“The Periodic Table”

Organizing the Elements Few elements (like Au and Cu), have been known for thousands of years - since ancient times Only about 13 had been identified by the year 1700. As more were discovered, chemists realized they needed a way to organize the elements. Chemists used the properties of elements to sort them into groups (families). Reactivity Metal/Nonmetal Physical appearance Compounds they were found in

Mendeleev’s Periodic Table Dmitri Mendeleev – a Russian chemist and teacher Arranged elements in order of increasing atomic mass (the first “Periodic Table”) _Left blanks_for yet undiscovered elements When they were discovered, he had made good predictions But, there were problems: Ar and K; Te and I (mass didn’t increase)

A better arrangement In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic number This is the arrangement used today

The Periodic Law says: When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties. Horizontal rows = periods There are 7 periods Vertical column = group (or family) There are 8 main groups identified by number & letter (IA, IIA, VIIA)

Areas of the periodic table Three classes of elements are: 1) metals 2) nonmetals 3) metalloids Metals: electrical conductors, have luster, ductile, malleable, found on the left hand side of the periodic table

Areas of the periodic table Nonmetals: generally brittle and non- lustrous, poor conductors of heat and electricity Some nonmetals are gases (O, N, Cl); some are brittle solids (S); one is a fuming dark red liquid (Br)

Metalloids on the Table Metalloids: border the line-2 sides Properties are intermediate between metals and nonmetals Notice the heavy, stair-step line? DRAW IT ON YOUR OWN TABLE

Metalloids on the Table

Squares in the Periodic Table The periodic table displays the symbols and names of the elements, along with information about the structure of their atoms:

Groups of elements - Family names Group IA – alkali metals Forms a “base” (or alkali) when reacting with water (not just dissolved!) Group 2A – alkaline earth metals Also form bases with water; do not dissolve well, hence “earth metals” Group 7A or 17 – halogens Means “salt-forming”

Groups of Elements (Family Names) Noble gases are the elements in Group 8A (also called Group18) Previously called “inert gases” because they rarely take part in a reaction; very stable = don’t react

Groups of elements - Family names Transition metals are in the “B” columns of the periodic table Chemistry is more complex than the Main Group columns (“A” Groups) A “transition” between the metal area and the nonmetal area Examples are gold, copper, silver

#1. Atomic Size/ Number of Electron Shells As we go down a group) each atom has another electron shell, so the atoms get bigger. Li Na K Rb

#2 - Atomic Number and Atomic Mass The exceptions are Ar and K; Te and I In these cases, the atomic mass of an element is greater than the one to the right of it. As we go down a group or across a row the atomic number and atomic mass increases. (with a few exceptions)

#3 Types of elements As you move from left to right on the periodic table, elements start as metals than transitions to metalloids and end on the right side as nonmetals.

#4 Reactivity Elements in the center of the periodic table have low reactivity. Reactivity increases as you move from the center to both the right and left side of the periodic table On the left hand side, reactivity increases as you move down On the right hand side, reactivity increases as you move up The very last column on the right hand side (Noble Gases) is completely unreactive.

#5 - Chemical/Physical Properties Elements in the same column on the periodic table have similar chemical properties (Reactivity, types of compounds formed, etc.) Some columns even have similar physical properties For example, Copper, Gold, and Silver are in a column. All are malleable, ductile, good conductors and have a low level of reactivity All are used in making coins and jewelry