PERIODIC TABLE MG MOLAR MASS' SERIES

We also described the law of multiple proportions, which states that the ratios of the masses of elements that form a series of compounds are small whole numbers. In Chapter 1 'Introduction to Chemistry', we described Dalton’s theory that each chemical compound has a particular combination of atoms and that the ratios of the numbers of atoms of the elements present are usually small whole numbers.

It is an extremely hard and inert material that is used to make cutting tools for machining hard metal alloys. 177 amuĬalculate the formula mass of Si 3N 4, commonly called silicon nitride. We could also find the formula mass of Ca 3(PO 4) 2 in one step by using unit conversions or a tabular format: + + = 310.177 amu 3Ca (3 atoms)(40. The formula mass of this molecular unit is calculated by adding together the atomic masses of three calcium atoms, two phosphorus atoms, and eight oxygen atoms.ī Taking atomic masses from the periodic table, we obtain 3 × atomic mass of calcium = 3 atoms ( 40. This compound is the principal source of calcium found in bovine milk.Ī Determine the number of atoms of each element in the empirical formula.Ĭ Add together the masses to give the formula mass.Ī The empirical formula-Ca 3(PO 4) 2-indicates that the simplest electrically neutral unit of calcium phosphate contains three Ca 2+ ions and two PO 4 3− ions. The structure of a molecule of Freon-11 is as follows:Ĭalculate the formula mass of Ca 3(PO 4) 2, commonly called calcium phosphate. Until recently, it was used as a refrigerant. 069 amuĬalculate the molecular mass of trichlorofluoromethane, also known as Freon-11, whose condensed structural formula is CCl 3F. 9994 amu C 2 H 6 O molecular mass of ethanol = 46. The same calculation can also be done in a tabular format, which is especially helpful for more complex molecules: 2C (2 atoms)(12. 9994 amu atom ) = 15.9994 amuĬ Adding together the masses gives the molecular mass: 24.022 amu + 6.0474 amu + 15.9994 amu = 46.069 amuĪlternatively, we could have used unit conversions to reach the result in one step, as described in Essential Skills 2 ( Section 3.7 'Essential Skills 2'): + + = 46.069 amu 011 amu atom ) = 24.022 amu 6 × atomic mass of hydrogen = 6 atoms ( 1. Among its many uses, ethanol is a fuel for internal combustion engines.Ī Determine the number of atoms of each element in the molecule.ī Obtain the atomic masses of each element from the periodic table and multiply the atomic mass of each element by the number of atoms of that element.Ĭ Add together the masses to give the molecular mass.Ī The molecular formula of ethanol may be written in three different ways: CH 3CH 2OH (which illustrates the presence of an ethyl group, CH 3CH 2−, and an −OH group), C 2H 5OH, and C 2H 6O all show that ethanol has two carbon atoms, six hydrogen atoms, and one oxygen atom.ī Taking the atomic masses from the periodic table, we obtain 2 × atomic mass of carbon = 2 atoms ( 12. The average mass of a monatomic ion is the same as the average mass of an atom of the element because the mass of electrons is so small that it is insignificant in most calculations.Ĭalculate the molecular mass of ethanol, whose condensed structural formula is CH 3CH 2OH.

Because a molecule or a polyatomic ion is an assembly of atoms whose identities are given in its molecular or ionic formula, we can calculate the average atomic mass of any molecule or polyatomic ion from its composition by adding together the masses of the constituent atoms. Although the mass number is unitless, it is assigned units called atomic mass units (amu). The mass number is an integer that is approximately equal to the numerical value of the atomic mass.

To calculate the molecular mass of a covalent compound and the formula mass of an ionic compound and to calculate the number of atoms, molecules, or formula units in a sample of a substance.Īs you learned in Chapter 1 'Introduction to Chemistry', the mass number is the sum of the numbers of protons and neutrons present in the nucleus of an atom.

Periodic table mg molar mass'