STEMSSCOPES READING (SET 2)

WHAT IS MATTER?

Table of Contents ……………………………... page 1

Properties of Matter …………………………… pages 2 - 3

Structure of Matter ………………………..…… pages 4 - 6

Chemical Properties and Interactions ……..… pages 7 - 8

Modeling Conservation of Matter ……………. pages 9 - 11

Electromagnetic Forces ………………………. pages 12 - 14

Gravity …………………………………….……. pages 15 - 16

Gravitational Forces ……………………….….. pages 17 - 18

Introduction to Fusion ………………………… pages 19 - 21

© 2016 Accelerate Learning, Inc.

Properties of MatterAll matter has properties. Properties are the characteristics or traits that make a particular material unique from other materials. The physical properties of a material can be measured without changing the materials molecular form or structure. Examples of physical properties include size, shape, color, melting and boiling point, solubility, density, magnetism, and electrical conductivity.

Physical properties help us understand and predict how certain materials will react under different circumstances. Plastic, for example, does not have good conductivity. Electricity does not flow easily through it. If we wanted to construct a device that easily moves electricity from one place to another, plastic would not be appropriate. Instead, we might choose wire made from copper or aluminum. On the other hand, if we wanted to make sure that someone using this device is not electrocuted, we would construct an outer casing of plastic around the device to prevent exposure to electrical charges by the user.

We use physical properties to group and classify materials. This allows us to select materials for specific purposes. The size and shape of the material is important when deciding how a material will be used. What about color, however? Objects that are white appear white because they reflect every color of the light spectrum and absorb none of them. Because they reflect light, they tend to be cooler in temperature. Conversely, black objects absorb every color and retain more light energy so they will be hotter. This is why light-colored clothing is cooler to wear than dark clothing.

Melting and boiling points indicate how a material will react when it is exposed to different intensities of heat. These properties are important when selecting materials that are used to make cooking utensils, in building construction, and in electrical appliances, just to give a few examples. Electrical conductivity is an important property used to determine what materials are used in electrical, lighting, and heating devices. High conductivity (low resistance) material is best such as in home wiring and low conductivity (high resistance) material such as the tungsten is used in light bulbs.

Physical properties are observable and measurable, or both. Several different procedures and instruments (besides the human eye) are used for this purpose. Rulers and balances provide data on size and mass. Heat sources and thermometers can identify melting and boiling points. Volume can be measured by using graduated cylinders, and density (compactness) can be measured by using Archimedes Principle of displacement.Physical properties are important characteristics of matter. Information about the physical properties of a variety of materials has been collected and recorded in standard reference books. These resources can be used to help determine the identity of unknown materials as well as provide information that will help predict how a material will react under different circumstances.

Structure of Matter

Atoms are the basic structure of all matter. Atoms can be combined to form molecules of various substances. Atoms make up all of the different kinds of matter in the universe, either as molecules of a single type of atom or in combination with other atoms. Atoms are the building blocks of everything around us.

Elements are pure substances composed of only one type of atom that cannot be broken down into any other substances by chemical or physical means. The Periodic Table of elements is a way of organizing all known elements by their physical and chemical properties. An element is identified by its specific chemical and physical properties. Each element has a chemical symbol, which is usually one or two letters representing the element. If the symbol for an element is a single letter, then the letter is always capitalized. If the symbol is two letters, then the first letter is always capitalized, and the second letter is lowercase.

The most abundant elements are within the first twenty: the top three rows and a portion of the fourth.

The symbols for each element are shown on the Periodic Table and are used to represent elements in chemical formulas and equations. Chemical symbols consist of letters of the Latin alphabet, although they are used by people of all languages. Examples of elements with symbols based on Latin names are copper (Cu - Cuprum), gold (Au - Aurum), and silver (Ag - Argentum). Although there are a little more than 100 different elements in the world, only a small number comprise a majority of the different systems on Earth.The most abundant elements on Earth are located within the first twenty elements on the Periodic Table. Elements consist of one type of atom distinguished by its atomic number, which represents the number of protons in its nucleus. An atom that has a different number of protons represents a completely different element. A water molecule has two hydrogen atoms (white) and one oxygen atom (red).

