Chemistry Review 1

Alief ISD Chemistry STAAR Review Reporting Category 1: Matter & Periodic Table C.4.A Differentiate between physical and chemical changes and properties. Physical & Chemical Properties Properties of substances can be classified as either physical or chemical. A physical property is a quality or a condition of a substance that can be observed or measured without changing the substance’s composition. Examples: shape, length, mass, volume, melting point, boiling point, state of matter, color, hardness, density and solubility. Physical properties can be used to identify a substance. A chemical property DESCRIBES the ability of one substance to change into a different substance. A chemical property differs from a physical property in that we can observe it ONLY by changing the composition of a substance. Examples: reactivity, flammability, heat of combustion, electronegativity, and ability to oxidize. Property Physical Chemical Description Can be observed without changing the substance into a different substance Examples Describing substances boiling point, color, density, solubility Can be observed when a substance changes into a different substance Describing substances reactivity with oxygen, or its flammability, or its toxicity Physical & Chemical Changes A physical change is a change that does not alter (or change) the chemical identity of a substance. The substance that exists before the change still exists after the change. Examples: cutting, crushing, or breaking into smaller pieces…also, phase changes are classified as physical changes; such as melting, evaporating, freezing…etc. A chemical change occurs when one or more substances change into one or more DIFFERENT substances. A substance present before the change happens is called a reactant; a substance produced as a result of the change is called a product. In a chemical change, the products have different chemical and physical properties from those of the reactants. Example: iron reacts with oxygen to product iron oxide (“rust”) 4 Fe + 3O2  2Fe2O3 How can you recognize a chemical change? Some signs are: formation of a gas, a change in color or odor, a change in temperature, the release of light or sound, and the formation of a precipitate. Change Description Examples Change is size, shape, or state; remains the same substance Freezing water, shredding paper, melting wax New substance is made; bonds between atoms are made or broken; often see a color change, temperature change, or the formation of gas or precipitate (solid) Burning wood, iron rusting Physical Chemical C.4.B Identify extensive and intensive properties. Types of Properties Physical and chemical properties of matter can be classified as either intensive or extensive. What is an intensive property? An intensive property is a property that IS NOT dependent on the amount of a substance. Different amounts of a substance will have the same intensive properties. Example: Pure water 0 will always boil at 100 C no matter what volume you start with. Boiling point is an intensive property. Also, the density of pure water at room temperature will always be 1 g/mL no matter how much water you have. Density is an intensive property. The more intensive properties that are known for a given substance, the easier it is to identify the substance. What is an extensive property? An extensive property is one that changes with the amount or size of a substance. Example: Water’s mass WILL change depending on the amount of water you have. Mass is an extensive property. Knowing an extensive property of a substance WILL NOT help identify it. Why? Extensive Properties and Intensive Properties Extensive properties Intensive properties • Dependent on the amount of a • Not dependent of the amount of a substance substance • Not dependent on the identity of a • Dependent on the identity of a substance substance • Examples: mass, length, volume, • Examples: density, boiling point, energy reactivity, solubility, specific heat, hardness C.4.C Compare solids, liquids, and gases in terms of compressibility, structure, shape, and volume States of Matter and Properties Property Compressible Shape Solid Basically no Fixed/rigid Volume Structure Fixed (constant) Forces keep particles in a rigid structure Liquid Basically no Takes container’s shape Fixed (constant) Intermolecular forces keep particles together but allow movement Gas Yes Fills up the whole space of container Changes Particles move freely, virtually no forces C.4.D Classify matter as pure substances or mixtures through investigation of their properties. Matter Matter: anything that takes up space and has mass This car represents matter because it has mass and is made from different materials Homogeneous: Composition-same all the way through Solution