Chemistry Reviewer 12 - STEM C and E PDF

GENERAL CHEMISTRY REVIEWER (GOOD LUCK EVERYONE) Lesson 1: Matter and Its Properties Particulate Nature of Matter - The kinetic particle theory states that matter is particulate in nature. This means that matter is made up of tiny part...

GENERAL CHEMISTRY REVIEWER (GOOD LUCK EVERYONE) Lesson 1: Matter and Its Properties Particulate Nature of Matter - The kinetic particle theory states that matter is particulate in nature. This means that matter is made up of tiny particles with empty spaces between them. The particles, called atoms, are in constant random motion and attractive forces exist between them. - The primary particles are called protons, neutrons, and electrons. - There are also other subatomic particles such as quarks and bosons. States of Matter Solids - The particles of a solid are closely packed in an orderly manner. - According to the kinetic particle theory, these particles are held together by strong attractive forces. - Their kinetic energy is just enough for them to vibrate and rotate in their fixed positions. - This explains the definite shape and volume of solid, its high density, and its slight compressibility. - It expands only very slightly when heated. Liquids - The particles of a liquid are loosely packed together. - There are spaces between them because the forces of attraction that hold the particles together are weaker than those in a solid. - This explains why a liquid can be slightly compressed and has a lower density compared to a solid. Gas - Gas particles are not held in fixed positions because they have a lot of kinetic energy. - The particles move rapidly and randomly in all directions. Thus, a gas has no definite shape. - The particles of a gas are far apart due to a very weak force of attraction between the particles. - This explains why a gas has a low density and is easily compressed to a smaller volume. Plasma - The fourth state of matter - Is a gaseous state of matter in which a part or all of the atoms or molecules are stripped off electrons forming positive ions and negative electrons. - A gaseous mixture of positive ions and electrons characterizes the fourth state of matter. - Most common form of matter in the universe but the least common on Earth.  Auroras are atmospheric disturbances caused by the presence of low density plasma. - Auroras are green and red flames of light stretching across the sky. - An aurora that occurs in the Earth’s Northern Hemisphere is called aurora borealis or northern lights. On the other hand, aurora australis or southern lights occur in the Southern Hemisphere. Bose-Einstein Condensate (BEC) - Scientists believe that there is a fifth state of matter, the Bose-Einstein Condensate (BEC). - The name is derived from the names of Albert Einstein and Satyendra Nath Bose, who predicted the fifth state of matter in 1924. - In a BEC, matter stops behaving as independent particles. It collapses into a single quantum state that can be described with a single, uniform wave function. - In 1995, the team of Eric Cornell and Carl Wieman of the University of Colorado at Boulder, produced the first condensate experimentally. This condensate is “colder” than a solid. - The Bose-Einstein condensate may occur when atoms have very similar (or the same) quantum levels, at temperatures very close to absolute zero (-273.15℃). Properties of Matter Physical properties are characteristics of a substance which can be observed without changing its composition. - Some examples of physical properties are boiling point, melting point, density, color, odor, hardness, electrical and thermal conductivities, tenacity, elasticity, and plasticity. Physical Properties of the Three States of Matter Property Solid Liquid Gas Shape Has its own shape Takes the shape of its Takes the shape of its container container Volume Has its own volume Has its own volume Fills the volume of its container Compressibility Very slight Very slight Easily compressible Density High High Low Diffusion Very slow Slow Fast Thermal Expansion Very slight Slight Expands infinitely  Chemical properties are characteristics that a substance exhibits when it undergoes changes in composition. - These properties are related to the kind of chemical changes that substances undergo during chemical reactions. - Some examples of chemical properties are flammability, reactivity, toxicity, and acidity. Intensive and Extensive Properties - All measurable properties of matter are either intensive or extensive. - The measured value of an intensive property does not depend on the amount of the sample. Properties such as density, temperature, and absorbency