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Classifying and Describing Matter. Classifying Matter. Substances. The units that make up all matter are called atoms. If all the atoms in a sample of matter have the same identity, that kind of matter is called an element.
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Substances • The units that make up all matter are called atoms. • If all the atoms in a sample of matter have the same identity, that kind of matter is called an element. • Matter that has the same composition and properties throughout is called a substance.
In order to be classified as an element, you must be found on the periodic table!
Compounds • A compound is a substance made up of more than one element bonded together. • Compounds often have properties that are different from the elements that make them up. • Elements and compounds cannot be reduced to more basic components by physical processes.
Chemical Formulas • Chemical formulas tell you which elements make up a compound as well as how many atoms of each element are present. • The formula of a compound communicates its identity and makeup to any scientist in the world.
What am I? • I am sodium. • My symbol is Na. • I am an element!
What am I? • I am hydrochloric acid • My formula is HCl (that is an L not an I) • I am a compound
What am I? • I am calcium carbonate • My formula is CaCO3 • I am a compound
What am I? • I am cubic zirconia • My formula is ZrO2 • I am a compound
Mixtures • When two or more substances (elements or compounds) come together but don’t combine to make a new substance, a mixture results. • The proportions of the substances in a mixture can be changed without changing the identity of the mixture. • Mixtures can be classified as homogeneous or heterogeneous.
Homogeneous Mixtures • Homogeneous mixtures (or solutions) are evenly mixed and considered to be the same throughout.
Heterogeneous Mixtures • Heterogeneous mixtures are not well mixed and the different parts can be easily seen.
Colloids • A colloid is a type of mixture that never settles. • Its particles are larger than those in solutions but not heavy enough to settle • A light beam is invisible as it passes through a solution, but is scattered as it passes through a colloid • This scattering of light by colloidal particles is called the Tyndall effect
Suspensions • A suspension is a heterogeneous mixture containing a liquid in which visible particles settle
Suspension Notice the two distinct layers
What am I? • I am salt water • I am a mixture of salts and water • I am a homogeneous mixture
What am I? • I am oil and vinegar • I am a mixture • I am a suspension
What am I? • I am milk • I am a mixture • I am a colloid
Solutions • To describe a solution, you may say that one substance is dissolved in another • The substance being dissolved is the solute and the substance that dissolves the solute is the solvent • Generally, the substance present in the largest amount is considered to be the solvent
Dissolving • Stirring a solution speeds up dissolving because it brings more fresh solvent in contact with more solute • Particle size is another factor in the speed of dissolving (the smaller the faster) • Increasing temperature will increase the rate at which most solids dissolve • Stirring or shaking a solution of gas in a liquid causes the gas to come out of a solution faster • Gases are more soluble in colder temperatures
Solubility of a substance is the maximum number of grams of the substance that will dissolve in 100 grams of solvent at a certain temperature A concentrated solution is a solution where there is more solute than solvent present A dilute solution is a solution where there is more solvent than solute present Solubility and Concentration
Saturation • A saturated solution is a solution that has dissolved all the solute it normally can hold at a given temperature • An unsaturated solution is any solution that can dissolve more solute at a given temperature • A supersaturated solution contains more solute than a saturated one has at that temperature
Physical Properties • Any characteristic of matter that you can observe without changing the substances that make up the material is known as a physical property. • Examples of physical properties include size, shape, color, density, melting and boiling points, texture, magnetism, volume, temperature, and odor
Physical Changes • A change in size, shape, or state of matter is called a physical change. • Physical changes do not change the identities of the substances in a material
Chemical Properties • A chemical property is a characteristic of a substance that indicates whether it can undergo a certain chemical change. • Examples of chemical properties include oxidation, combustibility, and flammability.
Chemical Changes • A change of one substance in a material to a different substance is a chemical change
What kind of change? • Candle wick is burning • Chemical Change • Candle is melting • Physical Change
What kind of change? • Bread is baked • Chemical Change
Nuclear Fission • The process of splitting a nucleus into two nuclei with smaller masses is called nuclear fission • The total mass of the products is slightly less than the mass of the original nucleus and the neutron • This small amount of missing mass is converted to a tremendous amount of energy during the fission reaction
Nuclear Fusion • Fusion fuses atomic nuclei together, while fission splits nuclei apart. • With nuclear fusion, lower-mass nuclei fuse together to form a single more massive nucleus + energy. • The sum of the masses of the two low-mass nuclei equals the mass of the single, massive nucleus plus the energy released (divided by c2). • Low mass nucleus + low mass nucleus = single massive nucleus + (energy released / c2) • Remember E = m c2 • The ``c'' is the symbol for the speed of light. • Nuclear fusion can power the Sun for about 10 billion years.
Fusion Reaction • Deutrium and Tritium are two isotopes of hydrogen that differ in the number of neutrons in the nucleus. • Notice that the products of nuclear fusion have less mass! The “missing” mass was converted to an incredible amount of energy!
A closer look at Nuclear Fusion… • Nuclear fusion is actually a little more complicated than shown in the previous slide…
Law of Conservation of Mass • The statement: “Matter is neither created nor destroyed during a chemical change” is known as the Law of Conservation of Mass • According to this law, the mass of all substances present before a chemical change equals the mass of all substances after the change. • Remember that a nuclear reaction is NOT a chemical reaction!
