The best type of chemical for cleaning will depend on what you want to clean. For example, water might work in many cases, but it won't remove oil from your hands. That is when you add soap. The molecules in soap have one end which is attracted to the oil molecules and another end attracted to water molecules (hydrophobic and hydrophilic ends, respectively). There are a host of other cleaning agents to consider though.

This site contains a discussion of the different types and how they work.

I like Borax - about 1/4 cup in a load of laundry to remove odors, along with laundry detergent.

It depends on what you want to clean, because different chemicals that need to be cleaned have different properties. Water is good for salts or sugars because it dissolves them, but is not good for oils or many nitrogen-containing compounds that it can't dissolve.

Bleach breaks down most things that contains carbon, but you don't want to bleach wooden furniture or clothes because it will break down the furniture and clothes just as it will whatever you're trying to clean off.

When something needs to be cleaned, it usually means that there is a material on the surface that you want to remove. A good way to remove materials from a surface is to dissolve them in a liquid and rinse them away, just like you dissolve salt or sugar in water. In fact, water is a great liquid for cleaning things, because it dissolves many materials. A material that dissolves in water is called water soluble.

However, some materials do not dissolve in water—they are not water soluble. One example is oil. Oil and water do not like to mix with each other, and therefore if you get oil on your hands, it is hard to wash it off with water alone.

There are many other materials that are soluble in oil but not in water. For example, if you walk on the beach and get tar on your feet, it will be easier to remove the tar with oil than with water. So, one way to clean both water-soluble and oil-soluble materials from surfaces is to first wash with water, and then wash with oil. That would be messy though! There is a better way: soap.

Soap is the common name for a type of material called a surfactant, also called a detergent. A surfactant is any material that has molecules with two sides, a side that likes water and a side that likes oil. Surfactants are both water-soluble and oil soluble. What this means is that you can take a solution of water and surfactant (one example of this is liquid dish soap), and it will dissolve materials that are soluble in water and materials that are soluble in oil! Common surfactants are sodium lauryl sulfate and sodium laureth sulfate which are found in many dish soaps and shampoos. Look at the ingredients lists of the soaps around your house and see if you can find these surfactants!

The most common household cleaning reagents are divided into several types. One type is acidic and includes all kinds of vinegars and other stronger substances. These can dissolve minerals that have stuck to surfaces, and some can break down protein and grease.

Another type is alkaline, which includes baking soda, lye, and bleach. These can dissolve protein as well as fats and oils. Both acidic and alkaline cleaners have electric charges in water.

A third major type of cleaner is called surfactants, which we most commonly encounter as soaps and detergents (dish detergent is an example). These cleaners typically have chemical structures that are larger than the structures of acidic and alkaline substances and can be good at degreasing as well.

A fourth type of cleaner is what we sometimes call organic solvents. These are liquids that are made of carbon and hydrogen atoms connected together. Organic solvents are particularly good at dissolving oil-based substances, including some paints and things such as tar. However, organic solvents are not as common as the other three types in household use because of their potential toxicity to humans; they should always be used with appropriate protective equipment (gloves, closed-toed shoes, masks as necessary) and abundant caution.