## Thursday, July 16, 2020

### What are Physical Properties of Matter?

Where are we going with this?
The point of this deck is to give the background information and examples so that we can differentiate between substances (pure and mixtures) based on physical and chemical properties.

What are Physical Properties of Matter?

physical property is any attribute, quality, or characteristic of a material that can be observed or measured without changing the composition of the substances in the material.

This "not changing the composition" thing is the key, here. It can change shape or even go from solid to liquid and be a physical property, but if it stops being something (like burning paper) then it is not a physical property.

The physical properties of a material can be used to help identify it. A sample can be compared to known quantities to determine if the sample is made from them. For example, if an unknown metal has a density of 10.5 g/cm, it might be silver. If the other properties of the unknown match other known properties of silver, then the conclusion that the sample is sliver might be well-founded.

Some physical properties are independent of the amount of the substance preset. Some physical properties change as the amount present changes.

There are many different properties that can be observed. The following are some examples.

Viscosity (intensive)
Viscosity is the tendency of a liquid to keep from flowing—its resistance to flowing.

viscosity
the degree to which something is thick, sticky, and semifluid in consistency, due to internal friction.

a quantity expressing the magnitude of internal friction, as measured by the force per unit area resisting a flow in which parallel layers unit distance apart have unit speed relative to one another.

One way to think about viscosity is to consider how "thick" a liquid is. Syrup is MORE viscous than water is.

The viscosity of a liquid usually decreases as its temperature goes up.

Conductivity (intensive)
Conductivity is the term used to express how well a material allows heat or electricity to flow.

conductivity
the degree to which a specified material conducts electricity, calculated as the ratio of the current density in the material to the electric field that causes the flow of current. It is the reciprocal of the resistivity.

(also thermal conductivity) the rate at which heat passes through a specified material, expressed as the amount of heat that flows per unit time through a unit area with a temperature gradient of one degree per unit distance.

Materials that have high conductivity, such as metals, are called conductors.

Hardness (intensive)
Hardness of a material relates to the degree to which its surface can be penetrated. For an object to scratch another object, it must be made of a material that has more hardness then the other.

hardness
a measure of how resistant solid matter is to various kinds of permanent shape change (such as bending, denting, and scratching) when a compressive force is applied.

Malleability (intensive)

Malleability is the ability of a solid to be hammered without shattering.

malleable
(of a metal or other material) able to be hammered or pressed permanently out of shape without breaking or cracking.

Most metals malleable to a greater degree than are other things, like ice or glass.

Ductility (intensive)

The degree to which a substance can elongate when pulled.

Examples: Chewing gum is very ductile. You can pull it and stretch it really far out of your mouth (although that is gross and germy). Carrots are not, compared to gum, very ductile. They snap off.

Flexibility (intensive)

Flexibility refers to how bendable something is. The more bendable something is the more flexible it is. If matter is not bendable then we call it rigid. Glass is rigid, and will break if you try to bend it too hard.

Elasticity (intensive)
Elasticity is the ability of an object or material to resume its normal shape after being stretched or compressed; sketchiness.

Melting and Boiling Points (intensive)
The melting point is the temperature at which a substance changes from solid to liquid. This same temperature is also the point at which the substance changes from a liquid to solid (freezing point).

The boiling point is the temperature at which a substance changes from a liquid to a gas. At this same temperature, gases condense into a liquid (condensation point).

Density (intensive)
Density is the ratio of a substance's mass to its volume and can be expressed mathematically as…

D=M/V

where D is the density, M is the mass, and V is the volume of the sample.

Density results from the number of protons, neutrons, and electrons in the atoms that make up the substances and how closely they are arranged to each other either in the substance.

Appearance (intensive)
How does it look? What is visually identifiable about the substance?

Some aspects of a physical appearance include its color, texture, or sheen. Uniformity of these things could also be a factor, or variances might indicate that the sample has some impurities in it.

Odor (intensive)

IMPORTANT NOTE: Don't sniff chemicals! You could die!

While it is dangerous to inhale chemicals, some of them do stimulate the olfactory nerves which results in the perception of odor.

Solubility (intensive)

Solubility is the degree to which a substance (solute) dissolves in a given solvent (other substance). Not everything dissolves in everything! There is a vast degree of variance in what will dissolve in what and to what degree! You need only watch a few TV commercials to know that Brand A dish soap will dissolve grease better than all the other! Let's just skip the laundry ads!

Solubility for a given substance might be noted in relationship to various solvents. How well does it dissolve in water? How about alcohol? How about mineral spirits? How about acetone?

Nail polish is a very intuitive example. Nail polish does not dissolve very well if at all in water. (If it did, it would come off with every hand wash!) It does, however dissolve readily in acetone (nail polish removers often are acetone).

Magnetivity / Magnetism (intensive*)

The degree to which a substance is attracted to or repelled by magnets and magnetic fields. Basically, do magnets stick to it or does it stick to iron?

*Larger samples of a magnetic substance will create a larger (i.e. stronger) magnetic pull, but the property is uniform regardless of sample size)

Specific Heat (intensive)

The capacity of a substance to hold energy in the form of heat.

If you have a dishwasher and have ever tried to unload it right after it was done, you know that the glass bowls will burn your fingers more than the plastic ones, but when the door opens, they are all the same temperature. Glass can hold heat better than plastic. Thus, the specific heat of glass is higher than the specific heat of plastic.

Specific heat is measured in a unit of energy per a unit of mass such as cal/gr or J/gr.

Opacity (intensive)

The capacity of a substance to block (usually limited to visible light) electromagnetic waves. Opacity ranges from transparent (light passes without diffusion), to translucent (some light passes but is diffused) to opaque (no light passes through).

While opacity is frequently used to discuss visible light, the same term applies to other types of radiation as well.

Mass (extensive)

The total amount of matter present, the sum of all the electrons, protons, and neutrons within the sample.

Volume (extensive)

The total amount of space occupied by the sample.

Density (intensive)

(D) is an intensive property of matter that is the ratio of mass (m) to volume (V) found by:

D = m/V