are intensive properties. - Extensive properties, such as mass, length, and volume, depend on the amount of the sample. More matter means more mass. Changes in Matter - The conversion of ice to water, then to steam and back is a very usual occurrence. Changes like these, which do not alter the composition of the substance, are called physical changes. - Chemical changes involve changes in the composition of substances. Food undergoes chemical changes as it is cooked. Burning and rusting also involve chemical changes. Lesson 2: Classification of Matter Mixtures - Most materials found in nature are mixtures. - They are combinations of two or more substances that can be separated by physical methods. - Mixtures differ from pure substances because they have variable composition. Mixtures can be classified as either homogeneous or heterogeneous. A homogeneous mixture has uniform composition and properties as seen by the naked eye. Seawater and air are examples of homogeneous mixtures. A heterogeneous mixture is not uniform in composition. - Any part of a system with uniform composition and particles is called phase. Thus, a heterogeneous mixture consists of two or more phases. Homogeneous mixtures are also called solutions. Usually, we think of solutions as homogeneous mixtures of liquids (such as fruit juice and water) or solids soluble in liquids (such as instant coffee in water). But this term also applies to mixtures of gases, liquids, or solids.  Some Common Types of Solutions System Examples gas in gas air, anesthetic gases gas in liquid carbonated beverages liquid in gas water vapor in air liquid in liquid vinegar, alcohol liquid in solid dental amalgam solid in liquid salt water solid in solid alloys, jewelry of gold or silver Suspensions are heterogeneous mixtures where the suspended particles can be seen and are large enough to be filtered. Colloids are generally classified as heterogeneous mixtures where the particles are bigger than those solutions but smaller than those of suspensions. Coarse Mixtures are heterogeneous mixtures where the particles can be separated mechanically. Separating Mixtures Some heterogeneous mixtures can be separated by: ➔ Decantation is the pouring of the liquid from a mixture to separate the liquid (decantate) from the solid particles. ➔ Filtration is the pouring of the mixture through a piece of paper (filter paper) which lets the liquid (filtrate) pass through but catches the solid. ➔ Floatation is the removal of suspended particles either by sedimentation or coagulation. ➔ Centrifugation is the settling of tiny suspended particles using a centrifuge. This hastens the settling of the precipitate in a suspension. Homogeneous mixtures or solutions can be separated by: ➔ Distillation makes use of the differences in boiling points. In a mixture of two liquids, the liquid with the lower boiling point boils and changes into gas first. The gas is then condensed back to a liquid (distillate). ➔ Fractional Distillation separates liquid mixtures whose components have boiling points that differ by just a few degrees. This is used in petroleum refineries. ➔ Crystallization occurs when simple seawater is allowed to evaporate. The salt crystallizes out. This is not limited to liquid solutions. Gemstones like diamonds and emeralds form when molten rocks cool.  ➔ Fractional Crystallization involves lowering the temperature of solutions so that the more metal component crystallizes out first, The solid is filtered out and the same process is repeated until no more solid cystallizes. ➔ A solution can be separated by allowing it to flow along a stationary substance. This is called chromatography. The components in an ink solution can be separated by passing the solution through a piece of paper. Elements and Compounds - An element is a substance that cannot be broken down into simpler substances by a chemical change. - There are so far 118 elements, ninety-four (94) of the elements occur naturally on Earth and the rest have been produced artificially. - The elements are grouped into three: metal, nonmetals, and metalloids - Metals are elements that form positive ions and have metallic bonds. - Nonmetals are chemical elements that lack the characteristics of a metal. - Metalloids are chemical elements that exhibit some metal and nonmetal properties. - Compounds are formed when two or more elements combine in a chemical change. - They are substances that can be broken down into simpler substances only by a chemical reaction. Lesson 3: Atomic Theory and Subatomic Particles In 1800s, John Dalton developed the Dalton’s Atomic Theory supported by Three Fundamental Laws: 1. Law of Conservation of Mass - Which states that the total mass in any chemical or physical change does not change. - The number of substances may change, the properties may also change, but the total amount of matter remains constant. 