The Life of Ions An Introduction to Ions and how they behave chemically: Characteristics of ions & ionic compounds Ionic Bonding Dissolution Balancing.

The Life of IonsAn Introduction to Ions and how

they behave chemically:•Characteristics of ions & ionic compounds

•Ionic Bonding

•Dissolution

•Balancing Total Ionic Equations

•Net Ionic Equations

•Carbonate and Acid Reactions

What is an Ion?

•An ion is a charged particle due to having either lost or gained electrons.

•The losing or gaining of electrons results in either an overall positive or negative charge on the atom.

•The charges of an ion are due to the number of protons (+ve charge) and number of electrons (-ve charge) not being balanced.

•A positively charged ion that loses electrons is known as cation.

•A negatively charged ion that gains electrons is known as an anion.

What is an Ion? - The Cation•A cation is an ion with a positive charge due to having a greater number of protons than electrons.

•It has an overall positive charge because it has lost one or more of its negatively charged valence electrons.

•The cation is usually a metal found on the left of the periodic table.

•These atoms are not stable as they usually have only 1 or 2 electrons in their outer (valence) shell. Remember that atoms like to have full outer shells and hence the Noble gases (group 8) are the most stable atoms.

Na

Sodium atom (2,8,1)

Na

Sodium ion + (2,8)

+ 1 electrone -

We can write this as;

Na Na+ + e-

+ +

Gr 8Gr 1

Gr 2

Gr 1&2 metals (exception Hydrogen) prefer to lose electrons to make a full outer shell

Gr 7Gr 6

Gr 6&7 non-metals prefer to gain electrons to gain a full outer shell

What is an Ion? - The Anion•A anion is an ion with a negative charge due to having a greater number of electrons than protons.

•It has a overall negative charge because it has gained one or more negatively charged valence electrons.

•The anion is a non-metal and is located on the right of the periodic table.

•These atoms are not stable if they are short only 1 or 2 electrons in their outer (valence) shell in order to make it full.

Cl

Chlorine atom (2,8,7)

Cl

Chloride ion- (2,8,8)

+ 1 electrone -

We can write this as;

Cl + e- Cl-

Note the change in suffix to ‘ide’ when non-metals form ions

_ _

What is an Ionic Compound?•An ionic compound is made up of positive and negative ions bound together.

•An ionic compound is made up of two parts, a metallic cation and non-metallic anion.

•Ionic compounds are usually solids at room temperature.

•They are bonded very strongly so therefore usually have high melting points.

•They dissolve in water to form aqueous solution that normally conduct electricity.

•Examples include NaCl, CaCO3, AgCl, CaCl2

Ionic Bonding

•The electrical forces created by the charges that hold ions together to form an ionic compound are known as ionic bonds. (Covalent bonds and metallic bonds are explained in the PowerPoint ‘Bonding’.)

•In ionic bonding, electrons are transferred from one atom to another.

•More than one anion or cation may be involved in order to ensure that all elements have a full outer shell.

•Let’s have a look at how the ionic compound NaCl is formed…

Consider Na (sodium) with one valence electron, and Cl (chlorine) with 7 valence electrons (they are both in period 3 and have 3 shells in total)

If Na donates its electron to Cl, both will have 8 electrons in their outer shell

Na will now have a full shell 2 and an empty shell 3 and Cl will have a full shell 3.

Na

Na (2,8,1)

Cl

Cl (2,8,7)

Na

Na+ (2,8)

Cl

Cl- (2,8,8)

Ionic BondingNaCl Example

ClNa Na Cl_+=

Na loses a –ve charge and becomes +ve

Cl gains a –ve charge and becomes –ve

The +ve cation is attracted to the –ve anion

Ionic BondingNaCl Example

We can write this equation as;

Na+ + Cl- NaCl

Mg

Mg (2,8,2)

O

O (2,6)

•Mg donates two electrons to O so that both atoms can gain a stable outer shell and form Magnesium oxide. How would you write this?

Mg

Mg2+ (2,8,)

O

O2- (2,8)

Ionic Bonding Example 2

We can write this equation as;

Mg2+ + O2- MgO

Mg

Mg (2,8,2)

Cl

Cl (2,8,7)

Cl

Cl (2,8,7)

Mg

Mg2+ (2,8,)

Cl

Cl- (2,8,8)

Cl

Cl- (2,8,8)


When the charges are equal we simply write the ionic compound showing the atoms involved. The positive ion is placed first. Examples include NaCl and MgO as seen.

When the charges don’t match for single atoms, we need to balance the charges by increasing the number of each atom involved until the charges do match…

Mg2+Total of 2 +ve charges

Cl-

Cl-

Total of 2 –ve charges

Ionic Bonding

Mg2+ + 2Cl- MgCl2

Example 3

•How do you write the ionic formula for Aluminium oxide?

