An Illustrated History of the Periodic Table
This is a book that a science teacher will find hard to put down. Better than a novel. I think I might be hooked on Tom Jackson’s work. I am now curious about his books about specific elements.
The formula for an acid has hydrogen as its positive part, such as hydrochloric acid, HCl (H+ and Cl–).
An acid indicator is a chemical that changes color when added to an acid. If the indicator is dry, such as litmus paper, the paper changes color when an acid solution touches the paper.
Facts: The video provides details about acids. Click around and discover the difference between weak and strong acids and how they affect acid indicators, including litmus.
Part I: Litmus Paper: Test for An Acid
Purpose: To identify a positive test for an acid using litmus paper.
1 strip of red litmus cut in half
1 strip of blue litmus cut in half
white index card
eyedropper (or stirring rod, craft stick, plastic knife)
1 teaspoon white vinegar
Determine the positive test for an acid using litmus using each of the following procedures.
1. Hold one end of one of the red litmus strip, then touch the opposite end of the strip in the vinegar. Repeat using one of the blue litmus strip. Discard these strips.
2. Lay the remaining red and blue litmus strips on the index card. Fill the eye dropper with vinegar, then place one drop of vinegar on the end of each of the litmus strips.
3. Stir the vinegar with a stirring rod, wooden craft stick, or plastic knife, then touch the wet end to dry end of each litmus strip on the index card.
Results: Each procedure produces the same results, the blue litmus turns red and the red litmus get wet.
Conclusion: Blue litmus can be used to identify an acid. Blue litmus turns red when it touches an acid solution.
Part II: Identifying an Acid with Blue Litmus
Purpose: To identify acids using litmus paper.
1. Testing Liquids for the Presence of an Acid
Use one of the testing procedures in Part I, replacing vinegar with other liquids, such as lemon juice, orange juice, etc…
2. Testing Solids for the Presence of an Acid
To test a solid, first crush the solid so that it can be dissolved in distilled water. For example, test a Vitamin-C tablet by crushing it with a rolling pin on a cutting board. Add 3 or 4 drops of distilled water to the powder. Stir to mix the water and aspirin powder. You do not have to dissolve all the powder. Then touch the liquid with a piece of blue litmus. When blue litmus turns red, it is a positive test for the presence of an acid.
Solid to test: detergent, baking soda, baking powder and cream of tartar.
1. H, element symbol: All elements have a symbol. Some symbols have one letter and some have two letters. The first letter of all element symbols are capitalized and if there is a second letter it is lower case.
For more information, see element symbols for natural elements.
2. Hydrogen, element name: The name, Hydrogen, is capitalized in the box, but elements are not proper names and do not have to be capitalized. Thus, Hydrogen or hydrogen is correct.
3. Atomic Number: This number is generally listed at the top of the box. The atomic number is a very important code. It tells you two things about the element:
(1) The atomic number is equal to the number of protons in the nucleus of every hydrogen atom. Since hydrogen has an atomic number of 1, every atom of hydrogen has one proton in its nucleus.
(2) The atomic number is equal to the number of electrons outside the nucleus of each of the element’s atoms. For hydrogen, with an atomic number of 1, every hydrogen atom has 1 electron outside its nucleus.
4. Mass Number: The mass number is generally at the bottom of the box. The mass number equals the total number of nucleons (protons + neutrons) in the nucleus of each of the element’s atoms.
Mass Number = # P + # N ( P is the symbol for protons, and N is the symbol for neutrons).
The difference between the atomic mass and the atomic number equals the number of neutrons in the nucleus of the element’s atoms.
For Hydrogen: The number of neutrons = 1 – 1 = 0
Atomic diagrams contains a circle to represent the nucleus of the atom with semicircles outside the nucleus to represent the energy levels in which electrons are found.
Note that the diagram for hydrogen has a nucleus with one energy level. Inside the nucleus is one proton, 1P. Outside the nucleus in the one energy level is one electron, 1 e –. Since hydrogen atoms have no neutrons, none are represented.
If you like science history, you will love Eric R. Scerri’s book
“The periodic Table.” Dr. Scerri has really dug into the historical
event leading up to the the naming of elements as well as the construction of the periodic table.
