Langsung ke konten utama

~ION~


An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protonsgiving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass ("go") between electrodes in a solution, when an electric field is applied. It is from Greek ιον, meaning "going".
An ion consisting of a single atom is an atomic or monatomic ion; if it consists of two or more atoms, it is a molecular orpolyatomic ion.

Contents

  [hide

[edit]Anions and cations

An anion (−) (pronounced /ˈæn.aɪ.ən/ an-eye-ən), from the Greek word ἄνω (ánō), meaning "up", is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).
Conversely, a cation (+) (pronounced /ˈkæt.aɪ.ən/ kat-eye-ən), from the Greek word κατά (katá), meaning "down", is an ion with fewer electrons than protons, giving it a positive charge. Since the charge on a proton is equal in magnitude to the charge on an electron, the net charge on an ion is equal to the number of protons in the ion minus the number of electrons.

[edit]General

[edit]History and discovery

Etymologically the word ion is the Greek ιον (going), the present participle of ιεναιienai, "to go". This term was introduced by English physicist and chemist Michael Faraday in 1834 for the (then unknown) species that goes from one electrode to the other through an aqueous medium.[1][2] Faraday did not know the nature of these species, but he knew that since metals dissolved into and entered solution at one electrode, and new metal came forth from solution at the other electrode, that some kind of substance moved through the solution in a current, conveying matter from one place to the other.
Faraday also introduced the words anion for a negatively charged ion, and cation for a positively charged one. In Faraday's nomenclature, cations were named because they were attracted to thecathode in a galvanic device and anions were named due to their attraction to the anode.

[edit]Characteristics

Ions in their gas-like state are highly reactive, and do not occur in large amounts on Earth, except in flames, lightning, electrical sparks, and other plasmas. These gas-like ions rapidly interact with ions of opposite charge to give neutral molecules or ionic salts. Ions are also produced in the liquid or solid state when salts interact with solvents (for example, water) to produce "solvated ions," which are more stable, for reasons involving a combination of energy and entropy changes as the ions move away from each other to interact with the liquid. These stabilized species are more commonly found in the environment at low temperatures. A common example is the ions present in seawater, which are derived from the dissolved salts there.
All ions are charged, which means that like all charged objects they are:
  • attracted to opposite electric charges (positive to negative, and vice versa),
  • repelled by like charges, and
  • when moving, travel in trajectories that are deflected by a magnetic field.
Electrons, due to their smaller mass and thus larger space-filling properties as matter waves, determine the size of atoms and molecules that possess any electrons at all. Thus, anions (negatively charged ions) are larger than the parent molecule or atom, as the excess electron(s) repel each other, and add to the physical size of the ion, because its size is determined by its electron cloud. Conversely, cations are generally smaller than the corresponding parent atom or molecule, for the same reason. One particular cation (that of hydrogen) contains no electrons, and thus is very much smaller than the parent hydrogen atom.

[edit]Natural occurrences

Ions are ubiquitous in nature and are responsible for diverse phenomena from the luminescence of the Sun, and the existence of ionosphere on Earth. Atoms in their ionic state may have a different color from neutral atoms, and thus light absorption by metal ions gives the color of gemstones. In both inorganic and organic chemistry (including biochemistry), the interaction of water and ions is extremely important an example is the energy that drives breakdown of ATP. The following sections describe contexts in which ions feature prominently and are arranged in decreasing physical length-scale, from the astronomical to the microscopic.

[edit]Astronomical

The remnant of "Tycho's Supernova", a huge ball of expanding plasma. The outer shell shown in blue is X-ray emission by high-speed electrons.
A collection of non-aqueous gas-like ions, or even a gas containing a proportion of charged particles, is called a plasma. >99.9% of visible matter in the Universe may be in the form of plasmas.[3] These include our Sun and other stars, the space between planets, as well as the space in between stars. Plasmas are often called the fourth state of matter because its properties are substantially different from solidsliquids, and gasesAstrophysical plasmas predominantly contain a mixture of electrons and protons (ionized hydrogen).

