Periodic+Trends

Mendeleev’s Periodic Table

Dmitri Mendeleev was a Russian scientist who created to first version of the periodic table that we use today. Mendeleev organized his table according to two different factors: atomic mass and valency. Valency refers to the combining capacity of an atom determined by the number of electrons that it will lose, add, or share when it reacts with other atoms.  In the 1860’s, when Mendeleev first started working on his periodic table, there were 63 known elements. Mendeleev started his work on the table by writing the name of each known element on a card along with its atomic mass, its chemical properties and its physical properties. He would organize the cards in different orders to see if he found any patterns. When the elements were lined up in order of increasing atomic mass, Mendeleev noticed that certain similarities in their chemical properties appeared periodically, or at regular intervals. This is where the name “Periodic Table of Elements” came from.

One periodically reoccurring chemical property was the combining ratio of certain elements. For example:  []   Above is a link to a picture of Mendeleev’s first periodic table, in which he grouped different elements by their combining ratios. As can be seen in this table and the table in the link below, Mendeleev left a lot of spaces blank. This is because he found gaps in the pattern he was finding between elements and predicted that these spaces would later be filled when new elements were discovered. In 1871, Mendeleev predicted the existence and the properties of three of these elements. By 1886, those three elements - scandium, gallium, and germanium – had been discovered, their properties very much like those that Mendeleev predicted. The fact that Mendeleev’s predictions were so accurate made most chemists believe his findings and accept his periodic table.   []  Periodic Law  The periodic law states that the physical and chemical properties of the elements are periodic functions of their atomic numbers. When the elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals. This discovery of this law was started by Mendeleev. Mendeleev ordered his periodic table according to atomic mass. However, there were a few elements that did not fit into his pattern. 40 years after Mendeleev’s table was published, in 1911, the English scientist Henry Moseley noticed that the elements in the periodic table were arranged in increasing order according to nuclear charge, or the number of protons in the nucleus. Thanks to Moseley, we now know that the atomic number, not the atomic mass, is the basis for the organization of the periodic table.
 * <span style="font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">The Elements Lithium (Li), Sodium (Na), and Potassium (K) all formed oxides in the ratio of two atoms per oxygen atom: R2O
 * <span style="font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">The Elements Beryllium (Be), Magnesium (Mg), and Calcium (Ca) all formed oxides in the ratio of one atom per oxygen atom: RO
 * <span style="font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Boron (B) and Aluminum (Al) formed R2O3
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Carbon (C) and Silicon (Si) formed RO2

<span style="font-size: 14pt; color: #00b050; font-family: 'Century','serif';">Physical and Chemical Properties and Physical vs. Chemical Change <span style="color: black; font-family: 'Century','serif'; mso-bidi-font-family: Arial;"> The properties of a substance can either be defined as physical properties or chemical properties. A physical property is a characteristic that can be observed or measured without changing the identity of the substance. Freezing and boiling points are examples of physical properties. Physical properties describe the substance itself, not how it can change into other substances. Physical change, therefore, is defined as a change in substance that does not involve a change in identity. Melting a material, cutting a material, and condensing a substance are all physical changes. Physical changes often include a change of state, the states being solid, liquid, and gas.

A chemical property describes how a substance transforms into a different substance. Chemical properties come into play when two substances are reacted. The chemical properties of the respective substance tell us how they will react with each other and what the products of the reaction will be. That chemical reaction is also known as chemical change. Chemical changes are when one or more substances are converted into a different substance.

Here are some examples of both physical and chemical changes: <span style="color: black; font-family: 'Arial','sans-serif';">


 * **Physical Changes** || **Chemical Changes** ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Aluminum foil is cut in half. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Milk goes sour. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Clay is molded into a new shape. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Jewelry tarnishes. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Butter melts on warm toast. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Bread becomes toast. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Water evaporates from the surface of the ocean. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Rust forms on a nail left outside. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">A juice box in the freezer freezes. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Gasoline is ignited. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Rubbing alcohol evaporates on your hand. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Hydrogen peroxide bubbles in a cut. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">A snowflake land on your hand and melts. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Food scraps are turned into compost in a compost pile. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Water condenses on the outside of a cold bottle of juice. || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">A match is lit. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';"> || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">You take an antacid to settle your stomach. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';"> || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">Your body digests food. ||
 * <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';"> || <span style="color: black; font-family: 'Century','serif'; mso-fareast-font-family: 'Times New Roman';">You fry an egg. ||
 * __Valence__ __Electrons__**
 * Periodic Group ||  || ## of Valence Electrons ||
 * Group 1 (I) ( [|alkali metals] ) ||  || 1 ||


