Introduction to Chemistry. Search for:. Physical and Chemical Properties of Matter. Learning Objective Recognize the difference between physical and chemical, and intensive and extensive, properties. Key Points All properties of matter are either physical or chemical properties and physical properties are either intensive or extensive. Extensive properties, such as mass and volume, depend on the amount of matter being measured. When atoms of two or more elements come together and bond, a compound is formed.
The compound formed can later be broken down into the pure substances that originally reacted to form it. Compounds such as water are composed of smaller units of bonded atoms called molecules. Molecules of a compound are composed of the same proportion of elements as the compound as a whole since they are the smallest units of that compound.
For example, every portion of a sample of water is composed of water molecules. Each water molecule contains two hydrogen atoms and one oxygen atom, and so water as a whole has, in a combined state, twice as many hydrogen atoms as oxygen atoms..
Water can still consist of the same molecules, but its physical properties may change. When matter changes from one state to another, temperature and pressure may be involved in the process and the density and other physical properties change.
The temperature and pressure exerted on a sample of matter determines the resulting form of that the matter takes, whether solid, liquid, or gas. Since the properties of compounds and elements are uniform, they are classified as substances.
When two or more substances are mixed together, the result is called a mixture. Mixtures can be classified into two main categories: homogeneous and heterogeneous. A homogeneous mixture is one in which the composition of its constituents are uniformly mixed throughout.
A homogeneous mixture in which on substance, the solute, dissolves completely in another substance, the solvent, may also be called a solution. Usually the solvent is a liquid, however the solute can be either a liquid, solid, or a gas. In a homogeneous solution, the particles of solute are spread evenly among the solvent particles and the extremely small particles of solute cannot be separated from the solvent by filtration through filter paper because the spaces between paper fibers are much greater than the size of the solute and solvent particles.
Other examples of homogeneous mixtures include sugar water, which is the mixture of sucrose and water, and gasoline, which is a mixture of dozens of compounds. Homogeneous Mixtures: Filtered seawater is solution of the compounds of water, salt sodium chloride , and other compounds. A heterogeneous mixture is a nonuniform mixture in which the components separate and the composition varies. Unlike the homogeneous mixture, heterogeneous mixtures can be separated through physical processes.
An example of a physical process used is filtration, which can easily separate the sand from the water in a sand-water mixture by using a filter paper. Some more examples of heterogeneous mixtures include salad dressing, rocks, and oil and water mixtures. Heterogeneous mixtures involving at least one fluid are also called suspension mixtures and separate if they are left standing long enough. Consider the idea of mixing oil and water together. Regardless of the amount of time spent shaking the two together, eventually oil and water mixtures will separate with the oil rising to the top of the mixture due to its lower density.
Heterogeneous Mixtures: separation of sand and water separation of salad dressing various mixtures within a rock. Mixtures that fall between a solution and a heterogeneous mixture are called colloidal suspensions or just colloids.
A mixture is considered colloidal if it typically does not spontaneously separate or settle out as time passes and cannot be completely separated by filtering through a typical filter paper. It turns out that a mixture is colloidal in its behavior if one or more of its dimensions of length, width, or thickness is in the range of nm. A colloidal mixture can also be recognized by shining a beam of light through the mixture. If the mixture is colloidal, the beam of light will be partially scattered by the suspended nanometer sized particles and can be observed by the viewer.
This is known as the Tyndall effect. In the case of the Tyndall effect, some of the light is scattered since the wavelengths of light in the visible range, about nm to nm, are encountering suspended colloidal sized particles of about the same size.
In contrast, if the beam of light were passed through a solution, the observer standing at right angles to the direction of the beam would see no light being reflected from either the solute or solvent formula units that make up the solution because the particles of solute and solvent are so much smaller than the wavelength of the visible light being directed through the solution. Colloidal Mixtures: Colloidal mixture have components that tend not to settle out. Milk is a colloid of liquid butterfat globules suspended in water.
Most substances are naturally found as mixtures, therefore it is up to the chemist to separate them into their natural components. One way to remove a substance is through the physical property of magnetism. For example, separating a mixture of iron and sulfur could be achieved because pieces of iron would be attracted to a magnet placed into the mixture, removing the iron from the remaining sulfur. The noble gases helium, neon, argon, krypton, xenon and radon are often used to make glowing signs by using electricity to ionize them to the plasma state.
At this extremely low temperature, molecular motion comes very close to stopping. Since there is almost no kinetic energy being transferred from one atom to another, the atoms begin to clump together. There are no longer thousands of separate atoms, just one "super atom. A BEC is used to study quantum mechanics on a macroscopic level. A BEC also has many of the properties of a superfluid , or a fluid that flows without friction. BECs are also used to simulate conditions that might exist in black holes.
Adding or removing energy from matter causes a physical change as matter moves from one state to another. For example, adding thermal energy heat to liquid water causes it to become steam or vapor a gas.
And removing energy from liquid water causes it to become ice a solid. Physical changes can also be caused by motion and pressure.
When heat is applied to a solid, its particles begin to vibrate faster and move farther apart. When the substance reaches a certain combination of temperature and pressure, its melting point , the solid will begin to melt and turn into a liquid. When two states of matter, such as solid and liquid, are at the equilibrium temperature and pressure, additional heat added into the system will not cause the overall temperature of the substance to increase until the entire sample reaches the same physical state.
For example, when you put ice into a glass of water and leave it out at room temperature, the ice and water will eventually come to the same temperature. As the ice melts from heat coming from the water, it will remain at zero degrees Celsius until the entire ice cube melts before continuing to warm. When heat is removed from a liquid, its particles slow down and begin to settle in one location within the substance.
When the substance reaches a cool enough temperature at a certain pressure, the freezing point, the liquid becomes a solid. Most liquids contract as they freeze. Water, however, expands when it freezes into ice, causing the molecules to push farther apart and decrease the density, which is why ice floats on top of water.
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