Chemistry: Matter & Measurement

Classification is arranging items into groups or categories according to some criteria. The act of classifying creates a pattern that helps you recognize and understand the behavior of any matter in your surroundings.

Gas Liquid Solid Total disorder Lots of empty space Disorder Some space Particles closer together Order Particles fixed in position Matter is usually defined as anything that has mass and occupies space.

Solids, Liquids, and Gases –Gases have no defined shape or defined volume Low density –Liquids flow and can be poured from one container to another Indefinite shape and takes on the shape of the container. –Solids have a definite volume Have a definite shape.

A classification scheme for matter.

Properties Properties can be classified as Intensive or extensive, depending on whether their value changes with the size of the sample. Intensive properties, like temperature and melting point, have values that do not depend on the amount of sample. Extensive properties, like length and volume, have values that do depend on the sample size.

–A physical change is a change that does not alter the identity of the matter. –A chemical change is a change that does alter the identity of the matter. –A compound is a pure substance that can be decomposed by a chemical change into simpler substances with a fixed mass ratio –An element is a pure substance which cannot be broken down into anything simpler by either physical or chemical means.

Sugar (A) is a compound that can be easily decomposed to simpler substances by heating. (B) One of the simpler substances is the black element carbon, which cannot be further decomposed by chemical or physical means.

Elements

The elements of aluminum, Iron, Oxygen, and Silicon make up about 88 percent of the earth's solid surface. Water on the surface and in the air as clouds and fog is made up of hydrogen and oxygen. The air is 99 percent nitrogen and oxygen. Hydrogen, oxygen, and carbon make up 97 percent of a person. Thus almost everything you see in this picture us made up of just six elements.

Names of Elements –The first 114 elements have internationally accepted names, which are derived from: The compound or substance in which the element was discovered An unusual or identifying property of the element Places, cities, and countries Famous scientists Greek mythology Astronomical objects.

Here are some of the symbols Dalton used for atoms of elements and molecules of compounds. He probably used a circle for each because, like the ancient Greeks, he thought of atoms as tiny, round hard spheres.

–Chemical Symbols There are about a dozen common elements that have s single capitalized letter for their symbol The rest, that have permanent names have two letters. –the first is capitalized and the second is lower case. Some elements have symbols from their Latin names. Ten of the elements have symbols from their Latin or German names.

Symbol Atomic Mass Atomic Number Charge (if ion)

H Hydrogen 1 1 Protons: 1 Neutrons: 0 Electrons: 1

Na Sodium Protons: 11 Neutrons: 12 Electrons: 11

Rhenium Re Protons: 75 Neutrons: 111 Electrons: 75

The Periodic Law

The History of the Modern Periodic Table

During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.

Johann Dobereiner Model of triads In 1829, he classified some elements into groups of three, which he called triads. The elements in a triad had similar chemical properties and orderly physical properties. (ex. Cl, Br, I and Ca, Sr, Ba)

John Newlands Law of Octaves In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

Dmitri Mendeleev In 1869 he published a table of the elements organized by increasing atomic mass.

Lothar Meyer At the same time, he published his own table of the elements organized by increasing atomic mass.

Dmitri Medeleev gave us a functional scheme with which to classify elements. –Mendeleev’s scheme was based on chemical properties of the elements. –It was noticed that the chemical properties of elements increased in a periodic manner. –The periodicity of the elements was demonstrated by Medeleev when he used the table to predict to occurrence and chemical properties of elements which had not yet been discovered.

Mendeleev left blank spaces in his table when the properties of the elements above and below did not seem to match. The existence of unknown elements was predicted by Mendeleev on the basis of the blank spaces. When the unknown elements were discovered, it was found that Mendeleev had closely predicted the properties of the elements as well as their discovery.

The Periodic Law –Similar physical and chemical properties recur periodically when the elements are listed in order of increasing atomic number.

The Modern Periodic Table

Henry Moseley In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number. *“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”

Introduction –The periodic table is made up of rows of elements and columns. –An element is identified by its chemical symbol. –The number above the symbol is the atomic number –The number below the symbol is the rounded atomic weight of the element. –A row is called a period –A column is called a group

(A) Periods of the periodic table, and (B) groups of the periodic table.

–Each period ends with a completely filled outer shell that has the maximum number of electrons for that shell. –The number identifying the A families identifies the number of electrons in the outer shell, except helium –The outer shell electrons are responsible for chemical reactions. –Group A elements are called representative elements –Group B elements are called transition elements.

Chemical “Families” –IA are called alkali metals because the react with water to from an alkaline solution –Group IIA are called the alkali earth metals because they are reactive, but not as reactive as Group IA. They are also soft metals like Earth. –Group VIIA are the halogens These need only one electron to fill their outer shell They are very reactive. –Group VIIIA are the noble gases as they have completely filled outer shells They are almost non reactive.

Four chemical families of the periodic table: the alkali metals (IA), the alkaline earth metals (IIA), halogens (VII), and the noble gases (VIIIA).

Metal: Elements that are usually solids at room temperature. Most elements are metals. Non-Metal: Elements in the upper right corner of the periodic Table. Their chemical and physical properties are different from metals. Metalloid: Elements that lie on a diagonal line between the Metals and non-metals. Their chemical and physical properties are intermediate between the two.

The periodic table is the most important tool in the chemist’s toolbox!

Experimentation and Measure Measurement is the comparison of a physical quantity to be measured with a unit of measurement-that is a fixed standard of measurement Measurement of Matter: SI (Metric) Units ~ is a decimal system. Quantities differing from the base unit by powers of ten are noted by the use of prefixes. Table 1 The seven fundamental units of measure Physical quantityName of unitAbbreviation Masskilogram kg Lengthmeter m TemperatureKelvin K Amount of substancemole mol Timesecond s Electric currentampere A Luminous intensitycandela cd_______

Table 3 Some SI Prefixes MultiplePrefix__Symbol__ petaP teraT 10 9 gigaG 10 6 megaM 10 3 kilok 10 2 hectoh 10decada decid centic millimYou need to memorize the most micro  common SI prefixes such as G, nanon M, k, d, c, m, , n and p picop femtof_______