Atomic Weight
Atomic Weight - Related Videos
01:25
Atomic Weight
0 Views •
2023
Protons and neutrons have approximately the same mass, about 1.67 × 10-24 grams. Scientists arbitrarily define this amount of mass as one atomic mass unit (amu) or one Dalton. Electrons are much smaller in mass than protons, weighing only 9.11 × 10-28 grams, or about 1/1800 of an atomic mass unit. As a result, they do not contribute much to an element's overall atomic mass. This means that, when considering atomic mass, it is customary to ignore the mass of any electrons and calculate the...
01:52
Atomic Mass
0 Views •
2020
Atoms — and the protons, neutrons, and electrons that compose them — are extremely small. For example, a carbon atom weighs less than 2 × 10−23 g. When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu). The amu was originally defined based on hydrogen, the lightest element, then later in terms of oxygen. Since 1961, it has been defined with regard to the most abundant isotope of carbon, atoms of which are...
02:44
Atomic Orbitals
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2020
An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution function indicates the total probability of finding an electron within the thin shell at a distance r from the nucleus. The atomic orbitals have distinct shapes which are determined by l, the angular momentum quantum number. The orbitals are often drawn with a boundary surface, enclosing densest regions of the cloud. The angular momentum...
03:24
Hybridization of Atomic Orbitals I
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2020
The mathematical expression known as the wave function, ψ, contains information about each orbital and the wavelike properties of electrons in an isolated atom. When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes. This process of combining the wave functions for atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals. The new orbitals that...
03:21
The Energies of Atomic Orbitals
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2020
In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are also observed. The attractive and repulsive forces are dependent on the distance between the particles, as well as the sign and magnitude of the charges on the individual particles. When the charges on the particles are opposite, they attract each other. If both particles have the same charge, they repel each other. As the magnitude of the...
FAQs
Each naturally occurring isotope contributes a portion of the final value equal to its isotopic mass multiplied by its fractional natural abundance. Summing these contributions produces the weighted result. An isotope present in greater abundance therefore influences the value more strongly than a less abundant isotope, making isotopic composition central to the calculation.
The carbon-12 atom establishes the reference point for the relative mass scale: one-twelfth of its mass serves as the comparison unit. Expressing other atomic masses against this common standard allows chemists to compare elements consistently and use those values in calculations involving moles, masses, and chemical formulas.
Variation occurs when the proportions of naturally occurring isotopes differ between samples. Since the weighted calculation depends on fractional abundance, a changed isotopic composition can shift the reported value even though the element itself is unchanged. This consideration becomes important when interpreting measurements from environmental or geochemical materials.
First, identify the naturally occurring isotopes and obtain each isotope’s mass and fractional abundance. Next, multiply each mass by its corresponding fraction. Finally, add all isotope contributions together. The resulting sum gives the value used for subsequent chemical calculations, provided the abundance data represent the material being analyzed.
Atomic weight supplies the element-specific mass values needed to relate microscopic composition to measurable sample mass. Chemists use these values in mole calculations and then apply the resulting quantities to stoichiometric relationships. Errors or inappropriate values can therefore affect calculated amounts, molecular masses, and the quantitative interpretation of chemical reactions.
In molecular formula determination and quantitative analysis, atomic weight helps convert measured masses into composition-based chemical information. Its dependence on isotope abundance also gives it a role in geochemistry, environmental science, and isotope-based studies, where differences in isotopic composition can help researchers interpret measurements from natural or analyzed materials.