Bonding Ionic Bonding & Metallic Bonding

Keeping Track of Electrons l The electrons responsible for the chemical properties of atoms are those in the outer energy level. l Valence electrons - The s and p electrons in the outer energy level. l Core (kernel)electrons -those in the energy levels below.

Keeping Track of Electrons l Atoms in the same column l Have the same outer electron configuration. l Have the same valence electrons. l Easily found by looking up the group number on the periodic table. l Group 2A - Be, Mg, Ca, etc.- l 2 valence electrons

Electron Dot diagrams l A way of keeping track of valence electrons. l How to write them l Write the symbol. l Put one dot for each valence electron l Don’t pair up until they have to X

The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons. l First we write the symbol. N l Then add 1 electron at a time to each side.

Write the electron dot diagram for l Na l Mg lClC lOlO lFlF l Ne l He

Electron Configurations for Cations l Metals lose electrons to attain noble gas configuration. l They make positive ions. (Cations) l If we look at electron configuration it makes sense. l Na 1s 2 2s 2 2p 6 3s valence electron l Na + 1s 2 2s 2 2p 6 -noble gas configuration

Electron Dots For Cations l Metals will have few valence electrons Ca

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

Electron Dots For Cations l Metals will have few valence electrons l These will come off l Forming positive ions Ca +2

Electron Configurations for Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions. (Anions) l If we look at electron configuration it makes sense. l S 1s 2 2s 2 2p 6 3s 2 3p valence electrons l S -2 1s 2 2s 2 2p 6 3s 2 3p 6 -noble gas configuration.

Electron Dots For Anions l Nonmetals will have many valence.electrons. l They will gain electrons to fill outer shell. P P -3

Stable Electron Configurations l All atoms react to achieve noble gas configuration. l Noble gases have 2 s and 6 p electrons. l 8 valence electrons. l Also called the octet rule. Ar

Ionic Bonding l Anions and cations are held together by opposite charges. (metal and non-metal) l Ionic compounds are called salts. l Simplest ratio is called the formula unit. l The bond is formed through the transfer of electrons. l Electrons are transferred to achieve noble gas configuration. l Atoms are generally far apart on table l EN difference of 1.7 or greater.

Ionic Bonding NaCl

Ionic Bonding Na + Cl -

Ionic Bonding l All the electrons must be accounted for! CaP

Ionic Bonding CaP

Ionic Bonding Ca +2 P

Ionic Bonding Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca

Ionic Bonding Ca +2 P -3 Ca P

Ionic Bonding Ca +2 P -3 Ca +2 P

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P Ca

Ionic Bonding Ca +2 P -3 Ca +2 P -3 Ca +2

Ionic Bonding Ca 3 P 2 Formula Unit

Writing Ionic Formulas Criss Cross Method Ca +2 P Ca 3 P2P2 Ca 3 P 2

Properties of Ionic Compounds l Crystalline structure. l A regular repeating arrangement of ions in the solid. l Ions are strongly bonded. l Structure is rigid. l High melting points- because of strong forces between ions.

Crystalline structure

Ionic solids are brittle

l Strong Repulsion breaks crystal apart.

Reactions of Metals l Lose electrons l Become positive ions (Cations) l Have smaller radii l Acquire the noble gas configuration

Reactions of Non-Metals l Gain electrons l Become negative ions (Anions) l Have larger radii l Acquire the noble gas configuration

Do they Conduct? l Conducting electricity is allowing charges to move. l Solids: –the ions are locked in place. –(NaCl s ) so NO conductivity. –Ionic solids are insulators. When melted,(NaCl l ) the ions can move around. So YES conductivity. –Ionic solids have high melting points. (800ºC) –Melted means molten l Dissolved in water(NaCl aq ) YES conductivity.

Metallic Bonds l Metal bonded to more metal. (Ag, Au, Sn, etc. all have metallic bonds.) l How atoms are held together in the metallic solid. l Metals hold onto their valence electrons very weakly. l Think of them as positive ions floating in a sea of electrons.

Sea of Electrons l Electrons are free to move through the solid. l Metals conduct electricity and heat.

Metals are Malleable l Hammered into shape (bend). l Ductile - drawn into wires.

Malleable

l Electrons allow atoms to slide by.

Ductile l Electrons can be drawn into a thin wire.

Energy Changes in Bond Formation l Chemical Bonds are forces that hold atoms together. l Energy is required to overcome these attractive forces and separate the atoms in a compound. l Breaking a bond  Endothermic –Energy on left side of rxn AB + 100J  A + B l Making a bond  Exothermic –Energy on right side of rxn A + B  AB + 100J

Energy and Stability l The greater the amount of energy released in forming the bond the greater its stability. l B + C  BC joules l K + L  KL joules (more stable)