mass number

Examples of mass number in the following topics:

• Atomic Number and Mass Number

  • The atomic number is the number of protons in an element, while the mass number is the number of protons plus the number of neutrons.
  • An element's mass number (A) is the sum of the number of protons and the number of neutrons.
  • The small contribution of mass from electrons is disregarded in calculating the mass number.
  • Isotopes of the same element will have the same atomic number but different mass numbers.
  • Determine the relationship between the mass number of an atom, its atomic number, its atomic mass, and its number of subatomic particles

• Balancing Nuclear Equations

  • To balance a nuclear equation, the mass number and atomic numbers of all particles on either side of the arrow must be equal.
  • The transformations of particles must follow certain conservation laws, such as conservation of charge and baryon number, which is the total atomic mass number.
  • To balance the equation above for mass, charge, and mass number, the second nucleus on the right side must have atomic number 2 and mass number 4; it is therefore also helium-4.
  • The result is an atomic mass difference of 4 and an atomic number difference of 2.
  • In order to solve this equation, we simply add the mass numbers, 214 for polonium, plus 8 (two times four) for helium (two alpha particles), plus zero for the electrons, to give a mass number of 222.

• Average Atomic Mass

  • For any given isotope, the sum of the numbers of protons and neutrons in the nucleus is called the mass number.
  • By adding together the number of protons and neutrons and multiplying by 1 amu, you can calculate the mass of the atom.
  • Then, calculate the mass numbers.
  • The chlorine isotope with 18 neutrons has an abundance of 0.7577 and a mass number of 35 amu.
  • To calculate the average atomic mass, multiply the fraction by the mass number for each isotope, then add them together.

• Converting between Mass and Number of Moles

  • A substance's molar mass can be used to convert between the mass of the substance and the number of moles in that substance.
  • By recognizing the relationship between the molar mass (g/mol), moles (mol), and particles, scientists can use dimensional analysis convert between mass, number of moles and number of atoms very easily.
  • Therefore, we can divide 10.0 g of Ni by the molar mass of Ni to find the number of moles present.
  • Given a sample's mass and number of moles in that sample, it is also possible to calculate the sample's molecular mass by dividing the mass by the number of moles to calculate g/mol.
  • Convert between the mass and the number of moles, and the number of atoms, in a given sample of compound

• Molar Mass of Gas

  • Molar mass (M) is equal to the mass of one mole of a particular element or compound; as such, molar masses are expressed in units of grams per mole (g mol–1) and are often referred to as molecular weights.
  • The molar mass of a particular gas is therefore equal to the mass of a single particle of that gas multiplied by Avogadro's number (6.02 x 1023 ).
  • The average molar mass of a mixture of gases is equal to the sum of the mole fractions of each gas, multiplied by their respective molar masses:
  • where m is the mass of the gas, and M is the molar mass.
  • What is the molar mass of the gas?

• The Law of Conservation of Mass

  • The law of conservation of mass states that mass in an isolated system is neither created nor destroyed.
  • However, Antoine Lavoisier described the law of conservation of mass (or the principle of mass/matter conservation) as a fundamental principle of physics in 1789.
  • In other words, in a chemical reaction, the mass of the products will always be equal to the mass of the reactants.
  • We can therefore visualize chemical reactions as the rearrangement of atoms and bonds, while the number of atoms involved in a reaction remains unchanged.
  • This assumption allows us to represent a chemical reaction as a balanced equation, in which the number of moles of any element involved is the same on both sides of the equation.

• Molar Mass of Compounds

  • The molar mass of a particular substance is the mass of one mole of that substance.
  • Chemists can measure a quantity of matter using mass, but in chemical reactions it is often important to consider the number of atoms of each element present in each sample.
  • One mole (abbreviated mol) is equal to the number of atoms in 12 grams of carbon-12; this number is referred to as Avogadro's number and has been measured as approximately 6.022 x 1023.
  • The characteristic molar mass of an element is simply the atomic mass in g/mol.
  • However, molar mass can also be calculated by multiplying the atomic mass in amu by the molar mass constant (1 g/mol).

• Mass-to-Mole Conversions

  • Mass-to-mole conversions can be facilitated by employing the molar mass as a conversion ratio.
  • The relative atomic mass is a ratio between the average mass of an element and 1/12 of the mass of an atom of carbon-12.
  • The molar mass value can be used as a conversion factor to facilitate mass-to-mole and mole-to-mass conversions.
  • The molar mass of water is 18 g/mol.
  • This video describes how to determine the number of moles of reactants and products if given the number of grams of one of the substances in the chemical equation.

• Mass-to-Mass Conversions

  • Mass-to-mass conversions cannot be done directly; instead, mole values must serve as intermediaries in these conversions.
  • It is not possible to directly convert from the mass of one element to the mass of another.
  • Because there is no direct way to compare the mass of butane to the mass of oxygen, the mass of butane must be converted to moles of butane:
  • With the number of moles of butane equal to 54 grams, it is possible to find the moles of O2 that can react with it.
  • A chart detailing the steps that need to be taken to convert from the mass of substance A to the mass of substance B.

• Mass Spectrometry to Measure Mass

  • Mass spectrometers separate compounds based on a property known as the mass-to-charge ratio: the mass of the atom divided by its charge.
  • A mass analyzer, which sorts the ions by mass by applying electromagnetic fields
  • Plasma gas is electrically neutral overall, but a substantial number of its atoms are ionized by the high temperature.
  • Mass analyzers separate the ions according to their mass-to-charge ratios.
  • There are many types of mass analyzers.