An Introduction to Ionic Bonding Unit XX, Presentation 1

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. –Dealing with transition metals is a bit more complex, but we still mostly deal with s and p electrons first l Core electrons -those in the energy levels below.

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

Electron Dot diagrams l A way of keeping track of valence electrons. l How to write them –Write the symbol. –Put one dot for each valence electron Don’t pair electrons up until there are no open spots left 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. l Until they are forced to pair up.

Write the electron dot diagram for l Na l Mg l C l O l F l Ne l He

Electron Configurations for Cations l Metals lose electrons to attain noble gas configuration. l They make positive ions. 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. 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. P

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

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

Stable Electron Configurations l All atoms react to achieve noble gas configuration. l Noble gases have 2 s and 6 p electrons. –Again, we ignore the d electrons –8 valence electrons. l This is called the octet rule. Ar

Stable Electron Configurations l Which elements on the periodic table do not achieve a true octet when making stable, naturally occurring ions? l H +1, Li +1, Be +2, B +3, H -1

Ionic Bonding l Anions and cations are held together by opposite charges. –Attraction between opposite charges is called electrostatics l Ionic compounds are called salts. –Salts are what is left over when an acid and base react

Ionic Bonding l The simplest ratio of the atoms in an ionic compound is called the formula unit. l Ionic bonds are formed through the transfer of electrons. l Electrons are transferred to achieve noble gas configuration for both atoms/ions.

Ionic Bonding Na Cl

Ionic Bonding Na Cl Electronegativity applies here. The chlorine has a higher attraction to the electrons so...

Ionic Bonding Na Cl The electron is transferred to the chlorine

Ionic Bonding Na Cl The electron is transferred to the chlorine

Ionic Bonding Na + Cl - Making the atoms into ions

Ionic Bonding Na + Cl -

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