Chemical Bonds Chemical Bond; an electrostatic force of attraction that holds atoms together so they act as a unit. This attractive forces results from opposite electrical charges: + and -. + and -.

Chemical Bonds Key Concepts 1) All chemical bonds, regardless of type, are the result of attractions between opposite electrical charges.

2) The type of chemical bonding in a substance determines the chemical and physical properties of the substance.

Graphite, Diamond and Buckminsterfullerene – are all made of carbon atoms bonded together in different patterns Diamond, Graphite Buckminsterfullerene Different Bonding Patterns

Different physical and chemical properties due to different types of bonding: Salt, Sucrose, Iron Different abilities to conduct heat and electricity Different reactivity with oxygen. IONIC BondingCOVALENT BondingMETALLIC Bonding

Examples of different types of bonding: Ionic, Covalent and Metallic Bonding Work 9-2 HW problems #1-3

Chemical Bonds 3) Making or Breaking Chemicals bonds always involves changes in Energy

Breaking Bonds Costs Energy - charges are being pulled away from + charges

Energy is released when bonds are formed - charges are spending more time near + charges

Net energy change = difference of cost of breaking old bonds vs energy released when new bonds are formed

Demo:NI 3 (s)  Video link Video link Video link

Energy Changes and Chemical Bonds Question: Why do chemical bonds form? Answer: The formation of a chemical bond lowers the energy of a group of atoms. Atoms bonded together are more stable than separated individual atoms. lower energy = more stable! higher energy = less stable!

Sample Bond Formation The Na atom has 1 valence e - : 3s 1 The Cl atom needs 1 valence e - : 3s 2 3p 5 By transferring the 1 electron from Na to Cl, both atoms reach the stable or inert configuration of s 2 p 6 (lower energy!).

Two Driving Forces for Bonding 1.Individual atoms seek to optimize their valence electron configurations by LOSING, GAINING, or SHARING electrons. 2. Bonding electrons are simultaneously attracted to two positively charged nuclei.

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Work 9-2 HW #4-8 Link to video Link to video

HW 9-3 #9

Example of Different Bonding Patterns: Single vs Double vs Triple Covalent Bonds Single Bond – share 2 e- between two atoms Double Bond- share 4 e- between two atoms Triple Bond – share 6 e- between two atoms

HW 9-3, #10

HW 9-3, #11

4) Chemical Bonds are usually formed by the overlap of atomic orbitals Example: Overlap of two 1s orbitals from 2 hydrogen atoms to form H 2 molecule Example: Overlap of two 1s orbitals from 2 hydrogen atoms to form H 2 molecule Notes p. 49

2 different types of atomic orbital overlap – sigma and pi bonds Sigma Bond – straight –on overlap Pi Bond side- by- side overlap of 2 p orbitals

Sigma Bonds straight-on” overlap of 2 atomic orbitals. Sigma Bonds (σ) : first bond between 2 atoms is the result of “straight-on” overlap of 2 atomic orbitals.

Pi Bonds Pi (π) Bonds 2 nd and 3 rd pairs of shared electrons are bonded by a “sideways” overlap of parallel p orbitals.

Single, Double and Triple Bonds explained in terms of Sigma and Pi Bonds First bond formed is always a sigma ( σ) bond. 2 nd and 3 rd Bonds formed are always pi ( π) bonds.

Double Bonds are formed from 1 sigma and 1 pi bond Sigma and Pi Bonding in Ethylene

Triple bonds are formed from 1 sigma and 2 separate pi bonds

Link to Sigma and Pi Bonds Link to Sigma and Pi Bonds (Show ethylene only)

HW 9-3 #12 (π) (σ)

HW 9-3, #13

5) Chemical bonds are not static (stationary); bonds can bend, stretch, and in some cases, twist or rotate. The best analogy to represent a chemical bond is a spring. Notes p. 50

Bonds in molecules bend, stretch and rotate when they absorb infared light

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Infrared Spectroscopy Chemical bonds absorb IR radiation, producing a spectrum that helps chemists identify the types of bonds. C-H from C=C stretch and O-H stretch regions C=O stretch from COOH pattern

Different types of bonds (single, double, triple) and different atoms absorb different quantized amount of IR light at different wavelengths

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