Overview
Test Series
Every atom is electrically neutral because its number of protons, which carry a positive charge, is equal to the number of electrons, which carry a negative charge. This balance ensures that the overall charge of the atom is zero.
However, most atoms can either gain or lose electrons, leading to a situation where the number of electrons differs from the number of protons. The charged particle that results from this imbalance is known as an ion.
Ionic compounds are created when ions with opposite charges form ionic bonds and create compounds. These compounds are made up of ions. The electron loss or gain of one atom is compensated by the electron loss or gain of another atom. This effectively means that one atom 'donates' an electron to the other atom it pairs up with.
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Here are some examples:
Cation | Anion | Formula |
---|---|---|
Na+ | Cl- | NaCl |
Ca2+ | Br- | CaBr2 |
Na+ | S2- | Na2S |
Mg2+ | O2- | MgO |
Na+ | SO42- | Na2SO4 |
Cr3+ | O-2 | Cr2O3 |
NH4+ | SO42- | (NH4)2SO4 |
For instance, Na+ is referred to as a sodium ion, Al3+ is an aluminium ion, Ca2+ is a calcium ion, and so on.
There are two ways to distinguish between these:
1. The charge of a positive ion is indicated by a Roman numeral in parentheses after the name of the element, followed by the word 'ion'. So, Fe2+ is referred to as the iron(II) ion, while Fe3+ is referred to as the iron(III) ion. This system is only used for elements that can form more than one common positive ion.
2. The second method uses two suffixes, -ic and -ous, attached to the stem of the name of the element. The -ic suffix is used for the higher of the two cation charges, and the -ous suffix is used for the lower. In many cases, the stem of the name of the element is derived from the Latin name for the element.
Element | Stem | Charge | Name |
---|---|---|---|
Iron | ferr- | 2+ | Iron (II) ion or ferrous ion |
3+ | Iron (III) ion or ferric ion | ||
Copper | cupr- | 1+ | Copper (I) ion or cuprous ion |
2+ | Copper (II) ion or cupric ion |
For example, F- is a fluoride ion, Cl- is a chloride ion, N3- is a nitride ion, etc.
A binary compound is a compound composed of two different elements. Each element may have more than one atom. A diatomic compound (or diatomic molecule) consists of two atoms, which may or may not be the same.
Ionic compounds are formed when metals combine with nonmetals. When naming binary ionic compounds, begin with the cation (and specify the charge if necessary), then name the nonmetal anion (using the stem of the element's name + -ide).
Do not use prefixes to indicate the number of each element present; this information is implied in the name of the compound.
For example:
Formula | Name |
---|---|
CaCl2 | Calcium chloride |
NaCl | Sodium chloride |
AlF3 | Aluminium fluoride |
KCl | Potassium chloride |
Ca3P2 | Calcium phosphide |
Ionic compounds are formed when metals combine with polyatomic ions.
The naming method for polyatomic ionic compounds is the same as for binary ionic compounds. The anion is named first, followed by the cation.
Do not use prefixes to indicate the number of each element present; this information is implied in the name of the compound.
For example:
Formula | Name |
---|---|
Ca(NO3)2 | Calcium nitrate |
(NH4)2SO4 | Ammonium sulfate |
NH4F | Ammonium fluoride |
CaCO3 | Calcium carbonate |
Fe(OH)3 | Iron (III) hydroxide or ferric hydroxide |
Cr3(PO4)2 | Chromium (II) phosphate |
CrPO4 | Chromium (III) phosphate |
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