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

1 2 3 4 5 6 7 8

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 levelthe 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

Nitrogen has 5 valence electrons to show.

First we write the symbol. NThen add 1 electron at a time to each side.Now they are forced to pair up.

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 anion will have either0 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-

loss of one valence

electron

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-

The same EC as Neon

e-

Formation of a CationUsing 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-

gain of one valence

electron

17p+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-

Formation of an AnionUsing 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-

17p+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 BondUsing Lewis Dot Diagrams

Na Cl+ -

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