The Periodic Table of Elements

Early Versions 1830: 55 elements had been discovered 1860’s: Dimitri Mendeleev discovered a system that applied to all elements

Mendeleev Father of the periodic table Noticed patterns when the elements were arranged by increasing atomic mass

Mendeleev Noted properties of elements Melting point Density Color Studied atomic mass and chemical bonds Compared mass to hydrogen

Mendeleev Noted that arranging elements according to atomic mass did not always produce similar groups Moved element cards into groups where they fit best Predicted other elements and their properties

Mendeleev 1869: Published the 1 st periodic table

The Modern Periodic Table New elements were added as they were discovered Early 1900’s: scientists learned about the atomic number

Reading the Periodic Table Contains over 100 squares: one for each element

Isotopes Atoms of a certain element ALWAYS have the same # of protons….DO NOT always have the same mass May have different number of neutrons Isotope Atoms of the same element that have a different number of neutrons

Isotopes Examples: Chlorine-35 Chlorine-37 Carbon-14

Reading the Periodic Table An element’s properties can be predicted from its location on the periodic table. groups/families periods

Groups/Families Elements in columns 18 columns Elements in each group have similar characteristics. Example: Group 1 are metals that all react violently with water; Group 17 reacts violently with elements from Group 1; Group 18 rarely reacts at all

Groups/Families EXAMPLES OF FAMILIES - Alkali Metals - Alkaline Earth Metals - Transition Metals - Halogen Gases - Inert Gases (Noble Gases)

Periods Horizontal rows Series of different elements from different groups Have very different properties

Why it Works! It’s based on the structure of atoms, especially the valence electrons!

Metals Most elements are metals. Found to the left of the zig-zag line. Elements are classified as metals based on physical properties. Hardness Shininess (luster) Malleability Ductility

Physical Properties Have luster (shiny) Good conductors of heat & electricity (transmit easily) High density Very high melting point Ductile (drawn into thin wires) Malleable (hammered into thin sheets) Most are solid at room temperature.

Chemical Properties Wide range of chemical properties Some are very reactive and combine quickly. (sodium) Some are unreactive. (gold) Other metals fall somewhere in between Corrosion: the process of reaction and wearing away of metals

Alloys A mixture of metals Combine the best properties of 2 or more metals into a single substance Ex: copper + tin = bronze Ex: copper + zinc = brass

Group 1: Alkali Metals From Lithium to Francium MOST reactive of ALL metals NEVER found uncombined in nature; exist as compounds Very soft & shiny Have 1 valence electron (lose easily) 2 MOST IMPORTANT: sodium & potassium (essential for life)

Group 2: Alkaline Earth Metals Not as reactive as group 1, but still more reactive than most metals NEVER found uncombined in nature Have 2 valence electrons (lose easily) 2 MOST COMMON: magnesium & calcium Magnesium: flash bulbs, alloys for airplanes, ladders Calcium: teeth & bones, muscles

Groups 3-12: Transition Metals Form a bridge between very reactive metals on the left and less reactive metals on the right So similar to one another that differences between nearby columns are difficult to detect Include the most familiar metals: iron, copper, nickel, silver & gold

Groups 3-12: Transition Metals Most are hard and shiny All are good conductors of electricity. Fairly stable, reacting slowly or not at all with water and air

Groups 13-16: Metals in Mixed Groups Metals to the right of the transition metals are not nearly as reactive as those on the left. Most familiar: aluminum, tin, lead

Lanthanides and Actinides Lanthanides: top row at the bottom of the periodic table Actinides: bottom row at the bottom of the periodic table Called rare earth elements Fall between alkaline earth metals and transition metals Placed at the bottom for convenience

Lanthanides Soft, malleable, shiny metals High conductivity Used in industry to make various alloys Different lanthanides are found together in nature; difficult to separate because of the similar properties

Actinides Only thorium and uranium exist on Earth in any significant amounts Uranium: used in nuclear power All elements after uranium were created artificially in a laboratory.

Nonmetals Lack most of the properties of metals Located to the right of the zigzag line

Physical Properties In general: opposite of metals Gases at room temperature; means they have low boiling points Dull Solid nonmetals are brittle. NOT malleable or ductile Lower densities than metals Poor conductors of heat and electricity

Chemical Properties Readily form compounds; except Group 18 Group 18 elements do not react with other elements. Many form molecules containing 2 atoms: diatomic molecules (O 2 ) Nonmetals can form compounds with metals (NaCl) or other nonmetals (CO 2 ).

Families of Nonmetals Carbon Family (Group 14) All have 4 valence electrons. Carbon is the only nonmetal in the group. 2 are metalloids; 2 are metals Carbon is special because it is important for life. ALL living things contain Carbon!

Families of Nonmetals Nitrogen Family (Group 15) All have 5 valence electrons. Only 2 nonmetals in this group: nitrogen & phosphorus N 2 makes up about 80% of our air; most living things can not use it in gas form Get nitrogen from food Phosphorus is not a stable element; always found in compound in nature. Used to make matches and flares

Families of Nonmetals Oxygen Family (Group 16) All have 6 valence electrons. Elements typically gain or share 2 electrons Oxygen we breathe = O 2 Ozone = O 3 Oxygen is very reactive and can combine easily with other elements. Oxygen: most abundant element in Earth’s crust; second most abundant in the atmosphere Sulfur is a common nonmetal in the Oxygen family

Families of Nonmetals Halogen Family (Group 17) All have 7 valence electrons. All but Astatine are nonmetals; Astatine is a metalloid Typically gain or share 1 electron ALL are very reactive; most are dangerous to humans Compounds that they form are useful: Flourine—toothpaste, nonstick cookware Chlorine—table salt Bromine—reacts with silver (photographic film)

Families of Nonmetals Noble Gases (Group 18) Also known as inert gases ALL have 8 valence electrons Do Not ordinarily form compounds Do not gain, share, or lose electrons; very stable and unreactive All exist in Earth’s atmosphere, but only in small amounts

Families of Nonmetals Hydrogen Simplest of all elements Generally contains only one proton and one electron Cannot be grouped in a family because its chemical properties are so different from other elements Makes up 90% of the atoms in the universe; only 1% of the mass of Earth’s crust, oceans, & atmosphere Rarely found on Earth as an element Mostly combined with oxygen (water)

Metalloids On zigzag line between metals & nonmetals 7 elements Some have characteristics of metals; some have characteristics of nonmetals Most useful property is their varying ability to conduct electricity Most common is silicon Sand, glass, cement

Metalloids Whether they conduct electricity depends on temperature, exposure to light, or presence of impurities Semiconductors: substances that under certain conditions can carry electricity, while under others it cannot Silicon & germanium Used to make computer chips, transistors, lasers