Chemistry is the study about how matter is put together, how atoms combine to form molecules, and how the molecules combine to make up the many kinds of matter around us.
Classification of Matter • Matter – identified and organized by properties • anything that has mass and takes up space • Properties • Chemical – ability to react/combine (both what it will and won’t react with) - will change the composition • Physical – characteristics observed or measured -will not change the composition
two kinds of physical properties help describe the behavior of a substance undergoing a physical change 1. Extensive- depends on the amount of matter Ex: mass, length, volume 2. Intensive- does not depend on the amount of Ex: density (regardless of size, each sample of a substance has the same density) color, crystalline shape, melting point, boiling point, phase of the matter (solid, liquid, gas), and refractive index (ability of material to bend light)
State (or phase) of matter is always a physical property: Solid, liquid, gas
Changes in Properties • Physical change - does NOT change the composition (identity) of the substance. Same substance remains after a change has taken place *Size: pounding, bending, grinding, pulling, or cutting does not change the chemical character of a substance. *Change of state: melting, boiling, vaporizing *Cutting a piece of wood into smaller pieces, tearing paper, dissolving sugar in water, hammering copper into a new shape are all examples of physical change.
Chemical change- DOESchange composition. After a change has taken place a new substance appears • Changes that produce a new kind of matter with new, different properties. Burning, digestion, fermenting all form new substances with new and different characteristics. • Sodium- a silvery, soft metal that reacts vigorously with water (Na) • Chlorine- a yellow-green gas that is highly- corrosive and poisonous (Cl) • Yet if these two elements are brought together, they combine to form a white crystalline solid. Table salt (NaCl), which neither reacts with water, nor is poisonous.
Evidence of a chemical change: Heatand/or light is produced Production of a gas (bubbles) Odor Color change 5. Formation of a precipitate – a cloudy solid which appears after mixing to clear solutions
Chemical Reactions - a Chemical change has taken place: 2 or more substances have chemically bonded together to create a new substance • Law of Conservation of Mass – matter is neither created nor destroyed. This states that mass remains constant during a chemical reaction. One of the greatest scientific achievements of the 18th century by a Frenchman, Lavoisier (1743-1794) Mass (of reactants) = Mass (of products) Before After
Chemical Equations: Reactant + reactant product + product (always on left) (always on right) ~ arrow shows directions Ex. 12 g of calcium reacts with 6 grams of fluorine gas to produce calcium fluoride. How many grams of product will be produced? 12 g Ca + 6 g F2 ____ g CaF2 (12 + 6) = (18)
Try it • During electrolysis you can separate water into hydrogen & oxygen. If 10.0g Hydrogen & 79.4 g Oxygen were produced, much water was there at the start? ____ g H2O 10.0 g H2 + 79.4 g O2 • 89.4 g H2O 10.0 g H2 + 79.4 g O2
Mixture- matter that contains two or more different materials • Phase- any region with a uniform set of properties Ex: sour milk, watery part is one phase while fat is the second phase
Mixtures are divided into two categories • 1. Heterogeneous mixture- a mixture that is composed of more than one phase • Ex: granite, sand • 2. Homogeneous mixture- materials that consist of only one phase. • If you break a piece of homogeneous matter into smaller pieces, each piece will have the same properties as every other small piece • Ex: salt water, window glass, and air
Separating Mixtures (physical separation) • Filtration – through a porous barrier, filters solids from liquids • Distillation – different boiling points 2 liquids: lowest boiling point vaporizes 1st • Crystallization – dissolved solids from a solutions rock candy left after water evaporates • Chromatography – different rate of travel through a medium identify chemicals, DNA testing, separates pigments, research
Pure Substances-homogeneous materials that always have the same composition • *Homogeneous mixtures are not pure substances, yet the substances that comprise them are evenly dispersed throughout the mixture
Pure Substances are divided into two categories • 2. Compounds- composed of more than one kind of atom (made from multiple elements on the P.T.) • Ex: water ~ H2O, table salt ~ NaCl • Compounds cannot be physically separated, they are chemically bonded • 1. Elements- substances composed of only one kind of atom (elements on the P.T.) • Ex: sodium ~ Na, Iron ~ Fe, Neon ~ Ne
Pure Substances Matter Homogeneous Mixture Heterogeneous Mixture Suspension Element Mixtures Colloid- Solutions Compound
Has Mass Has Volume(Occupies Space) Pure Substances Matter Homogeneous Mixture Heterogeneous Mixture Suspension Element Mixtures Colloid- Solutions Compound
