All matter can be identified by PHYSICAL PROPERTIES
Did you know that there are no two people from the past, present, or future that will have the same fingerprint? It sounds crazy but that maze of bumps and ridges on your skin is unique to you. Along with DNA, retinal scans, and dental records, fingerprints can be used to identify who we are.
Similarly, matter can be identified using PHYSICAL PROPERTIES. These are things we can observe about a sample of matter that can help us determine what type of substance or mixture it is. Let’s investigate several of the most common physical properties…
density
Density is the compactness of matter. For more information, check out the larger page on DENSITY!
melting/freezing point
The temperature required for a SOLID to melt into a LIQUID. It is also the temperature required for a LIQUID to freeze into a SOLID.
boiling/condensation point
The temperature required for a LIQUID to boil into a GAS. It is also the temperature required for a GAS to condense into a liquid. More detailed information can be found on the topic HERE
magnetism
Magnetism is the attraction of a metal to Iron, Cobalt, Nickel or Neodymium.
conductivity
Conductivity is the ability to allow electrons (electricity) to flow easily. Materials that stop or slow the flow of electrons are called insulators.
Conductivity is also the ability to allow HEAT to flow easily.
malleability
Malleability is the ability of a substance to be flattened or shaped when pounded or pressed. The opposite of malleability is brittleness. Substances that are brittle would shatter or powderize when pounded. Gold leafing is shown being made in the video below.
ductility
Ductility is the ability of a substance to be pulled into a thin, strong wire.
hardness
Hardness is the ability to RESIST being scratched. Moh’s hardness scale in Earth Science records diamond as the hardest mineral while Talc is the least. Diamond scratches everything else on the list. Talc can’t scratch anything on the list.
tensile strength
Tensile strength refers to the ability of a substance to resist pulling stress. Too much tension would cause a wire to snap. Fishing line, metal cables, structural “I” beams all have a tensile strength.
solubility
A substance is “soluble” if it is able to dissolve. Usually we think about dissolving in water but substances can change their solubility with different solvents like rubbing alcohol or acetone.
color
The color of a substance refers to the wavelengths of light that reflect off of the object. “White” isn’t a color but it reflects all of the colors to our eye. “Black” isn’t a color because no light is being reflected to our eyes. You can learn more about visible light by heading HERE.
luster
Luster refers to the shine of the substance. Some metals reflect light well while others are more dull in appearance.
odor
Some substances can be detected by our sense of smell. The term “odor” does not necessarily mean the smell is a bad one.
The properties are unique to each element but there are some general trends on the periodic table.
METALS (those elements colored blue on the diagram) typically have a high density, a high tensile strength, a high ductility, and are high on the hardness scale. Metals are typically good conductors of heat and electricity and only metals can be magnetic. They are typically solids at room temperature, silver or gray in color, and can have a high luster.
NONMETALS (colored in green on the diagram) typically have a low density, a low tensile strength, a low ductility, and are low on the hardness scale. Nonmetals are typically poor conductors of heat and electricity and none are can be magnetic. They are found in a variety of colors and some are even colorless.
METALLOIDS (colored in pink on the diagram) are the “Tex-Mex” of the periodic table. These elements are on the stair-step border between metals and nonmetals on the periodic table and have physical properties of both.
NOBLE GASES are a type of nonmetal but they are so special they get their own category. Noble gases are colorless, odorless, tasteless and (obviously) a gas at room temperature. While Neon itself is colorless it glows a bright red when electricity is sent through it. The sign below used to hang in Busch stadium and would “fly” every time the Cardinals hit a home run. Now it’s a billboard off of hwy 40/61 as your leave the ballpark.
The classification of matter:
All matter is either a pure substance or an impure mixture.
Substance – a particular kind of matter with uniform properties.
Elements
A “substance” is a type of matter that has the same properties throughout. The 118 elements (represented on the Periodic Table) are examples of a substance. Each one of the elements has a different set of properties that makes them unique. Their physical properties are like the fingerprint for the matter
Compounds
A “compound” is made when two or more elements CHEMICALLY BONDED together. The properties of a compound are unique and often don’t resemble the elements that make them up. An atom of Copper, another one of Sulfur and four atoms of Oxygen when chemically bonded makes CuSO4 . Copper sulfate is BLUE and has it’s own set of unique properties unlike the elements that make it up.
Remember that Mercury is a silver metallic liquid and Oxygen is a colorless gas. When bonded, Hg and O make an orange powder called a calx or rust.
Maybe even more impressive of a transformation is that a sweet, white powder known as glucose is made up the black powder of Carbon (that tastes like charcoal…because it is charcoal) bonded to two colorless, odorless, tasteless gases, Hydrogen and Oxygen. The properties of a compound are often totally different than the properties of the elements that are bonded. Chemistry is simply amazing!!
