Types of Solids

Intra V Inter

Intramolecular

• Type of bonding within the molecule

• Covalent• Ionic• Metallic

• Covalent • Simple molecular

solids with different intermolecular forces

Intermolecular

• Forces holding holding molecules together

• Van der Waals• Dipole-dipole• Hydrogen Bonding• These are the forces

which are broken when a substance melts of changes state. These forces are used to explain physical properties of molecules.

Van der Waals

• Weakest force holding molecules together.

• Exist between atoms and NON-POLAR MOLECULES

• The size of the force increases with size.• The bigger the atoms the bigger the force.• The more electrons the stronger the force.

Dipole-Diplole

• Exist between POLAR molecules

• Strength of the force increases with more Electronegative atoms.

• Green Line represents the force

Hydrogen Bonding

• This is the strongest form of intermolecular force in POLAR MOLECULES.

• Attraction between hydrogen atoms and the lone pairs of either N, O or F atoms (the 3 most electronegative atoms) on a different molecule. They attract each other because of the difference in their electronegativities.

•   So what should you look for to see if a substance has hydrogen bonding?

– Look for either an O, N or F atom in the molecule. – Look for a hydrogen atom attached to any of the

above named atoms. – TYPICAL PHYISCAL PROPERTIES– Unusually high melting and boiling points.

H

H

O

H

H

O

H

H

O

Hydrogen Bonding

Between the Lone pair on the O, N or F and the H on a neighbouring atom.

Hydrogen bonding in Water

Quick Test• For each of the molecules in the list, say

what type of intermolecular forces hold them together:

• hydrogen           

• ethanoic acid    CH3C-O-H          

• benzene  C6H6          

• ammonia           

• Iodine        

O

Polar or Non-Polar

• tetrachloromethane     CCl4   

• carbon dioxide               

• methane      CH4                  

• ethanol         CH3CH2OH                 

• trichloromethane  CHCl3

Properties of Molecules

• Generally• Non conductors of electricity• Low melting & boiling points• Why? Use FSEP – Force, Strength, Energy, Property

• When changing from a solid to liquid the forces to be broken are the intermolecular forces between molecules.

• These are relatively weak (van der waals etc)• Therefore require little energy to break • Hence a low melting point.

Why does I2 sublime?

• F

• S

• E

• P

• The intermolecular force of Van der Waals needs to be broken

• This is a weak force• Therefore little

energy is required to break

• Hence easily turns from solid to gas

Why does H2O have a higher m.p than H2Se even though Se is a bigger atom?

• F

• S

• E

• P

• H2O is polar & contains Hydrogen bonding whereas H2Se only contains Van der waals.

• Hydrogen Bonding is a stronger intermolecular force

• Therefore more energy is needed to break these bonds

• Hence a higher melting Point

Metallic Solids

• Contain Metallic Bonding

• Between metals

• Explains their typical physical properties

Metallic bonding

• Between one type of metal atom

• Electrons form a ‘sea of delocalised electrons’

• Bond is between electrons and positive nuclei called electrostatic attraction.

• The more valence shell of electrons the stronger the force of attraction

Metals Properties

• Good electrical conductors.

• Ductile, Malleable

• Hard solids

• Good heat conductors

• High melting & boiling points

Electrical Conductors

• Metals contain metallic bonding which has a sea of electrons

• The electrons are mobile and able to carry current to complete the circuit

Solids with High Melting points

• F

• S

• E

• P

• Metals contain metallic bonding, electrostatic attraction between sea of electrons and positive nuclei.

• This is very strong force of attraction

• It therefore requires a large amount of energy to break it.

• Hence metals have a high melting point

Ionic Crystals

• Exists between positive metal ions and negative non-metal ions.

• This is a strong force of electrostatic attraction.

• There are very many ionic bonds in an ionic compound such as sodium chloride, arranged in giant lattice structures.

• Ionic compounds have high melting points and high boiling points.

NaCl Crystal

Properties

• Many ionic compounds are soluble in water, but not all. Ionic compounds are polar as is water.

• The solid crystals DO NOT conduct electricity because the ions are not free to move to carry an electric current.

• However, if the ionic compound is melted or dissolved in water, the liquid will now conduct electricity, as the ion particles are now free.

Melting Points

• F

• S

• E

• P

• Ionic compounds are made up of oppositively charged particles held together by electrostatic forces of attraction

• This force is a very strong attraction

• Therefore a large amount of energy are needed to break them

• Hence they have high melting points.

Identify the type of solid

• I2

• MgO• Mg

• MgCl2• Cl2• HCl

Order of strength so far..

• Van der Waals

• Dip- dip

• Hydrogen Bonding

• Ionic Bonding

• Metallic Bonding

Giant Covalent Molecules

• Exist in special covalently bonded substance

• Consists of many Atoms bonded to atoms by a covalent bond in a giant structure

Diamond

• Each carbon bonded to 4 other carbons

• In a 3D structure

• Similarly SiO2 – silica (sand)

Diamond Properties

• High melting point – 4 very strong covalent bonds to break

• Non- conductor of Electricity as no free ions or electrons

• Non- polar therefore doesn’t dissolve in water

• Hard as strong covalent bonds in all directions

Graphite

• Each Carbon covalently bonded to 3 other Carbons

• Arranged in layers weak van der waals holding them together

• Free electrons not involved in bonding in between layers

Graphite Properties

• High melting point as bonded by strong covalent bonds

• Good conductor of electricity as delocalised electrons between layers

• Non- polar therefore doesn’t dissolve in water

• Soft as layers can slide over each as weak VdW forces between layers

Conclusion of Strength of forces holding solids together

• Covalent – Giant Macromolecular

• Metallic

• Ionic Crystals

• Simple molecules – Hydrogen Bonding- Dipole – Dipole

- Van der Waals