Are you confused by all the numbers on a periodic table? Here's a look at what they mean and where to find important elements. Show One number you will find on all periodic tables is the atomic number for each element. This is the number of protons in the element, which defines its identity. How to Identify It: There isn't a standard layout for an element cell, so you need to identify the location of each important number for the specific table. The atomic number is easy because it is an integer that increases as you move from left to right across the table. The lowest atomic number is 1 (hydrogen), while the highest atomic number is 118. Examples: The atomic number of the first element, hydrogen, is 1. The atomic number of copper is 29. Most periodic tables include a value for atomic mass (also called atomic weight) on each element tile. For a single atom of an element, this would be a whole number, adding the number of protons, neutrons, and electrons together for the atom. However, the value given in the periodic table is an average of the mass of all isotopes of a given element. While the number of electrons does not contribute significant mass to an atom, isotopes have differing numbers of neutrons, which do affect mass. How to Identify It: The atomic mass is a decimal number. The number of significant figures varies from one table to another. It's common to list values to two or four decimal places. Also, the atomic mass is recalculated from time to time, so this value may change slightly for elements on a recent table compared with an older version. Examples: The atomic mass of hydrogen is 1.01 or 1.0079. The atomic mass of nickel is 58.69 or 58.6934. Many periodic tables list numbers for element groups, which are columns of the periodic table. The elements in a group share the same number of valence electrons and thus have many common chemical and physical properties. However, there wasn't always a standard method of numbering groups, so this can be confusing when consulting older tables. How to Identify It: The number for the element group is cited above the top element of each column. The element group values are integers running from 1 to 18. Examples: Hydrogen belongs to element group 1. Beryllium is the first element in group 2. Helium is the first element in group 18. The rows of the periodic table are called periods. Most periodic tables do not number them because they are fairly obvious, but some tables do. The period indicates the highest energy level attained by electrons of an atom of the element in the ground state. How to Identify It: Period numbers are located on the left-hand side of the table. These are simple integer numbers. Examples: The row starting with hydrogen is 1. The row starting with lithium is 2. Some periodic tables list the electron configuration of an atom of the element, usually written in shorthand notation to conserve space. Most tables omit this value because it takes up a lot of room. How to Identify It: This isn't a simple number but includes the orbitals. Examples: The electron configuration for hydrogen is 1s1. The periodic table includes other information besides numbers. Now that you know what the numbers mean, you can learn how to predict periodicity of element properties and how to use the periodic table in calculations.
In order to continue enjoying our site, we ask that you confirm your identity as a human. Thank you very much for your cooperation.
SfC Home > Physical Science > Chemistry > by Ron Kurtus (revised 10 November 2004) A molecule or compound consists of at least two atoms that are chemically bonded. The chemical formula of a molecule or compound states how many atoms of each element are in one of its molecules. This formula is similar to an algebraic formula in its use of symbols. The description of a compound with numbers and symbols is called a chemical formula. Some formulae can be quite complex. Questions you may have include:
This lesson will answer those questions. A molecule is the chemical combination of two or more atoms. They can be of the same element, such as in the oxygen molecule (O2) or different as in the water molecule (H2O). A compound is a molecule that is made up of at least two different elements. The water molecule is a compound. When atoms of different elements combine to form a compound, the result is a new substance that has different properties than the original elements. A good example is when the poisonous green chlorine gas is combined with the explosive metal sodium to form the white salt crystals we use in our food. The study of Chemistry is mainly interested in the formation of chemical compounds, since there are so many possible combinations of elements. Chemical formulasChemical formulas (or more correctly: formulae) are designations of molecules and compounds in shorthand notation, similar to that used in Algebra. Shorthand for elementsElements can be written as abbreviations or in a shorthand notation. For example, He denotes helium, Fe denotes iron, and Cl denotes chlorine. A chemical formula is writing the elements of a compound, using their abbreviations. Designation of a moleculeThe combination of two or more elements to form a molecule is designated by writing their abbreviations next to each other. For example carbon monoxide is written as CO. The order in which the elements are written is typically alphabetical, but there are a number of exceptions for historical reasons and to clarify the geometry of the molecule. Number of atoms in a moleculeIf there is more than one atom of a type in the molecule, the formula shows it by a small number after the symbol. For example, water is H2O, which means there are 2 atoms of hydrogen and one atom of oxygen in the molecule. Carbon dioxide is CO2, which means there is one atom of carbon and two atoms of oxygen in the molecule. Number of moleculesTo show the number of molecules, a full sized number is located in front of the molecule. For example 4 molecules of carbon dioxide is designated as:
This means there are a total of 4 C atoms and 8 O atoms in the combination. A way to remember this--taken from Algebra--is to think of it as 4 x (CO2). Complex formulasJust as in Algebra, you can use parentheses to separate parts in a complex formula. One example is the formula for nitroglycerin, a highly explosive substance.
This formula shows that nitroglycerin consists of 3 atoms of C, 5 atoms of H and then 3 NO3 nitrate ions. If the parentheses were not used, you might have a formula like:
The number of atoms for each element would be correct, but it wouldn't help to describe the true structure of the nitroglycerin molecule. Remember that molecules are 3-dimensional collections of atoms. In more complex molecules—especially in organic substances—the configuration becomes important. SummaryThe number of atoms of each element in a chemical formula is designated by the small number behind each element symbol. If there is no number, it is assumed there is only one of that element. A large number in front of a compound designates how many units there are of that compound. Parentheses can be used to designate a special structure, where other molecules are attached to the larger, complex molecule. Look for the formula for success Resources and referencesRon Kurtus' Credentials WebsitesChemical Formulas - From the University of Waterloo, Canada Chemistry Resources Books(Notice: The School for Champions may earn commissions from book purchases) Top-rated books on Chemistry Questions and commentsDo you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible. Share this pageClick on a button to bookmark or share this page through Twitter, Facebook, email, or other services: Students and researchersThe Web address of this page is: Please include it as a link on your website or as a reference in your report, document, or thesis. Copyright © Restrictions Where are you now?School for Champions
|
What does the big number in front of an element mean?
Postagens relacionadas
direito autoral © 2024 mesadeestudo Inc.