[edit]Related technology

Ions can be non-chemically prepared using various ion sources, usually involving high voltage or temperature. These are used in a multitude of devices such asmass spectrometersoptical emission spectrometersparticle acceleratorsion implanters and ion engines.
As reactive charged particles, they are also used in air purification by disrupting microbes, and in household items such as smoke detectors.
As signaling and metabolism in organisms are controlled by a precise ionic gradient across membranes, the disruption of this gradient contributes to cell death. This is a common mechanism exploited by natural and artificial biocides, including the ion channels gramicidin and amphotericin (a fungicide).
Inorganic dissolved ions are a component of total dissolved solids, an indicator of water quality in the world.

[edit]Chemistry

[edit]Notation

[edit]Denoting the charged state

Equivalent notations for an iron atom (Fe) that lost two electrons.
When writing the chemical formula for an ion, its net charge is written in superscript immediately after the chemical structure for the molecule/atom. The net charge is written with the magnitude before the sign; that is, a doubly charged cation is indicated as 2+ instead of +2. Conventionally the magnitude of the charge is omitted for singly charged molecules/atoms; for example, the sodium cation is indicated as Na+ and not Na1+.
An alternative (and acceptable) way of showing a molecule/atom with multiple charges is by drawing out the signs multiple times; this is often seen with transition metals. Chemists sometimes circle the sign; this is merely ornamental and does not alter the chemical meaning. All three representations of Fe2+shown in the figure are thus equivalent.
Mixed Roman numerals and charge notations for the uranyl ion. The oxidation state of the metal is shown as superscripted Roman numerals, whereas the charge of the entire complex is shown by the angle symbol together with the magnitude and sign of the net charge.
Monatomic ions are sometimes also denoted with Roman numerals; for example, the Fe2+ example seen above is occasionally referred to as Fe(II) or FeII. The Roman numeral designates the formal oxidation state of an element, whereas the superscripted numerals denotes the net charge. The two notations are therefore exchangeable for monatomic ions, but the Roman numerals cannot be applied to polyatomic ions. It is however possible to mix the notations for the individual metal center with a polyatomic complex, as shown by the uranyl ion example.

[edit]Sub-classes

If an ion contains unpaired electrons, it is called a radical ion. Just like uncharged radicals, radical ions are very reactive. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions. Molecular ions that contain at least one carbon to hydrogen bond are called organic ions. If the charge in an organic ion is formally centered on a carbon, it is termed a carbocation (if positively charged) or carbanion (if negatively charged).

[edit]Formation

[edit]Formation of monatomic ions

Monatomic ions are formed by the addition of electrons to the valence shell of the atom, which is the outer-most electron shell in an atom, or the losing of electrons from this shell. The inner shells of an atom are filled with electrons that are tightly bound to the positively charged atomic nucleus, and so do not participate in this kind of chemical interaction. The process of gaining or losing electrons from a neutral atom or molecule is called ionization.
Atoms can be ionized by bombardment with radiation, but the more usual process of ionization encountered in chemistry is the transfer of electrons between atoms or molecules. This transfer is usually driven by the attaining of stable ("closed shell") electronic configurations. Atoms will gain or lose electrons depending on which action takes the least energy.
For example, a sodium atom, Na, has a single electron in its valence shell, surrounding 2 stable, filled inner shells of 2 and 8 electrons. Since these filled shells are very stable, a sodium atom tends to lose its extra electron and attain this stable configuration, becoming a sodium cation in the process
Na → Na+ + e
On the other hand, a chlorine atom, Cl, has 7 electrons in its valence shell, which is one short of the stable, filled shell with 8 electrons. Thus, a chlorine atom tends to gain an extra electron and attain a stable 8-electron configuration, becoming a chloride anion in the process:
Cl + e → Cl
This driving force is what causes sodium and chlorine to undergo a chemical reaction, where the "extra" electron is transferred from sodium to chlorine, forming sodium cations and chloride anions. Being oppositely charged, these cations and anions form ionic bonds and combine together to form sodium chloride, NaCl, more commonly known as rock salt.
Na+ + Cl → NaCl

