Chemical Bonding Atoms in combination

Basics of Bonding There are 3 main types of bonding that we will look at in this PowerPoint All bonding is due to electrostatic charges of the atoms and involves the valence electrons Like charges repel and opposite charges attract – let’s look at that with two atoms in close proximity Attraction Repulsion e e e e

Ionic Bonding Produces an ionic compound Ionic compounds are compounds that form between a metallic atom and a non-metallic atom Occurs when electrons are transferred from the metal to the non-metal atom

Ionic Bonding Metals in Ionic bonding Lose valence electrons Achieves a stable valence of 8 Gains a positive charge to become a positive ion The charge is the number of valence electron it has to lose Examples… Na (2,8,1) becomes Na+ (2,8) Li (2,1) becomes Li+ (2) K (2,8,8,1) becomes K+ (2,8,8) Ca (2,8,8,2) becomes Ca2+ (2,8,8) Al (2,8,3) becomes Al3+ (2,8)

Ionic Bonding Non-metals in Ionic bonding Gain valence electrons Achieves a stable valence of 8 Gains a negative charge to become a negative ion The charge is the number of valence electron it gains Examples… F (2,7) becomes F- (2,8) Cl (2,8,7) becomes Cl- (2,8,8) Br (2,8,8,7) becomes Br- (2,8,8,8) O (2,6) becomes O2- (2,8) N (2,5) becomes N3- (2,8)

Ionic Bonding – Example 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)

Formation of NaCl Cl Na _ Cl _ + + = Na loses a –ve charge and becomes +ve Cl gains a –ve charge and becomes -ve We can write this as; Na + + Cl - = NaCl

Formation of NaCl Cl- Na+ Part of a crystal lattice of sodium chloride. When Na and Cl combine they attract each other and from what is called a crystal lattice…

Another Example… 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 Mg Mg 2+ (2,8,) O O 2- (2,8)

When the charges don’t equate… Mg Mg (2,8,2) Cl Cl (2,8,7) Cl Cl (2,8,7) Mg Mg 2+ (2,8,) Cl Cl- (2,8,8) Cl Cl- (2,8,8)

Writing formulae… 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 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- Total of 2 – ve charges MgCl 2

Here’s one for you to try… 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 Then swap the number of charges to the number of atoms eg. Al 3+ plus O 2- Al 2 O 3

Let’s check this… Al 3+ Total of 6 +ve charges O2- Total of 6 –ve charges Formula written as Al 2 O 3

Covalent Bonding Produces a covalent compound Covalent compounds are compounds that form between two atoms that are NON METALLIC Occurs when electrons are shared This is different to IONIC compounds where electrons are……….Transferred

1p Consider two hydrogen atoms Each atom has a single proton in its nucleus and one electron in its outer shell 1p Each Hydrogen atom shares its electron with the other giving each 2 electrons in its the first shell H2H2 Covalent Bonding - Example

Electron dot Diagram We show the sharing of electrons between atoms in covalent compounds via electron dot diagrams H Each atom ends up with a stable number of electrons in its outer shell How many electrons will this usually be? Yes-Usually 8 – (except where the outer shell is the first shell) ONLY the electrons in the outer shell (the valence shell) are involved in sharing

Lets look again at H 2 1p The bonding here can be shown like this; H H A single molecular bond is formed when the two atoms share an electron each This is the structural formula

Oxygen - O 2 O O OO Since the oxygen atoms share two pair of electrons this is a double bond O Outer shells

O 2 as an electron Dot diagram O Two pairs of shared electrons O Six valence electrons Now has 8 electrons in outer shell

And some others……. N H Outer shells Ammonia NH 3 N H H H H N H H Lone Pair HH

NH 3 as an electron Dot diagram N Outer shell electrons of Nitrogen Outer shell electrons of Hydrogen H

Lets look at methane - CH 4 This is a covalent compound consisting of one carbon atom and four hydrogen atoms H C + HHH H C H H H H C H H H

CH 4 as an electron Dot diagram C Outer shell electrons of Carbon H Outer shell electrons of Hydrogen

Now you try some… Have a go at drawing the electron dot diagram of N 2 Now try H 2 0 Try CO 2 When you have completed the electron dot diagrams, show how you would write the structural formula of these covalent compounds (with lines as bonds)

Metalic Bonding Produces a metallic compound Metallic compounds are compounds that form between two metallic atoms Metals on the left hand side of the periodic table lose electrons easily and form +ve ions (cations) The electrons are not transferred like in ionic bonding, nor are they shared as in covalent bonding, instead they ‘float’ around the cations The electrons are not tied to a shell but move freely through the lattice.

Metalic Bonding Na+ ion _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Negative electrons ‘float’ between the positive metal ions

Recapping Ionic bonding forms ionic compounds where electrons are donated from metals to non-metals Covalent bonding forms covalent compounds where electrons are shared between two non-metals Metalis bonding forms a metalic compound where electrons ‘float’ freely between the positive metallic ion

The End