1. Gases take the shape and volume of their container.
2. Gases will mix evenly and completely when confined to same container. This means that if you mix two or more gases, they form a solution. Air is an example of a solution of gases, which is made up of oxygen, nitrogen, and other gases.
3. Gases have much lower densities than liquids and solids.
4. Gases are most compressible of states of matter. This means that gases when squeezed take up less space. Another description is that the volume of a gas decreases when pressure on the gas increases and vise versa.
Science Standards and Clues
Design an experiment that tests the effect of force on an object.
1. Test the effect of force on one variable.
2. Ask a well defined question that contains an independent and dependent variable.
Example: What effect does pressure have on the volume of a gas?
FYI: Pressure is the force on an area.
3. State a testable hypothesis
Example: Since gases are very compressible, an increase of pressure on a gas will cause the volume of the gas to decrease.
4. Select and use appropriate equipment.
Example: The diagram above shows a mini-vacuum pump that can be used to investigate how changes in pressure affects the volume of a gas.
Note: A food
5. Design and plan an experiment to test the hypothesis.
Clues: Since most gases are invisible, you will need to have gas trapped inside a material that can expand, such as marshmallows or shaving cream.
The following video provides research information for this investigation.
The video also has great teaching ideas for demonstrating the molecular motion of gases and how this motion creates pressure.
The video has enriched information, such the equation for Boyle’s Gas Law.
Note: I am revising the following information. I had the opportunity to speak with one of the directors of LCR Hallcrest, a company that makes chameleon dyes.
The pencils in the picture are called chameleon pencils. While chameleons change colors in response to different stimuli, such as temperature, emotions, and illness, the dye used on the pencils respond only to temperature changes.
Thermochromic is the term used to describe a color change due to a change in temperature.
1. Cold Activated Dye: Clear to Color
This dye is clear at room temperature, but has a color change when the temperature decreases. Different dyes have a different color at specific temperatures.
2. Heat Activated Dye: Color To Clear
The Leuco dye used on the indicated pencil is heat activated. This means that at normal room temperature, the dye has a color. But, when heated the dye molecules rearrange and their new position is transparent to visible light.
The pencil on the left is covered with a green mixture made by combining yellow paint and blue Leuco dye. Yellow + Blue —-> Green
To better understand how blue and yellow reflected light make the pencil look green, see Visual Perception.
When heated the blue color from the dye becomes clear and the yellow paint, which is not affected by the heat, is visible. (The pencil painted with yellow paint is a control used to show that heat doesn’t affect the paint’s color.)
Enriched Information About Color Changes Products
Leuco dyes which have the property of changing from a color state to a clear state when a stimulus is applied, and then returning to a colored state when the stimulus is removed are called reversible Leuco dyes. The stimuli for the color change depends on the dye. Stimuli includes heat and light. Those that are heat sensitive are considered thermochromic. Those that are light sensitive are considered photochromic.
Liquid Crystals, like Leuco dyes are thermochromic.
For more detailed information about thermochromic materials, see Heat Sensitive Dye
|A+ Projects in Chemistry has ideas for simple chemistry experiments with enriched information that can be used to design and develop chemistry science projects.
The periodic table of elements was designed independently about the same time by two different scientists. Credit is given to Dmitri Mendeleev, a professor of chemistry in St. Petersburg, Russia because he published the first version of the table in 1869. Julius Lothar Meyer (1830-1895), a chemistry professor in Tuebingen, Germany, prepared a table but didn’t published it until 1870. Mendeleev’s table differed from Meyer’s in that he left spaces and predicted that elements with certain properties would be discovered. This turned out to be true, thus Mendeleev’s table was widely accepted and the modern periodic table is based on Mendeleev’s table.
As more and more elements were discovered, chemists saw similarities in them. They noticed that groups of elements had similar properties. Over time, scientists searched for ways to organize elements and many different systems were used.
In 1869 the Russian scientist Dmitri Mendeleev (1834-1907) developed a system that the modern arrangement of the periodic table is based on.
Mendeleev’s arrangement of the elements was in order of increasing atomic masses.
He made a table of the elements similar to that of a monthly calendar, which has columns (vertical groups) and rows (horizontal groups).