 * Group 2 (II) ( [|alkaline earth metals] ) ||  || 2 ||


 * Groups 3-12 ( [|transition metals] ) ||  || 2 ||


 * Group 13 (III) ( [|boron group] ) ||  || 3 ||


 * Group 14 (IV) ( [|carbon group] ) ||  || 4 ||


 * Group 15 (V) ( [|nitrogen group] ) ||  || 5 ||


 * Group 16 (VI) ( [|chalcogens] ) ||  || 6 ||


 * Group 17 (VII) ( [|halogens] ) ||  || 7 ||


 * Group 18 (VIII) ( [|noble gases] ) ||  || 8 ||

·

= __Metals, Metalloids, Nonmetals__ =



As you can see from the picture above, the elements of the periodic table are separated into three main types: Metals, Nonmetal and metalloids. In this section we will explore what physical properties and chemical properties separate one type from another and how the different types act differently.

The modern periodic table is our bases for these separations, therefore, it is important for us to understand how the periodic table is set up and a little bit of its history. The modern periodic table can trace its roots back to Dmitri Mendeleev’s table, which was initially organized in 1869. Mendeleev realized that if elements were organized by weight, a pattern would appear in which certain elemental properties would be seen periodically in every column. Knowing the pattern helped scientists of the time to predict the properties of the elements that were yet to be discovered.

In 1914, Henry Moosely experimentally determined the Atomic Number (number of protons) of elements, and once that had real significance, it was determined that arranging elements by number rather than weight, was the best way. This is how our modern periodic table is arranged.

Mendeleev’s original table: [|http://chemistry.about.com/od/imagesclipartstructures/ig/Science-Pictures/Mendeleev-s-Periodic-Table.-0EA.htm] ,

Very good Modern Periodic table: [|http://www.dayah.com/periodic/] Metals

The most numerous of the three categories with 82 elements (more then 75% of total), Metals are found to the left of the metalloid staircase pictured above. Metals are characterized by being… >Physical Properties -Lustrous (shiny) -Good Conductors of Heat and electricity -Very dense -Hard to melt (High melting point) -Very Ductile/ Malleable (Can be stretched and deformed with pressure) -Usually solids at Standard Temp and Pressure (except mercury) >Chemical Properties -Low electron affinity (Lose electrons easily) -Corrode Easily (slowly wear away i.e. rust) -Good reducing agents (adds electrons to other elements) -all have 1-4 valence electrons

Subcategories of Metal

Alkali Metals The Following elements make up the Alkali Metals subgroup…

-Sodium -Lithium -Potassium -Francium -Rubidium -Caesium Alkali Metals are extremely reactive and are therefore never found in nature in their pure form. This is because they only have one valance electron and they loose that fairly easily. That is especially true as you move lower down in the periodic table the alkali metals become less stable and more reactive. Francium, for example, is so unstable that scientists estimate that only an ounce of it can be found in earths crust at any point in time. The alkali metals are usually silver, except for caesium which has a golden tinge, soft, low-density metals, which react readily with halogens to form salts (Table salt is Sodium and chlorine), and with [|water] to form strongly basic hydroxides (and biiiig explosions).

Very cool video demonstrating the reactivity of Alkali Metals with water [|http://video.google.com/videoplay?docid=-2134266654801392897]

Good website on the individual elements within the alkali family [|http://www.chemtopics.com/elements/alkali/alkali.htm]

Alkaline Earth Metals The Following elements make up the alkaline earth metals

-Beryllium -Calcium -Barium -Magnesium -Strontium -Radium

With an oxidation number of +2, alkaline earth metals are the second most reactive of the metal groups. They are called alkaline because when they are mixed in solutions they are likely to form basic (AKA alkaline) solutions that have a pH greater then 7. Alkaline earth metals are typically lustrous, and most are white or silvery in color. They glow different colors when they are heated. Calcium glows orange, strontium a very bright red, and barium an apple green. Physically they are soft, though not as soft as the group one alkali metals.

