Ionic and Covalent

bonding

By Ms Buicke

Ionic and Covalent Bonding

SyllabusOC42 Recall that ionic bonding is an attraction between positive and negative ions; describe the bonding in NaCl and MgO as examples. OC43 State what a molecule is, understand that covalent bonds involve the sharing of pairs of electrons, and describe the bonding in H2, O2, H2O, CH4 as examples of covalent bonding. OC44 Investigate the ability of ionic and covalent substances to conduct electricity  

What are molecules?

A group of atoms which are joined together are called molecules.The chemical formula for water is H20 because a molecule of waterconsists of two hydrogen atoms joined to an oxygen atom. The formula For methane is CH4. It has this formula because a molecule of methaneConsists of an atom of carbon joined to four atoms of hydrogen.

Methanemolecule

Chemical bonding.

The atoms in a molecule are held together by forces of attraction called chemical bonding. Bonding occurs because all atoms try to have a full outer shell, and will lose, gain or share electrons in order to do so.

Our understanding of chemical bonding is made a lot easier if we first study a rule called the octet rule.

Octet rule: when bonding occurs, atoms try to have eight electrons in the outer orbit.

If you look at the periodic table you will see that the noble gases ( group 8 or 0) have 8 electrons on their outer shell as a result noble gases are very unreactive and will not form a bond with any other element.

Exercise: can you name three noble gases and give a use for one of the noble gases you have named.

Three noble gases you should know:

Helium: chemical formula He, it is a colorless, odorless, tasteless gas. Used in blowing up balloons.

Neon: chemical formula Ne, used in signs

Argon: chemical formula Ar, used in light bulbs

Chemical reactions take place so that the elements can obtain the very stable arrangement of the noble gases.There a two types of chemical bonding 1) Covalent bonding,2) Ionic bonding.

Ionic bonding occurs when an atom loses or gains electronsCovalent bonding occurs when an atom shares electrons. 

Ionic bonding

An ionic bond is a bond formed by the force of attraction between two oppositely charged ions.An ion is a charged atom ie an atom which has gained or lost an electron.

How is an ion formed?If an atom loses an electron then it becomes a positive ion.If an atom gains an electron then it becomes a negative ion. In ionic bonding positive ions are attracted to negative ions forming an ionic Bond.

There are two examples of ionic bonding which we need to know:

1) Sodium chloride NaCl 2) magnesium oxide MgO

 

Sodium chloride NaCl:The atomic number of sodium is 11It has an electronic configuration of 2,8,1 this means that sodium most lose its outer electron to be stable.

The atomic number of chlorine is 17It has an electronic configuration of 2,8,7 this means chlorine needs to gain an electron to become stable.

When a sodium atom bonds with a chlorine atom the sodium atom loses its outer electron to form a positive ion while the chlorine atom gains an electron to form a negative ion.

The two atoms now have opposite charges and because opposite charges attract both atoms move off together as a sodium-chloride (NaCl) molecule.

A sodium atom and a sodium ion:

A chlorine atom and chloride ion:

Sodium chloride:

What is sodium chloride?Sodium chloride is the chemical term for table salt.

This is the structureof the sodium chlorideMolecule.

Magnesium oxide MgO

The atomic number of magnesium is 12.It has an electronic configuration of 2, 8, 2. This means that it needs to lose the two electrons which it has in its outer shell in order to have a complete outer shell.

The atomic number of oxygen is 8.Oxygen has an electronic configuration of 2, 6. This means it needs to gain two electrons in order to have a complete outer shell. When a magnesium atom bonds with an oxygen atom the sodium atom loses its two outer electrons to form a positive ion while the oxygen atom gains two electrons to form a negative ion.

The two atoms now have opposite charges and because opposite charges attract both atoms move off together as a magnesium-oxide (MgO) molecule.

When a magnesium atom bonds with an oxygen atom the sodium atom loses its two outer electrons to form a positive ion while the oxygen atom gains two electrons to form a negative ion.

The two atoms now have opposite charges and because opposite charges attract both atoms move off together as a magnesium-oxide (MgO) molecule

Magnesium atom and magnesium ion:

Oxygen atom and oxide ion:

Magnesium Oxide:

You must know how to draw the ionic bonds of both Sodium Chloride andMagnesium Oxide.

Covalent Bonding:A covalent bond is formed when atoms combine by sharing electrons so thatEach atom has a stable outer shell of electrons.In covalent bonding neither atom wants to donate electrons as they both need electrons to achieve a full outer shell. The solution is they share electrons.

Remember: sharing is caring!! C for caring C for covalent bond.

We need to know 4 examples of covalent bonding.1) H2 2) CH4 3)H2O 4) 02

 

Examples of covalent bonding: (i) A hydrogen molecule (H2)The atomic number of hydrogen is 1.It needs to have two electrons in its outer shell, and so if it ‘bonds’ with another hydrogen atom and they both ‘share’ their electron with each other, it has the effect of allowing both atoms to have a complete outer shell. 