[edit]Formation of polyatomic and molecular ions

An electrostatic potential map of thenitrate ion (NO
3
). The 3-dimensional shell represents a single arbitraryisopotential.
Polyatomic and molecular ions are often formed by the gaining or losing of elemental ions such as H+ in neutral molecules. For example, when ammoniaNH3, accepts a proton, H+, it forms the ammonium ionNH+
4
. Ammonia and ammonium have the same number of electrons in essentially the same electronic configuration, but ammonium has an extra proton that gives it a net positive charge.
Ammonia can also lose an electron to gain a positive charge, forming the ion ·NH+
3
. However, this ion is unstable, because it has an incomplete valence shellaround the nitrogen atom, making it a very reactive radical ion.
Due to the instability of radical ions, polyatomic and molecular ions are usually formed by gaining or losing elemental ions such as H+, rather than gaining or losing electrons. This allows the molecule to preserve its stable electronic configuration while acquiring an electrical charge.

[edit]Ionization potential

The energy required to detach an electron in its lowest energy state from an atom or molecule of a gas with less net electric charge is called the ionization potential, or ionization energy. The nth ionization energy of an atom is the energy required to detach its nth electron after the first n − 1 electrons have already been detached.
Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron in its outermost shell, so in ionized form it is commonly found with one lost electron, as Na+. On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as Cl. Caesium has the lowest measured ionization energy of all the elements and helium has the greatest.[4] The ionization energy of metals is generally much lower than the ionization energy of nonmetals, which is why metals will generally lose electrons to form positively charged ions while nonmetals will generally gain electrons to form negatively charged ions.

[edit]Ionic bonding

Ionic bonding is a kind of chemical bonding that arises from the mutual attraction of oppositely charged ions. Since ions of like charge repel each other, they do not usually exist on their own. Instead, many of them may form a crystal lattice, in which ions of opposite charge are bound to each other. The resulting compound is called an ionic compound, and is said to be held together by ionic bonding. In ionic compounds there arise characteristic distances between ion neighbors from which the spatial extension and the ionic radius of individual ions may be derived.
The most common type of ionic bonding is seen in compounds of metals and nonmetals (except noble gases, which rarely form chemical compounds). Metals are characterized by having a small number of electrons in excess of a stable, closed-shell electronic configuration. As such, they have the tendency to lose these extra electrons in order to attain a stable configuration. This property is known as electropositivity. Non-metals, on the other hand, are characterized by having an electron configuration just a few electrons short of a stable configuration. As such, they have the tendency to gain more electrons in order to achieve a stable configuration. This tendency is known as electronegativity. When a highly electropositive metal is combined with a highly electronegative nonmetal, the extra electrons from the metal atoms are transferred to the electron-deficient nonmetal atoms. This reaction produces metal cations and nonmetal anions, which are attracted to each other to form asalt.

[edit]Chemical applications

Gas-like ions and solvated ions both have tremendous impact on chemical analysis and synthesis.

[edit]Mass spectrometry

[edit]Catalysis

[edit]Transition metal ions catalysis
[edit]Templated synthesis of organic compounds

[edit]Common ions

Common Cations
Common NameFormulaHistoric Name
Simple Cations
AluminiumAl3+
CalciumCa2+
Copper(II)Cu2+cupric
HydrogenH+
Iron(II)Fe2+ferrous
Iron(III)Fe3+ferric
MagnesiumMg2+
Mercury(II)Hg2+mercuric
PotassiumK+kalic
SilverAg+
SodiumNa+natric
Polyatomic Cations
AmmoniumNH+
4
OxoniumH3O+hydronium
Mercury(I)Hg2+
2
mercurous
Common Anions
Formal NameFormulaAlt. Name
Simple Anions
ChlorideCl
FluorideF
BromideBr
OxideO2−
Oxoanions
CarbonateCO2−
3
Hydrogen carbonateHCO
3
bicarbonate
HydroxideOH
NitrateNO
3
PhosphatePO3−
4
SulfateSO2−
4
Anions from Organic Acids
AcetateCH3COOethanoate
FormateHCOOmethanoate
OxalateC2O2−
4
ethandioate
CyanideCN