On a calendar, the rows represent a specific period of time, which is seven days also called a week. The columns represent a specific day of the week, and each day is given a name. On the calendar shown, day- 1 or the first day of every week is Sunday. No matter which day of the week you select, seven days later falls on the same day of the week. In other words, if you select Wednesday the 1st, seven days later will be Wednesday the 8th.
Mendeleev found that his arrangement of the elements, like the calendar, had similar patterns of repeated properties. Things with a repeating pattern are said to be periodic. The time of one week is the repeating pattern for a calendar. Mendeleev’s periodic table of element had repeated patterns of physical and chemical properties.
Like a calendar, Mendeleev’s arrangement of the elements formed a table with columns representing elements that are alike. These vertical columns are called groups. The table of groups on the periodic table of elements and the names for each group is shown.
In order for Mendeleev to arrange the elements by their properties, he had to leave some blank spaces in his table. Mendeleev’s periodic table was based on the idea that the physical and chemical properties of the elements are periodic functions of their atomic masses.
But, listing the elements in order by their mass resulted in some element not properly fitting in Mendeleev’s table. Mendeleev assumed that his table was correct and that the error was in the mass of the “misfit” elements.
In 1913, experiments performed by the English scientist Henry Mosely (188701915) showed that physical and chemical properties of elements are periodic functions of their atomic numbers (number of protons in an atom of an element). This solved the problem of the “misfit” elements.
The modern periodic table of elements is arranged by the atomic numbers of each element. The periodic table shown here is very basic, showing only the symbols and atomic numbers for each element. The group numbers as well as the row numbers are also labeled.
Matter is anything that has mass and takes up space, such as water. The photo shows water first falling and filling and collecting at the bottom of the waterfall. When the collected water increases in volume, the water spills over a rock boundary.
Water takes up space. Volume is the amount of space that matter occupies.
Metric volume measurements include:
liter and milliliter as well as cubic centimeters or cubic meters.
English volume measurements include:
gallon, quart, pint, and cup as well as cubic inches, cubic feet, or cubic miles.
Water also has mass, which means it is made up of physical particles. Don’t confuse mass with weight. While they are related, they are not exactly the same.
Note: It would be correct to say that matter has both volume and inertia.
The artist’s rendition of a tsunami striking a small village is a visual representation of a large amount of water with a great amount of inertia.
There is no stopping a tsunami.
Matter based upon its physical and chemical structure, can be defined as any substance made up of elements and/or compounds
A substance is matter of one chemical composition. Elements and compounds are substances.
An element is made of one kind of atom, which is the smallest particle of an element that retains the properties of the element. Examples of elements are gold, sulfur, oxygen, helium, and calcium.
Compounds are made up of two or more atoms.
Water ( H2O ) is a compound made up of hydrogen (H) and oxygen (O).
Sodium chloride ( NaCl ) is a compound made up of sodium (Na) and chlorine (Cl). a
There are two types of compounds:
Covalent compounds (molecules): The atoms in covalent compounds are held together by special bonds called covalent bonds. These bonds are strong because the atoms share electrons.
Ionic compounds: The atoms in ionic compounds are held together by forces between charged particles. These bonds are called ionic bonds.
A simple way to explain the difference between covalent and ionic compounds is to compare the dissolving of table sugar and table salt in water.
Table sugar, called sucrose is a covalent compound. When a spoon of sucrose is dissolved in water, the sugar crystals break apart until they separate into single particles called molecules. The formula for one sucrose molecule is C12H22O11. Even though this molecules has 45 atoms it is still too small to be visible.
Table salt, called sodium chloride is an ionic compound. When a spoon of sodium chloride is dissolved in water, the salt crystals break apart until the atoms separate from each other.When the atoms pull apart, one atom always “steals” an electron from the other atom. Atoms that have lost an electron have a positive charge and atoms that have gained an electron have a negative charged. Charged atoms are called ions.
In sodium chloride, the chlorine atom is the “electron thief,” thus the symbol for sodium with its extra atom is Na 1+. Chlorine lost an electron so it The formula for one sucrose molecule is C12H22O11. Even though this molecules has 45 atoms it is still too small to be visible.
I like this definition of matter. Now mass can be defined as the amount of matter in a substance.
Note: At a more microscopic level, one could say that matter is made up of what atoms, ions, and molecules are made of.