2. Law of Definite Composition - Formulated by John Proust (1754-1826) - a french chemist - It states that when elements combine to form compounds, they do so in definite proportions (fractions) by mass. 3. Law of Multiple Proportions - For a theory to be successful, it must not only explain current observations, it must also predict results of future observations. - This law states that if two elements (A and B) combine to form different compounds, the different masses of one element (B) that c combine with a fixed  mass of another (A) can be expressed as a ratio of small whole numbers such as 1:2, 2:3, 3:4, and so on. Atoms - “Indivisible” is the literal meaning of atom in ancient Greek. - The idea of atoms was convinced and developed by the Greek philosopher, Leocippus (ca. 490-unknown B.C.) and his student Democritus (ca. 460-ca. 370 B.C.), more than 2,400 years ago. - Democritus said that the atoms were indivisible, indestructible, and the smallest particle of matter. - This concept of atoms refuted the idea of Empedocles that the world was composed of air, earth, fire, and water. This persisted through Roman times but was refuted during the Middle Ages because the models were based on reasoning and imagination rather than on experimental evidence. - By the seventh century, atoism had arrived in Isaac Newton’s work on light. He conceived that light was made of “corpuscles” or particles, although a later theory held that light was made of waves. Dalton’s Atomic Theory - It was in the late 1700s when chemists were able to relate chemical changes to individual atoms. At that time, John Dalton (1766-1844), an English chemist and physicist, stated his atomic theory based on approximately 150 years of investigation by scientists such as Robert Boyle, Joseph Priestly, and Antoine Lavoisier. - Daltons’ atomic theory can be summarized in four hypotheses (or postulates). 1. Matter is composed of tiny, indivisible spheres called atoms. 2. Atoms of the same element are identical, but atoms of one element are different from those of all other elements. 3. Atoms of different elements combine in simple whole number ratios to form compounds. 4. Atoms cannot be created or destroyed during a chemical change. Atoms of one element cannot be changed into atoms of different elements. - Dalton’s model of the atom was accepted for about 100 years because he used it to support two fundamental laws of nature - the law of conversion of mass and the law of definite composition. Cathode Rays and Electrons - William Crooks (1832-1919), an English chemist, used a powerful vacuum pump to nearly evacuate glass tubes fitted with metal electrodes. When these were connected to an external source of electricity, he noticed a flash of light or “ray” coming from the negative electrode (cathode) and moving to the positive electrode (anode). This ray  was called cathode ray. These experiments marked the beginning of picture tubes in television and computer display tubes. - Observations made in discharge tubes (cathode ray tubes) by W. Crookess, Joseph John (J.J.) Thomson, and other scientists suggested the existence of negatively charged particles which were later called electrons. The same term (electron) was used by George Stoney earlier in 1874, to describe the charge of a single unit of electricity. - Experimental evidences of cathode rays exhibit the following properties: 1. Cathode rays travel from the negative electrodes to the positive electrodes in straight lines 2. The rays are deflected by magnetic or electric fields 3. The rays possess kinetic energy. Objects placed along its path cast a shadow. 4. The nature of the rays does not change regardless of the kind of metal for the cathode, the gas in the tube, the metal wires, and the materials used to produce current. Thomson concluded that electrons are part of all atoms. Plum Pudding Model - Another important finding was the fact that although electrons have negative charges, the overall charge of atoms is zero. So atoms must contain enough positive charge that cancels the negative charge. - Thomson proposed a model of an atom as a positively-charged sphere where the electrons are embedded. - This model is sometimes referred to as a “plum pudding model” where the plums are the electrons, or as a “watermelon model” with the electrons as the seeds of a watermelon, or “raisin cake model” where the raisins are the electrons. Radioactivity - In 1895, the German physicist Wilhelm Rontgen (1845-1923) discovered that highly energetic rays could penetrate matter. These rays could not be deflected by a magnet and did not consist of charged particles like the cathode rays. Roentgen called these X-rays. - In 1896, Henri Becquerel (1852-1908), a French physicist, associated X-rays with fluorescent materials. He used a uranium ore containing fluorescent material and found that it emitted radiation continuously even when it was not fluorescing. - One of Becquerel's students, Marie Curie, suggested the name “radioactivity” for this phenomenon. Any material such as uranium that spontaneously emits radiation is said to be radioactive. - At Becquerel’s encouragement, Marie and her husband, Pierre began their famous experiments to isolate the radioactive components of uranium, radium, and polonium. This proved that atoms have internal structure. This was supported by Thomson through the result of his work on cathode rays. - Further study on the nature of radioactivity led by Ernest Rutherford identified two types of radiation from radioactive materials - alpha and beta rays.  - Alpha rays (α) are particles with a positive charge of +2. - Beta Rays (β) consist of negatively charged electrons which are attracted to positively charged plates. - The third form of radiation is not affected by the electric field. Discovered by Paul Villard, which is Gamma Rays. - Gamma Rays (γ) are electromagnetic radiation of extremely high penetrating power. - Additional radioactive elements were later discovered by the Curies, Rutherford, and Frederick Soddy. They also found out that chemical properties of radioactive elements change as it undergoes radioactive decay. - Disintegration of the nucleus of an atom (ionizing radiation). Symbols of each Radiation Ernest Rutherford (The Nucleus) - In 1910, the British physicist Ernest Rutherford (1871-1937) gave his 21-year-old student, Ernest Marsden a research project to verify Thomson’s model of the atom. - Marsden and Hans Geiger, Rutherford’s assistant, used alpha particles to probe the atom. They thought that alpha particles should go through thin gold foil undeflected. However, they were surprised when a very small fraction-about 1 in 8000 - of the alpha particles bounced back at large angles. - From the result of his students’ experiments, Rutherford explained that the few positively charged alpha particles that bounced back at large angles must have collided with a very tiny but concentrated mass of positive charge. - This refuted the atomic model of Thomson. He proposed that most of the mass and positively charged parts of the atom, the protons, must be concentrated in a small region  called the nucleus. He thought that electrons are distributed in the space outside the nucleus of the atom. James Chadwick - The discovery of the third particle atom occurred in 1932. - James Chadwick (1891-1974), one of Rutherford’s former students, showed that each uncharged particle emitted by radioactive atoms has a mass approximately equal to a proton. - These neutral particles were called neutrons. - Chadwick revised Rutherford’s nuclear model and proposed that the nucleus contains protons and neutrons. Atomic Numbers, Mass Numbers, and Isotopes - An atom of an element can be identified by knowing how many protons and neutrons are present in the nucleus. - Atomic number (Z) is equal to the number of protons contained in an atom of an element. It is also equal to the number of electrons in a neutral atom. - Mass number (A) is equal to the sum of the number of protons and neutrons contained in an atom of an element. - Atoms of a given element have the same atomic number but can have different mass numbers. These are called isotopes. Examples: ADDITIONAL INFORMATIONS Nucleus - protons and neutrons Isotopes - can be stable and unstable Radioactive Decay - nuclear transformation Atom - has a central core called the nucleus Nucleus - is a positive charge. The nucleus is very small compared to the total mass of the atom but the mass of the atom is concentrated in the nucleus. Electrons - are scattered around the nucleus Number of Atomic Number = Number of Protons and Electrons Gold Foil - Rutherford’s experiment, also called as “Alpha Scattering Experiment” Alpha particle is the same helium atom Alpha particle is POSITIVE The alpha consist a material called gold GOLD - most malleable metal Property of Gold - malleability (ability of metal to be hammered into sheets) Nucleons - particles inside the nucleus ( protons and neutrons) Number of protons + electron = atomic weight Proton particle is the same as a hydrogen atom