Atomic Structure

Each atom consists of a central core with negatively charged electrons revolving around the core. The core consists of positively charged protons and uncharged neutrons. The core is called the nucleus of an atom. An atom as such is electrically neutral. Atoms of different elements have different and unique characteristics. Although all atoms are made up of protons, neutrons and electrons, it is the way these subatomic particles are arranged that gives each of the atom its unique characteristics.

The dimension of an atom is of the order of 10-10 m. This unit of measurement is called an Angstrom and is written as A°. That is 10-10 m = 1 A°. On a 1 cm marking on your ruler, you can place 10 crore Hydrogen atoms side by side!! A nucleus of an atom is more compact and its approximate size is of the order of 10-15 m. This unit of measurement is called as Fermi and is written as fm. That is 10-15m= 1fm. It has to be noted here that both the nucleus as well as the atom is not a point like particle, but has a certain definite size or dimensions.

Mass of protons, neutrons and electrons are very small. A proton is 1.672 6 x 10-27 kg, a mass of neutron is 1.674 x 10-27 kg. A neutron therefore is slightly heavier than a proton. An electron weighs 9.1.93 x 10-31 kg. Thus a mass of an electron is about 1830 times smaller than a proton. Now you can imagine how small an atom is!!

From our above discussion, we can see that an atom of any element would weigh very less. It has been an established convention in Physics, to say that the atomic weight of an element is a number representing the sum of the constituent protons and neutrons. The number of protons is represented as Z, the number of neutrons is represented as N and the atomic weight is represented as A (A= Z+N).

Solutions and Mixtures

Before we dive into solutions, let's separate solutions from other types of mixtures. Solutions are groups of molecules that are mixed up in a completely even distribution. Hmmm. Not the easiest way to say it. Scientists say that solutions are homogenous systems. Other types of mixtures can have a little higher concentration on one side of the liquid when compared to the other side. Solutions have an even concentration throughout the system. An example: Sugar in water vs. Sand in water. Sugar dissolves and is spread throughout the glass of water. The sand sinks to the bottom. The sugar-water could be considered a solution. The sand-water is a mixture.

Pretty much. Solutions can be solids dissolved in liquids. They could also be gases dissolved in liquids (such as carbonated water). There can also be gases in other gases and liquids in liquids. If you mix things up and they stay at an even distribution, it is a solution. You probably won't find people making solid-solid solutions in front of you. They start off as solid/gas/liquid-liquid solutions and then harden at room temperature. Alloys with all types of metals are good examples of a solid solution at room temperature. A simple solution is basically two substances that are going to be combined. One of them is called the solute. A solute is the substance to be dissolved (sugar). The other is a solvent. The solvent is the one doing the dissolving (water). As a rule of thumb, there is usually more solvent than solute.

Liquid Basics

The second state of matter we will discuss is a liquid. Solids are hard things you can hold. Gases are floating around you and in bubbles. What is a liquid? Water is a liquid. Your blood is a liquid. Liquids are an in-between state of matter. They can be found in between the solid and gas states. They don't have to be made up of the same compounds. If you have a variety of materials in a liquid, it is called a solution.

One characteristic of a liquid is that it will fill up the shape of a container. If you pour some water in a cup, it will fill up the bottom of the cup first and then fill the rest. The water will also take the shape of the cup. It fills the bottom first because of gravity. The top part of a liquid will usually have a flat surface. That flat surface is because of gravity too. Putting an ice cube (solid) into a cup will leave you with a cube in the middle of the cup; the shape won't change until the ice becomes a liquid.

A special force keeps liquids together. Solids are stuck together and you have to force them apart. Gases bounce everywhere and they try to spread themselves out. Liquids actually want to stick together. There will always be the occasional evaporation where extra energy gets a molecule excited and the molecule leaves the system. Overall, liquids have cohesive (sticky) forces at work that hold the molecules together.

Another trait of liquids is that they are difficult to compress. When you compress something, you take a certain amount and force it into a smaller space. Solids are very difficult to compress and gases are very easy. Liquids are in the middle but tend to be difficult. When you compress something, you force the atoms closer together. When pressure go up, substances are compressed. Liquids already have their atoms close together, so they are hard to compress. Many shock absorbers in cars compress liquids in tubes.