Variable Composition Can be physically separated Homogeneous Mixture Uniform Throughout (But Proportions can Vary) Heterogeneous Mixture Not uniform Throughout Ex. Lumpy Mixtures Colloid- Don’t settle out Particles larger than molecule Scatters light (Tyndall Effect) Ex. Smoke, Fog Suspension Solid in Liquid Eventually settle out Ex. Muddy water Wood, granite, blood Solutions Particles are atoms, ions, or molecules Won’t scatter light Ex. Salt Water, Steel, Air
Pure Substances Definite Composition Homogeneous Can’t be physically separated Element Made of atoms Cannot be further separated by chemical or physical means (on periodic table Mendeleev arranged in rows-periods Columns- groups/families) Compound Chemical combinations of 2 or more atoms. (elements chemically bonded) Cannot by separated by physical means (CaCl2, NaCl, Sugar, C6H12O6)
Has Mass Has Volume(Occupies Space) Pure Substances Definite Composition Homogeneous Can’t be physically separated Variable Composition Can be physically separated Matter Homogeneous Mixture Uniform Throughout (But Proportions can Vary) Heterogeneous Mixture Not uniform Throughout Ex. Lumpy Suspension Solid in Liquid Eventually settle out Ex. Muddy water Wood, granite, blood Element Made of atoms Cannot be further separated by chemical or physical means (on periodic table Mendeleev arranged in rows-periods Columns- groups/families) Mixtures Colloid- Don’t settle out Particles larger than molecule Scatters light (Tyndall Effect) Ex. Smoke, Fog Solutions Particles are atoms, ions, or molecules Won’t scatter light Ex. Salt Water, Steel, Air Compound Chemical combinations of 2 or more atoms. (elements chemically bonded) Cannot by separated by physical means (CaCl2, NaCl, Sugar, C6H12O6)
Law of Definite Proportions Regardless of amount, a compound is always composed of the same elements in the same proportion by mass % by Mass = Mass of element x 100 Mass of compound • If compounds have the same % by mass, they must be the same 80 g sample of compound contains 20 g of hydrogen. What is the percent by mass of hydrogen? 20 g x 100 = 25% 80 g
If 7 g of iron combine with 3 g of oxygen, what is the % by mass of iron? Of oxygen? • Hint: Find the total mass 1st % iron = 7g x 100 = 70% 10 g %oxygen = 3g x 100 = 30% 10g
Try it • Sample 1 contains 15.0 g of H2 and 120.0 g of O2 • Sample 2 contains 2.0 g of H2 and 32.0 g of O2 Are they the same compound?
Sample 1 contains 15.0 g of H2 and 120.0 g of O2 • Sample 2 contains 2.0 g of H2 and 32.0 g of O2 Are they the same compound? Sample 1 H2 : 15 x 100 = 11% 15 g + 120 g = 135 g 135 O2 : 120 x 100 = 89% 135 Sample 2 H2 : 2 x 100 = 6% 2 g + 32 g = 34 g 34 O2 : 32 x 100 = 94% 34 Different percentages so these are different compounds
Intro to the Periodic Table Vertical columns Horizontal rows • called groups or families. • Elements in a group have similar chemical & physical properties. • Numbered from 1-18 from left to right • called periods. • Elements within a period have properties that change progressively across the table.
Metals – (left side) are good conductors of heat and electricity; shiny metallic luster (mostly silver or grayish white); malleable (hammered or rolled into thin sheets); ductile (string into a wire); properties vary according to groups • Nonmetals – (right side) elements that are poor conductors of heat and electricity, dull (no luster); some are gases at room temperature. Br is a liquid; C, P, Se, S & I are solid and much more brittle than metals • Metalloids – (on the stair-step line) – elements that have characteristics of both metals and nonmetals to a limited degree. Less malleable than metals, but not as brittle as nonmetals; some have luster, some don’t; semiconductors of electricity (used in semi-conducting materials found in computers, calculators, watches, TV’s and radios)
Branches of Chemistry • OrganicChem – study of carbon – containing compounds • InorganicChem – all substances not classified as organic (mainly those that do not contain carbon) • PhysicalChem – the study of properties and changes of matter and their relation to energy • AnalyticalChem – identification of the components and composition of materials • Biochemistry – substances and processes occurring in living things • TheoreticalChem – uses math and computers to understand the principles behind observed chemical behavior and to design and predict new compounds
Scientific Method Science- Body of knowledge gained through systematic observation, experimentation, and study of the physical world.
Math- the language of Science: 16th century-Science made huge progress when it was discovered that nature can be analyzed and described when scientific findings are expressed mathematically they are easy to verify or disprove be experiment • Galileo Galilei(1564-1642) Italian Physicist • Francis Bacon (1561-1626) English philosopher • Co-Founders of scientific method ~ Extremely effective in gaining, organizing, and applying new knowledge
Scientific method – systematic approach to do research, answer questions, and solve problems • Recognize a problem • Make an educated guess-a hypothesis-about the answer • Predict the consequences of the hypothesis • Perform experiments to test predictions • Formulate the simplest rule that organizes the main ingredients: hypothesis, prediction, and experimental outcomes • http://www.youtube.com/watch?v=zrzMhU_4m-g