Cooling of a trapped ion to the quantum regime

Neutral atoms and charged ions can be cooled down to extremely low temperatures (i.e., to microkelvins, 1 millionth of a degree above absolute zero) using laser techniques. At these low temperatures, the particles have often ...

Near ground-state cooling of 2-D trapped ion crystals

Researchers have been trying to cool macroscopic mechanical oscillators down to their ground state for several decades. Nonetheless, past studies have merely attained the cooling of a few selected vibrational modes of such ...

What causes ionic wind?

The phenomenon of ionic wind has been known about for centuries: by applying a voltage to a pair of electrodes, electrons are stripped off nearby air molecules, and the ionized air collides with neutral air molecules as it ...

Plant cellulose prevents short circuits in batteries

(Phys.org)—In order to prevent short circuits in batteries, porous separator membranes are often placed between a battery's electrodes. There is typically a tradeoff involved, since these separators must simultaneously ...

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Ion

An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.

Since protons are positively charged and electrons are negatively charged, if there are more electrons than protons, the atom or molecule will be negatively charged. This is called an anion (pronounced /ˈænaɪən/; an-eye-on), from the Greek ἀνά (ana), meaning 'up'.

Conversely, if there are more protons than electrons, the atom or molecule will be positively charged. This is called a cation (pronounced /ˈkætaɪən/; cat-eye-on), from the Greek κατά (kata), meaning 'down'.

An ion consisting of a single atom is called a monatomic ion. If it consists of two or more atoms, it is called a polyatomic ion. Polyatomic ions containing oxygen, such as carbonate and sulfate, are called oxyanions.

When writing the chemical formula for an ion, its charge is written as a superscript '+' or '−' following a number indicating the difference between the number of protons and the number of electrons. The number is omitted if it is equal to 1. For example, the sodium cation is written as Na+, the '+' indicating that it has one less electron than it has protons. The sulfate anion is written as SO42−, the '2−' indicating that it has two more electrons than it has protons.

If an ion contains unpaired electrons, it is called a radical ion. Just like neutral radicals, radical ions are very reactive.

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