CHEMICAL BOND

Is a mutual electrical attraction between the nuclei and valence electrons of different atoms holding atoms together.

Chemical Reactivity Octet Rule – atoms lose or gain or

share electrons to fill their outer energy levels with 8 electrons to be stable Noble gases – stable (least

reactive)ns2np6

Alkali Metals and Halogens – most reactive

All other elements – varied reactivity

How reactive an element is depends on how close it is to having a full octet. The closer it is, the more reactive.

Types of Chemical Bonding

Ionic Bonding – Metals tend to lose electrons to form positive ions or cations, and nonmetals tend to gain electrons to form negative ions or anions. The electrical attraction between large number of cations and anions is called Ionic Bonding.

Covalent bonding- results from the sharing of electron pairs between two atoms.

Polar vs Nonpolar Covalent Nonpolar Covalent Bonds – the

bonding electron pairs are shared equally• The diatomic elements- H2, N2, O2,

F2, Cl2, Br2, I2 Polar Covalent Bonds – the bonding

electrons are pulled closer to one atom• Water, HCl

Dipole – molecule with partial positive and partial negative regions (polar covalent compounds)

Electronegativity – the ability of an atom in a chemical compound to pull shared electrons closer to itself

Classifying Bond Types

The difference in electronegativity values of two bonded atoms determines what type of bond has formed between them (0% to 5%)less than 0.3 = nonpolar (5% - 50%)from 0.3 to 1.7 = polar (above 50%)greater than 1.7 = ionic

change numbers for Honors class

Problems based on Electronegativity Difference

1. Predict the bond type between sodium and fluorine in NaF, which is used in fluoridation of drinking water.2. Predict the type of bond present between carbon and hydrogen in polyethylene.3. Predict the bond type present between carbon and fluorine in the polymer Teflon.4. Predict the bond type present between Phosphorus and oxygen in a DNA molecule.

Covalent Bonding and Molecular compounds

Molecule – the smallest unit of a covalent compound. A molecule is a neutral group of atoms that are held together by covalent bond.

Characteristic of the Covalent Bond

Bond Length- is the average distance between two bonded atoms at their minimum potential energy.

Bond energy- is the energy required to break a chemical bond and form neutral isolated atoms.

By sharing valence electrons in overlapping orbitals, each atom feels the effect of noble gas (ns2 np6) stable configuration.For example in fluorine moleculeF 1s 2s 2p bonding electron pair in overlapping orbital

F 1s 2s 2p

Electron dot notation or Lewis Structures

Representation of the valence electrons around an atom

Drawing Lewis Structures of Compounds

1. Draw individual Lewis Structure for each atom in compound

2. Count number of valence electrons3. Arrange atoms: atom with most unpaired

electrons in center, other atoms around it with their unpaired electrons facing central atom

4. Circle electrons that form bonds

5. Redraw structure replacing circled electron pairs with long dashes (chemical bonds)

6. Count number of electrons in structure, make sure it has the same number as step 2, make sure all atoms except hydrogen satisfy octet rule

Examples: Cl2 CH3I C2H4 N2

Class work Problems

Draw Lewis structure for each of the following compounds and write the number of valence electrons for each structure

1. H2 4. HCl 7. H2S 10. CH2Cl2

2. C2H6 5. SCl2 8. AsF3 11. SiH4

3. CHF3 6. C2H2 9. HCN 12. N2F2

Resonance Structure- When molecule has two or more possible Lewis structures, those structures are called Resonance structures.

Valence Shell Electron Pair Repulsion (VSEPR) Theory

Predicts some molecular shapes based on the idea that pairs of valence electrons (lone pair and shared pair) surrounding an atom repel each other.