Examples of covalent bonding: (ii) An oxygen molecule (O2)

The atomic number of oxygen is 8. It has an electronic configuration of 2,

6. It needs to have 8 electrons in its outer shell, and so if it ‘bonds’ with another oxygen atom and they both ‘share’ two of their electrons with each other, it has the effect of allowing both atoms to have a complete outer shell.Oxygen has a double bond because both oxygen atoms share two electrons

Examples of covalent bonding: (iii) A water molecule (H2O)

The atomic number of hydrogen is 1 so it has 1 electron in its outer shell.The atomic number of oxygen is 8 so it has 6 electrons in its outer shell

Oxygen can share 1 electron with one hydrogen atom and a second electron with a second hydrogen atom,which has the effect of allowing all atoms to have a complete outer shell.

Covalent bonding in a water molecule

Examples of covalent bonding: (iv) A methane molecule (CH4)

The atomic number of hydrogen is 1 so it has 1 electron in its outer shell.The atomic number of carbon is 6 so it has 4 electrons in its outer shell. Carbon can share 1 electron with each of 4 different hydrogen atoms, which has the effect of allowing all atoms to have a complete outer shell.

Covalent bonding in the methane molecule

Properties of Ionic and covalent compounds:

Ionic compounds:

1) Consist of positive and negative ions

2) Solid at room temperature. this is because of the strong attraction between oppositely charged ions bonding in sodium chloride is very strong

3)Usually high melting and boiling points.

This is because there is a strong attraction between the ions, a lot of energy is

needed to separate them form each other.

4)Usually soluble in waterwater molecules are attracted to ions

and cause the ions to pull apart.

5) Conduct electricity when melted or dissolved in waterwhen ionic material is molten or dissolved in water the ions are free to move. These ions then carry the electric current.

Ionic compounds can’t conduct electricity when solid the ions are not free to move.

Covalent molecules:

1)Usually liquid or gas at room temperature. example: water is a liquid and methane is a gas 2) Usually low melting points the covalent bond is not that strong and not much energy is needed to separate them from each other.

3) Usually insoluble in waterCovalent compounds do not contain ions and water molecules are not attracted to covalent molecules.

4) Covalent compounds do not conduct electricity. there is no ions present.

3) Usually insoluble in waterCovalent compounds do not contain ions and water molecules are not attracted to covalent molecules.

4) Covalent compounds do not conduct electricity.There is no ions present.

To investigate the ability of ionic and covalent substances to conduct electricity.

In this experiment we try to distinguish between ion and covalent substances. To do this, we look at the ability of these Substances to conduct electricity.

If ions are present in the solution , the solution will conduct an electric current.If no ions are present in a solution, the solution will not conduct an electric current

Exam Questions

2012 (HL)

The diagram shows part of a crystal of sodium chloride. Name the type of

bonding in sodium chloride. Describe this type of bonding.

Name :

Describe:2012 (OL)

Choose the correct words from the list on the right, in each case, to

complete the statements bellow.

Ionic bonding involves an attraction between positive and negative

_____________.

Covalent bonding involves the sharing of pairs of

______________________.

ProtonsElectronsNeutronsions

2011 (OL)

Complete the following sentence using the correct word from the

list on the right.

Bonding that involves the sharing of electron pairs is called

____________________ .

IonicCovalent

2011 (HL)

The diagram shows the way the atoms bond together in a

molecule of water.

(i) What is a molecule?

(ii) Each hydrogen atom shares two electrons with the

oxygen atom. What name is given to the type of bonding

that involves the sharing of pairs of electrons?

(iii) In the space below, draw a diagram of a methane

molecule, CH4, showing the bonding between its atoms.

(iv) Describe a second type of chemical bonding and name a

compound which has this type of bonding.

2010 (HL)

A potassium atom has atomic number 19 and a mass number

of 39.

Complete the diagram using dots or crosses to clearly show

the arrangement of electrons in the potassium atom.

2010 (OL)

Water is a compound composed of two elements.

Name these two elements. 1 _______________________

2_______________________2009 (HL)

Atoms of elements can combine to form compounds using chemical bonds between their atoms. There are different types of chemical

bonds.

The diagram shows a group of water molecules with one enlarged

below with its constituent atoms identified by their atomic symbols.

(i) Name the type of bonding in the water molecule.

(ii)Describe this type of bonding.

(iii) Name one other compound with this type of bond

bonding

(b) The diagram shows sodium ions (+) and chloride ions (-) in part of a crystal of table

salt, sodium chloride.

(i) How are sodium ions and chloride ions formed from their atoms?

How? __________________________________ _______________________________________

(ii) What force holds the ions together in sodium chloride?

______________________________________________________________

(iii) Name one other compound that is composed of ions.

______________________________________________________________2009 (OL)

Different types of bond can be formed when atoms combine. What name

is given to the bond that involves an attraction

between positive and negative ions? ______________________________2008 (HL)

Why are the noble gases, group 8, very chemically unreactive?

2008 HL

Atoms of different elements can form compounds by bonding together.

What is an ionic bond?

True or false?Use your true/ false card to answer the following questions.

1) Carbon has 4 electrons on its outer shell? True/false2) Hydrogen has 3 electrons on it outer shell? True/false3) H2 is an example of a covalent bond? True/false4) The covalent bond structure of water (H20) looks like

this? True/false

5) Methane has the chemical formula CH7? True/false

6) A covalent bond is formed when atoms share electrons? True/false.

7) Covalent bonding in methane looks like this?True/false