Ion

An ion (/ˈaɪən, -ɒn/) is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by either chemical or physical means, via ionization.

In chemical terms, if a neutral atom loses one or more electrons, it has a net positive charge and is known as a cation.

If an atom gains electrons, it has a net negative charge and is known as an anion.

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 or polyatomic ion. Because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts.

In the case of physical ionization of a medium, such as a gas, what are known as "ion pairs" are created by ion impact, and each pair consists of a free electron and a positive ion.

History of discovery

The word ion is the Greek ἰόν, ion, "going", the present participle of ἰέναι, ienai, "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. Faraday did not know the nature of these species, but he knew that since metals dissolved into and entered a solution at one electrode, and new metal came forth from a 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.

JPEG

JPEG (/ˈdʒeɪpɛɡ/ JAY-peg) is a commonly used method of lossy compression for digital images, particularly for those images produced by digital photography. The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality.

JPEG compression is used in a number of image file formats. JPEG/Exif is the most common image format used by digital cameras and other photographic image capture devices; along with JPEG/JFIF, it is the most common format for storing and transmitting photographic images on the World Wide Web. These format variations are often not distinguished, and are simply called JPEG.

The term "JPEG" is an abbreviation for the Joint Photographic Experts Group, which created the standard. The MIME media type for JPEG is image/jpeg, except in older Internet Explorer versions, which provides a MIME type of image/pjpeg when uploading JPEG images. JPEG files usually have a filename extension of .jpg or .jpeg.

Ion (dialogue)

In Plato's Ion (/ˈaɪɒn/; Greek: Ἴων) Socrates discusses with Ion, a professional rhapsode who also lectures on Homer, the question of whether the rhapsode, a performer of poetry, gives his performance on account of his skill and knowledge or by virtue of divine possession. It is one of the shortest of Plato's dialogues.

Dialogue summary

Ion's skill: Is it genuine? (530a–533c)

Ion has just come from a festival of Asclepius at the city of Epidaurus, after having won first prize in the competition. Socrates engages Ion in a philosophical discussion. Ion admits when Socrates asks, that his skill in performance recitation is limited to Homer, and that all other poets bore him. Socrates finds this puzzling, and sets out to solve the "riddle" of Ion's limited expertise. He points out to Ion that art critics and judges of sculpture normally do not limit themselves to judging the work of only a single artist, but can criticize the art no matter who the particular artist.

The nature of poetic inspiration (533d–536d)