Chemistry Part 2 “Properties” Part 2

All substances have properties that we can use to identify them All substances have properties that we can use to identify them. For example we can identify a person by their face, their voice, height, finger prints, DNA etc.. The more of these properties that we can identify, the better we know the person. In a similar way matter has properties - and there are many of them. There are two basic types of properties that we can associate with matter. Physical properties can be observed or measured without changing the composition of matter. Physical properties are used to observe and describe matter. A few of many examples: Appearance – What does it look like? Texture – What does it feel like? Color – What shades and hues are noticeable? Odor – What scents does it produce? Melting Point – At what temperature does it turn to liquid? Boiling Point – At what temperature does it turn to a gas? Density – How tightly are it’s atoms packed? Electromagnetism – How does it interact with electricity and magnetic fields? Determining density or conductance will not change the before and after sample Measuring any of these properties will not alter the identity of the substance.

Chemical properties are only observable during a chemical reaction Chemical properties are only observable during a chemical reaction. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected for its chemical properties to be investigated. A few among many: Flammability – Will it catch fire? pH Balance – Will acid levels change? Toxicity – Is it harmful to life? Corrosion, Oxidation, Reactivity – Does it “disappear”? Rust? Will it react with other substances? To check for these properties, the substance you are left with will be different from the one you started with. These properties are a measure of the potential for something to change the very nature of matter involved. Which boat anchor will rust the quickest when exposed to seawater? We won’t know until we start the reaction. Some will rust quickly, some slowly, some not at all. We cannot tell by simply looking at them as they are....the answer is hidden in the atoms of the matter they are made from. This property is a chemical property!

Physical Changes occur when objects undergo a change that does not change their chemical nature. A physical change involves a change in physical properties. Physical properties can be observed without changing the type of matter.. An example of a physical change occurs when making a baseball bat. Wood is carefully crafted into a shape which will allow a batter to best apply force on the ball. Even though the wood has changed shape and therefore physical properties, the chemical nature of the wood has not been altered. The bat and the original piece of wood are still the same chemical substance. OR.... Freeze water into ice cubes. Melt them into liquid. Boil the water into gas. In any state, the substance will always remain H20.... its makeup has not been changed! Only a physical change has taken place.... The same element or compound is present before and after the change. The same molecule is present throughout the changes!

Chemical changes are changes substances undergo when they become new or different substances. For example, the fireworks we see on the 4th of July are actually metals such as magnesium and copper that change chemically as they light up the night skies with their fantastic colors. To identify a chemical change look for observable signs such as color change, bubbling and fizzing, light production, smoke, and presence of heat. When you burn wood (or anything else) a chemical change is taking place. What remains is not wood...It is gone forever and you can’t put it back to its original state! In a chemical reaction, bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another.