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Cations

Native gold nuggets

Have you ever gone digging for gold?

When the prospectors during the California Gold Rush (1848-1855) searched for gold nuggets in the earth, they were able to find these nuggets because gold is an unreactive material that exists in its elemental state in many places.  Not everyone was fortunate enough to find large nuggets such as those shown above, but a number of these miners did become very wealthy (of course, a large number of others went back home broke).

Many of the elements we know about do not exist in their native form.  They are so reactive that they are found only in compounds.  These non-elemental forms are known as ions.  Their properties are very different from those of the elements they come from.  The term comes from a Greek word meaning “move” and was first coined by Michael Faraday, who studied the movement of materials in an electrical field.

Cations

Electron configuration of sodium metal and sodium cation

Sodium loses an electron to become a cation.

Some elements lose one or more electrons in forming ions.  These ions are known as “ cations ” because they are positively charged and migrate toward the negative electrode ( cathode ) in an electrical field.  Looking at the periodic table below, we know that the group 1 elements are all characterized by having one s electron in the outer orbit and group 2 elements have two s electrons in the outer orbit.  These electrons are loosely attached to the atom and can easily be removed, leaving more protons in the atom that there are electrons, so the resulting ion has a positive charge. Cations can also be formed from electron loss to many of the transition elements.

The periodic table

Periodic table of elements, notated with group numbers.

The cations are designated by the symbol for the parent element and a plus charge as a superscript after the element symbol - the potassium cation would be indicated as K + .  Note that the charge is placed after the symbol and not before it.  The potassium ion is monovalent , meaning that it has lost one electron and has a +1 charge.  The symbol for the magnesium cation would be Mg 2+ or Mg ++ to indicate that it has lost two electrons and has a +2 charge, so the magnesium cation would be referred to as a divalent cation.

The cations are simply named as the parent element.  The sodium cation is still called “sodium.”  Often, the charge would be attached for clarity, so the sodium cation might be referred to as “sodium one plus.”  

Applications of Cations

Cations play important roles in our daily lives.  Sodium, potassium, and magnesium ions are essential for such processes as blood pressure regulation and muscle contraction. Calcium ion is an important part of bone structure.  Sodium ions can used in water softeners to remove other harmful elements.  We put sodium chloride (table salt) on our food and use it as a preservative.

Summary

  • Cations are formed by the loss of one or two electrons from an element.
  • Groups 1 and 2 elements form cations.
  • Cations are named according to the parent element.
  • Cation charges are indicated with a superscript following the chemical symbol.

Practice

Questions

Use the link below to answer the following questions:

http://dl.clackamas.edu/ch104-07/cations.htm

  1. How many electrons are there in the outer shell of Group IA elements?
  2. What is the charge of Group IA ions?
  3. How many electrons are there in the outer shell of Group IIA elements?
  4. What is the charge of Group IIA ions?

Review

Questions

  1. What is an ion?
  2. What is the cathode?
  3. Write the symbol for the barium cation.
  4. Write the symbol for the cesium cation.
  5. List three ways cations are useful.

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