Periodic Table The Periodic Table of Elements is

Periodic Table • The Periodic Table of Elements is the most important reference in chemistry, and it represents all the known chemical elements as well as those that are yet to be discovered. The elements are arranged in a systematic order to show their patterned recurring or ‘periodic’ chemical and physiological properties. Currently, there a total of 117 elements in the standard periodic chart.

PERIODIC TABLE • COLUMNS (GROUPS/FAMILIES) — vertical (* have similar but not identical properties) (atomic size increases from top to bottom)

• PERIODS — horizontal rows — Certain properties of elements vary in regular ways from left to right across a period. These properties include electron arrangement, reactivity, atomic size, and metallic properties.

• FAMILY 1 (ALKALI METALS) – Exception Hydrogen – Single electron in outermost energy level – 1 valence electron (+1) – Soft, silver-white, shiny metals – Good conductors of heat and electricity – Very reactive (never found as free elements)

• FAMILY 2 (ALKALINE EARTH METALS) – Never found in nature as an uncombined elements – Two electrons in outermost energy level – 2 valence electrons (+2) – Not as reactive as the alkali metals

• FAMILIES 3 TO 12 (TRANSITION METALS) – Do not fit into any other Family – Properties similar to one another but different from other Families – Good conductors of heat and electricity – Brightly colored (paints) – Most have 1 or 2 valence electrons – Lose either 1 (+1) or both (+2) BUT can also lose an electron from the next to outermost energy level – Sometimes can share electrons when they form bonds with other atoms – Form so many different compounds

Transition Metals • Transition metals are like main group metals in many ways: They look like metals, they are malleable and ductile, they conduct heat and electricity, and they form positive ions. The fact the two best conductors of electricity are a transition metal (copper) and a main group metal (aluminum) shows the extent to which the physical properties of main group metals and transition metals overlap.

Transition Metals • There also differences between these metals. The transition metals are more electronegative than the main group metals, for example, and are therefore more likely to form covalent compounds.

Transition Metals • Another difference between the main group metals and transition metals can be seen in the formulas of the compounds they form. The main group metals tend to form salts (such as Na. Cl, Mg 3 N 2, and Ca. S) in which there are just enough negative ions to balance the charge on the positive ions. The transition metals form similar compounds [such as Fe. Cl 3, Hg. I 2, or Cd(OH)2], but they are more likely than main group metals to form complexes, such as the Fe. Cl 4 -, Hg. I 42, and Cd(OH)42 - ions, that have an excess number of negative ions.

• FAMILY 13 (BORON FAMILY) – Three electrons in outermost energy level – 3 valence electrons (+3) – One metalloid (BORON) / others metals

METALLOIDS • A metalloid is an element with properties that are in between, or a mixture of, the properties of metals and nonmetals and thus is hard to classify as either a metal or a nonmetal.

METALLOIDS • Metalloids are the elements found along the stair-step line that distinguishes metals from non-metals. This line is drawn from between Boron and Aluminum to the border between Polonium and Astatine. The only exception to this is Aluminum, which is classified under “OTHER METALS". Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are semi-conductors. This means that they can carry an electrical charge under special conditions. This property makes metalloids useful in computers and calculators

Semiconductors • Also called metalloids • Not metals but have the some properties of metals • Ability to conduct heat and electricity under certain conditions • Si: used in computers and electronic devices • B: increases strength of steel • Sb: used as a fire retardant

• FAMILY 14 (CARBON FAMILY) – Four electrons in outermost energy level – 4 valence electrons – Carbon (nonmetal) / Si + Ge (metalloids) / Sn + Pb (metals)

• FAMILY 15 (NITROGEN FAMILY) – Five electrons in outermost energy level – 5 valence electrons (-3) – Tend to share electrons when they bond with other atoms

• FAMILY 16 (OXYGEN FAMILY) – Six electrons in outermost energy level – 6 valence electrons (-2) – Most elements in this Family share electrons when forming compounds

• FAMILY 17 (HALOGENS) – Seven electrons in outermost energy level – 7 valence electrons (-1) – Tend to GAIN only 1 electron to fill their outermost energy level – Very reactive – Never found free in nature – React with metals to form salts

Fluoride • Fluoride is a mineral that occurs naturally in many foods and water. Every day, minerals are added to and lost from a tooth's enamel layer through two processes, demineralization and remineralization. Minerals are lost (demineralization) from a tooth's enamel layer when acids -- formed from plaque bacteria and sugars in the mouth -- attack the enamel. Minerals such as fluoride, calcium, and phosphate are redeposited (remineralization) to the enamel layer from the foods and waters consumed. Too much demineralization without enough remineralization to repair the enamel layer leads to tooth decay.

Fluoride • Fluoride helps prevent tooth decay by making the tooth more resistant to acid attacks from plaque bacteria and sugars in the mouth. It also reverses early decay. In children under 6 years of age, fluoride becomes incorporated into the development of permanent teeth, making it difficult for acids to demineralize the teeth. Fluoride also helps speed remineralization as well as disrupts acid production in already erupted teeth of both children and adults.

Fluoride • Hexafluorosilicic acid (systematically named oxonium hexafluorosilanediuide and oxonium hexafluoridosilicate is an inorganic compound. It is commonly used as a source of fluoride for water flouridation.

• FAMILY 18 (NOBLE GASES)(INERT GASES) – Two/eight electrons in outermost energy level – 2 valence electrons (Helium) – 8 valence electrons (all others) – Normally unreactive

• RARE EARTH ELEMENTS – LANTHANOID SERIES – ACTINOID SERIES • All radioactive

Rare Earth Elements 1. any of a group of chemically similar metallic elements comprising the lanthanide series and (usually) scandium and yttrium. They are not especially rare, but they tend to occur together in nature and are difficult to separate from one another.

• CLASSIFICATION OF ELEMENTS – METAL: element that is a good conductor of heat and electricity, is shiny, has a high melting point, is ductile and malleable, and tends to lose electrons. – NONMETAL: element that is a poor conductor of heat and electricity, has a dull surface, low melting point, is brittle, breaks easily, and tends to gain electrons. – METALLOIDS: element that has properties of both metals and nonmetals.

• CLASSIFICATION OF ELEMENTS – LEFT— metals (tend to lose electrons) – RIGHTS — nonmetals (tend to gain electrons) – METALLOIDS — properties of both metals and nonmetals (either side of zigzag line)

• CLASSIFICATION OF ELEMENTS – Left to Right – Valence number charges (+1, +2, +3, +4, -3, -2, -1, 0, ) – Amount of energy needed to remove electrons shows periodic increase – Atomic size decreases ? ? ? WHY? ? ? ? ? – Becomes less metallic

Semiconductors • Also called metalloids • Not metals but have the some properties of metals • Ability to conduct heat and electricity under certain conditions • Si: used in computers and electronic devices • B: increases strength of steel • Sb: used as a fire retardant