Great website on the Alkaline Earth Metals uses and characteristics [|http://www.scienceclarified.com/everyday/Real-Life-Chemistry-Vol-1/Alkaline-Earth-Metals.html] Short video shows the properties and uses of alkaline earth metals and alkali metals [|http://www.youtube.com/watch?v=DFQPnHkQlZM]

Transition Metals The Transition Metals are defined by the IUPAC as “an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell”. The main characteristic, which separates Transition Metals from other metals is that their valance electrons are located on more then one shell. That is why they can exhibit different oxidation states depending upon what they arereacting with.

Good website on transition metals [|http://www.chem4kids.com/files/elem_transmetal.html] Nonmetals Nonmetals make up (almost) everything on the periodic table that isn’t a metal. On the periodic table, they are everything to the right of the metalloid staircase (Parts of group 14 to group 16). The Nonmetal subcategories are Halogens, Noble gases and “other metals”. The characteristics of nonmetals are… >Physical Properties -Poor Conductors of heat and electricity -They are brittle (Break easily) -No Luster (Not shiny) -Low density -Gases liquids or solids at Standard temperature and pressure (STP) >Chemical Properties -High electron affinities (Hard to remove electrons) -They are highly electronegative -Usually 4-8 valance electrons
 * -good oxidizing agents (Remove electrons to other elements)**
 * =Except noble gases**


 * Nonmetal Subgroups

Halogens The following elements make up the halogens group…

-Fluorine -Chlorine -Bromine -Iodine -Astatine

Because Halogens are so close to having a full valance shell, they react very easily. This is especially true for Fluorine, which reacts very often, however, as we move down the group, the halogens become less reactive. When a Halogen reacts with another element the resulting compound is called a halide. In many cases Halides are ionic compounds (NaCl) however, they can also be formed with covalent bonding. One interesting thing about Halogens is that at STP there is at least one halogen in every state (Liquid, Gas and Solid). They are the only group where this is true. In nature however, halogens can only be found in compounds or as ions, due to there high level of reactivity.

Noble Gases The elements that make up the Nobel gas group are…

-Argon -Helium -xenon -Krypton -Neon -radon

Because noble gases have a complete valance shell, they are relatively Unreactive. Even Helium, which only has two valance electrons, has a full outer shell because it can only hold two valance electrons. They are colorless and odorless in there natural state and are monatomic (not bound to itself. As opposed to oxygen which is usually O 2 ) they lighter noble gases (Helium, Neon and Argon) don’t react with other chemicals to form compounds. The heavier ones (Krypton, Xenon and Radon) react with other elements but only in rare cases (Often with Fluorine and Oxygen) cool video on the noble gases. Wait till the end to see what I mean [|http://www.youtube.com/watch?v=QLrofyj6a2s] Metalloids Elements Under the category of Metalloid are…

-Boron -Silicon -Germanium -Arsenic -Polonium **-Antimony -Tellurium

**There is debate as to whether polonium should be classified as a metal or metalloid because it does exhibit many qualities more associated with metals**

Between the metals and non-metal lies an intermediary category deemed: Metalloids. Also called “semi-metals”, metalloids possess some properties of metals and some of Nonmetals. Metalloids like germanium ad silicon are useful in that they are “semiconductors” meaning that they conduct electricity under special conditions and not as well metals

This fact makes them useful for building computers because they can be used to send electrical impulses on command.

__ Charges __ Each ion going across the periodic table has a specific charge on it. This occurs because the ions have either lost, or gained electrons. In a normal atom, there are an equal amount of electrons and protons, electrons having a negative charge, and protons a positive. When an ion loses electrons and becomes a cation and now has a positive charge because it now has more protons than electrons. When an ion gains electrons, it becomes an anion, which has a negative charge because it has more electrons than protons. The following table gives the charges for specific groups on the periodic table. However, groups 3-12 are missing. This is because the charges on these ions have to be calculated, and they are not always the same. (Alkali metals) || Group II 2+ (alkali earth metals) || Group III 3+ || Group IV 4+ || Group IV 4- || Group V 3- || Group VI 2- || Group VII - (Halogens) || H- (hydride) ||
 * //Charge on Ion// |||| 1+ || 2+ || 3+ || 4+ || 4- || 3- || 2- |||| 1- ||
 * //Example**// || H+ || Group I +

The ions in groups 3-12 have multiple charges, and are given below. However, you must decide what the charge is by actually examining the specific compound you are dealing with. You can tell what the charge is by seeing how many ions it must bond with.

