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The properties of matter

Let us now look at what we have learned about chemical bonds, intermolecular forces and the kinetic theory of matter, and see whetherthis can help us to understand some of the macroscopic properties of materials.

  1. Melting point
    Melting point
    The temperature at which a solid changes its phase or state to become a liquid . The process is called melting and the reverse process (change in phase from liquidto solid) is called freezing .
    In order for a solid to melt, the energy of the particles must increase enough to overcome the bonds that are holding the particlestogether. It makes sense then that a solid which is held together by strong bonds will have a higher melting point than one where the bonds are weak, because more energy (heat) is needed to breakthe bonds. In the examples we have looked at metals, ionic solids and some atomic lattices (e.g. diamond) have high melting points, whereas the meltingpoints for molecular solids and other atomic lattices (e.g. graphite) are much lower. Generally, the intermolecular forces between molecular solids are weaker than those between ionic and metallic solids.
  2. Boiling point
    Boiling point
    The temperature at which a liquid changes its phase to become a gas . The process is called evaporation and the reverse process is called condensation
    When the temperature of a liquid increases, the average kinetic energy of the particles also increases and they are able to overcomethe bonding forces that are holding them in the liquid. When boiling point is reached, evaporation takes place and some particles in the liquid become a gas. In other words, the energy of theparticles is too great for them to be held in a liquid anymore. The stronger the bonds within a liquid, the higher the boiling point needs to be in order tobreak these bonds. Metallic and ionic compounds have high boiling points while the boiling point for molecular liquids is lower.The data in [link] below may help you to understand some of the concepts we have explained. Not all of the substances in the table aresolids at room temperature, so for now, let's just focus on the boiling points for each of these substances. What do you notice?
    The melting and boiling points for a number of substances
    Substance Melting point ( ° C ) Boiling point ( ° C )
    Ethanol ( C 2 H 6 O ) - 114,3 78,4
    Water 0 100
    Mercury -38,83 356,73
    Sodium chloride 801 1465
    You will have seen that substances such as ethanol, with relatively weak intermolecular forces, have the lowest boiling point, while substances withstronger intermolecular forces such as sodium chloride and mercury, must be heated much more if the particles are to have enough energy to overcome theforces that are holding them together in the liquid. See the section below for a further exercise on boiling point.
  3. Density and viscosity
    Density and viscosity is not in CAPS - Included for Completeness
    Density
    Density is a measure of the mass of a substance per unit volume.
    The density of a solid is generally higher than that of a liquid because the particles are held much more closely together and therefore thereare more particles packed together in a particular volume. In other words, there is a greater mass of the substance in a particular volume. In general, densityincreases as the strength of the intermolecular forces increases.
    Viscosity
    Viscosity is a measure of how resistant a liquid is to flowing (in other words, how easy it is to pour the liquid from one container toanother).
    Viscosity is also sometimes described as the 'thickness' of a fluid. Think for example of syrup and how slowly it pours from one container into another. Now compare this to how easy it is to pour water. The viscosity ofsyrup is greater than the viscosity of water. Once again, the stronger the intermolecular forces in the liquid, the greater its viscosity.

It should be clear now that we can explain a lot of the macroscopic properties of matter (i.e. the characteristics we can see or observe) by understanding their microscopic structure and the way in which the atoms and molecules that make up matter are held together.

Exercise: forces and boiling point

The table below gives the molecular formula and the boiling point for a number of organic compounds called alkanes (more on these compounds in grade 12). Refer to the table and then answer the questions that follow.

Organic compound Molecular formula Boiling point ( ° C )
Methane CH 4 -161.6
Ethane C 2 H 6 - 88.6
Propane C 3 H 8 -45
Butane C 4 H 10 -0.5
Pentane C 5 H 12 36.1
Hexane C 6 H 14 69
Heptane C 7 H 16 98.42
Octane C 8 H 18 125.52
Data from: http://www.wikipedia.com
  1. Draw a graph to show the relationship between the number of carbon atoms in eachalkane and its boiling point. (Number of carbon atoms will go on the x-axis and boiling point on the y-axis).
  2. Describe what you see.
  3. Suggest a reason for what you have observed.
  4. Why was it enough for us to use 'number of carbon atoms' as a measure of the molecular weight of the molecules?

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
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Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
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Properties of longitudinal waves
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Source:  OpenStax, Siyavula textbooks: grade 10 physical science [caps]. OpenStax CNX. Sep 30, 2011 Download for free at http://cnx.org/content/col11305/1.7
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