Because compounds are chemically bonded together, they require chemical reactions to be unbonded from each other. It is possible to get the Carbon back from the sugar or break a water molecule back into Hydrogen and Oxygen atoms but it requires a chemical change.
‘
Mixtures – When two or more substances are PHYSICALLY combined
A mixture is NOT chemically combined and will not require chemistry to separate
Non-uniform mixture
NON-uniform mixtures (also called heterogenous mixtures) are found with two or more substances that are not evenly distributed. The composition of the substances changes throughout. Imagine reaching in to a bag of m&m’s with both hands. When you examine each hand it would be basically impossible to have the same number and color of candies in both collections. The composition is not the same throughout a bag of candy.
Other examples of a non-uniform mixture would be a bin of LEGOs, a homemade chili and concrete. None of these items have exactly the same ratio of ingredients all throughout the sample.
Uniform mixture
Uniform mixtures (also called homogenous mixtures) are found with two or more substances that so evenly distributed with each other that they cannot be distinguished. Brass and Bronze aren’t found on the periodic table. They are not elements. Instead they are a uniform mixture of Copper and Zinc (Brass) and Copper and Tin (Bronze). These mixtures are called alloys and they are formed when metals are melted together.
Milk that we buy at the grocery store is a uniform mixture. The water, sugars, fats, and proteins are all “homogenized” so that every sip is exactly the same. Milk on the farm won’t be this way.
Often, a mixture starts out as a non-uniform mixture and then the more concentrated sections go through diffusion. They eventually spread evenly across the entire mixture. The food coloring is very concentrated in the first beaker. Given time, the dye will spread evenly throughout. It is UNIFORM.
McGraw/Hill
Just like the food coloring pictured above, the chemicals in a pool will eventually spread evenly throughout. The same principle applies to particles in the air as well. Imagine that you are cooking on the stove and accidentally leave it too long. It begins to burn and smoke fills the kitchen. Initially, the scent would be very concentrated to the area around the kitchen but over time, the scent will become evenly distributed throughout the house. This is why we open up a door or window and turn on the fan. The smoke now tries to spread out over the entire neighborhood and it doesn’t smell so bad in the kitchen.
Substances can be separated from mixtures using their unique physical properties.
Mixtures are physically put together so we can separate the substances that make them up. In this section we will discuss several techniques we can use to isolate the things that make up a mixture.
Magnetism
Magnetism is the attraction between the metals Iron, Cobalt, Nickel, and Neodymium. These are the only four elements that are naturally magnetic. Other elements can be made to be magnetic if they are melted together with these elements. This metallic mixture is called an alloy. A junkyard can use a powerful electromagnet to separate magnetic from non-magnetic substances to help with recycling.
Filtration
Filtration is when we separate substances by their size. There was probably a time that you played at the beach or in the sandbox . When you use a filter, you are allowing substances that are smaller to pass through while larger substances are caught on top.
Dissolving
Dissolving occurs with a substance is broken down by a liquid into smaller and smaller particles. Usually, the particles are so small that they cannot be seen. Dissolving a substance can make it easier to move.
The particles that go into the liquid are called the SOLUTE. This would be the sugar in a pitcher of lemonade.. The liquid that does the dissolving is called a SOLVENT. Together, mixture is called a SOLUTION.
Decanting
Decanting is a fancy word for pouring a liquid off of a solid. It’s important that none of the solids leave the container so we use a stirring rod to block the spout of the beaker.
This technique also allows the liquid a definite path to leave the beaker. The surface tension of the liquid sticks to the stirring rod for a more accurate pour.
Evaporation
Evaporation occurs when a liquid becomes a gas. We can used this method to separate the solute from the solvent. Reading the ingredients on a Coca-Cola lets you know what solute is dissolved in the water to make the soda. We can get that back by turning the water to water vapor.
Distillation
Distillation is very similar to evaporation (boiling) except this process will collect the vapor that comes off of the mixture. When we collect the vapor and condense it back into a liquid it has been purified.
Fractional Distillation
Fractional distillation can remove a substance out of a mixture of liquids by using the unique boiling points of each substance. This process uses the same concept as “distillation” from above but does it several times over for different liquids in a mixture. Watch the demonstration below of the fractional distillation of crude oil.
Separation Funnel
The separation funnel is a teardrop shaped piece of glassware. Liquids are filled from the top and a stopper valve is located at the bottom. The purpose of this device is to separate liquids of different densities. The higher density liquid will be on the bottom and the lower density liquids will be found on the top. If we open up the valve the more dense liquid will drip out and with a little skill, you can learn to shut off the valve at the precise moment to not allow the lower density liquids through.
