MYP Chemistry Ionic Bonding and Ionic Compounds International College Spain

Electron Configuration in Ionic Bonding  OBJECTIVES: – Use the periodic table to infer the number of

valence electrons

in an atom, and draw it’s electron dot structure.

Electron Configuration in Ionic Bonding  OBJECTIVES: – Describe the formation of

cations (positive ions)

from metals, and of

anions (negative ions)

non-metals.

from

Valence Electrons  The electrons responsible for the chemical properties of atoms are those in the outer energy level.

 Valence electrons - The electrons in the outer energy level or shell – the highest occupied energy level  Inner electrons levels below.

-those in the energy

Keeping Track of Electrons  Atoms in the same column...

– Have the same outer electron configuration.

– Have the same valence electrons.

 Easily found: same as the main group number on the periodic table.  Group 2A: Be, Mg, Ca, etc.

– 2 valence electrons

Electron Dot diagrams  A way of keeping track of valence electrons.

 How to write them?

 Write the symbol.

 Put one dot for each valence electron  Don’t pair up until they have to.

X

The Electron Dot diagram for Nitrogen  Nitrogen has 5 valence electrons.

 First we write the symbol.

 Then add 1 electron at a time to each side.

 Until they are forced to pair up.

N

Write electron dot diagrams:  Na  Mg  C  O  F  Ne

Electron Configurations for  Cations Metals lose electrons to attain noble gas configuration.

 They make positive ions (cations)  If we look at the electron configuration, it makes sense to lose electrons:  Na

2,8,1

 Na

+ 2,8

1 valence electron noble gas configuration

Electron Dots For Cations  Metals will have few valence electrons (usually 3 or less) Ca

Electron Dots For Cations  Metals will have few valence electrons  These will come off Ca

Electron Dots For Cations  Metals will have few valence electrons  These will come off  Forming positive ions Ca 2+ Now make Sc an ion.

Pseudo-noble gas configuration

Electron Configurations for  Anions Nonmetals gain electrons to attain noble gas configuration.

 They make negative ions (anions)  Halide ions- ions from chlorine or other halogens that gain electrons  S

1s 2 2s 2 2p 6 3s 2 3p 4

6 valence electrons 

S 2 1s 2 2s 2 2p 6 3s 2 3p 6

configuration.

noble gas

Electron Dots For Anions  Nonmetals will have many valence electrons (usually 5 or more)  They will gain electrons to fill outer shell.

P P 3-

Stable Electron Configurations  All atoms react to achieve noble gas configuration.

 Noble gases have 8 outer shell (valence) electrons.

 Also called the octet rule.

Ar

Ionic Bonds The characteristics of an ionic bond.

Ions held together by……..

electrostatic attraction

Ionic Bonds  Characteristics of ionic compounds  electrical conductors when melted and when in aqueous solution.

 High m.p.

 Brittle, hard crystals

  Properties of ionic compounds 1.

2.

3.

You are provided with three ionic compounds For each carry out the following tests Heat a sample strongly in a test tube.

Add a spatula of the compound to 25 cm3 of water in a small beaker- stir Test the conductivity of the solution Repeat using two spatulas

 Ionic Bonding Anions and cations are held together by opposite charges.

 Ionic compounds are called salts .

 Simplest ratio is called the formula unit.

 The bond is formed through the transfer of electrons .

 Electrons are transferred to achieve noble gas configuration.

Ionic Bonding

Na Cl

Ionic Bonding

Na

+

Cl

-

Ionic Bonding  All the electrons must be accounted for

Ca P

Ca

Ionic Bonding

P

Ionic Bonding

Ca

2+

P

Ionic Bonding

Ca

2+

Ca P

Ca

2+

Ca

Ionic Bonding

P

3-

Ca

2+

Ca

Ionic Bonding

P

3-

P

Ca

2+

Ca

2+ Ionic Bonding

P

3-

P

Ionic Bonding

Ca Ca

2+

Ca

2+

P P

3-

Ionic Bonding

Ca Ca

2+

Ca

2+

P P

3-

Ionic Bonding

Ca

2+

Ca

2+

Ca

2+

P P

3 3-

Ionic Bonding

= Ca

3

P

2 Calcium Phosphide Formula Unit

Classwork problems (a) Show the bonding between the following 1.

Magnesium and Oxygen 2.

3.

Potassium and Chlorine Calcium and Fluorine 4.

5.

Lithium and Nitrogen Aluminium and Fluorine

Homework problems These are slightly harder 6.

Magnesium and Phosphorus 7.

8.

Beryllium and Nitrogen Calcium and Sulphur 9.

Magnesium and Nitrogen 10.

Aluminium and Oxygen

Properties of Ionic Compounds  Crystalline structure, usually solids  A regular repeating arrangement of ions in the solid  Ions are strongly bonded together.

 Structure is rigid.

 High melting points  Electrical conductors when melted  Electrical conductors in solution

Crystalline structure

Do they Conduct?

 Conducting electricity is allowing charges to move.

 In a solid, the ions are locked in place.

 Ionic solids are insulators.

 When melted , the ions can move around.

 Melted ionic compounds conduct.

– NaCl: must get to about 800 ºC.

 Dissolved in water they conduct (aqueous)

Bonding in Metals  OBJECTIVES: – Use the theory of metallic bonds to explain the physical properties of metals.

Bonding in Metals  OBJECTIVES: – Describe the arrangements of atoms in some common metallic crystal structures.

Metallic Bonds  How atoms are held together in the solid.

 Metals hold on to their valence electrons very weakly.

 Think of them as positive ions (cations) floating in a sea of electrons:

Sea of Electrons  Electrons are free to move through the solid.

 Metals conduct electricity.

+ + + + + + + + + + + +

Metals are Malleable  Hammered into shape (bend).

 Also ductile - drawn into wires.

 Both malleability and ductility explained in terms of the mobility of the valence electrons

Malleable + + + + + + + + + + + +

Malleable  Electrons allow atoms to slide by.

+ + + + + + + + + + + +

Ionic solids are brittle + + + + + + + +

Ionic solids are brittle  Strong Repulsion breaks crystal apart.

+ + + + + +

Crystalline structure of metal  If made of one kind of atom, metals are among the simplest crystals 1.

– Body-centered cubic: every atom has 8 neighbors – Na, K, Fe, Cr, W

Crystalline structure of metal 2. Face-centered cubic: – every atom has 12 neighbors – Cu, Ag, Au, Al, Pb 3. Hexagonal close-packed – every atom also has 12 neighbors – different pattern due to hexagonal – Mg, Zn, Cd

Alloys  We use lots of metals every day, but few are pure metals  Alloys mixtures of 2 or more elements, at least 1 is a metal  made by melting a mixture of the ingredients, then cooling  Brass: an alloy of Cu and Zn  Bronze: Cu and Sn

Why use alloys?

 Properties often superior to element  Sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware  Steels are very important alloys – corrosion resistant, ductility, hardness, toughness, cost

Why use alloys?

 Look up alloys in your text book  Types? a) substitutional alloy- the atoms in the components are about the same size  b) interstitial alloy- the atomic sizes quite different; smaller atoms fit into the spaces between larger  Amalgam- dental use, contains Hg