT = (0.96 atm)(2L)/(0.0821 L atm/mol K)(310 K) n = 0.075 mol 2. Units of Temperature: from fahrenheit to celsius to kelvin and back. Degrees Fahrenheit, (developed in the early 1700's by G. Daniel Fahrenheit), are used to record surface temperature measurements by meteorologists in the United States. However, since most of the rest of the world uses degrees Celsius (developed in the 18th Century), it is important to be able to convert from units of degrees Fahrenheit to degrees Celsius: Kelvin is another unit of temperature that is very handy for many scientific calculations, since it begins at absolute zero, meaning it has no negative numbers. (Note...the word "degrees" is NOT used with Kelvin.) The way to convert from degrees Celsius to Kelvin is: The three different temperature scales have been placed side-by-side in the chart below for comparison. Rutherford - Atomic Theory.
Empirical.htm. Now that the moles of each element are known, the empirical formula may be determined by dividing the moles of each element by the smallest number of moles. This yields a ratio of the number of each element in the empirical formula. The ratio of C:H:S has been found to be 4:4:1, thus the empirical formula is: C4H4S. The molar mass of the empirical formula is 84 g/mol.
Since the molecular weight of the actual compound is 168 g/mol, and is double the molar mass of the empirical formula, the molecular formula must be twice the empirical formula: C(4 x 2) H(4 x 2) S(1 x 2) which becomes C8H8S2 © Copyrght, 2001, L. Ladon. Isotopes. Pi bond. Electron atomic and molecular orbitals, showing a pi bond at the bottom right of the picture.
Two p-orbitals forming a π-bond. The Greek letter π in their name refers to p orbitals, since the orbital symmetry of the pi bond is the same as that of the p orbital when seen down the bond axis. P orbitals often engage in this sort of bonding. D orbitals also engage in pi bonding, and form part of the basis for metal-metal multiple bonding. Pi bonds are usually weaker than sigma bonds; the C-C double bond has a bond energy less than twice the C-C single bond bond energy; which leads to the conclusion that the p orbital overlap to form molecular orbitals is a weaker bond than when s orbitals overlap to form molecular orbitals. From the perspective of quantum mechanics, this bond's weakness is explained by significantly less overlap between the component p-orbitals due to their parallel orientation. Pi bonds result from overlap of atomic orbitals that are in contact through two areas of overlap.
Oxidation Numbers and Chemical Bonding. 6. Oxidation Numbers and Chemical Bonding Oxidation Numbers An element's oxidation number, sometimes called valence, is the number of electrons gained or lost when forming compounds. This characteristic is controlled by the electrons in the outer energy level (valence electrons). Atoms gain or lose electrons to get eight electrons in their outer shell. Elements with a positive oxidation number (usually metals) lose electrons when forming compounds. All chemical reactions occur between electrons in the outer energy level of atoms. The table below shows the elements and oxidation numbers that can be read from the periodic table. Stability in Atoms Certain electron arrangements are more stable than others. The most stable atoms - their outer energy level is full. Chemical Activity Metals increase in chemical activity as you go from right to left on a horizontal row and from top to bottom in a vertical column. The tendency of an atom to attract electrons is electron affinity.
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Block (periodic table) Blocks in the periodic table A block of the periodic table of elements is a set of adjacent groups. The term appears to have been first used (in French) by Charles Janet.[1] The respective highest-energy electrons in each element in a block belong to the same atomic orbital type. Each block is named after its characteristic orbital; thus, the blocks are: The block names (s, p, d, f and g) are derived from the quality of the spectroscopic lines of the associated atomic orbitals: sharp, principal, diffuse and fundamental, the rest being named in alphabetical order from g onwards, omitting j.[2][3] Blocks are sometimes called families. The following is the order for filling the "subshell" orbitals, according to the Aufbau principle, which also gives the linear order of the "blocks" (as atomic number increases) in the periodic table: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p, ...
Extended periodic table. No elements in this region have been synthesized or discovered in nature.[3] The first element of the g-block may have atomic number 121, and thus would have the systematic name unbiunium. Elements in this region are likely to be highly unstable with respect to radioactive decay, and have extremely short half lives, although element 126 is hypothesized to be within an island of stability that is resistant to fission but not to alpha decay. It is not clear how many elements beyond the expected island of stability are physically possible, if period 8 is complete, or if there is a period 9.
According to the orbital approximation in quantum mechanical descriptions of atomic structure, the g-block would correspond to elements with partially filled g-orbitals. However, spin-orbit coupling effects reduce the validity of the orbital approximation substantially for elements of high atomic number. Extended periodic table, including the g-block[edit] Pyykkö model[edit] End of the periodic table[edit] Valence Electrons. How to Write Electron Configurations and Orbital Diagrams. Dynamic Periodic Table. Lewis acids and bases. Diagram of Lewis acids and bases Diagram of Lewis acid and base bond types. For example, an s-LUMO Lewis acid such as the sodium ion (Na+), interacts with a Lobe-HOMO Lewis base such as the hydroxide ion (OH–), to give sodium hydroxide, a Type 7 complex.
The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms.[1] A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct. For example, OH− and NH3 are Lewis bases, because they can donate a lone pair of electrons.
Some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can either accept a pair of electrons or donate a pair of electrons, depending upon the reaction. Usually the terms Lewis acid and Lewis base are defined within the context of a specific chemical reaction. History[edit] Calculating Rates. Determining Reaction Rates The rate of a reaction is expressed three ways: Determining the Average Rate from Change in Concentration over a Time Period We calculate the average rate of a reaction over a time interval by dividing the change in concentration over that time period by the time interval. For the change in concentration of a reactant, the equation, where the brackets mean "concentration of", is Note: We use the minus sign before the ratio in the previous equation because a rate is a positive number.
Top Determining the Instantaneous Rate from a Plot of Concentration Versus Time An instantaneous rate is the rate at some instant in time. We determine an instantaneous rate at time t: by calculating the negative of the slope of the curve of concentration of a reactant versus time at time t. by calculating the slope of the curve of concentration of a product versus time at time t. Determining the Initial Rate from a Plot of Concentration Versus Time. Dipolar bond. A dipolar bond,[1] also known as a dative covalent bond[2] or coordinate bond[3] is a kind of 2-center, 2-electron covalent bond in which the two electrons derive from the same atom.
Examples[edit] Adduct of ammonia and boron trifluoride The term dipolar bond is used in organic chemistry for compounds such as amine oxides for which the electronic structure can be described in terms of the basic amine donating two electrons to an oxygen atom. The arrow → indicates that both electrons in the bond originate from the amine moiety. In a standard covalent bond each atom contributes one electron. Hexamminecobalt(III) chloride This electronic structure has an electric dipole, hence the name dipolar bond. An example of a dative covalent bond is provided by the interaction between a molecule of ammonia, a Lewis base with a lone pair of electrons on the nitrogen atom, and boron trifluoride, a Lewis acid by virtue of the boron atom having an incomplete octet of electrons. References[edit] Chemical Bonds.