The Periodic Table of Elements- Ch 5

Scientists use the periodic table to explain the chemical behavior of different groups of elements. An organized table of the elements is one of the most useful tools in chemistry.

Until 1750, scientists had identified only 17 elements, mainly metals, such as copper and iron. As the number of known elements grew, so did the need to organize them into groups based on their properties. In 1789, Antoine Lavoisier grouped the known elements into categories he called metals, nonmetals, gases, and earths. For the next 80 years, scientists looked for different ways to classify the elements. But no system worked for all the known elements.

In the 1860s, Dmitri Mendeleev developed an approach for organizing the elements His work was the foundation for the modern Periodic Table

Mendeleev organized the known elements in order of increasing mass, and a pattern emerged. The key was to break the elements into rows.

The modern periodic table is based on atomic number, or number of protons. 7 Nitrogen 14.007

Rows/Periods The horizontal organization of the periodic table

Columns/Families/Groups The vertical organization of the periodic table

There are four basic pieces of information listed for each element: Atomic number (# of Protons) Element symbol Element name Mass number ( # of protons +neutrons)

Look at the Periodic Table in your book…

Valence Electrons Now locate the groups with an “A”… The A groups in the periodic table are numbered from 1 through 8 & the group number matches the number of valence electrons in that group. Why do we care about valence electrons? Valence electrons play a key role in chemical reactions. Properties vary across a period because the number of valence electrons increases from left to right.

Elements in a group have similar properties because they have the same number of valence electrons. The properties are not identical because the valence electrons are in different energy levels.

Energy Levels, Orbitals, and Electrons Number of Orbitals Maximum Number of Electrons 1 2 4 8 3 9 18 16 32

Columns/Families/Groups So, as you keep counting the columns, you'll know how many electrons are in the outer shell. There are some exceptions to this when you look at the transition elements (those with a “B” at the top), but you get the general idea.

Rows/Periods In the periodic table, elements have something in common if they are in the same row. All of the elements in a period have the same number of atomic orbitals or levels. Each orbital/level can hold a fixed number of electrons Orbital 1 = 2 electrons Orbital 2 = 8 electrons Orbital 3 = 18 electrons Orbital 4 = 32 electrons The lower orbitals must be full before filling the upper orbitals.

Every element in the top row (the first period) has one orbital for its electrons, those in the second row (the second period) have two orbitals for their electrons, etc.

Example: Looking at the Periodic Table… Hydrogen, the first element in Period 1, has one electron in its first energy level. (1 electron total, in the 1st orbital) Lithium, the first element in Period 2, has one electron in its second energy level. (3 electrons total, 2 in the 1st orbital 1 in the 2nd) Sodium, the first element in Period 3, has one electron in its third energy level.(11 electrons total, 2 in the first orbital, 8 in the 2nd orbital, and 1 in the 3rd) This pattern applies to all the elements in the first column on the table.

Special Elements… Hydrogen (H) and helium (He) are special elements. Hydrogen can have the talents and electrons of two groups, one and seven. Hydrogen is sometimes missing an electron, and sometimes it has an extra. Helium is different from all of the other elements. It can only have two electrons in its outer shell. Even though it only has two, it is still grouped with elements that have eight (inert gases) because of its other characteristics.

Look at the Periodic Table in your book…

Metals The majority of the elements on the periodic table are classified as some type of metal. Metals are elements that are generally good conductors of electric current and heat. Except for mercury, metals are solids at room temperature. Most metals are malleable. Many metals are ductile; that is, they can be drawn into thin wires.

Transition metals The metals in groups 3 through 12 are called transition metals. Transition metals are elements that form a bridge between the elements on the left and right sides of the table. Transition elements, such as copper and silver, were among the first elements discovered. One property of many transition metals is their ability to form compounds with distinctive colors. Tend to be less reactive Can have more than one valence configuration.

Nonmetals Nonmetals generally have properties opposite to those of metals. Poor conductors of heat and electric current. Have low boiling points–many nonmetals are gases at room temperature. Nonmetals that are solids at room temperature tend to be brittle. If they are hit with a hammer, they shatter or crumble.

Metalloids Metalloid elements are located on the periodic table between metals and nonmetals. Metalloids are elements with properties that fall between those of metals and nonmetals. For example, a metalloid’s ability to conduct electric current varies with temperature. Silicon (Si) and germanium (Ge) are good insulators at low temperatures and good conductors at high temperatures.

Group Details… The Alkali Metals Sodium Group 1A - Single Valence Electron Extremely Reactive –found only in nature in compounds Reactivity increases from top to bottom of group

The Alkaline Earth Metals Group 2A – Have Two Valence Electrons Metals are harder than group 1 so melting points are higher Differences in reactivity among the alkaline earth metals are shown by the ways they react with water.

The Boron Family Group 3A or Group 13 all have three valence electrons. Contains Aluminum which is the most abundant metal in the Earth’s crust.

The Carbon Family Group 4A or group 14 has four valence electrons. Metallic nature increase from top to bottom. Life on earth could not exist without carbon. All living organisms have carbon in them

The Nitrogen Family Group 5A or group 15 has five valence electrons. Groups contains a wide range of physical properties.

The Oxygen Family Group 6A or group 16 has six valence electrons. Oxygen is the most abundant element in the Earth’s crust Sulfur was one of the first elements to be discovered.

The Halogens Group 7A or group 17 has 7 valence electrons. Despite their physical differences the halogens have similar chemical properties They are highly reactive non-metals with fluorine being the most reactive followed by chlorine

The Noble/Inert Gases Group 8A or group 18. Helium has 2 valence electrons all of the rest have 8 valence electrons The noble gases are colorless, and odorless and extremely unreactive. All noble gases except radon are used in neon lights.

When electric current passes through noble gases, they emit different colors. Helium emits pink, neon emits orange-red, argon emits lavender, krypton emits white, and xenon emits blue.