Ionic+Bonding

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 Ionic bonding usually occurs between two atoms that have a very big difference in their electronegativity values. Usually when the difference in electronegativity of two atoms is greater than 1.8, they form ionic bonding. //(you can get the electronegativity values of elements on page 8 of the data booklet) //

Most of the times ionic bonding occurs between a **metal** and a **non-metal**. This is because, metals usually have a low electronegativity while non-metal have a high electronegativity. Thus the difference in electronegativity is so high that ionic bonding occurs.

=How is IONIC bonding formed? = When and ionic bond is made, electrons are transferred from the less electronegative atom to the more electronegative atom. //For example: // Sodium (Na) reacts with Chlorine (Cl) to form an ionic compound called sodium chloride (NaCl).


 * Sodium is a metal so it has a low electronegativity. It will lose one electron (to chlorine) and therefore form a cation.




 * Chlorine is a non-metal so it has a high electronegativity. It will gain one electron from sodium and therefore form an anion.



//So, now we have a sodium ion and a chlorine ion: //

We know that opposite charge attract each other. Therefore the sodium cation would strongly attract the chlorine anion.



Therefore, in ionic bonding, it is the //strong electrostatic forces of attraction// between the //cations// and //anions// (sodium and chlorine in the above example), which hold the substance together.

=Ions formed by elements in groups 1-3 =

//All the elements in groups 1-3 of the periodic table form ionic compounds by losing their valence shell electrons to form a cation. //


 * That means that elements in group 1 lose one electron to form a cation with a charge of +1

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> Eg. Na ---> Na + + e -


 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">All elements in group 2 lose two electrons to form a cation with a charge of +2. Eg Ca 2+
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">All elements in group 3 lose 3 electrons to form a cation with a charge of +3. Eg Al 3+

=<span style="color: #4b07d5; font-family: Tahoma,sans-serif; font-size: 14pt;">Ions formed by elements in groups 5-7 =

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">All the elements in groups 5-7 are non-metals and hence form ionic compounds by gaining electron in order to complete their valence shells. //


 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Elements in group 5 have space for 3 electrons in their valence shell, so they gain 3 electrons to from an anion with a -3 charge. Eg. P 3-
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Elements in group 6 have space for 2 electrons in their valence shell, so they gain 2 electrons to form an anion with a -2 charge. Eg. O 2-
 * <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Elements in group 7 have space for 1 electron in their valence shell, so they gain 1 electron to forma an anion with a -1 charge. Eg. Cl -

//<span style="font-family: Tahoma,sans-serif;">Transition elements can also form ionic compounds. However, transition elements can form different ions with different charges. For example iron can form two different ions, of Fe 3+ and Fe 2+ //

//<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">(All of these information on the charges of the different ions are summarized in a table at the end of this page.) //

=<span style="color: #4b07d5; font-family: Tahoma,sans-serif; font-size: 14pt;">How does and ionic compound look like? =

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">As earlier stated, an ionic bond is formed by the electrostatic forces of attraction between anions and cations. Therefore, these anions and cations together form a 3-dimensional structure called a lattice. This is because the structure has regular row and columns of cations and anions.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">The figure below shows a front view of a sodium chloride lattice. You can see that each chlorine atom is surrounded by 4 sodium atoms. We have rows and columns of cations (Na + ) and anions (Cl - ). <span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">However this is a 3-dimensional structure. Look at the figure below. Therefore in addition to each chlorine being surrounded by 4 sodium atoms, there is one sodium atom in the front and one at the back of each chlorine. Therefore each chlorine atom is surrounded by 6 sodium atoms and vice versa.

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">

=<span style="color: #4b07d5; font-family: Tahoma,sans-serif; font-size: 14pt;">What are polyatomic ions? =

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">These are ions that consist of a group of atoms. For example SO 4 2- is a polyatomic ion because the 2- charge is on the whole structure (meaning that the 2- charge does not come from the Oxygen or the Sulphur but belongs to both of them).

<span style="font-family: Tahoma,sans-serif; font-size: 14pt;">Therefore in reaction involving polyatomic ions, the polyatomic ion acts like a single atom. For example in the reaction of Mg and <span style="font-family: Tahoma,sans-serif; font-size: 14pt;"> SO 4 2-, the Mg reacts with the entire SO 4 and therefore the compound that is formed is MgSO 4 (this is because the +2 charge on Mg cancels out the -2 charge on SO 4 )

=<span style="color: #4b07d5; font-family: Tahoma,sans-serif; font-size: 14pt;">Summary of different ions and their charges =


 * = ANIONS ||||||||= CATIONS ||
 * = 1- ||= 2- ||= 3- ||= 1+ ||||= 2+ ||= 3+ ||
 * = Fluoride(F - ) ||= Oxide(O 2- ) ||= Nitride(N 3- ) ||= Hydrogen(H + ) ||= Magnesium(Mg 2+ ) ||= Calcium(Ca 2+ ) ||= Aluminium(Al 3+ ) ||
 * = Chloride(Cl - ) ||=  ||=   ||= Sodium(Na + ) ||= Manganese(Mn 2+ ) ||= Iron (Fe 2+ ) ||= Chromium(Cr 3+ ) ||
 * =  ||=   ||=   ||= Potassium(K + ) ||= Cobalt (Co 2+ ) ||= Nickle (Ni 2+ ) ||= Iron (Fe 3+ ) ||
 * =  ||=   ||=   ||= Copper(I)(Cu + ) ||= Copper(II) (Cu 2+ ) ||= Zinc (Zn 2+ ) ||=   ||
 * =  ||=   ||=   ||= Silver(Ag + ) ||= Lead (Pb 2+ ) ||= Tin (Sn 2+ ) ||=   ||
 * = Hydroxide(OH - ) ||= Carbonate(CO 3 2- ) ||= Phosphate(PO 4 3+ ) ||= Ammonium(NH4 + ) ||=  ||=   ||=   ||
 * = Nitrate (NO 3 - ) ||= Sulfate (SO 4 2- ) ||=  ||=   ||=   ||=   ||=   ||
 * = Hydrogen Carbonate (HCO 3 - ) ||=  ||=   ||=   ||=   ||=   ||=   ||
 * = Hydrogen Carbonate (HCO 3 - ) ||=  ||=   ||=   ||=   ||=   ||=   ||

By the end of this lesson you should be able to:
 * predict from electronegativity values or by looking at the periodic table, whether two elements will from an ionic compound when reacted.
 * To describe an ionic bond as an electrostatic force of attraction between oppositely charged ion
 * Deduce the ions formed by elements in groups 1-3, and 5-7
 * Know the formula of common polyatomic ions.
 * Know that transition metals can from differendt ion.
 * Know that an ionic compound has a lattice structure.
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The photos above were taken from the following: (NaCl front view) [] (accessed 26/03/2012) (NaCl 3-D structure) [] (accessed 26/03/2012)