Only a few elements exist in nature as pure elements. Examples include nitrogen gas (N2), oxygen gas (O2), gold (Au), carbon (C), silver (Ag), and copper (Cu). Many metals exist in pure element form. Most matter consists of atoms combined with other atoms in a set ratio or proportion called compounds. For example, water is a compound made of the elements hydrogen and oxygen. The ratio of these elements is two hydrogen atoms and one oxygen atom (H2O) for each molecule of the compound water. Carbon dioxide gas is another example of a compound. Any sample of carbon dioxide is always made of part carbon to two parts oxygen (CO2 ). Salt, or sodium chloride, is made of one part sodium to one part chlorine (NaCl).

When elements are combined to make a compound, the new substance has properties different from those of the original elements. For example, table

salt is made of two elements, sodium and chlorine. The properties of table salt do not represent the properties of the individual elements. Sodium in element form is a highly reactive metal, and chlorine is usually a yellow-green gas in its natural state. When combined to make salt, the properties of the compound are considerably different.

Chemical Properties and Interactions

While all substances are made from at least one or more of the 100 plus elements found in the periodic table, substances made from only one type of atom or molecule are considered pure. Pure substances are consistent throughout, no matter the amount of the substance present. Pure substances have physical and chemical properties that can be used to identify the substance. While many pure substances share one or more physical and/or chemical properties, a unique combination of properties identifies each pure substance. As temperature increases, water can go from a solid (ice) to a liquid (water) to a gas (water vapor).

For example, at sea level, water has the physical properties of being solid at temperatures of 0o C and lower, gas at temperatures at and above 100o C, and liquid at any temperature in between. Some chemical properties of water are that it is a universal solvent and that it is made of molecules of two hydrogen atoms and one oxygen atom. Water is not flammable, colorless, tasteless, and odorless. When a drop of water is placed on a non-absorbent surface, it beads up. An easy way to tell whether this is water, vinegar, or alcohol is to smell it.

Any amount of a pure substance in the same given conditions will still have the same properties. This allows a substance to be identified by its properties. For example, three colorless liquids - water, alcohol, and vinegar - can be identified based on the property of odor.

When properties change after two or more substances interact, a chemical reaction has taken place. For example, salt water can be separated into water and salt using evaporation. The resulting water and salt have the same properties as water and salt did before mixing into salt water. No chemical reaction took place. In contrast, when silver nitrate and sodium chloride react in aqueous solution, sodium nitrate and silver chloride are formed. The silver chloride precipitates from solution. A chemical reaction took place.

Modeling Conservation of Matter

Matter can undergo both physical and chemical changes. In a chemical change, bonding of atoms changes and new substances are formed. However, conservation of matter states that the number and type of atoms in the reactant(s) is exactly equal to the number and type of atoms in the product(s). The total mass of reactants is equal to the total mass of products. Because conservation of matter is true, chemical equations can be balanced. The required amounts of reactant(s) and the expected yield of product(s) can be calculated.

Most chemical reactions in everyday experience happen in open systems. Especially when a gas is involved as either a reactant or a product, conservation of matter is difficult to demonstrate. Closed systems contain all products and can be used to observe conservation of matter at the

macroscopic level. Since conservation of matter implies conservation of mass, sensitive scales are frequently used to demonstrate this chemical law. Chemical changes are frequently accompanied by changes in appearance of a substance, such as light being produced, bubbles forming, etc. But the actual rearranging of bonds is not visible, as atoms are much too small to observe directly. Therefore, models become critical for understanding.

A model in science is anything that can represent an object, law, or theory or that can be used as a tool for understanding. Every model is created for a purpose, and all models are imperfect. A road map is a model of the real road, used by drivers to find their way. But it is clear that no map shows everything a driver encounters along the road. Scientific models also are created for a purpose and are imperfect. Students should know that chemical equations are models of chemical reactions. Chemical equations are useful to show the relative amounts of chemicals involved and can be used to predict how much reactant is required or product produced. Physical objects, such as marshmallows, Styrofoam or plastic balls, toothpicks, and other items, can be used to model conservation of matter. It is important that students deliberately and consistently label the objects in the model with what they represent (for example, white marshmallow is carbon, toothpicks are chemical bonds).

In the Hook, students work with glow sticks. Common commercially available glow sticks use hydrogen peroxide, phenyl oxalate ester, and a fluorescent dye, which determines the color of the light produced. The first two chemicals are kept separate until mixed by breaking the glass inside the stick. Mixing the chemicals produces energy, which is turned into visible light by the dye.

