Affinity is the tendency of a chemical species such as an atom or moleculeto react with another to form a chemical compound. There are also more specific uses of the word, such as electron affinity. The affinity of a drug is its ability to bind to its biological target (receptor, enzyme, transport system, etc.). chemical affinity The force causing certain atoms to combine with others to form molecules.
Electron affinity reflects the ability of an atom to accept an electron. It is the energy change that occurs when an electron is added to a gaseous atom. Atoms with stronger effective nuclear charge have greater electron affinity.
The reaction that occurs when an atom takes an electron may be represented as:. Another way to define electron affinity is as the amount of energy needed to remove an electron from a singly charged negative ion:. Electron affinity is one of the trends that can be predicted using the organization of elements in the periodic table. Nonmetals typically have higher electron affinity values than metals. Chlorine strongly attracts electrons.
Mercury is the element with atoms that most weakly attract an electron. Electron affinity is more difficult to predict in molecules because their electronic structure is more complicated. Keep in mind, electron affinity values only apply to gaseous atoms and molecules because the electron energy levels of liquids and solids are altered by interaction with other atoms and molecules.
Even so, electron affinity has practical applications. It is used to measure chemical hardness, a measure of how charged and readily polarized Lewis acids and bases are. It's also used to predict electronic chemical potential.
The primary use of electron affinity values is to determine whether an atom or molecule will act as an electron acceptor or an electron donor and whether a pair of reactants will participate in charge-transfer reactions.
Sometimes the values are given in terms of magnitudes relative to each other. If the value of electron affinity or E ea is negative, it means energy is required what is affinity in chemistry attach an electron. Negative values are seen for what are steroids good for nitrogen atom and also for most captures of second electrons. It can also be seen for surfaces, such as diamond.
For a negative value, the electron capture is an endothermic process:. The same equation applies if E ea has a positive value. Electron capture for most gas atoms except noble gases releases energy and is exothermic. Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert. Helmenstine holds a Ph.
She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. Updated March 02, Key Takeaways: Electron Affinity Definition and Trend Electron affinity is the amount of energy required to detach one electron from a negatively charged ion of an what is a gastrointestinal endoscopy or molecule.
Electron affinity follows a trend on the periodic table. It increases moving down a column or group and also increases moving from left to right across a row or period except for the noble gases. The value may be either positive or negative. A negative electron affinity means energy must be input in order to attach an electron to the ion. Here, electron capture is an endothermic process. If electron affinity is positive, the process is exothermic and occurs spontaneously.
Cite this Article Format. Helmenstine, Anne Marie, Ph. Electron Affinity Definition in Chemistry. Watch Now: Trends in the Periodic Table. Ionization Energy Definition and Trend. The Periodic Properties of the Elements. Clickable Periodic Table of the Elements. Periodic Table Definition in Chemistry.
Chemical Affinity a term used to describe the capacity of a substance to react with another substance or to describe the degree of resistance of the resulting compound to decompose into the initial components. At various times, attempts were made to evaluate chemical affinity in terms of various reaction parameters. Mar 02, · Electron affinity is the amount of energy required to detach one electron from a negatively charged ion of an atom or molecule. It is indicated using the symbol Ea and is usually expressed in units of kJ/mol. Electron affinity follows a trend on the periodic table. Affinity is the tendency of a chemical species to react with another species to form a chemical compound. Chemical affinity depends on both stereochemistry and electrostatic interactions. Electron affinity is the amount of energy released or spent when an electron in added to a neutral atom.
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View AQA revision. View OCR revision. View Edexcel revision. View CIE revision. View WJEC revision. View Eduqas revision. There are multiple, more specific, uses of the term, such as chemical affinity and electron affinity. Chemical affinity exclusively refers to the tendency of a chemical species to react with another.
For example, we say that fluorine has a very high affinity for hydrogen. This is because the two species combine readily to form HF, as seen in this equation:. Affinity can also be referred to as the tendency of certain atoms or molecules to aggregate or bond together.
For example, a positively charged molecule will have affinity for a negatively charged molecule. The affinity of a chemical species depends on the stereochemistry and the electrostatic interactions. Stereochemistry relates to every aspect of the spatial relationships of atoms within a molecule.
This becomes especially important in biological systems, where molecules may have the same constituent atoms but the shape of the molecule is different — this is called a stereoisomer. Stereoisomers will, therefore, have different affinities for certain molecules. Electrostatic interactions can also be called van der Waals forces — it is defined as the attraction or repulsion interactions between two molecules with electrical charges.
An excellent example of this is found in the DNA double helix. The delta positive and delta negative ends of the polar N-H bond in DNA bases form an electrostatic attraction — this is shown in the diagram below.
Van der Waals forces are a type of non-covalent molecular interaction. This is the type of molecular force which operate in liquid water. So, when these forces are broken perhaps by heat , the water molecules no longer interact and form water vapour. Electron affinity, denoted as E ea , refers to the amount of energy released or spent when an electron is added to a neutral atom. The electron affinity is therefore a measure of the attraction between and incoming electron and the nucleus.
So, the stronger the attraction, the more energy will be released. Non-metal elements tend to have a higher electron affinity than metals in the periodic table. Electron affinities are used to develop and electronegativity scale for atoms.
The first electron affinity is defined as the amount of energy released when 1 mole of gaseous atom each gain an electron. They always have negatives values, as a negative value shows a release of energy, and the values are set. For example, the first electron affinity of bromine is kJ mol The second electron affinity is the energy required to add a single electron to each ion in 1 mole of gaseous 1- ions to create 1 mole of gaseous 2- ions.
This is only normally encountered in oxygen and sulphur both group 6 elements. As you may suspect, this takes a lot of energy to do. In terms of pharmaceuticals, drug affinity is how well a certain drug can bind to its intended receptor. A faster or stronger binding means a higher affinity. In more statistical terms, it is the probability that a drug will bind to an available receptor at any given point in time.
In order for a drug to successfully bind to a receptor, the functional groups on the drug must interact with the receptor site. It is characterised by K a — this is called the equilibrium constant. It is important to note that in pharmacology, affinity is not the same as efficacy. Efficacy is defined as the ability of a drug to produce a maximum response. So, affinity is how likely a drug is to bind to a receptor, but the efficacy is what happens once that drug is bound.
You will also need to remember that both agonists and antagonists have affinity for receptors. What is chemical affinity? What is electron affinity? This is in a gaseous state and forms a negative ion. What is drug affinity?
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