•First work out how many charges each atom has

•Al has a +3 charge and O has a -2 charge


Al 3+

Al 3+

Total of 6 +ve charges

O2-

O2-

O2-

Total of 6 –ve charges

Now write this as an equation;

2Al3+ + 3O2- Al2O3

Dissolution•Dissolution is the dissolving or dissociation of an ionic compound into its component ions in water.

•When this happens, the strong bonds between the anions and cations are therefore broken.

•When an ionic salt such as NaCl is placed in water the positive ends of the water molecules are attracted to the negatively charged chloride ions & the negative end of the water molecule are attracted to the positive Na ions.

•Because the water molecules are constantly moving, they pull the Na+ and Cl- ions out of the crystal lattice and into the surrounding solution.

•Note: some ionic compounds are almost insoluble in water, such as limestone (CaCO3) & ionic compounds in bones.

Cl- Cl- Cl- Cl- Cl-

Cl- Cl- Cl- Cl- Cl-

Cl- Cl- Cl- Cl- Cl-

Na+ Na+ Na+ Na+

Na+ Na+ Na+ Na+

Na+Na+Na+Na+

DissolutionH+

H+

O -

H+

H+O

-

H+

H+

O -

Attraction between ions and water

We can write the formula as:

NaCl(s) Na+(aq) + Cl-(aq)

http

://w

ww

.che

m.u

iuc.

edu/

web

Fun

Che

m/N

etIo

nic/

Ioni

cRxn

s4.h

tm

If we take the salts AgNO3(s) and FeCl3(s) and dissolve them in water the following ions dissociate in solution:

Dissolution

AgNO3(s) FeCl3(s)

Ag+

NO3-

Fe3+

3Cl-

We can write the formulas as:

•AgNO3(s) Ag+(aq) + NO3-(aq)

•FeCl3(s) Fe3+(aq) + 3Cl-(aq)

Dissolution

http

://w

ww

.che

m.u

iuc.

edu/

web

Fun

Che

m/N

etIo

nic/

Ioni

cRxn

s4.h

tm

To check whether the ions have dissociated we can test them to see if they conduct electricity.

Does this investigation suggest the ions conduct electricity?

AgNO3(aq) in solution

FeCl3(aq) in solution

•Make sure that you have the same number and type of atoms on either side of the arrow. That is, the reactants and products must balance each other.

•Include the state in which the ion or compound exists.

•The best way to learn is to have a go…

When writing chemical equations;

Total Ionic EquationsWhen conducting chemical investigations, it is necessary to record what happens by writing a chemical equation.

Total Ionic Equations

Let’s say we mix some limestone with water. This is how we would write it…

CaCO3(s) CaO(s) + CO2(g)

The states of matter have been included, does it balance?

Example 1

Products

•1 Ca

•1 C

•3 O

Reactants

•1 Ca

•1 C

•3 O

Yes! It is balanced as there is the same number of each type of atom on each side

Total Ionic EquationsTry this one…

HCl + Ca CaCl2 + H2

Include the states of matter:

Example 2

Products

•2 H

•2 Cl

•1 Ca

Reactants

•1 H

•1 Cl

•1 Ca

Does it balance?

HCl(aq) + Ca(s) CaCl2(s) + H2(g)

Not balanced

2HCl(aq) + Ca(s) CaCl2(s) + H2(g)

Balance by adding ‘2’ in front of the HCl & check:

Have a go at balancing the formula for this reaction…

Total Ionic Equations More Examples

(NH2)2CO(aq) + H20(l) NH3(aq) + CO2(g)

Reactants

•2 N

•6 H

•1 C

•1 O

Products

•1 N

•3 H

•1 C

•1 O

Answer:

(NH2)2CO(aq) + H20(l) 2NH3(aq) + CO2(g)

Now let’s have a look at what happens when we mix our two solutions of dissociated AgNO3 & FeCl3

http

://w

ww

.che

m.u

iuc.

edu/

web

Fun

Che

m/N

etIo

nic/

Ioni

cRxn

s4.h

tm

In this case the soluble ions from AgNO3

and FeCl3 have formed an insoluble salt. This white salt is known as a precipitate

as it does not dissociate.

Total Ionic Equations Precipitation reaction 1

Total Ionic Equations Precipitation reaction 1

If we were to filter this solution in the laboratory…

…we would be able to separate the solid from

the mixture

Here is the formula for this precipitation reaction. Which product has formed the white precipitate?

Total Ionic Equations

AgNO3(aq) + FeCl3(aq) AgCl(s) + Fe(NO3)3 (aq)

Now balance this equation

To balance the Cl:

AgNO3(aq) + FeCl3(aq) 3AgCl(s) + Fe(NO3)3 (aq)

To balance the Ag and the NO3:

3AgNO3(aq) + FeCl3(aq) 3AgCl(s) + Fe(NO3)3 (aq)

Precipitation reaction 1

Net Ionic Equations•In many reactions, not all ions participate in forming new compounds and are said to be spectator ions. A net ionic equation does not include the spectator ions.