In activity 3, students design an airbag, given constraints such as inflation speed. While the first airbag patent was filed during World War II, mandatory automobile airbags date back to the late 1990s. Commercial airbags consist of three parts, a nylon bag, a sensor, and an inflation system. The inflation system reacts sodium azide with potassium nitrate to produce nitrogen gas. The

gas escapes through tiny holes, allowing the bag to deflate as a person moves around. The whole process takes 40 msec, less than the blink of an eye! While airbags save lives, they can also injure small children, and adults not wearing seatbelts. Research is ongoing to allow variable inflation speed and amount as well as positioning additional airbags around the car to further protect all occupants.

Electromagnetic Forces

Charged particles exert forces on one another. The most fundamental rule of electricity is that like charges repel one another, and opposite charges attract one another. For example, if an electron were moved into a region near another electron, the electrons would repel, or push away, each other. If the electron were moving near a proton, however, the proton would experience a force pulling it toward the electron. The strength of this force varies at different locations around the electron: closer to an electron, the force is stronger; farther from the electron, and the force is weaker, forming an electric field.

An electric field is a force field surrounding every charged particle. You can think of an electric field as a region of arrows surrounding a charge, with

each arrow representing a force. The arrows in the electric field tell you how much force another charge would feel if it were placed at a particular location in the field. The arrows also tell you in which direction the force would act. So, the arrows representing the electric field of an electron would show the force that a proton would experience if moved into any location near the electron.

In general, a charged particle’s electric field decreases as distance from the charge increases. A proton that is close to an electron experiences a very strong, attractive force. Conversely, a proton that is far from an electron would experience a much weaker force.

A magnet, or magnetized material, is an object with a north and south pole that produces a magnetic field. Certain objects (particularly metals such as iron) that enter the magnetic field are attracted to the magnet. However, magnets also have an important connection to electricity.

Magnetism results from the spinning of electrons in a material. All electrons spin; a spinning electron creates a tiny, magnetic field with a north and a south pole. In non-magnetized materials, these electrons spin in different directions and their fields cancel out. However, in magnetized materials, the electrons all spin in the same direction. The magnetic fields of each tiny electron combine to produce a magnetic material. Ferromagnetic materials, such as iron, are materials that are not naturally magnetized, but they can become magnetized easily in the presence of a magnetic field. (The chemical symbol for iron is Fe, from the Latin word ferrum. So, the prefix ferro- typically refers to iron.) For example, if you hold a magnet over a pile of iron shavings, the iron shavings will become magnetized.

Just as all charged particles are surrounded by electric fields, all magnets are surrounded by magnetic fields. The magnetic field flows out of the north pole of a magnet and into the south pole. Magnetic fields exert forces on other

magnets. As a rule, like poles repel each other, and opposite poles attract each other. Magnetic fields also exert forces on moving charged particles.

Gravity

Gravity is a physical force by which objects attract or pull towards each other. All matter has mass, which is the amount of an object in a specific volume. In comparison, weight is the gravitational force exerted on a given object that is at rest on the larger body’s surface. When you step on a scale, you are measuring the force of the Earth’s gravity pulling downward on your mass. The weight of an object depends on the strength of the gravitational force acting on it. An object weighs less where there is less gravity, but has the same mass. The Moon has only 1/81 as much mass as the Earth. A person therefore weighs less on the Moon than on the Earth. A satellite like the International Space Station is being pulled toward the Earth, but it is moving so fast around us that it “misses” the Earth as it falls. The orbital motion exactly counterbalances the Earth’s gravitational attraction and so everything is weightless in the International Space Station. Gravity is what holds the planets in our solar system in orbit around the Sun.The gravitational force on Earth continually pulls everything toward the planet’s center. As a result, a ball tossed in the air falls to the ground. Snowflakes produced in the clouds float down from the sky and leaves fall from trees. Rivers in the mountains flow downward toward oceans, and glaciers tumble down from mountains to form icebergs in oceans and lakes. The pull of Earth’s gravity downward is why rockets flying into orbit require engine boosters to push them up.

Everything on Earth experiences other types of forces besides gravity, among which are friction, elasticity, pushing, and pulling. Suppose you were to drop two objects with different masses at the same time from the same height.

Ignoring all the other forces, especially air friction, the Earth’s gravity causes the two objects to fall (accelerate) downward at the same rate. They will both reach the Earth’s surface at the same time.

Fifteenth-century physicist Isaac Newton was inspired by his observations of objects falling in nature and used them as the basis of his Theory of Universal Gravitation. Newton proposed that the force of gravity attracts all matter to all other matter, and that force can be calculated knowing the masses of the two attracting objects and the distance between their centers. The less massive and/or the farther apart two objects are, the less the gravitational force between them. Generally we think about gravity on the scale of planets. It is important to note that all objects have gravity acting between them, even between you and an orange in Spain. This gravitational interaction is much much weaker than between you and the Earth so it seems negligible.

