Ionic Bonding (Part I) One Atom’s Loss (of an Electron) is Another Atom’s Gain

Chemical Bonds The forces that hold groups of atoms together and make them function as a unit. Ionic Bonds: the transfer of electrons Covalent Bonds: the sharing of electrons

Chemical Bonding Characteristics Ionic –Metal with Non-metal –Transfer of electron(s) –Strong bond…high melting point Covalent –Non-metal with Non-metal –Sharing of electron(s) Non-polar (equal distribution of electrons) Polar (uneven electron distribution) –Weak bonds…low melting points Single, double and triple bonds

 Compounds in which two or more ions are held together by electrical attraction.  The positive ions are called cations.  The negative ions are called anions.  Ionic compounds usually form large crystals that can be seen with the naked eye.  Ionic compounds with smaller crystals may appear as powders. What are Ionic Compounds?

 All ionic compounds form crystals—the attraction between cations and anions is conducive to the ordered stacking that makes up crystals.  Ionic compounds tend to have high melting and boiling points—to break the positive and negative charges apart for either melting or boiling, it takes a huge amount of energy. Properties of Ionic Compounds

 All ionic compounds are very hard and brittle. It takes a lot of energy to pull ionic charges apart. If one gives a large crystal a strong enough impact, such as that from a hammer, one typically uses so much energy that the crystal doesn't break in only one place. Instead, it shatters.  When ionic compounds dissolve in water, they yield solutions that conduct electricity. The positive and negative ions that become separated from each other in a water solution allow electrons to flow much better than in plain water. Ionic compound are often called salts and salt-water conducts electricity. Properties of Ionic Compounds

Valence electrons are the electrons in the atom’s highest numbered energy level. They are the ones left over after the noble gas shorthand: the Lewis Dot Diagram dots! Bonding Uses Valence Electrons

Valence Electrons are…?  The electrons responsible for the chemical properties of atoms, and are those in the outer energy level.  Valence electrons - The s and p electrons in the outer energy level  the highest occupied energy level  Core electrons – are those in the energy levels below.

Keeping Track of Electrons  Atoms in the same column... 1)Have the same outer electron configuration. 2)Have the same valence electrons.  The number of valence electrons are easily determined. It is the group number for a representative element  Group 2A: Be, Mg, Ca, etc.  have 2 valence electrons

Electron Dot diagrams (or Lewis Dot diagrams) are…  A way of showing & keeping track of valence electrons.  How to write them?  Write the symbol - it represents the nucleus and inner (core) electrons  Put one dot for each valence electron (8 maximum)  They don’t pair up until they have to (Hund’s rule again!!) X

The Electron Dot diagram for Nitrogen l Nitrogen has 5 valence electrons to show. l First we write the symbol. N l Then add 1 electron at a time to each side. l Now they are forced to pair up. l We have now written the electron dot diagram for Nitrogen.

 Find the element’s group.  Group 1A elements get 1 Lewis dot.  Group 2A elements get 2 Lewis dots.  Group 3A elements get 3 Lewis dots.  Group 4A elements get 4 Lewis dots.  Group 5A elements get 5 Lewis dots.  Group 6A elements get 6 Lewis dots.  Group 7A elements get 7 Lewis dots.  Group 8A elements get 8 Lewis dots. Simple Way to Figure Lewis Dots (Before I made you do all that hard work with electron configuration and then noble gas shorthand.)

In forming compounds, atoms gain, lose, or share one or more valence electrons in such a way that they achieve the electron configuration of the nearest noble gas in the periodic table. This means that an ion will have either 0 or 8 Lewis dots. Octet Rule

 Atoms lose or gain electrons to form ions  Cations are positive ions  metals generally form cations  Anions are negative ions  non-metals generally form anions  Ionic compounds are held together by electrostatics—the positive charge of the cation attracting the negative charge of the anion. Ionic Bonding

Formation of a Cation 11p + sodium atom Na e-e- loss of one valence electron e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- sodium ion Na + 11p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- The same EC as Neon e-e-

Formation of a Cation Using Lewis Dot Diagrams Sodium atom loss of one valence electron Sodium ion Na + Na

Formation of Anion 17p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- gain of one valence electron 17p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- chlorine atom Cl chloride ion Cl - The same EC as Argon e-e-

Formation of an Anion Using Lewis Dot Diagrams Chlorine atom loss of one valence electron Chloride ion Cl - Cl

Formation of Ionic Bond 11p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- 17p + e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- e-e- sodium ion Na + chloride ion Cl -

Formation of an Ionic Bond Using Lewis Dot Diagrams NaCl + - NaCl

Ionic Bonding: Two Examples

 METAL + NONMETAL  Important metal ions  group 1A - lose 1 electron (+1)  group 2A - lose 2 electrons (+2)  group 3A - lose 3 electrons (+3)  Important non-metal ions  group 7A (-1), group 6A (-2), group 5A (-3), group 4A (-4)  Transition metals also form ionic compounds  Their behavior is less predictable  Iron forms Fe +2 or Fe +3 ; Copper forms Cu + or Cu +2 Ionic Compound

 Subtracting a negative charge from an atom makes the resulting ion positive.  Adding a negative charge to an atom makes the resulting ion negative.  Multiple subtractions or additions of negative charges results in multiply charged positive ions and multiply charged negative ions, respectively. The Formation of Ions Means That Negatively Charged Electrons are Transferred (Protons Stay Put in the Nucleus)

 For ions, protons and electrons cannot be equal in number.  In the case of positive ions (cations), for each unit of positive charge, there will be one less electron than the number of protons in the nucleus.  In the case of negative ions (anions), for each unit of negative charge, there will be one more electron than the number of protons in the nucleus. In Atomic Structure, Protons and Electrons Were Equal in Number