Atoms & Elements What is Chemistry? • The study of matter of matter and its changes What does a chemist do? • Chemists analyze substances • Chemists create or synthesize new substances • Chemists create models and test the power of theories • Chemists measure the physical properties of substances Areas of chemistry • Analytical chemistry • Organic chemistry • Inorganic chemistry • Physical chemistry • biochemistry Careers in chemistry • Quality control chemist • Industrial research chemist • Forensic chemist • Environmental chemist • Sales representative • Chemical educator Scientific Method • Consists of three parts: • Observation • Explanation through the creation of a theoretical model • Testing the model Observations • A statement(s) that describe what we see, touch, feel, smell, or taste (the five senses) Conclusion • A statement as to what one thinks about a series of observations Data • Facts that are learned by observing some physical, chemical or biological system Scientific Law • A broad generalization, based on the results of many experiments • Scientific laws are expressed in terms of mathematical equations: (Examples: E = mc2, PV = nRT , PV= C) Classification of Matter • Matter is anything that has mass and occupies space • Matter can be classified as elements, compounds, or mixtures Elements • Substances that cannot be decomposed further by ordinary chemical means. • All elements can be identified by a chemical symbol Elements (cont.) • The first letter is always capitalized • The second letter (if there is one) is always lowercase Compounds • A substance that is composed of two or more different elements in which elements are always combined in a fixed ratio Examples of compounds • Carbon dioxide (CO2) • Water (H2O) • Ammonia (NH3) • Glucose (C6H12O6) • Sodium chloride (NaCl) Mixtures • Materials that have variable composition • Two types of mixtures: a) homogeneous and b) heterogeneous Homogeneous Mixtures • Homogeneous mixtures have properties that are identical throughout the sample • All solutions are considered to be homogeneous mixtures Examples of homogeneous mixtures • Air (a mixture of gases) • Alloys (brass, bronze, sterling silver, steel) • Rubbing alcohol (isopropyl alcohol and water) • Saltwater Heterogeneous Mixtures • Heterogeneous mixtures consists of regions (phases) which are not uniform. Examples of Heterogeneous Mixtures • Oil & water • Salads • Soups • Blood • Milk Physical and Chemical Changes • Physical change: A change in which no change in the composition occurs. No nes substances are formed • Chemical change: A change in which the composition of the substance is changed Examples of physical changes • Ice melting • Water boiling • Dissolving sugar in water • Alcohol changing into a vapor Examples of chemical changes • Sugar fermenting into alcohol • Iron rusting • Silver tarnishing • Butter turning rancid Properties of Matter • Physical Properties: Properties which does not involve a change in chemical composition (Examples: density, melting point, boiling point, solubility, malleability, etc.) Chemical properties • Properties which describe a chemical change which takes place • Examples: Sugar decomposes when heated, iron changes to rust when exposed to moist air Extensive Properties • A property that depends on the size of the sample • Examples: Volume, mass, and length Intensive properties • Properties that are independent of sample size Examples of Intensive Properties • Color • Melting point • Boiling point • Density • Electrical conductivity • Intensive properties are better in identifying than extensive properties States of Matter • Solid: Definite shape & volume • Liquid: Definite volume, but indefinite shape • Gas: Indefinite shape & volume Law of conservation of mass • States that matter cannot be created nor destroyed • Mass is conserved Law of definite proportions • States that in a given chemical compound, elements are always combined in the same proportions by mass Dalton’s Atomic Theory • Matter consists of tiny particles called atoms • Atoms are indestructible • In any sample of a pure element, all atoms are identical in terms of mass and other properties Dalton’s atomic theory (cont.) • The atoms of different elements differ in mass and other properties • When atoms of different combine to form compounds, new and more complex particles form Law of multiple proportions • Whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers. Law of Multiple Proportions (cont) • Example: Sulfur can react with oxygen to form two different compounds: SO2 SO3 Subatomic Particles • Consists of protons, neutrons, and electrons • Protons possess a positive charge • Electrons possess a negative charge • Neutrons possess a neutral (no) charge • Protons and neutrons are located in the nucleus of the atoms • Electrons move about the nucleus Isotopes • Atoms that have the same number of protons, but different number of neutrons Atomic number & Mass number • Atomic number : number of protons • Mass number: number of protons & neutrons Atomic mass • Weighed average of all isotopes that compose that element • Units are expressed in atomic mass units (amu) for each atom • Carbon-12 is used as the standard Atomic Mass Unit • Symbolized as u • 1/12 the mass of the carbon-12 isotope • Average atomic masses can be determined from isotopic abundances The periodic table • Developed by Mendeleev in 1871 • His table arranged elements based on increasing atomic mass • Modern periodic table arrange elements based on increasing atomic number • Horizontal rows are called periods • Vertical rows are called groups or families Groups & families of elements • Representative elements: (Groups IA- VIIIA) • Alkali metals (Group IA) • Alkaline earth metals (Group IIA) • Halogens (Group VIIA) • Noble gases (Group VIIIA) • Transition elements (B groups) • Inner transition elements a) lanthanides (58-71) b) actinides (89-103) Characteristics of Metals • Solid (except Hg) • Exhibit a luster (shiny) • Ductile • Malleable • Good conductors of heat/electricity Characteristics of nonmetals • Solids, gases, and one liquid • Solids are brittle • Poor conductors of electricity/heat • Not malleable • Not ductile Metalloids • Possess characteristics between those of metals and nonmetals • Tend to serve as semiconductors • Examples: silicon, boron, germanium, tellurium, etc.
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