Ionic and Covalent bonds

Definitions Ion an atom that has gained or lost one or more electrons Cation a positively charged ion Anion a negatively charged ion

Energy Level Diagram Sodium Ion Na+ Energy e- e- e- e- e- e- 3p e- e- It could GAIN seven electrons to become more stable. Or… e- e- 1s Or it could LOSE one electron to become more stable.

All physical systems tends towards a configuration of lowest energy Sodium will LOSE an electron.

Energy Level Diagram Chlorine Energy e- e- e- e- e- e- 3p e- e- 3s e- It could gain ONE electron to become more stable. Or… e- e- 1s Or it could lose SEVEN electrons to become more stable.

Gaining an electron would require the least amount of energy! Energy Level Diagram e- e- e- e- e- e- 3p e- e- Energy 3s e- e- e- e- e- e- 2p e- e- Chlorine Ion Cl- 2s e- e- 1s Gaining an electron would require the least amount of energy!

Valence electrons Electrons in the outermost s and p orbitals These are the most reactive

Energy Level Diagram Sodium Energy 3p e- 3s e- e- e- e- e- e- 2p e- e- Has only ONE electron in its outermost s and p orbitals. Therefore, it has one valence electron. 1s

Energy Level Diagram Chlorine Energy e- e- e- e- e- 3p e- e- 3s e- e- Has SEVEN electrons in its outermost s and p orbitals. Therefore, it has seven valence electrons. 1s

An easier way to draw the valence electrons is through… Lewis dot structures

Sometimes atoms get together and one or more electrons jumps from one atom to another… …this causes both atoms to have opposite charges (ions)… …which then causes these ions to be attracted to each other. Ionic Bond

But why? Chlorine has a greater attraction for electrons than Sodium For example… Chlorine has a greater attraction for electrons than Sodium But why? Electronegativity / Chlorine = catcher

Ionic bonds Occur between metals and nonmetals Like Sodium and Chlorine or Potassium and Fluorine

In an ionic bond, electrons are first lost or gained, resulting in the formation of ions. K

K F

K F

K F

K F

K F

K F _ + An ionic bond forms from the attraction between the positive K+ ion and the negative F- ion _ K + F Potassium (K+) ion [cation] Fluoride (F-) ion [anion]

K F _ + An ionic bond forms from the attraction between the positive K+ ion and the negative F- ion _ K + F The compound potassium fluoride (KF) consists of potassium (K+) ions and fluoride (F-) ions

Properties of Ionic Compounds Ionic Bonds Properties of Ionic Compounds Electrons are exchanged Ions are formed Ions “stick together” magnetically to form compound Formed between metals and nonmetals Electronegativity difference >1.7 Cation + Anion = “salt” Forms crystals (ordered arrangements of ions) Conduct electricity when dissolved or melted High melting/boiling points Hard and brittle Rarely burn Formation is always exothermic

Covalent bonds Occur between two nonmetals Like Hydrogen and Chlorine Chlorine and Chlorine

In covalent bonding, atoms still want to achieve the lowest energy level possible (which means filling up all eight of their valence seats.) But rather than losing or gaining electrons, atoms now SHARE an electron pair.

All physical systems tends towards a configuration of lowest energy Covalent bonds attempt to fill up all eight of their valence seats… Just like noble gases! All physical systems tends towards a configuration of lowest energy

Chlorine forms a covalent bond with itself Cl2

Cl Cl How will two chlorine atoms react? Each chlorine atom wants to gain one electron to fill all of its seats.

Cl Cl

Cl Cl

Cl Cl

Cl Cl

Cl Cl The octet is achieved by each atom sharing the electron pair in the middle.

Cl Cl Full 8 seats (octet) Full 8 seats (octet)

Cl Cl The octet is achieved by each atom sharing the electron pair in the middle.

Single bonds are abbreviated with a dash Cl Cl This is the bonding pair It is a single bonding pair It is called a SINGLE BOND Single bonds are abbreviated with a dash

Single bonds are abbreviated with a dash Cl Cl This is the bonding pair It is a single bonding pair It is called a SINGLE BOND Single bonds are abbreviated with a dash

Single bonds are abbreviated with a dash Cl Cl circle the electrons for each atom that completes their octets Single bonds are abbreviated with a dash

This is the chlorine molecule Cl Cl This is the chlorine molecule Cl2 circle the electrons for each atom that completes their octets

Covalent bonds But you need to learn this! …and this. You know this… But you need to learn this! …and this. Remember: Covalent bonds occur between two nonmetals!

O2 Oxygen can also form a covalent bond with itself. But it needs to form two bonds since it is in Group 6A. How can this be done?

O

O Each atom has two unpaired electrons

O

O O

O O

O O

Both electron pairs are shared.

O O 6 valence electrons plus 2 shared electrons = full octet

O O 6 valence electrons plus 2 shared electrons = full octet

O O Two bonding pairs, making a double bond.

O O = For convenience, the double bond can be shown as two dashes.

This is the oxygen molecule, = This is the oxygen molecule, O2

Properties of Covalent Compounds Covalent Bonds Properties of Covalent Compounds Electrons are shared No ions are formed Formed between two nonmetals Electronegativity difference is minimal Low melting and boiling points Typically soft and squishy Usually do not dissolve in water as well as ionic compounds Don’t conduct electricity Sometimes burn

Covalent bonds Two kinds… Polar Covalent Bond Shared electrons spend more time closer to one of the bonding atoms For example – H20 Non-Polar Covalent Bond Shared electrons do not spend more time closer to one of the bonding atoms For example – 02

Polar covalent bonds Shared electrons spend more time closer to one of the bonding atoms The electrons spend more time near the oxygen atom. H H Oxygen The probability distribution for shared electrons.

How can you tell if you have a polar or non-polar covalent bond? ELECTRONEGATIVITY Electronegativity is the power of an atom to attract electrons The higher the value, the more electronegative the element

Remember probability distribution?

Non-polar covalent bonds Shared electrons do not spend more time closer to one of the bonding atoms The probability distribution for shared electrons is shared by both. Oxygen Oxygen

Every element (except the nobles) have electronegativity

Non-polar covalent bond If the electronegativity difference between the two nonmetals is less than 0.3 Polar covalent bond If the electronegativity difference between the two nonmetals is 0.3-1.7

Review Ionic bond Between a metal and nonmetal Electrons are lost/gained and the resulting change in charge attracts the ions together Covalent bond Between two nonmetals Electrons are shared between the atoms Polar/Non-polar Ruled by electronegativity