Electron Pairs can determine Molecular Shape

Hybridization

The phenomenon of mixing up of different orbitals of same energy level of an atom to produce equal number of hybrid-orbitals of same energy and identical properties is known as hybridization. A hybrid orbital contains maximum two electrons with opposite spin.

sp3 hybridization of Carbon in methane CH4- tetrahedral shape

sp2 hybridization of Boron in BF3 – trigonal planar shape

sp-hybridization of Beryllium in BeCl2 – linear shape

Valence Electrons and Ions Valence Electrons – the electrons in the

outer most energy level

Ion – atom that gained or lost electron(s) Cation – ion with positive charge (lost

e-) Anion – ion with negative charge

(gained e-)Show them how to determine the number of valance electrons using the periodic table

The outer most s and p orbitals are the same as the outer most energy level, they are also sometimes called the valance shell

Metals vs. Nonmetals

Metals form cations (+

ions) by losing electron Use Bohr

models to explain why

Nonmetals form anions (-

ions) by gaining electrons Use

Bohr models to explain why

Ions & Parent Atoms Ions and their parent atoms have different

chemical properties. Ions and atoms chemical properties

depend on their number of valence electrons

Since Na and Na+1 have a different number of valence electrons they have different propertiesNa burns when placed in water, but Na+ does not and is used in our bodies all the time

Since Na and Na+1 have the same atomic number, they are the same elementSame number of protons which identifies the element

Polyatomic ions – ion made of 2 or more atoms bonded together (pg 238)

Ionic Bonds Strongest type of chemical bond First, electrons are transferred from one

atom to another to form cations and anions

Then, ions of opposite charge attract each other

Ionic Compounds Any compound involving a cation and

anion aka – salt Conduct electricity when melted or

dissolved in water

Electricity can only be conducted when charged particles (like ions) are free to move around. They cannot move when they are in solid form

Ionic compounds don’t form moleculesCrystal Lattice – repeating pattern of ions (different

pattern for different compounds). Lattice Energy is the energy released when one mole of an ionic crystalline compound is formed from gaseous ions. Very high melting points Very hard & brittle

Compare and Contrast of Covalent bonds and Ionic Bond- Complete the compare and contrast on poster (Use any graphic organizer). Write how the two bonds are similar. Write how bonds are different in regards to- how bonds is formed (how are valence

electrons involved)? What combination of elements form bond? what is the smallest unit? How is naming and writing formula rules are

different or same? Give examples. how are properties of ionic compounds differ

from molecular compounds? Refer page 179.

Intermolecular forces-• the forces of attraction between the molecule. • are generally weaker than chemical bonds-

covalent or ionic

• the force of attraction between polar molecules are known a dipole-dipole forces

• The intermolecular force in which a hydrogen atom that is bonded to highly electronegative atom is attracted to unshared pair of electrons of electronegative atom in a nearby molecule is known as Hydrogen bonding. Example-water

Metallic Bonding Is the chemical bond that results from

the attraction between metal atoms and the surrounding a sea of electrons.

Freedom of electrons to move in a network of metal atoms accounts for the metal’s high electrical and thermal conductivity.

Shiny appearance of metal surface- loose electrons become excited easily and fall back to lower energy level emitting light

Malleability and ductility of metal is possible b/c metallic bonding is the same in all directions throughout the solid.

Use Electron-dot notation to demonstrate the formation of ionic compounds (with their name and formula) involving the following:1. Aluminum and chlorine2. Calcium and oxygen3. Sodium and oxygen4. Lithium and nitrogen5. Rubidium and sulfur6. Magnesium and nitrogen7. Aluminum and nitrogen8. Strontium and bromine9. Barium and oxygen10. Calcium and Arsenic

Complete Nomenclature Packet

Oxidation Numbers The charges on the ions composing an ionic compound reflect the electron distribution of the compound. In order to indicate the general distribution of electrons among the bonded atoms in molecular compound or a polyatomic ion, oxidation numbers or oxidation states are assigned to the atoms composing the compound or ion.

Assigning Oxidation Numbers:1. The atoms in a pure element have an oxidation

number of zero. Ex O2 Have oxidation number of zero.

2. The more electronegative element in binary molecular compound is assigned negative(anion). The less electronegative atom is assigned the number equal to positive charge( cation).

3. The algebraic sum of the oxidation numbers of all atoms in a neutral compound is zero.

4. The algebraic sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge on the ion.

Assign oxidation numbers to each atom in the following compounds or ions.1. HCl2. CF4

3. PCl34. SO2

5. PO42-

6. PO33-

7. MnO4-

8. Cr2O72-