Properties of Some Representative Elements Class Notes

The Periodic Table

Mendeleeve, a Russian chemist in the 1870's, was the first to successfully partially arrrange the known elements into a chart that we call today the periodic table. He arranged the elements according to increasing atomic size. When he did this he noticed that certain elements grouped themselves into vertical groupings called families or groups. The periodic table was later rearranged by Mosely. He arranged the elements by increasing atomic number. This is the periodic table we are now familiar with.

Elements of the periodic tble are arranged in groups (columns) and periods (rows). Groups contain elements with similar properties and have the same electron configuration in their outer shells. These electrons in the outer shell are called valence electrons. They determine the properties and chemical reactivity of the element and participate in chemical bonding. As you go down a group atomic size increases and as you go across a period, atomic size generally decreases.



Groups can further be catagorized in Representative Elements and the transition metals. Representative elements are Groups I & II on the left and Groups III - VIII on the right. Transition metals are the groups left in the middle of the periodic table.


Group IA also called Alkali Metal Group

The alkali metals all share the same characteristics. These characteristics include:

1. They are all soft metals, easily cut with a knife.

2. They all contain one valence electron which is given up easily in a chemical compund.

3. They are all soluble in water.

4. They are very reactive with oxygen forming oxides.

5. They are very reactive with water forming hydroxides.

6. They are so reactive to oxygen and water that they do not occur in nature in their pure state and must be stored under some inert liquid to keep them from reacting.

7. Their reactivity increases as you go down the group because their size increases making it easier for an electron to be removed.


Video of Sodium and Potassium Reacting With Water


Group IIA or Alkaline Earth Metals Group

The characteristics that alkaline earth metals share are:

1. They are not as soft as the Group IA metals.

2. They all contain two valence electrons.

3. They are too reactive to occur in nature in their pure state, but NOT as reactive as alkali metals.

4. They react more mildly with oxygen to produce oxides of metals and will only react with water at temperatures where the water is steam.

5. Their reactivity increases as you go down the column due to the increase in size and ease that electrons can be removed.



Group VIA - the Oxygen Family or Chalcogens

This group contains two common elements, oxygen and sulfur. Oxygen exists in two forms: O2 the most stable form and O3 ozone. Ozone is produced by lightning. Sulfur exists in many forms at different temperatures. The most common form is a ring of 8 sulfur atoms joined together. At temperatures above 165 o C, sulfur joins into a chainlike molecule to form several other forms.

Chalcogens contains 2 nonmetals (oxygen and sulfur), 2 semiconductors (selenium and tellurium) and one radioactive metal (polonium).



pH

You determine the pH of a substance to describe its acidity or alkalinity.

A pH < 7 indicates it is acid.

A pH = 7 indicates it is neutral.

A pH > 7 indicates it is basic (alkaline).


You will be determining the pH of a solution using two different methods: pHydrion paper and Universal Indicator.


pHydrion Paper

Tear a small piece of pHydrion paper off. Dip a clean stirring rod into the solution you are testing. Touch the tip of the stirring rod to the pHydrion paper. Compare to the chart while your paper is wet.

Do Not Wait Until The Paper is Dry to Compare.


Universal Indicator

A Universal Indicator is a mixture of several indicators making it sensitive to a wide pH range. Each component of the universal indicator changes color at a different pH value, making the indicator display a range of colors according to the pH of the test solution. At pH = 1 (strong acid) it is red, at pH = 7 (neutral ) it is green, and at pH = 13 (strong alkali) it is purple.

Image courtesy of Fundamental Photographs

Photo Copyright Fundamental Photographs, NYC, www.fphoto.com



Flame Tests

Metal ions give off characteristic and intense colors when placed in a flame. A flame test can then be used to visually identify a unknown metal in an ionic salt.


Colors

Lithium, Li CARMINE-RED
Strontium, Sr SCARLET-RED
Calcium, Ca RED-ORANGE
Sodium, Na YELLOW-ORANGE
Barium, Ba YELLOW-GREEN
Potassium, K VIOLET-PURPLE

What Causes That Burst of Color?

When the metal ions are heated, the electrons in the outer shell absorbs energy. The electrons then become "excited" and move to a higher energy level that they are not supposed to be in. Once in that higher energy level, they fall back to the level they are supposed to be in and as they fall back they release the energy they absorbed. This released energy is in the form of light which is the color you see.

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about fireworks here.


How To Do A Flame Test

You need a clean nichrome wire loop. Clean the loop by dipping it into HCl acid, then rinse with distilled water. Test for cleanliness by inserting the loop into the bunsen burner flame. If a burst of color occurs, the loop is not clean. A clean loop is then dipped into a test solution, then placed into the outer portion of the flame. Watch for a short burst of color.

Flame Test Movies at Northwest University


Lighting The Bunsen Burner - The Proper Procedure

1. The gas jet has a blue gas valve handle. Attach the rubber hose to it after first inspecting the hose for cracks.

2. The Bunsen Burner has two parts: the barrel which controls the air, and the screw valve on the bottom which controls the gas. Gas enters the barrel of the burner from the center of the base, controlled by a valve in the base. Air enters through an opening at the bottom of the barrel where it screws into the base.

3. Check the spark lighter to make sure it sparks.

4. Close the Burner screw valve, then open it one turn.

5. Adjust the barrel to have about a 1/4 inch opening for air. The amount of air admitted is governed by the postion of the barrel. When the barrel is screwed down, the air opening is small.

6. Turn on gas at gas jet.

7. Hold spark lighter directly over the barrel and strike.

8. If burner does not light after a couple of strikes, turn gas off. Wait a few seconds, readjust burner and try again.


Adjusting the Air Mixture

To make the flame burn hotter & larger open the air valve by adjusting the barrel slowly.

To make the flame burn cooler & smaller close air valve by adjusting barrel slowly.

HOT FLAME = BLUE

COOL FLAME = YELLOW Too little air to gas ratio.


Increasing Size of Flame

To increase or decrease the size of th flame, turn thescrew valve on bottom of burner. Do not control by the gas jet handle!



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last updated: February 3, 2014