Elements and The Periodic Table



Elements and the Periodic Table

Elements are the simplest form of matter and are made up of the same atoms. They cannot be broken down, but they can lose their individual physical and chemical properties in a compound. Most elements are monatomic; their elementary particles contain a single unit, the atom. All the metals and some non-metals are monatomic. A monatomic element should be written without a subscript because the number 1 is understood (Examples: Na, Fe, Ra, U, Al). Seven elements are diatomic; their elementary particles, when formed, contain two like atoms. The subscript 2 should be used.

The Seven Diatomic Elements

I2 Iodine

Br2 Bromine

Cl2 Chlorine

F2 Fluorine

O2 Oxygen

N2 Nitrogen

H 2 Hydrogen

(Memory helper: I Bought Cement For Our New House)

Although subscripts are not used on the periodic table, know that Phosphorus (P4) is tetratomic and Sulfur (S8) is octatomic.

There are more than 116 elements on the periodic table; ninety elements are found in nature. All elements beyond #92 (uranium) are laboratory-made and radioactive. Technetium (#43) and promethium (#61), although less complex than uranium, are not found in nature.

Elements in the Body

O2 Oxygen 65.0%

C Carbon 17.5%

H2 Hydrogen 10.2%

N2 Nitrogen 2.4%

Ca Calcium 1.6%

All others 3.3%

The earth’s crust, deep below the oceans, is made up of three kinds of rocks. These rocks are composed mostly of two elements, oxygen and silicon, which account for more that 75% of the crust’s weight.

Elements in the Earth’s Crust

O2 Oxygen 49.5%

Si Silicon 25.8%

Al Aluminum 7.5%

Fe Iron 4.7%

Ca Calcium 3.4%

*All others 9.1%

*Such as sodium, magnesium, and hydrogen

Oxygen is colorless and odorless; it makes up one-fifth of the air. Silicon, in its pure state is a brown powder, or dark gray or black crystal.

The periodic table arranges elements in order of increasing atomic numbers. The atomic number is the number of protons; since an atom is electrically neutral, the atomic number also indicates the number of electrons surrounding the nucleus.

Periods – horizontal rows, ordered in increasing size and atomic number, elements typically have same number of energy levels

Groups – families, vertical column, have similar physical and chemical properties

The current IUPAC system numbers the groups 1-18. An older system (still in use) identifies each group by a number and the letter A or B. The group A elements are made up of Group IA (1A) through Group VIIA (7A) and Group VIIIA. Group A elements (Groups 1, 2, and 13-18) are called representative elements because they exhibit a wide range of both physical and chemical properties. The representative elements can be divided into three broad classes:

1. Metals – (Except hydrogen) on left side of periodic table

2. Alkali metals – Group I (1A), except for hydrogen-react vigorously, even explosively with water

3. Alkaline earth metals – Group 2 (IIA)

Most of the remaining elements that are not Group A elements are also metals. These include the transition metals (Groups 3-12) and the inner transition metals, which together make up the Group B elements. Copper, iron, gold, and silver are familiar transition metals. The inner transition metals, which appear below the main body of the periodic table, are also called rare-earth elements.

Chalcogens – Group 16 (VIA) , ore-forming

Halogens – Group 17 (VIIA) , combine with metals to form salts

Noble gases – Group 18 (Group VIIIA or 0) , inert gases, tend to not react

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Kinds of Elements

I. Metals

1. Luster, shine

2. Color- gray, orange, yellow

3. Solids, except mercury which is a liquid at room temperature

4. Malleability – hammered into sheets

5. Ductility – ability to be drawn into wire

6. Conductivity of electricity – in both the solid and liquid phases

7. Relatively high boiling point

8. Conductivity of heat

9. Tenacity – strong, resist being pulled apart

10. Relatively high melting point

11. Except for hydrogen, metals are on the left side of the periodic table

12. Francium is the most active metal

II. Non-metals

1. Generally have low boiling points

2. Soft solid

3. Some (sulfur) are brittle solids

4. Some (oxygen and chlorine) are gases at room temperature

5. Generally nonlustrous

6. Generally poor conductors of electricity

7. One, bromine, is a fuming dark-red liquid at room temperature

8. Includes noble gases (Group VIIIA or 0) and halogens (Group VIIA)

9. Occupy upper right corner of periodic table

10. Fluorine is the most active non-metal

III. Metalloids

1. Semi-metals

2. Properties of metals and non-metals

3. Sometimes brittle

4. Border bold black line on the periodic table

5. Boron, silicon, germanium, arsenic, selenium, antimony, tellerium, polonium, astatine

6. Silicon and germanium are used in the manufacture of computer chips and solar cells

IV. Noble gases

1. Nonreactive

2. Outer energy level is filled

3. Colorless

4. Group 18 (VIIIA or 0)

5. Helium, neon, argon, krypton, xenon, radon

Liquid elements – bromine, mercury

Gas elements – hydrogen, nitrogen, oxygen, fluorine, chlorine, helium, neon, argon,

krypton, xenon, radon

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