Group 3
Sc 3+ Y 3+ La 3+ Ac 3+

Group 4
Ti 4+ 3+ Zr 4+ Hf 4+

Group 5
V 5+ 4+ Nb 5+ 3+ Ta 5+

Group 6
Cr 3+ 2+ Mo 6+ W 6+

Group 7
Mn 2+ 4+ Tc 7+ Re 7+

Group 8
Fe 3+ 2+ Ru 3+ 4+ Os 4+

Group 9
Co 2+ 3+ Rh 3+ Ir 4+

Group 10
Ni 2+ 3+ Pd 2+ 4+ Pt 4+ 2+

Group 11
Cu 2+ 1+ Ag 1+ Au 3+ 1+

Group 12
Zn 2+ Cd 2+ Hg 2+ 1+ As the chart above shows, Non-metals often form negative ions, while metals form positive ions. The charge of an atom is important for bonding, because it affects the number of other ions that it must bond with. For example, if you want to bond a +3 ion with a -1 ion, you need 3 of the -1 ions to bond with the +3. However, if you have one +4 ion and one -2 ion, you only need two of the -2, instead of 4. This is because you are allowed to simplify the amount that you have. So if you have a +6 and a -2, you only need 3 of the -2 ions. This is because each ion when formed, must have a neutral charge. When bonding the ions, you must look at the charge, disregard the negative sign, and make that many of the other ion. The point is that the overall charge of the new ion will be 0, and for this reason, a negative ion must bond with a positive ion, and not with another negative ion.

Polyatomic ions have charges as well, and are given in the table below. However, even when these ions bond, they will still need an overall charge of 0.

1- ions
acetate CH3COO- hydrogen sulfite (bisulfite) HSO3- benzoate C6H5COO- hydroxide OH- chlorate ClO3- hypochlorite OCl- chlorite ClO2- nitrate NO3- cyanide CN- nitrite NO2- dihydrogen phosphate H2PO4- perchlorate ClO3- hydrogen carbonate (bicarbonate) HCO3- permanganate MnO4- hydrogen sulfate (bisulfate) HSO4- thiocyanate SCN- hydrogen sulfide (bisulfide) HS-

2- ions
carbonate CO32- silicate SiO32- chromate CrO42- sulfate SO42- dichromate Cr2O72- sulfite SO32- hydrogen phosphate HPO42- thiosulfate S2O32- oxalate C2O42-

3- ions
borate BO33- phosphate PO43- When these polyatmic ions lose or gain an oxygen, the charge of the ion will change accordingly. The importance of the charge lies in that it dictates how many ions are needed in bonding as detailed above. It is important that in bonding, the overall charge becomes zero, and adjusting the amount of ions in a compound based on their charges, is the way to ensure this.

<span style="font-size: 14pt; color: #548dd4; font-family: 'Century','serif';">Reactivity <span style="font-family: 'Century','serif';"> <span style="font-family: 'Century','serif';">Reactivity is the rate at which a chemical substance tends to undergo a chemical reaction. <span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">It refers to how likely or vigorously an atom is to react with other substances. This is usually determined by how easily electrons can be removed (ionization energy) and how badly they want to take other atom's electrons (electronegativity) because it is the transfer or interaction of electrons that is the basis of chemical reactions. The reactivity of an element depends on where it is located in the periodic table of elements. <span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Metals <span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">This happens because the farther to the left and down the periodic chart you go, the easier it is for electrons to be given or taken away, resulting in higher reactivity. <span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Non-metals <span style="font-size: 11pt; color: black; line-height: 115%; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman'; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">This happens because the farther right and up you go on the periodic table, the higher the electronegativity, resulting in a more vigorous exchange of electron
 * <span style="color: #18605a; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Period **<span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';"> - reactivity decreases as you go from left to right across a period.
 * <span style="color: #18605a; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Group **<span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';"> - reactivity increases as you go down a group
 * <span style="color: #18605a; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Period **<span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';"> - reactivity increases as you go from the left to the right across a period.
 * <span style="color: #18605a; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';">Group **<span style="color: black; font-family: 'Times New Roman','serif'; mso-fareast-font-family: 'Times New Roman';"> - reactivity decreases as you go down the group.