Gravitational Forces

Gravity is one of the fundamental forces of nature. Newton’s Law of Gravitation states that the force depends on the gravitational constant multiplied by the ration of the product of the masses and the distance squared. It is calculated between pairs of objects. The force on one of the objects in the pair has the same magnitude, or strength, as the force on the other object, but it points in the opposite direction. The force on the first object points toward the second object. The force on the second object points toward the first object. Both objects feel the same magnitude of force. Gravity cannot be calculated from other physical constants. It was shown that spherical masses behave as if all mass is concentrated in their centers. This finding simplifies distance measurements, as the diameter of the object does not matter, only the distance between the centers.

The gravitational constant was measured by Henry Cavendish some seventy-one years after Newton’s death. Cavendish used an instrument called a torsion balance, which allowed him to measure the attraction between small lead balls. Since gravity is a very weak force, many precautions had to be taken to minimize disturbances caused by other forces such as air currents. More precise measurements in 2007 arrived at G = 6.693 10-11 cubic meters per kilogram second squared. The gravitational constant does not appear to vary over the age of the universe.

Gravity has several important characteristics. It has unlimited range. This means that all objects in the universe are attracted to all other objects in the universe. Since the force decays with distance squared, the attraction of very distant objects can usually be ignored, unless they have large mass. Gravity is a very weak force. So, although you attract the pencil on your desk, and it attracts you, the force between you and the pencil is too small to make the pencil move. On the other hand, since Earth has a large mass, the pencil is attracted to Earth, and if dropped, will fall. Earth is also attracted to the pencil, but since the pencil’s mass is so small, the movement of Earth towards the pencil is too small to be noticed. Gravity is always attractive, never repulsive.

Gravity has an important role in the appearance and function of the universe. Immediately after the Big Bang, scientists propose that matter was unevenly distributed throughout the expanding universe. Gravitational attraction between atoms allowed clumps of matter to form, which eventually formed celestial bodies. The orbits of planets are governed by gravitational attraction between stars and planets, and among planets. Moons are captured by planets when relatively slow-moving objects pass too closely to a planet. Astronomers infer the existence of invisible bodies based on their effects on observable orbits.

Introduction to Fusion

Nuclear ProcessesNuclear fusion is a nuclear reaction in which two atomic nuclei collide at very high speeds and combine to form a new type of atomic nucleus. This process is called nucleosynthesis. This reaction violates the law of conservation of matter, as part of the matter is converted to photons (energy). The most common fusion is hydrogen turned into helium. The fusion of nuclei lighter than iron generally releases energy. The fusion of heavier elements generally absorbs energy. Heavy-element fusion occurs only rarely, during extreme astrophysical events such as supernovae.

Astrophysicists discovered the origin of heavy elements in the 1950s, after World War II and its extensive research into nuclear processes as part of the Manhattan Project. The seminal paper was published in 1957, known by the author initials B2FH. Because it required the contribution of many scientists over many years, few outside the scientific community realize the importance of this publication. The authors laid out eight different processes to explain how almost all elements are produced inside stars and supernovae. Stars produce different elements, depending on their temperatures and densities. Several lighter elements are thought to have been produced during the Big Bang at the beginning of the universe.

The discovery of technetium inside some stars was particularly important. The most easily produced isotope of technetium has a half-life of 3 x 105 years, far shorter than the age of the universe. Therefore, this technetium had to be produced in the star itself, and not only during the Big Bang and its immediate aftermath.How do these elements get out of stars and contribute to other celestial objects, including Earth? Mixing and mass loss allow some elements to leave the stars that produced them and get into space. Other elements are ejected during the collapse of a red giant into a white dwarf star. Star explosions termed supernovae both produce and eject heavier atoms. Uneven distribution of matter allows gravity to collect matter into denser objects, including planets.

Fusion has been proposed as a source of energy on earth. Unfortunately, the conditions required to produce fusion are difficult to achieve and maintain. To date, almost all fusion reactions have required more energy input than they have produced in output. In the late 1980s, two researchers claimed to have achieved nuclear fusion at room temperature, termed cold fusion. Further experiments have been unable to reproduce their results, and there is no

theory for how cold fusion could occur. Research and development of hot fusion, the kind observed inside stars, is ongoing.

© 2016 Accelerate Learning, Inc.