In Chemistry there are 3 types of bonds: IONIC COVALENT METALLIC

IONS

What are ions? Ions are charged particles. They are formed when neutral atoms LOSE or GAIN electrons Atoms with incomplete outer electron shells are unstable. By either gaining or losing electrons, atoms can obtain full outer electron shells and become stable. IONS only form when atoms react. It is only when they react will they lose or gain electrons.

- + If we “take away” the electron we’re left with just a positive charge: + Metals (& hydrogen) lose electrons when they react to form positive ions +

- - + If we add an electron we’re left with a negative charge: - - + - Non-metals gain electrons when they react to form negative ions +

How is a sodium ion formed? Sodium atom: Sodium ion: 11 protons = +11 11 protons = +11 11 electrons = -11 10 electrons = -10 Total charge = 0 Total charge = +1 + Na Na loses 1 electron 2.8.1 (partially full outer shell) [2.8] (full outer shell)

How is a magnesium ion formed? Magnesium atom: Magnesium ion: 12 protons = +12 12 protons = +12 12 electrons = -12 10 electrons = -10 Total charge = 0 Total charge = +2 2+ Mg Mg loses 2 electrons 2.8.2 (partially full outer shell) [2.8]2+ (full outer shell)

How is a fluoride ion formed? Fluorine atom: Fluoride ion: 9 protons = +9 9 protons = +9 9 electrons = -9 10 electrons = -10 Total charge = 0 Total charge = -1 - F F gains 1 electron 2.7 (partially full outer shell) [2.8]- (full outer shell)

How is a sulfide ion formed? Sulfur atom: Sulfide ion: 16 protons = +16 16 protons = +16 16 electrons = -16 18 electrons = -18 Total charge = 0 Total charge = -2 2- S S gains 2 electrons 2.8.6 (partially full outer shell) [2.8.8]2- (full outer shell)

What is a compound ion? Ions can be made up of a single atom or a group of atoms. An ion made up of a group of atoms is called a compound ion. What atoms are present in the following compound ions? Ion Formula Charge Atoms present O H hydroxide OH- -1 S O O O O sulfate SO42- -2 nitrate NO3- -1 N O O O C O O O carbonate CO32- -2 N H H H H ammonium NH4+ +1

IONIC BONDING

What Is An Ionic Bond It is the electrostatic forces of attraction between oppositely charged ions Ionic bond + - NOTE: In an ionic bond the electrons are always transferred from the metal to the non-metal

DOT AND CROSS DIAGRAMS FOR IONIC BONDS

SODIUM CHLORIDE Na Cl SODIUM ATOM 2,8,1 CHLORINE ATOM 2,8,7 Sodium transfers 1 electron to chlorine so both atoms will gain full outer shells

SODIUM CHLORIDE + Na Cl SODIUM ION 2,8 CHLORIDE ION 2,8,8 both ions now have ‘full’ outer shells; ie they have the electronic configuration of a noble gas

The Formation of Sodium Chloride - Summary Ions are formed when the chlorine atom pulls a single electron completely away from a sodium atom, giving both atoms a full outer shell of electrons. This gives a much more stable structure. Start the animation to see how ionic sodium chloride is formed...

Cl Mg Cl CHLORINE ATOMS 2,8,7 MAGNESIUM ATOM 2,8,2 MAGNESIUM CHLORIDE Magnesium transfers two electrons one to each chlorine

Cl Mg Cl CHLORIDE IONS 2,8,8 MAGNESIUM ION 2,8 MAGNESIUM CHLORIDE 1- 2+ Mg CHLORIDE IONS 2,8,8 1- MAGNESIUM ION 2,8 Cl

MAGNESIUM OXIDE Mg O MAGNESIUM ATOM 2,8,2 OXYGEN ATOM 2,6

MAGNESIUM OXIDE Mg O

MAGNESIUM OXIDE 2+ 2- Mg O OXYGEN ION 2,8 MAGNESIUM ION 2,8

COVALENT BONDING

Covalent Bonding is when a pair of electrons are shared between two or more non-metals In this type of bonding electrons are NOT transferred Ions are NOT formed as metals are NOT involved Dot & Cross Diagrams for covalent bonding look very different to that of ionic bonding. This time the shells are overlapping and not separate Electrons which are shared will be shown in the overlap

HYDROGEN H H atoms share a pair of electrons to form a single covalent bond A hydrogen MOLECULE is formed Hydrogen atom needs one electron to complete its outer shell Another hydrogen atom also needs one electron to complete its outer shell WAYS TO REPRESENT THE MOLECULE H H H H PRESSING THE SPACE BAR WILL ACTIVATE EACH STEP OF THE ANIMATION

HYDROGEN H H H H both atoms need one electron to complete their outer shell atoms share a pair of electrons to form a single covalent bond DOT AND CROSS DIAGRAM H H H H

