T HE P ERIODIC T ABLE

D EVELOPMENT OF THE P ERIODIC T ABLE Antoine Lavoisier ( ) In the late 1700s Lavoisier compiled a list of all known elements. He organized the 33 known elements into four categories: gases, metals, nonmetals, and earths.

N EW D EVELOPMENTS With the industrial revolution and advances in science in the 1800s, new elements were discovered. With new discoveries meant a requirement for a new way to organize and categorize the elements.

In the 1860s chemists finally agreed on a method for determining atomic mass. With this agreement, allowed for a new way to organize the elements.

John Newlands ( ) In 1864 Newlands proposed a design for organizing the elements. He noticed that when the elements were arranged by increasing atomic number, their properties repeated every eighth element. He termed this pattern as the law of octaves. This law was criticised since it did not work for ALL elements.

Meyer & Mendeleev Both Meyer and Mendeleev were also focusing on the atomic mass of the elements. Mendeleev is credited with more of the findings since he published before Meyer. Mendeleev noticed that when the elements were placed in increasing atomic mass there was a periodic pattern in their properties.

Mendeleev organized the elements into columns. His periodic table was widely accepted.

Dmitri Mendeleev was born at Tobolsk, Siberia in 1834 and died in Mendeleev is best known for his work on the periodic table; arranging the 63 known elements into a Periodic Table based on atomic mass, which he published in Principles of Chemistry in 1869.

Mendeleev organized the periodic table based on order of recurring chemical and physical properties. He grouped substances with similar properties together. He left gaps where he thought undiscovered elements should be and predicted some of the properties of the undiscovered elements.

Moseley ( ) Moseley decided to organize the elements based on their atomic number. There were some issues with Mendeleev’s periodic table. As more elements were discovered, they found that some of these elements did not fit into the periodic table well based on atomic mass.

Moseley’s arrangement based atomic number lead to a perfect pattern of periodic properties. Periodic Law: the statement that there is a clear periodic pattern of chemical and physical properties of the elements when they are arranged by atomic number.

M ODERN P ERIODIC T ABLE The modern periodic table of elements arranges the elements into columns and rows. The columns are known as groups or families. The rows are known as periods.

G ROUPS /F AMILIES Group 1: Alkali Metals They are highly reactive Have only ONE valence electron They are shiny, have the consistency of clay, and are easily cut with a knife They have low melting points

R EACTIVE We will be describing elements according to their reactivity. Elements that are reactive bond easily with other elements to make compounds. Some elements are only found in nature bonded with other elements. What makes an element reactive? An incomplete valence electron level. All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level (This is called the rule of octet.) Atoms bond until this level is complete. Atoms with few valence electrons lose them during bonding. Atoms with 6, 7, or 8 valence electrons gain electrons during bonding.

Group 2: Alkaline Earth Metals They are never found uncombined in nature They have two valence electrons They have higher melting and boiling points than group 1

Transition Metals They are good conductors of heat and electricity The compounds of transition metals are usually brightly colored and are often used to color paints. Transition elements have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Some transition elements can lose electrons in their next-to-outermost level

Group 13: Boron Family This family includes a metalloid (boron), and the rest are metals. This family includes the most abundant metal in the earth’s crust (aluminum)

Group 14: Carbon Family Atoms of this family have 4 valence electrons. This family includes a non-metal (carbon), metalloids, and metals. The element carbon is called the “basis of life.” There is an entire branch of chemistry devoted to carbon compounds called organic chemistry

Group 15: Nitrogen Family The nitrogen family is named after the element that makes up 78% of our atmosphere. This family includes non-metals, metalloids, and metals. Atoms in the nitrogen family have 5 valence electrons. They tend to share electrons when they bond

Group 16: Oxygen Family Atoms of this family have 6 valence electrons. Most elements in this family share electrons when forming compounds

Group 17: Halogens Halogens have 7 valence electrons, which explains why they are the most active non-metals. They are never found free in nature Halogen atoms only need to gain 1 electron to fill their outermost energy level. They react with alkali metals to form salts

Group 18: Noble Gases Noble Gases are colorless gases that are extremely un- reactive. One important property of the noble gases is their inactivity. They are inactive because their outermost energy level is full. Because they do not readily combine with other elements to form compounds, the noble gases are called inert. The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. All the noble gases are found in small amounts in the earth's atmosphere

Rare Earth Metals The thirty rare earth elements are composed of the lanthanide and actinide series. One element of the lanthanide series and most of the elements in the actinide series are called trans- uranium, which means synthetic or man-made