The three states of matter generally identified are: solid, liquid and gas. A fourth state of matter that is less commonly discussed is plasma. Plasma forms when a gas is heated, such as on the Sun or other stars, as well as during fluorescence inside a fluorescent light, such as on the Sun.
For more information about plasma see Chem4Kids: Matter: Plasma
The following information is about the three more commonly known states of matter: solid, liquid, gas.
States of Matter : Solid, Liquid, Gas
Ice is water in the solid form. This form, like all solids has a specific volume and shape. For example, an ice cube made in a mold takes the shape of the mold. But, one should not identify solids as taking the shape of their container because when you put an ice cube in a glass, the ice cube retains the shape it had before being in the glass.
Ice is colder than the water in a liquid or a gas state. This means that ice has less thermal energy, thus the molecules of water making up ice move slower. The freezing point of water is the temperature at which liquid water changes to a solid.
The freezing point for water is 320F (O0 C).
The melting point for water is also 320F (O0 C).
Liquid water has no special name. I say water when I am referring to liquid water. It can also depend on the content of the information about water. All liquids take the shape of their container, flow easily, and have a specific volume.
Gas is a state of matter that doesn’t have a set volume. Instead, if a gas is in a closed container, the gas has the volume and shape of the container. Water in a gas state is called
It is important to know that something gets colder because it loses heat. Heat is the transfer of energy from something that is hot to something that is cold. In other words, ice in a glass of water is not adding “cool” to the water. Instead, the water is transferring heat to the ice.
The state of matter depend on the thermal energy of the particles that the matter is made of. The particles of water are called molecules. As the thermal energy of water molecules increase, the molecules move faster and if possible move apart. Gases have the most thermal energy and single gas particles move in a straight line until they hit some boundary and bounce back in another direction.
As the thermal energy of liquid water molecules decreases, the water molecules move slower and get closer together. At freezing point of water, the water molecules bond together forming a six-sided ring.
Cohesion is the name of the attractive force between like molecules. This force is not very strong, so the molecules have to be close together and with little motion.
Kids can model hexagonal ice crystal units. The diagram is an overhead view showing the head, arms and hands of students. Each color represents a single water molecule with the circle (student head) being oxygen, the colored lines (student arms) represent bonds and the white circles (student hands) are hydrogen atoms.
The completed hexagon is made of six different students. Note that each kid only connects to one other kid in the hexagon. This connection is made by placing a hand on the shoulder of the kid next to them. Their second hand connects to a kid that will form a joining hexagon. In other words, each kid (water molecule) links to two different kids (water molecules).
The ice crystal units made of water molecules are many layers deep and spread out in all directions. This student model will be on one plane and can stretch out as far as there are kids to connect to.
The Following Terms Describing Opposite Changes of Matter Processes Are Described In This Article, How Energy Affect States of Matter
melting —->freezing; evaporation —->condensation; vaporization—>condensation;
For this article, heat will be the energy source and water molecules the substance gaining or losing energy. So, what happens when water molecules gain or lose energy?
Energy is needed for motion, the more energy a substance has the faster is its motion. The reverse is also true, as energy is decreased, the motion of a substance decreases.
I will start with ice, the solid phase of water. In this phase, the motion of water molecules is more like a vibration instead of their zipping around from one place to another. The natural force of attraction between the the molecules holds them in a rigid hexagonal shape as shown in the drawing. Note that only one level of molecules is drawn. Actually, layers of these hexagonal cells attach to each other on all sides forming a three-dimensional structure.
The hexagonal shape of ice crystal units or cells gives snowflakes their six-sided shape. shape. In ice, six water molecules combine forming a hexagon. This is why snowflakes have a six-sided shape.
I’ll assume that the ice is at the freezing point of water, which is 32o F (0o C). When ice is heated, at first there is no temperature change. This is because temperature increases are due to an increase in the motion of molecules. Instead of moving faster, the molecules use the heat energy to break away from from the hexagonal structure they are in. Even when some of the water molecules are no longer part of the ice structure, they are still at 32 o F (0 o C). This is because as long as there is ice present, added energy goes to breaking the bonds in the hexagonal rings. The liquid water molecules do not move independently. But neither do they stay attached to specific water molecules as in ice. Instead, in less time than you measure–picoseconds–the water molecules form bonds between each other, break away and bond with other water molecules, and so on. Once all the ice melts, then any additional energy added causes the liquid water to increase in temperature.
