Ionic Bonding and Ionic Compounds

Atoms and Ions  Atoms are the building blocks of matter (solids, liquids and gases).  For example:  Copper wire is made of copper atoms.  Diamond is made of carbon atoms.  Oxygen gas is made of oxygen atoms.  Atoms have a negatively charged particle called electrons that spin around their nucleus.  Atoms are neutral because the protons equal the electrons.

How do Ions form?  Ions are atoms with charges (+ or -).  Some atoms have a tendency to either lose or gain electrons.  They do this to become stable, that is, to have a fully filled valence shell.  When atoms lose/gain e’s, they become ions.  When ions attract to each other, they form ionic compounds via a chemical bond known as ionic bonding.  Ionic compounds are neutral compounds.

Worksheet on Ion formation

Ionic Compound - Example

Example 1: Sodium ion  Sodium atom (11 e’s) has the electron configuration (2,8,1).  The 3 rd electron shell has a capacity for a maximum of 8 e’s.  However, in this case, there is only 1 valence electron.  Hence, sodium atom is unstable.  It is easier for sodium atom to lose 1 e than to gain another 7e’s  Thus, sodium atom loses that 1 e  It now has one less electron (but protons remain unchanged)

Example 2: Chloride ion  Chlorine atom (_____e’s) has the electron configuration (_______).  The 3 rd electron shell has a capacity for a maximum of 8 e’s.  However, in this case, there _________ valence electrons.  Hence, chlorine atom is _____________ as it is partially filled.  It is easier for chlorine atom to lose/gain _____ an electron than to lose/gain _____ e’s  Thus, chlorine atom loses/gains ____ e  It now has one _____ electron (but protons remain unchanged)

When ions attract….

Illustration using Electron Structure diagrams…

Ionic Bonding  Is a bond formed between positive and negative ions as a result of electrostatic attraction between them.  Electrostatic force is the attraction of positive and negative particles.  Positive ions are called cations.  Metals lose electrons to form cations.  Negative ions are called anions.  Non-metals gain electrons to form anions.

Properties of Ionic Compounds  Are hard, brittle crystalline solids at room temperature.  Have high melting points.  EXPLANATION  The positive and negative ions are held together by strong electrostatic attraction in a 3-Dimensional network lattice. Hence they are strong and also large amounts of heat energy is needed to break its bonds (change the solid into liquid – melting process).  Good conductors of electricity in molten form and in solution form but not in solid state.  EXPLANATION  This is because in melted/dissolved, the ions are free to move and carry electric current but in solid state, the ions are fixed position.

Example of An Ionic Compound - NaCl  Has a melting point of 800°C  Hard, brittle crystalline solid  Positive and negative ions (Na+ and Cl-) are tightly packed and arranged in a 3- dimensional network lattice.  Each ion is surrounded by 6 oppositely charged ions via strong electrostatic attraction.  When dissolved in water or melted, the ions dissociate and are free to move and hence conduct electricity (able to carry electric current)  Diagram of NaCl  A look within

Work Set  Text Questions  Page 78 Numbers 9-10, 12  Page 81 Numbers  Page 82 Numbers  Page 85 Numbers 20, 21  Page 86 Number 22

Naming and Writing formula of Ionic Compounds  Cations (positive ions) are written first followed by anion (negative ions).  Ionic compounds are neutral substances. Hence the charges on cations and anions cancel each other.  The formula is just shows a ratio of ions bonding – it is not the whole molecule – there is more ions than what is shown by the formula.  Deriving formula of ionic compounds uses the “cross-over method”

Polyatomic Ion

How to Name and Derive Formulae?  EXAMPLE  Youtube videos….  

Task  Naming Hydrated Compounds  Text, page 85,86  Summarise in no more than 5 lines  Give 5 examples – names and their formula