Atomic Mass Of Co

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In our discussion of the atomic theory, we examined water and hydrogen peroxide, which are both compounds formed from the gases oxygen and hydrogen. We'll see later that volumes of gases tell us about the combining ratios of atoms, but we'll now focus on masses of substances. Everyone knows that eating a 'balanced diet' means eating the correct masses of various foods. This is so because the foods provide atoms and molecules which must be in the correct weight ratio for our bodies to use in synthesizing proteins and other biomolecules.

  • Amu (atomic mass unit): the standard unit of measurement of atomic mass. The mass of one carbon-12 atom is set at 12 amu; the atomic mass of atoms of all other elements is determined relative to the mass of carbon-12. Avogadro’s number: the number of units in one mole: 6.022 × 1023, which is the number of atoms in 12 grams of carbon-12.
  • Cobalt is a chemical element with atomic number 27 and symbol Co. Know the Uses of Cobalt, Atomic Mass of Cobalt, Chemical Properties of Cobalt & more at BYJU'S.

Average Atomic Mass. Since many elements have a number of isotopes, and since chemists rarely work with one atom at a time, chemists use average atomic mass. On the periodic table the mass of carbon is reported as 12.01 amu. This is the average atomic mass of carbon. No single carbon atom has a mass of 12.01 amu, but in a handful of C atoms the.


So mass is a very important characteristic of atoms—it does not change as chemical reactions occur. Volume, on the other hand, often does change, because atoms or molecules pack together more tightly in liquids and solids or become more widely separated in gases when a reaction takes place. From the time Dalton’s theory was first proposed, chemists realized the importance of the masses of atoms, and they spent much time and effort on experiments to determine how much heavier one kind of atom is than another.

The chemical symbol for Cobalt is Co. Atomic Mass of Cobalt. Atomic mass of Cobalt is 58.9332 u. Note that, each element may contain more isotopes, therefore this resulting atomic mass is calculated from naturally-occuring isotopes and their abundance. The unit of measure for mass is the atomic mass unit (amu). Atoms, elements and the periodic table. Description Classroom Ideas. An explanation of how the mass of atoms varies depending upon the.

Dalton, for example, studied a compound of carbon and oxygen which he called carbonic oxide. He found that a 100-g sample contained 42.9 g C and 57.1 g O. In Dalton’s day there were no simple ways to determine the microscopic nature of a compound, and so he did not know the composition of the molecules (and hence the formula) of carbonic oxide. Faced with this difficulty, he did what most scientists would do—make the simplest possible assumption. This was that the molecules of carbonic oxide contained the minimum number of atoms: one of carbon and one of oxygen. Carbonic oxide was the compound we now know as carbon monoxide, CO, and so in this case Dalton was right. However, erroneous assumptions about the formulas for other compounds led to half a century of confusion about atomic weights.

Since the formula was CO, Dalton argued that the ratio of the mass of carbon to the mass of oxygen in the compound must be the same as the ratio of the mass of 1 carbon atom to the mass of 1 oxygen atom:

[dfrac{text{Mass of 1 C atom}}{text{Mass of 1 O atom}}=dfrac{text{mass of C in CO}}{text{mass of O in CO}}=dfrac{text{42}text{.9 g}}{text{57}text{.1 g}}=dfrac{text{0}text{.751}}{text{1}}=text{0.751}label{1}]

In other words the mass of a carbon atom is about three-quarters (0.75) as great as the mass of an oxygen atom.

Notice that this method involves a ratio of masses and that the units grams cancel, yielding a pure number. That number (0.751, or approximately ¾) is the relative mass of a carbon atom compared with an oxygen atom. It tells nothing about the actual mass of a carbon atom or of an oxygen atom–only that carbon is three-quarters as heavy as oxygen.

The relative masses of the atoms are usually referred to as atomic weights. Their values were are in a Table of Atomic Weights, along with the names and symbols for the elements. The atomic-weight scale was originally based on a relative mass of 1 for the lightest atom, hydrogen. As more accurate methods for determining atomic weight were devised, it proved convenient to shift to oxygen and then carbon, but the scale was adjusted so that hydrogen’s relative mass remained close to 1. Thus nitrogen’s atomic weight of 14.0067 tells us that a nitrogen atom has about 14 times the mass of a hydrogen atom.

The fact that atomic weights are ratios of masses and have no units does not detract at all from their usefulness. It is very easy to determine how much heavier one kind of atom is than another.


Atomic Mass Of Compounds

Example (PageIndex{1}): Mass of an Oxygen Atom

Use the Table of Atomic Weights to show that the mass of an oxygen atom is 1.33 times the mass of a carbon atom.