Remember: This information is what is currently accepted as true but only a few years ago there was a different explanation. As technology improves, more accurate models are proposed. Scientists should always keep an open mind and NEVER dogmatically accept ideas. You may be the one to discover a better model for water’s different states of matter.
Freezing is the opposite of Melting. Freezing occurs when a liquid loses energy. As energy is lost, molecules move slower, and the attractive force between like molecules (cohesion) pulls the molecules close and holds them in a relatively fixed position.
Vaporization is the physical change of a liquid to a gas. An increase in energy can cause vaporization. Between water’s freezing point and boiling point, water molecules can vaporize, meaning the molecules change from a liquid state to a gas state.
Vaporization below the boiling point is called evaporation.
Evaporation occurs at the surface of water when heat from the air above the water is transferred to the surface water molecules. When a surface water molecule gains enough energy to break free from the bond it has with other water molecules around it, it moves upward and mixes with air. The single water molecule has more energy, moves independently and is a gas.
Vaporization at boiling point is called boiling.
Boiling occurs beneath the surface of water. Bubbles of water vapor form, rise to the surface and break through the surface layer of water. Just like in evaporation, the individual water molecules escape into the air. The difference is that these water molecules released at boiling point have more energy.
Condensation is the opposite of vaporization. Condensation occurs when a gas loses energy, slows in motion so that its cohesive force pulls the molecules close, but the molecules still have enough energy to break away from one connection only to connect with another molecule. There is constant movement as the water molecules cling and break away from each other.
Example: Water drop form on the outside surface of a glass containing ice water. The water drop form because water vapor in the air condense on the cold surface of the glass. The more humid the air, the more condensation.
Note: Condensation is the name of the process of a gas changing into a liquid. Condensation is also the term used for the liquid that forms.
Dew forms when water vapor in the air condenses on the cool outdoor surfaces, such as grass, flowers, cars, etc….The temperature at which dew forms is called dew point. Dew point is not a specific temperature, instead it depends on the amount of water in the air. Humidity is a measure of the amount of water in the air. An increase in humidity results in an increase in dew point.
Sublimation is the process by which a solid substances changes to a gas. The substance does not melt. Dry ice is a substance that sublimes. Dry ice is actually frozen carbon dioxide gas. Carbon dioxide freezes at -78o C. Not even your freezer can keep dry ice from subliming because the air in your freezer is much warmer than the solid dry ice.
The white smoke that appears around dry ice is actually a cloud of water droplets. As the frozen carbon dioxide sublimes, the carbon dioxide gas is so much colder than the water vapor in the air that the vapor condenses. The tiny water drops that form are just like those in clouds and fog as well as steam and your exhaled breath on a very cold day.
Deposition is the reverse of sublimation. When a gas loses energy and changes directly to a solid without going through the liquid phase, it is called deposition.
The formation of frost is an example of deposition. For frost to form, surfaces have to be below the dew point temperature. This results in the atmospheric water vapor to change directly into a solid when it touches the cold surfaces.
NOTE: Frost is not frozen dew.
Paper is made of plant fibers. In the process of making paper, the fibers overlap forming a massive network of tunnels in all directions throughout the paper. The chemical molecules making up the fibers are attractive to water water molecules. Adhesion is the name of the force of attraction between two unlike molecules.
FYI: I think of adhesive tape to remember this force. Adhesive tape is what I use to secure a bandage to skin. The tape molecules are attracted to skin molecules, thus the tape sticks.
Paper absorbs water because the paper molecules and water molecules attract, thus stick together.
Imagine an animated view of a paper fiber tunnel in a piece of paper. The water molecules and paper molecules are holding on to each other and helping each other move through the tunnel. Once the walls of the tunnel are covered the space between the walls would be empty (technically filled with air). But the water molecules have a strong attraction for each other. Cohesion is the force of attraction between like molecules.
The water molecules holding onto the fiber walls also hold onto water molecules forming a bridge of water molecules that spans the space between the wall. In other words, the fiber tunnel is filled with water. As the water molecules move up the fiber walls the water molecules spanning the space of the tunnel are pulled along. This is called capillary action.
|Chemistry Experiments and Investigations For Every Kid|