5th entry(chem) : Osmosis

What is osmosis?

Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration.

Cell membranes are completely permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.

Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecules across biological membranes is essential to many processes in living organisms. The energy which drives the process is usually discussed in terms of osmotic pressure.

What is osmotic pressure?

Osmosis is a selective diffusion process driven by the internal energy of the solvent molecules. It is convenient to express the available energy per unit volume in terms of "osmotic pressure". It is customary to express this tendency toward solvent transport in pressure units relative to the pure solvent. If pure water were on both sides of the membrane, the osmotic pressure difference would be zero. But if normal human blood were on the right side of the membrane, the osmotic pressure would be about seven atmospheres! This illustrates how potent the influence of osmotic pressure is for membrane transport in living organisms.


References:
http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.html
http://www.tvdsb.on.ca/WESTMIN/science/sbi3a1/cells/Osmosis.htm

4th entry(chem) : Diffusion

What is Diffusion?

The process Diffusion is a net transport of molecules from a region of higher concentration to one of lower concentration by random molecular motion.

Basically, it is the movement of molecules from an area of high concentration to a lower area.

When the molecules are even throughout a space - it is called EQUILIBRIUM.

Concentration gradient is a difference between concentrations in a space.

Experiment:

Consider two containers of gas A and B separated by a partition. The molecules of both gases are in constant motion and make numerous collisions with the partition. If the partition is removed as in the lower illustration, the gases will mix because of the random velocities of their molecules. In time a uniform mixture of A and B molecules will be produced in the container.
The tendency toward diffusion is very strong even at room temperature because of the high molecular velocities associated with the thermal energy of the particles.


References:
http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/diffus.html
http://en.wikipedia.org/wiki/Molecular_diffusion
http://www.biologycorner.com/bio1/diffusion.html

3rd entry(chem) : What are ions?

What are ions?
An ion is an electrically charged particle obtained from an atom or chemically bonded group of atoms by adding or removing electrons. Now what this means is that an ion is the result of taking away, or adding, electrons to an atom or a chemically bonded group of atoms. By taking away, or adding, these electrons, the particle takes on an electrical charge. Atoms are electrically neutral as they contain an equal number of positive and negative charges. An atom that adds an extra electron to it becomes a negatively charged ion. This type of ion is called an anion. An atom which loses one or more of its electrons now has a positive charge, and is called a cation.

For example, a sodium atom can lose one of its electrons and form a sodium cation. Now, instead of being Na, it would be Na+1. This means that the sodium atom has an overall positive charge of +1. Another example would be a neutral atom of Sulfur, S. If this atom of S were to gain two electrons it would become S-2. The sulfur atom would now have a total negative charge of -2.

How many protons and electrons does an ion have?

An ion has 16 protons and 18 electrons.

References:
http://www.cartage.org.lb/en/themes/sciences/chemistry/Generalchemistry/Matter/Atoms/AtomsIons/AtonsIons.htm
http://www.chem4kids.com/files/atom_ions.html

2nd entry(chem) : What are molecules?

A molecule is a definite group of atoms that are chemically bonded together. They are tightly connected by attractive forces. A molecular formula is a chemical formula that gives the exact number of different types of atoms in a molecule. Some simple molecular substances are carbon dioxide, CO2; ammonia, NH3; and water, H2O.
The atoms that are in a molecule are not just stuffed together without any order. The atoms are chemically bonded to one another in order to form a definite arrangement. A structural formula is a chemical formula which shows how the atoms are bonded to one another to form a molecule. A good example is the structural formula for water, H-O-H. Those two horizontal lines connecting the H with the O (hydrogen and oxygen) represent the chemical bonds joining the atoms.

What are chemical bonds?
A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. The explanation of the attractive forces is a complex area that is described by the laws of quantum electrodynamics.

What is the laws of quantum electrodynamics?

It is a quantum field theory of the electromagnetic force.
Taking the example of the force between two electrons, the classical theory of electromagnetism would describe it as arising from the electric field produced by each electron at the position of the other.



References:
http://www.cartage.org.lb/en/themes/sciences/chemistry/Generalchemistry/Matter/Atoms/AtomsIons/AtonsIons.htm
http://hyperphysics.phy-astr.gsu.edu/Hbase/forces/qed.html
http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
http://en.wikipedia.org/wiki/Chemical_bond

1st entry(chem) : What are atoms?

An atom is...
an extremely small particle of matter that retains its identity during chemical reactions. During the latter nineteenth century a series of experiments showed that atoms are comprised of smaller particles. An atom consists of a nucleus and one or more electrons surrounding the nucleus.
The nucleus, the core of the atom, has the majority of the mass of the atom, and a positive charge. An electron is a very light particle which circles the nucleus. It has a negative charge. In an electrically neutral atom, the number of electrons equals the positive charge on the nucleus. The nucleus of the atom is composed of two smaller particles called neutrons and protons.

What is a proton?
A proton has a positive charge equal in magnitude to the negative charge of an electron. This means that in an electrically neutral atom (one with an equal number of protons and electrons), the postive charge of the protons, combined with the negative charge of the electrons, would result in no charge because they would cancel each other out. A proton's mass, however, is a whopping 1836 times that of the electron. A neutron has a mass almost identical to a proton's, but it has no electrical charge associated with it.

Elements

An element is a substance that is made entirely from one type of atom. For example, the element hydrogen is made from atoms containing a single proton and a single electron. If you change the number of protons an atom has, you change the type of element it is.

Atomic Number

In chemistry the number of protons in the nucleus of an atom is known as the atomic number, which determines the chemical element to which the atom belongs.


References:
http://www.chem4kids.com/files/art/atom_struct1.gif
http://www.cartage.org.lb/en/themes/sciences/chemistry/Generalchemistry/Matter/Atoms/AtomsIons/AtonsIons.htm