Reviewer in Science 9 (Second Quarterly) PDF

Reviewer in Science 9 (Second Quarterly) MODULE 1 Rutherford’s nuclear atomic model describes the atom as mostly empty space. Its mass is concentrated in the nucleus that consist of protons and neutrons. However, it could not explain the chemical properties of elements. Bohr’s at...

Reviewer in Science 9 (Second Quarterly) MODULE 1 Rutherford’s nuclear atomic model describes the atom as mostly empty space. Its mass is concentrated in the nucleus that consist of protons and neutrons. However, it could not explain the chemical properties of elements. Bohr’s atomic model describes the atom like a solar system, where the electron is found only in specific circular paths, or orbits, around the nucleus. In the Bohr model, each electron carries a fixed amount of energy and does not lose energy as long as it stays in its given orbit. The fixed energies that the electrons have are called energy levels. An electron that has received enough energy can jump to a higher energy level. When the electron returns to a lower energy level, energy is emitted in the form of light. The Bohr model was later replaced by a model of the atom that showed that electrons are not limited to fixed orbits around the nucleus. Through mathematical calculations, scientists explained that there is only a probability that the electron can be found in a certain volume in space around the nucleus. This volume or region of space around the nucleus where the electron is most likely to be found is called an atomic orbital Schrodinger formulated a mathematical equation that describes the behavior of the electron. The solution to the equation is used to calculate the probability of finding the electron at a particular region in space around the nucleus. The quantum mechanical model of the atom describes the atom as having a nucleus at the center around which the electrons move. This model describes a region in space where the electron is most likely to be found. An electron is imagined to be a cloud of negative charge having a certain geometrical shape. The electrons are arranged in principal or main energy levels that consist of one or more sublevels.  The way in which electrons are distributed in the different orbitals around the nucleus of an atom is called the electron configuration. Filling of electrons start from lower energy level to highest energy level. Glossary: Atomic orbital – the region of space in which there is a high probability of finding the electron in an atom Electron configuration – the distribution of electrons within the orbitals of the atoms of an element Quantum number- a number that specifies a property of an orbital or an electron  HYDROGEN- 1s1 MODULE 2 The valence electrons are the outermost electrons which are directly involved in chemical bonding. Lewis symbol is composed of the symbol of the element and dots which represent the number of valence electrons of an atom that can easily be determined through the family/group number in the Periodic Table of Elements.  Atoms form bonds with one another to become stable and attain the electronic configuration of the noble gas nearest it. An ionic bond involves complete transfer of electrons, thus ions are formed. It involves metals with low electronegativity and non-metals with high electronegativity. A covalent bond involves the sharing of electrons that results in the formation of covalent compound whose representative particle is a molecule. As a whole, a molecule does not carry a charge. Two identical non-metallic atoms always form covalent compound such as N2, O2, H2, F2 and other diatomic molecules. Metallic bonding exists in metals through the attraction between the freely moving valence electrons and the positively charged metal atom. The valence electrons of these metal atoms are usually called “sea of electrons.” Glossary: Anion a negatively charged particle Cation a positively charged particle chemical bond the force or energy that holds atoms or ions together Covalent bond a bond formed when atoms share electrons to attain stability electronegativity is a measure of the tendency of an atom to attract electron Ionic bond a bond which involves complete transfer of electrons ionization energy is the energy required to remove an electron from the outermost energy level of an atom ions charged particles luster the property of metals to reflect light malleable the property of metals to be hammered into thin sheet Valence Electron the electrons at the outermost energy of level or orbit MODULE 3 Organic compounds are compounds that are primarily composed of carbon atoms, which are chemically bonded with hydrogen and other elements such as oxygen, sulfur, and nitrogen. Organic compounds are naturally produced by living organisms but can also be produced artificially. Organic compounds such as gasolene, kerosene, ethyl alcohol, isopropyl alcohol, formaldehyde, acetic acid, acetone, and lubricating oil have important uses. These uses are based on their specific chemical properties. Alcohols are a group of organic compounds that contain a hydroxyl group, -OH, that is chemically bonded to a carbon atom in the compound. They have special uses such as a disinfectant, fuel, and as a main component (ethyl alcohol) of liquor and other alcoholic drinks. acetone is used as a cleaning agent like a nail polish remover formaldehyde/Formalin is used in preserving organic materials like an animal specimen. This is also the compound used in embalming human cadavers. LPG (liquefied Petroleum gas) is used as a fuel gas in heating appliances, cooking equipment, and vehicles. Methane is a gas that occurs naturally in the earth's atmosphere and is often used fuel in heating and cooking Lubricating oil prevents the metal surface from any type of corrosion and roughness. Alkanes. Alkanes are hydrocarbon compounds where atoms only form single bonds with other carbon atoms. Alkenes. Alkenes are hydrocarbon compounds which have double bonds between carbon atoms. Alkynes. Alkynes are hydrocarbon compounds which have triple bonds between carbon atoms.