Bonding

REVIEW• Valence electrons: Electrons in highest occupied

energy level– Can use electron dot structures to show valance electrons

What would be the electron dot structure for Na? Cl? Ne?

Review

• Octet Rule: Atoms loose or gain electrons to have a full outer energy level– Bonding!!

Bonding1. Ionic Bonds: Anions and cations attract

each other

2. Covalent Bonds: Atoms share electrons

3. Metallic Bonds: Free floating valance electrons around positive charge metal ions

Ionic Bonds• Cations: Loss of valence electrons to produce a

positively charged ion with stable octetelectron configuration

Na Na+ Ne MgMg2+

Ionic Bonds• Cations: Loss of valence electrons to produce a

positively charged ion with stable octetelectron configuration

Na 1s22s22p63s1

Na+ 1s22s22p6

Ne 1s22s22p6

Mg 1s22s22p63s2

Mg2+ 1s22s22p6

Ionic Bonds• Anions: Gain of valence electrons to produce

negatively charged ion with stable octetelectron configurationClCl-

ArOO2-

Ne

Ionic Bonds• Anions: Gain of valence electrons to produce

negatively charged ion with stable octetelectron configurationCl 1s22s22p63s23p5

Cl- 1s22s22p63s23p6

Ar 1s22s22p63s23p6

O 1s22s22p4

O2- 1s22s22p6

Ne 1s22s22p6

Ionic Bonds

Ionic Bonds• What would happen if Mg combined with Cl?

Ionic Bonds• Formula Unit: the lowest whole-number ratio of ions

in an ionic compound.

1Na: 1Cl NaCl

What would it be for magnesium chloride?

Ionic Bonds• Compound Properties:– Solids– Repeating crystal structure– Stable– High Melting Point

Covalent Bonds• Holds molecules together

• (through sharing valance electrons)• Diatomic molecule: has ONLY 2 atoms

• Molecular formula: shows how many atoms of each element are in a molecule

• How is this different from a formula unit?

REVIEW!

• Covalent bonds are made so atoms can have a full outer valence shell through sharing electrons– OCTET RULE

Covalent Bonds• Three types of covalent bonds:– Single: 1 pair of electrons are shared– Double: 2 pairs of electrons are shared– Triple: 3 pairs of electrons are shared

Covalent Bonds• Single Covalent Bonds– Electron dot structure: Shows VALENCE electrons as dots

– Structural formula: Shows SHARED electrons as lineH-H

Covalent Bonds• Single Covalent Bonds:– Draw the electron dot structure and structural formula for:

Electron Dot For Each Atom Electron Dot For Molecule Structural Formula

H2O

F2

NH3

CH4

Unshared/Lone Pair: valence electrons not involved in bond

Covalent Bonds• Double and triple bonds– Draw the electron dot structure and the structural formula for:

Electron Dot For Each Atom Electron Dot For MoleculeStructural Formula

O2

N2

CO2

CO

Covalent Bonds• Polar covalent bond: electrons are not equally shared

Due to electronegativity!

Covalent Bonds

• Molecule Properties:– Low melting and boiling points– Liquid or gas – No ions and No Charge

Attractions Between Molecules• Van der Waals Forces:– Dipole interactions: positive region of one polar

molecule is attracted to negative region of another polar molecule

– Dispersion forces: random electron motion in one nonpolar molecule effects the electron motion in a neighboring nonpolar molecule

Attractions Between Molecules• Hydrogen Bonds: A hydrogen covalently bonded

to a very electronegative atom weakly bonds to an unshared pair of electrons on another electronegative atom

Review: Types of AttractionsIonic Bond

Covalent Bond

Hydrogen Bond

Dipole Interactions

Dispersion Forces

Strongest

Weakest

• Why do ionic compounds have higher melting points than molecules?

Ionic Compounds have to break an ionic bond to melt.Molecules have to break a hydrogen bond, dipole

interaction, or dispersion force to melt.

Organic MoleculesBiology Review!

• Covalent Bonds• Polymers: large molecules made by repeating

subunits– DNA– Protein– Carbohydrates

• Made possible by Carbon

Organic Molecules

• DNA– Subunit: Nucleotide

Organic Molecules

• Protein– Subunit: amino acids

Organic Molecules

• Carbohydrates– Subunits: Saccharides (sugars)