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Compare and contrast between metallic / ionic / covalent bonding

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Desmond Sin

on 6 May 2011

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Transcript of Compare and contrast between metallic / ionic / covalent bonding

Compare and contrast between metallic / ionic / covalent bonding Ionic Bondings -Structure consisting of a giant lattice of cations and anions, held together by strong electrostatic forces of attraction.
-Ionic bond is the electrostatic forces of attraction between two oppositely charged ions. High melting and boiling points
Solid at room temperature Why?

Lots of energy needed to overcome strong electrostatic forces of attraction between cations and anions is giant ionic lattice during melting and boiling Good conductor of electricity in aqueous
or molten state but not solid state Why?

Ions are held in fixed positions by
strong electrostatic forces of attraction,
and are not free to move, no charge carriers
in solid state.

Aqueous or molten state, the ions are free
to move and can act as charge carriers. Generally soluble in water but not in organic solvents

Soluble if energy released when water molecules interact with the cations and anions is greater than the electrostatic forces of attraction between the cation and anions. Very brittle

Ions get displaced with little stress applied

ions with similar charge repel each other Metallic bondings -Structure consisting giant metallic
lattice of regularly arranged cations
surrounded by a sea of delocalised electrons.

-Metallic Bond is the electrostatic force of
attraction between the positive ions and the
sea of delocalised electrons. Number of delocalised electrons and size of cations
determine strength of metallic bond

Bigger cations and more electrons causes metallic bond to be stronger High melting and boiling points
Solid at room temperature Why?

-Large amount of energy needed to overcome the strong electrostatic forces of attraction between the giant lattice of cations and sea of delocalised electrons Good conductor of electricity in all states Why?

Sea of delocalised electrons act as mobile charge carriers
to conduct electricity Malleable and Ductile

-Because delocalised electrons move to allow the cation layers to slip past one another smoothly when a stress is applied. Covalent Bonding A chemical bond formed by the sharing of one or more electrons between atoms. Dative Bonding (Special Case)

- Donor atom donates a lone pair of electrons to the acceptor atom.
Sigma bonds

Orbitals overlap head on

All single bonds Pi bonds

Orbitals overlap side on, not possible for s orbitals

Only occurs if atoms already held by sigma bonds.

Double bonds--1 sigma bond and 1 pi bond
Triple bonds-- 1 sigma bond and 2 pi bonds Electronegativity and Polarity

-Different atoms have different electronegatity.
-More electronegative atom acquire a negative charge and the other atom acquire a partial positive charge
-When different atoms form covalent bond, results in dipole and polar bond Bond energies

Bond lengths (shorter lengths stronger)
Bond types (sigma bonds stronger)
Number of bonds (more bonds will cause it to be stronger) Insoluble in water but soluble in organic solvents.

-Absence of ions, hence energy is not released when water molecules interact Simple Covalent structures Doesn't conduct electricity at all states.

-No mobile charge carriers Low melting and boiling points

-Intermolecular forces of attraction between molecules are weak,
little energy required to overcome. Van Der Waal's forces

-A type of intermolecular force Factors for strength of attraction

-The more electrons, the stronger it is

-The larger the surface area of molecule, the stronger the forces of
attraction Hydrogen Bonding

-10 – 50 times stronger than Van der Waals’ forces

-Hydrogen atom bonded to nitrogen, oxygen or fluorine and a pair of non-bonding electrons (lone pair) on the nitrogen, oxygen or fluorine atom of a neighboring molecule.

-Strength of bonds
Fluorine>Oxygen>Nitrogen Giant Covalent structures
Exaple used--carbon
Allotropes of carbon--Diamond and Graphite Diamond High Boiling and melting points

-Strong covalent bonds throughout

-Lots of energy needed to overcome these strong covalent bonds -Also known as macromolecules

-Thousands of atoms are joined together by strong covalent bonds throughout the structure to give a 3D lattice. Generally insoluble

no possible attractions could occur which could outweigh the attractions between the covalently bound carbon atoms. Non conductor of electricity (except graphite)
No free electrons in covalent molecules as all electrons are involved in bonding
Therfore no mobile charge carriers Graphite Conductor of electricity

-Each carbon molecule is bonded to 3 other carbon atoms.

-One free electron per carbon molecule is delocalized

-Presence of free electrons to act as mobile charge carriers Reflections

I did not do too well for this term's test, mainly because i did not grasp the concepts
well enough. However, after doing this ACE activity, i managed to understand the concepts
much better than before. A mindmap which flows through in sequence is really helpful to understand things better, especially if all the ideas are compiled by myself. Althugh it took me quite some time to finish, I think that this activity is beneficial and useful.
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