H Cl H Cl Cl H HYDROGEN CHLORIDE atoms share a pair of electrons to form a single covalent bond Chlorine atom needs one electron to complete its outer shell Hydrogen atom also needs one electron to complete its outer shell WAYS TO REPRESENT THE MOLECULE H Cl H Cl PRESSING THE SPACE BAR WILL ACTIVATE EACH STEP OF THE ANIMATION

METHANE H Each hydrogen atom needs 1 electron to complete its outer shell H C H WAYS TO REPRESENT THE MOLECULE H C H H H A carbon atom needs 4 electrons to complete its outer shell Carbon shares all 4 of its electrons to form 4 single covalent bonds PRESSING THE SPACE BAR WILL ACTIVATE EACH STEP OF THE ANIMATION

C C H H H C H H C H H H H H H H H H H METHANE atom needs four electrons to complete its outer shell each atom needs one electron to complete its outer shell Carbon shares all 4 of its electrons to form 4 single covalent bonds H H C H H DOT AND CROSS DIAGRAM H C H H

N H N H H N H H H H H AMMONIA WAYS TO REPRESENT THE MOLECULE Each hydrogen atom needs one electron to complete its outer shell H N H H H N H H H Nitrogen can only share 3 of its 5 electrons otherwise it will exceed the maximum of 8 A LONE PAIR REMAINS Nitrogen atom needs 3 electrons to complete its outer shell PRESSING THE SPACE BAR WILL ACTIVATE EACH STEP OF THE ANIMATION

N N H N H H N H H H H H H H H H AMMONIA atom needs three electrons to complete its outer shell each atom needs one electron to complete its outer shell Nitrogen can only share 3 of its 5 electrons otherwise it will exceed the maximum of 8 A LONE PAIR REMAINS H N H H N H H H

WATER Each hydrogen atom needs one electron to complete its outer shell H O WAYS TO REPRESENT THE MOLECULE H H O H H O Oxygen can only share 2 of its 6 electrons otherwise it will exceed the maximum of 8 2 LONE PAIRS REMAIN Oxygen atom needs 2 electrons to complete its outer shell PRESSING THE SPACE BAR WILL ACTIVATE EACH STEP OF THE ANIMATION

WATER H O H O H H atom needs two electrons to complete its outer shell each atom needs one electron to complete its outer shell Oxygen can only share 2 of its 6 electrons otherwise it will exceed the maximum of 8 TWO LONE PAIRS REMAIN H O H H O H

Multiple Covalent Bonds In all the examples shown so far, the covalent bonds formed are single bonds, formed when one pair of electrons is shared between two atoms. The following examples show how double and triple covalent bonds can be formed between atoms. There are no known examples of quadruple covalent bonds.

OXYGEN O O O O each atom needs two electrons to complete its outer shell each oxygen shares 2 of its electrons to form a DOUBLE COVALENT BOND O O This time 4 electrons are being shared between the oxygen atoms

Double Bonds in an Oxygen Molecule Oxygen atoms form simple molecules (diatomic) by sharing single electrons. Each oxygen atom has two spaces in its outer shell, and can share these with the other oxygen atom, which also donates two electrons to the bond. The sharing of two pairs of electrons constitutes a double covalent bond.

Double Bonds in an Oxygen Molecule The diagram shows the oxygen atoms sharing four electrons in total, forming a double covalent bond. As a result of this sharing, both atoms effectively have a full outer shell of electrons. An oxygen molecule, O2 is the result.

Triple Bonds in a Nitrogen Molecule Nitrogen atoms form simple molecules (diatomic) by sharing single electrons. Each nitrogen atom has three spaces in its outer shell, and can share these with the other nitrogen atom, which also donates three electrons to the bond. The sharing of three pairs of electrons constitutes a triple covalent bond.

Triple Bonds in a Nitrogen Molecule The diagram shows that the nitrogen atoms can share six electrons in total, forming a triple covalent bond. As a result of this sharing, both atoms effectively have a full outer shell of electrons. A nitrogen molecule, N2 is the result. This bond is one of the strongest covalent bonds in nature.

Example 2 X X X O C O X O=C=O X X X X X X X X This is a double bond as each atom shares 2 pairs of electrons to each gain 8 electrons in their outer shell.

METALLIC BONDING

METALLIC BONDING This type of bonding always occurs in metals ONLY A metallic bond is the electrostatic force of attraction between the delocalised electrons and the positive metal ions (cations)

Free delocalised electrons Metal atoms lose electrons to become POSITIVE IONS Free delocalised electrons In a metal the atoms LOSE SEVERAL OF THEIR OUTER ELECTRONS which drift around between the metal ions as FREE ELECTRONS.

As they have LOST a few electrons, the atoms become POSITIVE IONS In a metal the atoms LOSE SEVERAL OF THEIR OUTER ELECTRONS which drift around between the metal ions as FREE ELECTRONS. As they have LOST a few electrons, the atoms become POSITIVE IONS Metal atoms. Notice all the atoms are the same size i.e. same atom of an element. This makes the structure regular Free (“delocalised”) electrons