•When writing a net Ionic equation we start by including all of the dissociated ions in the solutions (both reactants and products).

•When the ions are written clearly we can easily identify and cancel out the spectator ions.

•We can rewrite the equation we were just working on as a net ionic equation by writing the dissociated ions first…

Net Ionic Equations

First of all, rewrite the equation showing all the dissociated ions:

3AgNO3(aq) + FeCl3(aq) 3AgCl(s) + Fe(NO3)3 (aq)

3Ag+ + 3NO3- + Fe3+ + 3Cl- 3Ag+ + 3Cl- + Fe3+ + 3NO3

-

Then identify the precipitate formed:

3Ag+ + 3NO3- + Fe3+ + 3Cl- 3AgCl + Fe3+ + 3NO3

-

Now cancel out the spectator ions present both sides of the equation that are not involved in forming the precipitate:

Reduce & add states:

3Ag+ + 3Cl- 3AgCl

Ag+(aq) + Cl-(aq) AgCl(s)

Precipitation reaction 1

Balanced total equation:

Net Ionic Equations

Rewrite the equation stating all the ions involved:

Balance this equation and have a go at writing it as a net equation where water is the product formed and CuO is not soluble:

Balanced:

Can you pick the mistake in the above equation?:

Cancel out spectator ions and write as a Net Ionic Equation:

HCl(aq) + CuO(s) CuCl2(aq) + H20(l)

2HCl(aq) + CuO(s) CuCl2(aq) + H20(l)

2H+ + 2Cl- + CuO Cu + 2Cl- + H20

2H+ + 2Cl- + CuO Cu2+ + 2Cl- + H20

2H+(aq) + CuO(s) Cu2+(aq) + H20(l)

Another Example

Net Ionic Equations Precipitation reaction 2

•Another precipitation example…

•Barium chloride (BaCl2) is a soluble compound containing barium ions and chloride ions

•Sodium sulfate (Na2SO4) is a soluble compound containing sodium ions and sulfate ions.

•When these two solutions are mixed together a white precipitate of barium sulfate (BaSO4) is formed.

•Write the total equation and then the net ionic equation for this reaction keeping it balanced at all times…



Equation with dissociated ions:

Cancel out spectator ions and rewrite as net ionic equation:

BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

Ba2+(aq) + SO42-(aq) BaSO4(s)

Ba2+(aq) + 2Cl-(aq) + 2Na+(aq) + SO42-(aq) BaSO4(s) + 2Na+(aq) + 2Cl-(aq)

Compare the ‘total’ equations to the ‘net’ equations. Identify some possible benefits and drawbacks of

using each type of equation.




Cancel out spectator ions and rewrite as net ionic equation:

Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)

Lead nitrate (Pb(NO3)2) and potassium iodide (KI) are both soluble. When solutions of these two are mixed a yellow precipitate of lead iodide (PbI2) forms. Write a full balanced equation and then a net ionic equation for this reaction.

Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) PbI2(s) + 2K+ + 2NO3

-(aq)

Pb2+(aq) + 2I-(aq) PbI2(s)

Carbonate and Acid Reactions•When acids and carbonates react they produce carbon dioxide and water.

•Let’s have a look at an example…See if you can write a total ionic equation and then a net ionic equation with the reactants nitric acid (HNO3) and sodium carbonate (Na2CO3).

•Don’t forget to balance the number of atoms first, and when necessary balance the ionic charges as well.

•Your starting point is…HNO3 + Na2CO3 CO2 + H2O + NaNO3

Carbonate and Acid Reactions

HNO3(aq) + Na2CO3(aq) CO2(g) + H2O(l) + NaNO3(aq)

2HNO3(aq) + Na2CO3(aq) CO2(g) + H2O(l) + 2NaNO3(aq)Balanced total equation:


Unbalanced equation with states of matter:

2H+(aq) + 2NO3-(aq) + 2Na+(aq) + CO3

2-(aq) CO2(g) + H2O(l) + 2Na+(aq) + 2NO3

-(aq)

Cancel out spectator ions and write as a Net Ionic Equation:

2H+(aq) + CO32-(aq) CO2(g) + H2O(l)

The End – Well done!!! (you have completed some challenging equations. Here are a few fun ones)

•Question: What is the name of this compound? Ba(Na)2

•Answer: Banana!!!!!

•Question: What is this the formula for? H, I, J, K, L, M, N, O?

•Answer: H2O (H to O!!!!)

The Life of Ions An Introduction to Ions and how they behave chemically: Characteristics of ions & ionic compounds Ionic Bonding Dissolution Balancing.

Documents