[edit]See also

Komentar

Postingan populer dari blog ini

Laporan Percobaan Perubahan Entalpi Reaksi

BAB I PENDAHULUAN 1.1   Latar Belakang Kita mengetahui bahwa dalam kegiatan pembelajaran Kimia, tentunya juga kita berkecimpung dalam dunia Termokimia (Thermochemistry). Dimana termokimia ini selalu berhubungan dengan energi . Energi merupakan sesuatu yang penting dalam kehidupan kita. Banyak kejadian di sekitar kita, bahkan di dalam tubuh kita yang melibatkan energi, baik melepas maupun memerlukan. Proses fotosintesis, metabolisme, gerak, pembakaran, dan memasak adalah contoh kejadian yang melibatkan energi. Memasak membutuhkan energi berupa panas. Sebagai contoh nyata, masakan tidak akan masak dengan sendirinya tanpa ditambahkan panas dari luar. Termokimia ini sendiri terjadi pada reaksi kimia (Chemical Reaction). Reaksi kimia ini melibatkan melibatkan kalor reaksi (q) dengan mematuhi Hukum Kekekalan Energi (Law of Conservation of Energy). Kalor reaksi ini sama dengan perubahan entalpi reaksi (Enthalpy Change of Reaction) atau yang biasa disingkat dengan ∆H. Perubahan enta

Laporan Penurunan Titik Beku

BAB I PENDAHULUAN 1.1   Latar Belakang      Perubahan fase zat cair ke padat disebut membeku. Hal ini banyak terjadi dilingkungan sekitar kita, terutama di negara yang memiliki musim dingin. Setiap zat mengalami pembekuan dengan waktu yang berbeda-beda, sebab titik beku yang dimiliki oleh masing-masing zat berbeda. Semakin tinggi titik bekunya maka zat tersebut akan cepat mengalami pembekuan.      Negara yang bermusim dingin mengalami proses pembekuan yang berlangsung cepat sekali, mulai dari air yang berada di alam bebs maupun air dalam radiator kendaraan bermotor, karena hal itu sangat merugikan maka untuk menanggulangi hal tersebut dilakukan penurunan titik beku. Penurunan titik dengan cara menambahkan suatu zat anti beku kedalam radiator. Penurunan titik beku terjadi karena terjadi kenaikan tekanan cairan dalam radiator, sehingga cairan membeku dalam suhu yang lebih rendah dari pelarutnya. Penurunan titik beku larutan encer sebanding dengan konsentrasi massanya. Titik

~Laporan Titrasi Asam-Basa~

BAB I PENDAHULUAN 1.1   Latar Belakang Berbicara masalah reaksi asam-basa atau yang biasa juga disebut reaksi penetralan, maka tidak akan terlepas dari titrasi asam-basa. Perlu dipahami terlebih dahulu bahwa reaksi asam-basa atau reaksi penetralan dapat dilakukan dengan titrasi asam-basa. Adapun titrasi asam-basa ini terdiri dari titrasi asam kuat-basa kuat, titrasi asam kuat-basa lemah, titrasi basa lemah-asam kuat, dan titrasi asam lemah-basa lemah. Titrasi asam-basa ini ditentukan oleh titik ekuivalen (equivalent point) dengan menggunakan indikator asam-basa. Setelah mengetahui hal tersebut, perlu juga kita ketahui bahwa titrasi merupakan suatu metode untuk menentukan kadar suatu zat dengan menggunakan zat lain yang sudah dikethaui konsentrasinya. Titrasi biasanya dibedakan berdasarkan jenis reaksi yang terlibat di dalam proses titrasi, sebagai contoh bila melibatan reaksi asam basa maka disebut sebagai titrasi asam basa, titrasi redox untuk titrasi yang melibatkan reaksi