Question:

Why is the average atomic mass of many elements is not a whole number?

Answer:

The average atomic mass is not a whole number because based on the percentage of isotopes of each element. So, no whole number.

More Info:


atomic mass

The atomic mass (ma) is the mass of an atomic particle, sub-atomic particle, or molecule. It may be expressed in unified atomic mass units; by international agreement, 1 atomic mass unit is defined as 1/12 of the mass of a single carbon-12 atom (at rest). When expressed in such units, the atomic mass is called the relative isotopic mass (see section below).

The atomic mass or relative isotopic mass refers to the mass of a single particle, and is fundamentally different from the quantities elemental atomic weight (also called "relative atomic mass") and standard atomic weight, both of which refer to averages (mathematical means) of naturally-occurring atomic mass values for samples of elements. Such averages are expected to have a variance according to the sample source for the collection of nuclides that make up a sample of a chemical element (each of which has its own exact characteristic atomic mass). Such mixtures reflect various abundance ratios of isotopes of the element as the ratios naturally occur in the place where the element sample was collected. By contrast, atomic mass figures refer to identical particle species; due to the exactly identical nature of species of atomic particles, atomic mass values are expected to have no intrinsic variance at all. Atomic mass figures are thus commonly reported to many more significant figures than atomic weights.

Chemistry
Chemical properties

A chemical property is any of a material's properties that becomes evident during a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated. However a catalytic property would also be a chemical property.

Chemical properties can be contrasted with physical properties, which can be discerned without changing the substance's structure. However, for many properties within the scope of physical chemistry, and other disciplines at the boundary between chemistry and physics, the distinction may be a matter of researcher's perspective. Material properties, both physical and chemical, can be viewed as supervenient; i.e., secondary to the underlying reality. Several layers of superveniency]clarification needed[ are possible.

Mass Stoichiometry
Nuclear chemistry

Nuclear chemistry is the subfield of chemistry dealing with radioactivity, nuclear processes and nuclear properties.

It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. This includes the corrosion of surfaces and the behavior under conditions of both normal and abnormal operation (such as during an accident). An important area is the behavior of objects and materials after being placed into a nuclear waste storage or disposal site. ass the atoms colliade they make a baby


Nuclear physics

Nuclear physics is the field of physics that studies the constituents and interactions of atomic nuclei. The most commonly known applications of nuclear physics are nuclear power generation and nuclear weapons technology, but the research has provided application in many fields, including those in nuclear medicine and magnetic resonance imaging, ion implantation in materials engineering, and radiocarbon dating in geology and archaeology.

The field of particle physics evolved out of nuclear physics and is typically taught in close association with nuclear physics.

Isotope
Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Elements are divided into metals, metalloids, and non-metals. Familiar examples of elements include carbon, oxygen (non-metals), silicon, arsenic (metalloids), aluminium, iron, copper, gold, mercury, and lead (metals).

The lightest chemical elements, including hydrogen, helium (and smaller amounts of lithium, beryllium and boron), are thought to have been produced by various cosmic processes during the Big Bang and cosmic-ray spallation. Production of heavier elements, from carbon to the very heaviest elements, proceeded by stellar nucleosynthesis, and these were made available for later solar system and planetary formation by planetary nebulae and supernovae, which blast these elements into space. The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars, after the lighter gaseous elements and their compounds have been subtracted. While most elements are generally viewed as stable, a small amount of natural transformation of one element to another also occurs at the present time through decay of radioactive elements as well as other natural nuclear processes.


Atomic weight

Relative atomic mass (symbol: Ar) is a dimensionless physical quantity, the ratio of the average mass of atoms of an element (from a single given sample or source) to 1/12 of the mass of an atom of carbon-12 (known as the unified atomic mass unit). The term is equivalent to atomic weight, which is the older term, and which is also sample (source) specific. Thus, two samples of a chemical element that normally consists of more than one isotope, collected from two widely spaced natural solid sources on Earth, are expected to have slightly different relative atomic masses (atomic weights).

Both the terms relative atomic mass and atomic weight are sometimes loosely used to refer to a technically different standardized expectation value, called the standard atomic weight. This value is the mean value of atomic weights of a number of "normal samples" of the element in question. For this definition, "[a] normal sample is any reasonably possible source of the element or its compounds in commerce for industry and science and has not been subject to significant modification of isotopic composition within a geologically brief period." These standard atomic weights are published at regular intervals by the Commission on Isotopic Abundances and Atomic Weights of the International Union of Pure and Applied Chemistry (IUPAC) The "standard" values are intended as mean values that compensate for small variances in the isotopic composition of the chemical elements across a range of ordinary samples on Earth, and thus to be applicable to normal laboratory materials. However, they may not accurately reflect values from samples from unusual locations or extraterrestrial objects, which often have more widely variant isotopic compositions.


Periodic table

The periodic table is a tabular arrangement of the chemical elements, organized on the basis of their atomic numbers, electron configurations, and recurring chemical properties. Elements are presented in order of increasing atomic number (the number of protons in the nucleus). The standard form of the table consists of a grid of elements laid out in 18 columns and 7 rows, with a double row of elements below that. The table can also be deconstructed into four rectangular blocks: the s-block to the left, the p-block to the right, the d-block in the middle, and the f-block below that.

The rows of the table are called periods; the columns are called groups, with some of these having names such as halogens or noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet to be discovered or synthesized, elements. As a result, a periodic table—whether in the standard form or some other variant—provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences.

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