What are chemical changes? Chemical bonds are formed when atoms attach to other atoms. Chemical bonds are forces that hold atoms together. Forming or breaking these bonds change the chemical properties of a substance. This leads to chemical changes which produce new substances with chemical properties that are different from those of the original substances. An example of a chemical change is when charcoal burns, molecules of oxygen from the air bond with the carbon in the coal, producing new molecules of carbon dioxide. Signs of a chemical change include color change, the formation of gases, and the release of light and heat. Describing Chemical Changes A chemical reaction is another name for a chemical change. A chemical reaction consists of two parts which are the reactant and product. The substance present before a chemical change is a reactant. The substance produced by a chemical change is a product. A chemical reaction uses letters and numbers to represent the amounts of reactants and products involved in a chemical change. An arrow separates the reactants on the left from the products on the right. 2Na + 2H₂O → 2NaOH + H₂ 2 sodium + 2 water → 2 sodium hydroxide + hydrogen There are equal numbers of atoms on both sides which means the chemical equation is balanced. This is called the law of conservation of mass in which matter is not destroyed or created during a chemical reaction. However they might form new substances. What are chemical reactions? There are 3 major types of chemical reactions. They are Synthesis, Decomposition, and Replacement reactions. In synthesis reactions, elements or compounds combine to form new compounds. An example is rust which comes from the combination of oxygen and iron atoms. A decomposition reaction occurs when a complex compound breaks down into simpler substances. The bubbles in soda come from the decomposition reaction of carbonic acid. Replacement reactions occur when elements or molecules switch places. An example is zinc in hydrochloric acid forms zinc chloride and hydrogen gas. Speed of Chemical Reactions The rate of a chemical reaction depends on many factors such as temperature, concentration, pressure, and the amount of surface area of solid reactants. Increasing pressure forces particles in a smaller area to make contact. Temperature increase causes particles to move faster, and increasing the concentration means particles is more likely to make contact. What are exothermic and endothermic reactions? Exothermic reactions release energy and keep going on until it is stopped. An example is a welder’s torch which produces a rapid exothermic reaction. Endothermic reactions absorb energy but needs a constant supply of light energy to continue. An example is photosynthesis.

What are the different properties of elements? Elements have chemical properties which describe the way a substance reacts with other substances. Metals are shiny and bend easily. They also conduct heat and electricity. Metals are separated into alkali metals, alkaline earth metals, and transition metals. Alkali metals are soft and extremely reactive and can easily form compound with other substances. Alkaline earth metals are light and soft but not that reactive. Transition metals are hard and shiny and react slowly with other substances. Metalloids are semiconductors and conduct electricity but stop electricity from flowing at low temperatures. Nonmetals are usually gas and are poor conductors. Noble gases like neon and xenon do not react naturally with other elements. What are acids and bases? Indicators such as litmus paper and red-cabbage juice change color when they are in the presence of acids or bases. A pH scale measure how acidic or basic a substance is and runs from 0 to 14. The lower it is the more acidic it is and if it is higher than 7 then it is basic. 7 means neutral and an example is distilled water. Acids taste sour and turn indicators red or pink. They release hydrogen ions in solutions. Bases taste bitter and turn indicators blue or green. They release hydroxide ions in solutions. Uses of Acids and Bases Strong acids are used to make plastic, explosives and textiles. Acids are also used in your stomach. Strong bases are used in batteries and in cleaning and bleaching. Bases also break down and dissolve substances which make them good cleaning agents. This is also due to the fact that they are slippery and break down grease and oil. What are the properties of salts? There are many kinds of salt. Salt is a compound formed by a reaction between an acid and base. When an acid and base of equal strength is mixed, then they react. This process known as neutralization produces water and salt. The sodium and chloride in table salt are held together by ionic bonds which form when one atom takes an electron from another atom. Many salts dissolve easily in liquid. They are electrolytes, which mean that they allow an electric current to flow when dissolved in a liquid such as water.

What are some common carbon compounds? Carbon bonds itself in many ways, taking on many forms such as diamonds or coal. Many carbon compounds are organic compounds which are the chemical building blocks of all known living things. Carbon is also part of inorganic compounds. Carbon dioxide is formed by the combination of one carbon atom and two oxygen atoms. Carbon dioxide is a gas required for many life functions and to keep objects cold. Some carbon compounds such as carbon monoxide are dangerous. It forms when fuel does not burn completely and can be very poisonous and prevent blood from carrying oxygen to the rest of the body. Carbon also bonds with hydrogen to form methane. Methane, a natural gas, is used to heat homes throughout the world and can be chemically changed to make many useful compounds. What organic compounds are in your body? All the compounds that form the cells and tissues in your body are made of elements found in the food you eat. Carbon is the most common of these compounds so it is essential for human beings to live. Nucleic acids are an organic compound that are found in the cell’s chromosomes and store and transfer the data on the building of proteins in your body. Lipids, proteins, and carbohydrates are also the chemical building blocks of life. Carbohydrates are your body’s main source of energy and are made up of carbon,hydrogen,and oxygen. They are found in grain foods such as pasta and bread. Lipids are organic compounds carbon-hydrogen bonds and include fats and cholesterol. They are contained in foods such as cheese and butter. They store and release much more energy than other organic compounds but remain in your body as fat. Proteins are also important organic compounds in the human body and are used for important functions such as cell growth and repair. Fish, meat, and vegetables contain protein. How do people use organic compounds? Organic compounds are important components in many products that we use such as soap, fuel, and rubber. A plastic also has many uses, and is a molded material that can retain its shape. They are organic compounds made up of carbon and hydrogen. Some are found naturally in the horns of animals but most are synthetic or made by humans.

What is radioactivity? The number of protons in an atom determines what element that atom has. Some isotopes are unstable because the atoms have too much nuclear energy. The atoms get rid of this energy by giving off invisible rays or particles. Elements that gives off energy in rays or particles are considered radioactive. The energy given off by radioactive elements such as radium and polonium is called radiation. The Geiger counter is used to detect radioactivity. As an atom gives off radiation, the nucleus of the atom decays. The amount of time it takes half of the atom to decay is called half-life. Uranium has a half-life of 4.5 billion years. There are three common forms of radiation. Alpha particles are made of two protons and two neutrons and are large, heavy, and slow which means they cannot penetrate many materials. Beta particles are electrons and are fast, light, and able to penetrate some materials. Gamma rays are not particles but electromagnetic waves. They have lots of energy which means that they penetrate most materials. What are two types of nuclear energy? One type of nuclear reaction is called nuclear fission. Nuclear fission is the splitting of a nucleus into two or more. Nuclear fission produces more free neutrons and release energy. If large nuclei are present, neutrons released by splitting one atom will strike other atoms causing a chain reaction, a reaction in which products keep the reaction going. Because the forces in an atomic nucleus is strong, lots of energy is released. Nuclear Fusion Splitting nuclei of heavy atoms into smaller atoms releases energy. Another way to release energy is to merge nuclei with smaller masses to form one nucleus with a greater mass. This process is called nuclear fusion and occurs at high temperatures. How is radioactivity used? Radiation can help people since they can destroy any type of cell, including harmful ones like cancer cells. Doctors use radioactivity to detect diseases. Radioactive materials can also produce electricity. However exposure to radiation for a long time is very harmful.