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Salts

Chemical elements are usually present in nature in the combined state. The combined state of elements is referred to as "compounds". Compounds are formed when two or more elements combine together to form a bond between them.

At room temperature salts are solids crystalline substances that contain the cation of a base and the anion of an acid. Hydrated salts contain specific numbers of water molecules as a part of their crystalline structure. Salts can be prepared by reacting an appropriate acid with one of a number of other materials. There are different types of compounds depending upon the nature of the bond formed. Two main types of compounds are covalent compounds and ionic compounds.

 

What is a Salt?

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A salt is an ionic compound formed by the neutralization reaction between an acid and a base. Common salt is sodium chloride, formed by the neutralization of sodium hydroxide, a base and hydrochloric acid, an acid.

NaOH + HCl NaCl + H2O
A salt can be any ionic compound, like KCl, MgBr2, etc.

Some other examples are

Example: 1

KOH + HBr KBr + H2O

Potassium bromide is formed from Potassium hydroxide and hydrogen bromide. KOH is an alkali or a base and HBr is an acid. The above reaction is also a neutralization reaction.
Example: 2

Ca(OH)2 + H2SO4 CaSO4 + 2H2O

In this case, calcium sulfate is formed from calcium hydroxide, a base and sulfuric acid, an acid. The neutralization reaction yields calcium sulfate, a salt.

Inorganic Salts

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Inorganic chemistry deals with the study of elements, and their physical and chemical properties. Salts are ionic compounds, made from the elements present in the periodic table. Metals and non metals combine to form salts. Metals form positive ions and non metals form negative ions. The combination of positive and negative ions makes up an ionic compound or rather, an inorganic salt.

Formation of positive and negative ions

  1. The majority of the elements in the periodic table are metals. There are very few non-metals, in the range of 20. Metals like the s- block metals, have their outermost electron, mostly 1 or 2, are held loosely.
  2. This is the result of the outermost s electron being extremely well shielded from the nuclear charge.
  3. The electron is only weakly held to the atom, so it is easily lost, to make positive ions. Example: Li+ , Ca2+, etc.
  4. The halogens, on the other hand, the group VII elements do not have the outer most electrons shielded properly. Thus, they take an extra electron very easily. Example: F-, Cl-, etc.
Similarly, the VI group, also can accept two electrons. Example: O2-, S2-, etc. Group VI elements also have less shielding effect on their outermost electron. This makes them to easily accept two electrons from metals, thereby forming negative ions.

Ionic Salts

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Salts that are formed from ions are ionic salts. Ions are elements, with one or more electron lesser than the original atom or more the original atom itself.

Example: Na+ + Cl- NaCl

Note that the sodium chloride salt is formed from positive sodium ion and the negative chloride ions. When an element accepts electron, it acquires a negative charge, while the element which donates an electron acquires a positive charge. The positive and negative charge on the top of the elements makes them "ions"

Evidence for the formation of ions

  • Ions are formed when an atom is ionized in a gaseous state. The energy required to ionize an element is called its ionization energy.
  • When substances like sodium chloride, are dissolved in water, then the solution starts conducting electricity.
  • The conduction of electricity is best explained by the presence of ions in the sodium chloride solution.
  • When the ions break free from the crystal, they conduct current through the solution, the ions become free to move.

Elements forming ionic compounds


To form an ionic bond, an element has to lose electron or gain electron. The metals of group I and group II of the periodic table have the greatest tendency to lose electrons and turn into positive ions. The non- metals of group VI and VII have the greatest affinity for electrons and readily change into negative ions. The relative ease with which these elements make ions shows that they can form ionic compounds or ionic salts.
  1. To find two elements that are bound to make an ionic compound, the metal towards the bottom of Group I and the top of group VII can be chosen.
  2. For example, Rubidium fluoride, Rb+F- and potassium chloride, K+Cl- are both distinctly ionic. There are many such examples of combination salts resulting from groups II and Group VI, like Mg2+O2-.
  3. These ionic salts, are formed due to the attraction between the oppositely charged ions that keep an ionic crystals.
  4. There is a large number of repulsions between the ions having the same charge, but these are outweighed by the attractions of oppositely charged ions.
  5. And, when these ions combine, there is always a decrease in energy and the salt crystal formed also has lesser energy than the separate elements.
  6. The difference in the energy is given out as heat, forming an exothermic reaction.

Mineral Salts

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The salts or compounds are inorganic salts that are essential for the normal functioning of a human body. Salts like sodium chloride, potassium and magnesium ions, etc are essential for the normal functioning of human body.

The term mineral here denotes compounds that are not organic. Organic compounds are so called because they were found first in living organisms. It was soon observed that acids react with bases and form less corrosive substances, called mineral salts.

Some of the essential mineral salts/ions present in human body are,

Extracellular Organelles Cytoplasm
Na+, Ca2+, Cu2+, etc K+, Mg2+, Fe2+, Co2+, Ni2+, Zn2+, etc. K+, Mg2+

List of Salts

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There are varieties of salts based on the groups the ions are coming from. The ions can occur in various combinations, and thus result in many kinds of salts. Though they are all ionic in nature, some salts are commonly found in nature.  

Some examples of such salts and the groups the ions belong to are

Group I Group VII
Salt
Na+ Br-
NaBr
Li+ I-
LiI
K+ Cl-
KCl
Rb+ F-
RbF
Cs+ F-
CsF

Group II
Group VI
Salt
Be2+ O2- BeO
Mg2+ O2- MgO
Ca2+ S2- CaS
Sr2+ S2- SrS
Ba2+ O2- BaO

Group I
Group VI
Salt
Na+ O2- Na2O
K+ S2- K2S
Cs+ O2- Cs2O
Rb+ S2- Rb2S

Group II Group VII
Salt
Be2+ Cl- BeCl2
Mg2+ Cl- MgCl2
Ba2+ F- BaF2
Ca2+ I- CaI2

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