Chemical Bonds

CHEMICAL BONDING IONIC, COVALENT &

METALLIC

**An atom has relatively high potential energy in the form of valence electrons.

**Nature minimizes the potential energy by shifting valence electrons to form chemical bonds.

**By bonding with other atoms, potential energy is decreased creating stable compounds.

ClDot Diagram Practice Sheet

Chemical Bonds—it’s all about potential energy!

The Noble Gases, group 8A, do not react with other elements.

• Described as “stable”, “inert”, and “inactive”.

• The outer most “s” and “p” sublevels are completely filled with 8 electrons, satisfying the octet rule.

Ne

The Octet Rule

• **The formation of this octet releases energy, reducing the potential energy – and making the element STABLE.

• The stable conditions created by the octet rule leads to the theory that **elements combine with each other to achieve noble gas electron configurations.

III. Types of Chemical Bonds

Ionic Bonding— e- are transferred from the outer shell of one atom to the outer shell of another atom.

2 Na + Cl2 2 NaCl

Na

NaClCl

ClNa

ClNa

+

Ionic bonds involve ions—cations (+) and anions (-)

**Metals and Nonmetals

The overall NRG change in ionic bonding is always exothermic (releases NRG)

Na + NRG Na+ + e-**removal of an e- is an endothermic process that requires NRG--ionization NRG**

+ e- Cl-1 + NRG Cl

**addition of an e- is an exothermic process that releases NRG—electron affinity**

Movement of ions into a crystalline structure as exothermic—releases NRG!!

Na+ + Cl- NaCl

Cl-

Cl-

Cl-

Cl-

Na+ Na+

Na+Na+

Na+

YOUR TURN…

Using dot diagrams, show what happens when aluminum combines with bromine. Remember the valence electrons!

Al

Br

Gro

up 1

3

Gro

up 1

7

Al Al

Br

1. Write the dot diagram for aluminum

2. Separate the electrons to prepare for bonding

3. Write the dot diagram for bromine

*How many Br will you need?

AlBr3

The overall reaction will result in ionic bonds between one aluminum and three bromine.

Al Br+

The product of this reaction can be represented by a Lewis structure. A Lewis structure shows the bonding between atoms using dots diagrams to illustrate the behavior of valence e-.

Al + 3 Br

Al

Br

Br

Br

Al Br

Br

Br

Al Br Br

Br

The resulting Lewis structure formed by the ionic bonding between aluminum and bromine looks like this….

AND this…

AND this…

Some chemical compounds cannot be represented by just one Lewis structure. Such compounds are constantly altering or “resonating”.

Although each Lewis structure of aluminum bromide is slightly different, the chemical properties are identical.

Al BrB

r Br

Resonance refers to bonding in compounds that cannot be correctly represented by a single Lewis structure.

IV. Energy and Ionic Bonding

A. Ionization NRG—the amount of NRG needed to remove an e- from an atom. Metals have low ionization NRG’s while nonmetals have high ionization NRG.

WHY ?

Metals have low ionization NRGs

s-block p-block

*2nd and 3rd ionization energies are HIGHER than the 1st ionization NRG

Nonmetals have high ionization NRG because nonmetals are closer to satisfying the octet rule!

YOUR TURN…

Using dot diagrams, draw the Lewis structures that result when the following elements form ionic bonds:

A. Potassium + chlorine

B. Magnesium + fluorine

*Don’t forget to indicate the formation of cations and anions

YOUR TURN…

Using dot diagrams, draw the Lewis structures that result when the following elements form ionic bonds:

A. Potassium + Chlorine

B. Magnesium + Fluorine

K Cl K Cl+

FMg + F FMg

K+ Cl-

Oxidation # = Charge of IonMaking Ionic Compounds- Cation + AnionWhen you make an ionic compound ONLY the number moves.

•NOT the charge. Okay…So Let’s Cross and Drop!!!!!!

NH4+ and PO4

3-

(NH4)3 PO4

K+ O2-

K2O

Al S

Al2S3

3+ 2-

The nature of a bond is determined by differences in electronegativity.

The GREATER the electronegativity difference, the MORE ionic the bonding.

An electronegativity difference of 1.67 or more is considered an ionic bond.

Element Electronegativity

Fluorine 4.10

Chlorine 2.83

Bromine 2.74

Sodium 1.01

Lithium 0.97

Cesium 0.86

“Perhaps one of you gentlemen wouldn’t mind telling me just what outside the window you find so attractive…?”

V. COVALENT BONDS

*Covalent bonds are formed when atoms SHARE e-

*Instead of forming ions (crystalline structure), a molecule is formed.

*Formed from 2 or more nonmetals.

A. Diatomic molecules—these bonds are formed between two atoms of the same element

When the atoms are of the same element this is called a nonpolar covalent bond since the electrons are equally shared.

Diatomic Molecules -- Br, I, N, Cl, H, O, F

Remember: “Br I N Cl H O F”

B. Covalent bonds between unlike elements

1. One atom has more attraction of an electron than the other atom, so the electrons are unequally shared. This is called a polar covalent bond.

**The difference in electronegativity in a covalent bond is less than 1.67**

Important Concepts…

**The difference in electronegativity in an ionic bond is greater than 1.67**

Diatomic molecules—atoms of the same element form nonpolar covalent bonds (Br2, I2, N2, Cl2, H2, O2, F2)

Polyatomic ions—a charged group of covalently bonded atoms. Polyatomic ions combine with ions of opposite charge to form ionic compounds.

Crystalline structure

Molecule

VI. Differences Between Ionic and Covalent Bonds

1. Ionic compounds are formed between metals and nonmetals or polyatomic ions. When dissolved in water, ionic compounds will form ions in solution:NaCl + H2O Na+ + Cl - + H2O

FeSO4 +H2O Fe+2 + SO4-2 +H2O

2. Properties of IONIC substances:

• React faster than molecular substances

• Stronger bonds than covalent bonds and therefore have higher melting points

• Many are soluble in water (dissolve in water)

• Conduct electricity

• Low Volatility (ability to turn into a gas)-low or no odor

• Many exist as crystals

• Metals bonded with non-metals

• Electronegativity difference is higher than 1.67.

• Generally form solids.

3. COVALENT bonds form MOLECULAR compounds. These are molecules made of two nonmetals.

4. Properties of MOLECULES:

• Weaker bonds than ionic compounds therefore have low melting points.

• Generally form gases or liquids

• Insoluble in water

• Highly Volatility (ability to turn into a gas)-strong odor

• Nonconductors (good insulators)

• Electronegativity difference is lower than 1.67.

Metallic Bonds

The third type of chemical bond is the metallic bond.

Properties of metals include:

1. Conductors of electricity and heat

2. Lustrous or shiny

3. Malleable

4. Ductile

Sea of Electrons

All metal atoms have the SAME attraction for valence electrons. This allows the **electrons to move freely from one atom to the next.

**The electrons are said to be “delocalized” because they are NOT held in one location – called “sea of electrons.”

C. All metal atoms have the SAME attraction for electrons. This allows the electrons to move freely from one atom to the next.

D. The electrons are said to be “delocalized” because they are NOT held in one location.

E. If an external field is applied, the electrons will flow through the metal creating an electric current or the electrons may interact with light to give metal its luster or shine.

F. The number of delocalized electrons determines how strong the metallic properties will be. The more delocalized electrons, the “more” metallic the properties.