The Periodic Table and Trends of the Elements By Diane Lunaburg 2001 1

In this show you will learn about the most important tools in chemistry--the periodic table of elements. Each element is made of a particular atom whose properties depend on the structure of the atom. The periodic table organizes the elements in a way that shows periodicity, or uniform and predictable changes of those properties. If you can recognize the trends of the periodic table, you do not need to memorize all the facts about each element.

History of the Periodic Table In 1869 A Russian chemist named Dmitri Mendeleev organized the elements into a table that became the basis of the modern periodic table. He used the atomic weights of the elements to arrange them. He even predicted the existence of elements based on gaps in the sequence of the atomic weights. He also placed the elements in columns to show periodic similarities of the elements.

The Modern Periodic Table In 1913 an English chemist named Henry Moseley discovered the number of positive charges in the nucleus of an atom and rearranged the periodic table using the atomic number or number of protons in the atom. This also lead to what is know as: The Periodic Law. This states that a periodic pattern appears in the physical and chemical properties of the elements when they are arranged in order of increasing atomic number.

The modern periodic table has about 109 known elements on it.

Each box on the periodic table has information about the element it represents.

Remember: Atomic number: Elemental Symbol: Average atomic mass: The number of protons in the atom Elemental Symbol: Always begins with a capital letter and may be followed by lower case letters. It represents the element Average atomic mass: The average of the naturally occurring isotopes of each element. Oxidation number: The charge acquired by an atom when it gains or loses an electron.

The Periodic Table displays a variety of physical properties

The Periodic table arranges elements into a series of vertical columns called groups or families and horizontal rows called periods.

What is a group or family? Elements arranged in a vertical column on the periodic table have similar chemical properties because they have the same number of valance electrons, electrons in the s and p orbital. This is because the number of valance electrons an atom has governs how it behaves in chemical bond. The characteristics of elements within a group would be more similar than elements within a period.

The valence electrons are the electrons in the outer shell of an atom The valence electrons are the electrons in the outer shell of an atom. According to the octet rule, an atom wants a full outer shell and will gain or lose electrons to make it happen. When they do they become charged. The charge they acquire is called their oxidation number. All noble gases have full outer shells and are in turn non-reactive.

What is a Period? The physical and chemical properties of elements gradually change as you move across a period.

The elements of the periodic table can be grouped a number of ways as seen above.

Remember the characteristics of Metal? They are usually gray solids at room temperature They are sometimes lustrous They are malleable and ductile they are good conductors of heat and electricity They usually form positive ions  Ductile Malleable

The Alkaline Earth Metals The representative elements are also broken into groups or families. Hydrogen The Alkali Metals The Alkaline Earth Metals The Halogens The Noble Gases Other Nonmetals

Hydrogen Hydrogen usually stands in a class by itself. It is a colorless, flammable gas at room temperature. It is like a nonmetal at room temperature but under extreme temperatures and pressures it can behave like a metal. It has one electron in its outer shell and will form an ion with an oxidation state of +1. This is similar to the alkali metal group so it is placed at the top of that group. Sometime, however it is placed by itself at the middle of the periodic table to indicate its uniqueness.

The Alkali Metals Group 1 The Alkali metals are group 1 on the periodic table. They are usually soft dull metals.

Alkali Metals They have one valance electron and usually have an oxidation state of +1 They are very reactive with oxygen or moisture They dissolve easily in water and form basic solutions

The Alkaline Earth Metals Group 2 The alkaline earth metals are group 2. They are also soft and dull gray. The Alkaline Earth Metals are also fairly reactive but do not dissolve as easily in water. Because of this they are often found as deposits in soil.

The Transition Metals The transition metal are group 3-12. They have metals that exhibit a variety of properties from magnetic, orange luster, and even liquid. They exist in a variety of oxidation states depending on what they are bonding with.

The inner Transition Metals The inner transition metals from 58-71 are the Lanthanide. They are a part of period 6. They are very large atoms. The inner transition metals from 90-103 are the Actinides. They are part of period 7. All of the elements occurring after Uranium are man made and most exist only for a short time before decaying into more stable atoms.

The Halogens Group 17 The halogens are group 17. They have 7 electrons in their outer shell. They would like to gain 1 electron to satisfy the octet rule. When they do they gain a -1 oxidation state. They usually bond with alkali metals to form salts. By themselves, halogens are diatomic molecules.

The Noble Gases Group 18 The noble gases are group 18. They have a complete outer shell. All elements have 8 electrons in their outer shell except Helium. Helium has only one s orbital and therefore can only hold 2 electrons which fills the orbital. Because they satisfy the octet rule naturally they are non-reactive or inert. They exist as single atoms in a gas state at room temperature.

Other Nonmetals Nonmetals have a variety of The rest of the elements may be broken into their own groups named for the top element or spoken about collectively. Other Nonmetals Nonmetals have a variety of colors, states and properties. They are brittle and poor conductors of heat and electricity. They usually form negative ions to satisfy the octet rule. They also tend to form covalent bonds with one another.

Periodic Trends Atomic Radii: The distance from the nucleus to the outer edge of the electron cloud Ionic Radii: The distance from the nucleus to the edge of the electron cloud of an ion. Ionization Energy: The amount of energy needed to remove an electron from an atom Electron Affinity: The energy change that occurs when an atom gains an electron. Electronegativity: The ability of an atom to attract electrons toward itself from a covalent chemical bond.

Atomic Radii

Atomic Radii Atomic Radii increases as you go down a group because of adding energy levels. Atomic Radii decreases as you go across a period because of an increasing pull from the added protons of the nucleus. + +

D e c r e a s e Smallest I nc r ease Largest

Ionization energy is the amount of energy it takes to remove and electron from an atom. You will notice it takes more energy to remove electrons from atoms that almost have their octet or have an octet.

Electron Affinity Electron affinity is the amount of energy required to capture an electron. If an atom has a negative (-) electron affinity it mean it needs no energy and actually releases it when an electron is captured. If an atom has a positive (+) electron affinity it means it needs energy to capture an electron. Atoms with an almost complete octet need little to no energy to capture an electron. Atoms with only 1 or 2 electrons in their outer shell need a lot of energy to capture an electron.

Electronegativity Electronegativity is usually important when determining if a covalent bond would be polar or non-polar. Very high Electronegativity means the atom will completely capture the electrons which result in an ionic compound. + - Electronegativity is the tendency of an atom to pull electrons in a shared bond closer to itself creating a bond that is polar. Polar means slightly more negative on one side and slightly more positive on the other.

You must subtract the values of electronegativity to determine it the bond is covalent, polar covalent or ionic Electronegativity Electronegativity of 0.0 to 0.4 is a covalent bond. Covalent shares the electrons equally Electronegativity of 0.4 to 2.1 is a polar bond. Polar is slightly negative on one side Electronegativity of 2.1 to 4.0 is an ionic bond. Ionic has electrons captured by one atom.