Solution The actual masses of the atoms will be in the same proportion as their relative masses. Atomic weights of oxygen is 15.9994 and carbon is 12.011. Therefore

(dfrac{text{Mass of an O atom}}{text{Mass of a C atom}} = dfrac{text{relative mass of an O atom}}{text{relative mass of a C atom}} = dfrac{text{15.9994}}{text{12.011}} = dfrac{text{1.332}}{text{1}})

or Mass of an O atom = 1.332 × mass of a C atom

The atomic-weight table also permits us to obtain the relative masses of molecules. These are called molecular weights and are calculated by summing the atomic weights of all atoms in the molecule.

Example (PageIndex{2}): Mass of a Water Molecule

Atomic Mass Of Co

How heavy would a water molecule be in comparison to a single hydrogen atom?

Solution First, obtain the relative mass of an H2O molecule (the molecular weight):

2H atoms: relative mass = 2 × 1.0079 = 2.0158

1 O atom: relative mass = 1 × 15.9994 = 15.994

1H2O molecule: relative mass = 18.0152


(dfrac{text{Mass of a H}_2text{O molecule}}{text{Mass of a H atom}} = dfrac{text{18.0152}}{text{1.0079}} = text{17.8740})

The H2O molecule is about 18 times heavier than a hydrogen atom.

From ChemPRIME: 2.5: Atomic Weights

Contributors and Attributions

  • Ed Vitz (Kutztown University), John W. Moore (UW-Madison), Justin Shorb (Hope College), Xavier Prat-Resina (University of Minnesota Rochester), Tim Wendorff, and Adam Hahn.

Below is a quick explanation of all the items on the fact sheets


Basic Information

Symbol- Each element is assigned a chemical symbol. This symbol usually originates from its name or its Latin name. For example, silicon has a chemical symbol 'Si'. Each element's symbol is composed of a capital letter followed by one or two lowercase letters.
Atomic Number- Each atom has an atomic number. This atomic number is equal to the number of protons in the nucleus of that particular atom. For example, the element cobalt (Co) has an atomic number of 27. This atomic number is also the number of protons in the atom. Therefore, Co has 27 protons.
Mass- The mass of an atom, expressed in atomic mass units (AMU), is roughly equal to the number of protons plus the number of neutrons. This is because both the protons and the neutrons in an atom have a relatively equal mass. The mass of an electron is so insignificant that it is not represented in the atomic mass. Since not all atoms have only one isotope1, the atomic mass is the average of all isotopes, once abundance is computed. For example, if you took a container of the element hydrogen (H), 99.984% of it would be H-1, 0.0156% of it would be H-2, and 0% of the hydrogen would be H-3. Since H-1 has one proton and no neutrons, its mass is 1. Because H-2 has one proton and one neutron, its mass is 2. Therefore, when you compute the percentages of the isotopes of H in any container, you find that the atomic mass of H is actually 1.0079. If the atomic mass of a particular element is shown in parentheses, such as (145) for Promethium (Pm), the atomic mass reflects that of the most stable isotope1, and is not the average atomic mass for all isotopes of the element. Atomic masses used on this periodic table are from the IUPAC 1995 recommendations.
Melting Point- The melting point of any element is the temperature at which the element changes from a solid to a liquid or from a liquid to a solid. Even though water is not an element, I will be using it in this example. Water freezes and ice melts at 0 °C (32 °F). Therefore, the melting point of water is 0 °C. The melting point is provided in degrees Celsius, Fahrenheit, and Kelvin. The melting point of a substance is also the freezing point.
Boiling Point- The boiling point of any element is the temperature at which it changes from a liquid to a gas or from a gas to a liquid. You probably know that water changes to steam and steam changes to water at a temperature of 100 °C (212 °F). The boiling point of water is 100 °C. Therefore, the boiling point is also the condensation point. The boiling point is provided in degrees Celsius, Fahrenheit, and Kelvin.
Number of Protons/Electrons- The number of protons/electrons in any atom is always equal to the atomic number of the atom. Each atom has a neutral charge, and since a proton has a positive charge and an electron has a negative charge, in order to achieve a neutral charge, the number of protons and electrons must equal. A particle that is not neutral (has either more or less electrons) is known as an ion.
Number of Neutrons- The number of neutrons in an atom is equal to the number of protons in an atom subtracted from the mass of the atom rounded to the nearest integer. This is true because both neutrons and protons have an atomic weight of approximately 1 AMU2 (see mass). Since atoms often have more than one isotope1, the number of neutrons listed on the element fact sheets is only valid for the most abundant isotope of any element.
For example, boron (B) has an atomic mass of 10.81 and an atomic number of 5. When you round 10.81 to the nearest integer, the result is 11. When you subtract the number of protons (equal to the atomic number) from the atomic mass, the result is 6. Therefore, the most common isotope of boron has 6 neutrons.
Classification- The classification of any element relates to its properties. Each periodic table may use different group names and classify each element a little differently. This periodic table uses 9 families:

Crystal Structure- The term 'Crystal Structure' refers to the way in which the atoms are arranged within an a substance (element). This property explains the way an element cleaves, or breaks apart physically. For example, an element with a cubic crystal structure, such as aluminum (Al), will break into cubes. Each side of the cube should have a straight edge.
Density- The density of an element refers to how closely its atoms are packed together. This is measured in grams per cubic centimeter. Take, for example, magnesium (Mg). Its density at 293 degrees Kelvin (20 degrees Celsius, 67 degrees Fahrenheit) is 1.738 g/cm3. This means that if you have a block of magnesium at room temperature (293 Kelvin), and you decide to cut a cube measuring 1 x 1 x 1 cm, the mass that you will cut will be 1.738 grams. The greater the density of an element is, the 'heavier' the element is.
Color- The color of an element refers to its physical reflection of light under normal conditions. For example, tin (Sn), will have a white color at room temperature. These properties may change if tin was heated to its melting point, where it would become a liquid, or if it was shown under a light with a color other than white.
Other Names- Some elements have more than one name or spelling. This may be caused by either local spelling or a naming dispute. For example, the element aluminum (Al) is spelled aluminum in the United States, but is spelled (and pronounced) aluminium in most otherEnglish-speaking countries, including Great Britain, Canada, and Australia.
A naming dispute has occurred between the American Chemical Society (ACS) and the International Union for Pure and Applied Chemistry (IUPAC) over elements 104-109. ACS has used the discoverer's suggested names, while IUPAC decided to leave the naming process up to a panel of 20 members. Until this naming dispute is resolved, this periodic table will use the systematic Latin names automatically assigned to newly discovered elements.
More information about the naming of heavy elements is available.

Atomic Structure

Number of Energy Levels- The number of energy levels refers to how many 'electron shells' or places where electrons can be an element has. An element with 4 shells, such as zinc (Zn), has 4 different areas where an electron is likely to be found.
Electron Arrangement- The electron arrangement of an atom refers to the number of electrons in each energy level. For example, carbon (C) has 6 electrons. Its atom arrangement shows that the six electrons are divided up into two shells, with 2 and 4 electrons, respectively.
Electron Configuration- The electron arrangement described above can be further described to include information about orbitals, shells, and more. This explanation is beyond the scope of this document, but if you are already aware of what these numbers mean, they are provided here for you.
Bohr Models- On this periodic table, Bohr models are now available for all 112 known elements. These models are designed to give some idea of how the electrons are spread over the energy levels. However, the Bohr model is now considered inaccurate among most scientists. This is because Bohr models show that electrons travel on specific paths or orbitals, a theory which has now been replaced by one that states that an electron has a greater probability of being in a certain area (or 'energy level') of the atom.

Half Lives

Half Lives- Half lives are defined as being the average time it takes for half of the atoms of a radioactive element to decay into their daughter elements. For example, carbon-14 (an isotope of carbon used for dating fossils) has a half life of 5730 years. This means that if you take a container of carbon-14, and leave it unchanged for 5730 years, about 50% of the carbon will remain as carbon-14, and the other 50% will decay to carbon-14's daughter element (nitrogen). If you wait for another 5730 years, about 25% of the container will be composed of the original carbon, and the other 75% will be atoms of nitrogen. Some elements, especially the heavier ones, have half lives of just a few milliseconds. For example, ununbium-277 (Uub) has a half-live of just 280 milliseconds. This means that in one second of ununbium's existence, 94% of it will radioactively decay into its daughter element.


Date of Discovery- The date of discovery of any element refers to the year in which is was first isolated and identified as an element. Some elements were discovered by early civilizations, and have an unknown discovery date.
Discoverer(s)- The discoverer of an element is defined as the first person to have identified the element. In more recent years, teams of scientists have been working on the identification of new elements, allowing more than one name to be put in this field.
Name Origin- The name origin of an element is the language/object/property/person that gives an element its name. Some elements have been assigned names of famous scientists, important mythological characters, or places. Other element's names come from foreign languages, such as Latin. The most recently discovered elements have a temporary, systematic name, assigned by IUPAC3.
Symbol Origin- When the chemical symbol of an element does not correspond to its name, its symbol origin is given on this periodic table. For example, the element lead has the chemical symbol 'Pb'. The symbol origin is from the Latin word 'plumbum', which means 'lead'.
Uses- Each element's most common uses, as an element or a compound containing the element, is written in this field.
Obtained from- The method of obtaining an element is also given under this section. Some elements are obtained from minerals, others are obtained from methods such as electrolysis of a mineral, while others are man-made.

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Atomic Weight Practice Problems

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1: An isotope is an atom of any element with the same number of protons and electrons as all the other atoms of this particular element, but with a different atomic mass (and number of neutrons).
2: AMU- Atomic Mass Unit(s)
3: IUPAC- International Union for Pure and Applied Chemistry

Atomic Mass Of Cobalt

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