Heterogeneous: Composition-different & can see the different parts Pure Substance Mixture that is clear and you can’t see the parts (dissolved) Composed of elements and has a constant composition Mixture Composed of different parts that can easily be seen [not chemically bonded] Elements hot tea hot tea Composed of elements chemically bonded; in set ratio type of atom and composition This is a GOLD coin. Gold is an element on the periodic table. Au C.5.A Explain the use of chemical and physical properties in the historical development of the Periodic Table. Compounds Basic part of matter; Made up of only one This is WATER. Water is composed of hydrogen and oxygen in the ration of 2hydrogen atoms to every 1-oxygen atom How were chemical and physical properties used in the development of the periodic table? As scientists learned how to isolate elements from compounds, the number of known elements increased rapidly in the early 1800s. Scientists looked for patterns and similarities in the properties of elements in order to classify the growing number of discovered elements. Mendeleev organized known elements that shared similar chemical and physical properties (like Li, Na, and K which react violently with H2O to make H2) into the periodic table. The periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties. Mendeleev arranged the elements in his periodic table in order of increasing atomic mass. Over time, other scientists added to his work to create the periodic table now ordered by increasing atomic number. Vocabulary you will need to know to understand the organization of Periodic Table: Vocabulary word Valence electrons Definition Electrons in an atom’s outermost orbital shell; can be gained, lost. Or shared in a chemical reaction Picture How many valence electrons are shown in the picture above? Periodic table Chart of elements ordered by atomic number and grouped by number of valence electrons; chemical and physical properties vary predictably in the table (trends exist horizontally and vertically) Row or period Elements are in order of increasing atomic number; atomic number = number or protons = number of electrons (if neutral) Chemical elements in the first period: 1 2 H He Chemical elements in the second period: 3 4 5 6 7 8 9 10 Li Be B C N O F Ne Etc…. Column or group (family) Elements in a group have the same number of valence electrons and have similar physical and chemical properties. Group 18 called Inert or Noble Gases What is Group 1 called? Group 17? C.5.B Use the Periodic Table to identify and explain the properties of chemical families, including alkali metals, alkaline earth metals, halogens, noble gases, and transition metals. Metals Good conductor, ductile, malleable, shiny; located on left of the zigzag line on PT Nonmetals Poor conductor, brittle dull; located on right of the zigzag line of PT Metalloids (semimetals) Conductor under some conditions; located on top and bottom of zigzag line What are the main chemical families on the periodic table? Periodic Table of Elements +1 0 Alkali Metals Noble Gases +2 -1 Alkaline Earth Metals Halogens Oxidation #’s vary Transition Metals Description of Main Families of the Periodic Table Main Families Alkali Metals Alkaline Earth Metals Halogen Noble Gases/Inert Gases Transition Metal Description and Oxidation Number(s) Very reactive metal; wants to lose 1 electron; +1 Reactive metal; wants to lose 2 electrons; +2 Reactive nonmetal; “salt-formers”; wants to gain 1 electron; -1 Inert (not readily reactive) nonmetal; has full outer shell (8 valence electrons except He has 2); 0 Metal in table’s center; has partially filled shell and variable 1+ 2+ oxidation numbers (like Cu or Cu ) Oxidation number: represents electrons gained or lost when forming compounds Anion: negative charge; when atoms gains electrons example: anion F- (oxidation # -1 because it gains one electron) 2+ Cation: positive charge: when atoms lose electrons example: cation Ca (oxidation # +2 because calcium loses 2 electrons) C.5.C Use the Periodic Table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy. Trends in the Periodic Table Property Atomic radius Ionic radius Electronegativity Ionization energy Description and Trend Direction (s) As you move down a family atomic radius increases; as you move from left to right the atomic radius decreases. For anions (gains electrons) the ionic radii increases; for cations (lose electrons) the ionic radii decreases Atom’s tendency to attract electron’s; Electronegativity increases as you move left to right (excluding noble gases); Electronegativity decreases as you move down a family Energy needed to remove an electron from an atom; Ionization energy increases as you move left to right; Ionization energy decreases as you move down a family.