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Periodic Table

PERIODIC TABLE

The periodic table used today has elements arranged in order of increasing atomic numbers.

The periodic table is based on periodic law which states that the physical and chemical properties of elements are functions of their atomic numbers.

The periodic table contains information such as atomic number, symbol name, atomic mass and electron configurations. Since the electron configuration determines chemical behavior, elements of the same family have similar properties.

FAMILY CHARACTERISTICS:

NOBLE GASES (Group 18) are the gas family on the far right side of the periodic table.. These gases are characterized as being unreactive elements. Noble gases have electron configurations with full s or p orbitals, which makes them very stable. Noble gases like neon and argon are used in lighted signs. Helium is used for inflation since it very light and weight.

ALKALI METALS (Group 1) are soft high reactive metals. When mixed with water they form a slippery solution that can remove grease. Alkali metals are bases, and are highly reactive because they have only one electron in the outermost shell. Alkali metals are good conductors of electricity. Sodium is used in street lamps and fog lights. Lithium is used as a medication to treat depression.

ALKALI EARTH METALS (Group 2) are harder, denser, stronger, and have higher melting points that the group 1 metals. These metals are less reactive than group 1 because they have 2 electrons in the outer shell. In order for them to have a full outer shell they must loose two electrons. Magnesium is used in construction because of its strength and lightness. Calcium is the best know of the alkali earth metals.

 

TRANSITION ELEMENTS (Group 3-12) are all metals. Transition metals are not as reactive as metals in groups 1 & 2. They are harder denser and have higher melting points than groups 1 and 2. Transition elements do not have similar electron configurations as do groups 1 & 2.

There are two more periods of transition elements located at the bottom of the periodic table.

The LANTHANIDES include elements 58-71. The lanthanides are shiny reactive metals.

The ACTINIDES are elements 90-103. Acitinides are radioactive because they have unstable nuclei. For example uranium provides fuel for nuclear power.

THE MAIN BLOCK ELEMENTS (Groups 13-18) are also called the representative elements because they display many different chemical and physical properties. Within this group are metals, metalloids, nonmetals and noble gases.

The HALOGENS (Group 17) are highly reactive because they are only one electron short of a full outer shell. Halogens react readily with group 1 alkali metals to form compounds know as salts. For example Sodium (group 1) and Chlorine (group 17) form table salt (NACL).

HYDROGEN is a group all its own, because hydrogen has only one electron. Hydrogen reacts rapidly with most of the other elements. Hydrogen when combined with oxygen makes water. Hydrogen when combined with oxygen and carbon make proteins, lipids, and carbohydrates.

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PERIODIC TRENDS

ATOMIC RADIUS

The atomic radius is the distance between the nucleus and the outermost shell of an atom.

Atomic radius increases as you move down the groups for two reasons.

1. As you move down the peroiodic table electrons shells are added making the electron cloud larger.

2. The sheilding effect causes the electron cloud to be expanded, because as the number of electrons increases the electrons in the outmost shells do not feel the full effect of the pull of the nucleus.

Atomic radius decreases as you move across the periods because as you move from left to right another proton is added to the atom. This causes the nucleus to have a stronger pull on the electron clouds, pulling them in closer to the nucleus, and causing the atomic radius to shrink.

IONIZATION ENERGY

An ion is created when an atom loses or gains an electron.

Ionization energy is the amount of energy needed to remove an electron from an atom.

A + energy ----> A+ and e-

Ionization energy decreases as you move down a group of elements. As you move down the group the electrons are in higher energy levels and are less affected by the pull of the nucleus. Additionally, the sheilding effect also causes ionization energy to decrease.

Ionization energy increases as you go across a period because as you move across the periodic table you are adding more protons to the nucleus which exert more of a pull on the electrons. The stronger pull of the nucleus, the more energy is needed to remove it.

ELECTRON AFFINITY

Electron Affinity is the ability to attract and hold an extra electron.

The more negative the electron affinity, the more easily an atom can take in an extra electron.

As you move from left to right across a period, the electron affinity increases because the nuclear charge increases to added protons and the atomic radius decreases.

As you move down a group the electron affinity decreases because of the shielding effect and the atomic radius.

ELECTRONEGATIVITY

The electronegativity of an atom is the tendency of the atom to attract electrons to itself during a chemical reaction.

Electronegativity is measured in terms relative to Fluorine, which is the most electronegative element.

The noble gases are not included in electronegitivity measurement because they are so chemically un-reactive.

Electronegativity decreases as you go down a group and tends to increase as you go across the period.

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