Chapter 1: Matter, Energy, and the Origins of the Universe

Transcription

1 Chapter 1: Matter, Energy, and the Origins of the Universe Problems: , science: study of nature that results in a logical explanation of the observations chemistry: study of matter, its properties, and the changes it undergoes In what fields is chemistry used today? How is it used? 1.2 MATTER: AN ATOMIC VIEW We study matter at different levels: macroscopic: the level which we can observe with the naked eye e.g. geologists study rocks at the macroscopic level microscopic: the level which we can observe using a microscope e.g. scientists study tiny animals, plants, or crystals at the microscopic level atomic or molecular (also called particulate): at the level of atoms and molecules can only be observed using the most powerful microscopes most atoms and molecules are a few nanometers in size The term nanotechnology refers to materials created or developed by manipulating atoms and/or molecules CHEM161: Chapter 1 page 1 of 7

2 1.1 CLASSES OF MATTER matter: anything that has mass and occupies volume pure substance: a single chemical consisting of only one kind of matter Two types of pure substances: elements: consist of only one type of atom atoms cannot be broken down into smaller components by chemical reaction e.g. copper wire (Cu), sulfur powder (S 8 ) Examples also include sodium (Na), barium (Ba), hydrogen gas (H 2 ), oxygen gas (O 2 ), and chlorine gas (H 2 ). compounds: consist of more than one type of atom and have a specific chemical formula Examples include hydrogen chloride (HCl), water (H 2 O), sodium chloride (NaCl) which is table salt, barium chloride (BaCl 2 ) Two or more pure substances can combine to form mixtures. mixtures: consist of many compounds and/or elements, with no specific formula Matter having variable composition with definite or varying properties can be separated into component elements and/or compounds e.g. Any alloy like brass, steel, 10-K to 18-K gold (anything less than 24K gold); course mixtures like sea water, carbonated soda; air is a mixture consisting of nitrogen (~78%), oxygen (21%), and other trace gases. Mixtures can be homogeneous or heterogeneous: Homogeneous mixtures have a uniform appearance and composition. e.g. solutions (e.g salt water, soda, etc.), metallic alloys, etc. Heterogeneous mixtures do not have a uniform composition e.g. chocolate chip cookie, coarse mixture of sand and iron filings CHEM161: Chapter 1 page 2 of 7

3 1.6 STATES OF MATTER Matter exists in one of three physical states: solid, liquid, gas Ex. 1: A few drops of food coloring are added to a beaker of water. How would you expect the water to appear after a few minutes? Explain why. Ex. 2: If you add a drop of food coloring on top of an ice cube, would you expect the same result? Explain why. To understand matter, we must recognize how particles behave at the molecular level. gas: Volume is variable, particles are widely spaced, Takes the shape of the container because particles are moving If container volume expands, particles move apart to fill container If container volume decreases, particles move closer together particles are in constant random motion liquid: Fixed (or constant) volume, but shape can change Takes the shape of the container because particles are moving Particles are packed closely together but move around each other solid: Has definite shape, rigid volume Particles can only vibrate in place CHEM161: Chapter 1 page 3 of 7

4 1.5 PROPERTIES OF MATTER Intensive Properties: properties independent of quantity (e.g. density, boiling point, etc.) Extensive Properties: properties that depend on quantity (e.g. mass, volume, etc.) PHYSICAL AND CHEMICAL PROPERTIES AND CHANGES Physical Properties: physical state (solid, liquid, gas) color density melting and boiling points electrical and heat conductivity solubility (amount of solid that dissolves in liquid) hardness odor Chemical Properties: how a substance reacts with other substances e.g. hydrogen reacts explosively with oxygen CHEMICAL VERSUS PHYSICAL CHANGES Physical Change: a process that does not alter the chemical makeup of the starting materials e.g. changing shape, changing physical state, dissolving e.g. boiling water, melting ice, hammering gold into foil, dissolving salt in water Note in the images below the chemical makeup of H 2 O does not change as it goes from a solid to a liquid and to a gas. CHEM161: Chapter 1 page 4 of 7

5 Know the terms for transitions from one physical state to another! freezing: liquid solid melting (or fusion): solid liquid condensing: gas liquid vaporizing: liquid gas deposition: sublimation: gas solid (without liquid phase) solid gas (without liquid phase); e.g. dry ice sublimes. CHEMICAL CHANGE: a process that does changes the chemical makeup of the starting materials We can use space-filling models to show what happens at the molecular-level when H 2 and O 2 react to form water (H 2 O) of each molecule. Notice that the H 2 O has a different chemical makeup than H 2 and O 2. The following examples are all chemical changes that convert the reactants to completely different compounds and/or elements. release of gas bubbles (fizzing) formation of insoluble solid (precipitation) oxidation of matter (burning or rusting) CHEM161: Chapter 1 page 5 of 7

6 Ex. 1: Consider the following molecular-level representations of different substances: For each figure above, indicate if it represents an element, a compound, or a mixture AND if it represents a solid, liquid, or gas. A: element compound mixture solid liquid gas B: element compound mixture solid liquid gas C: element compound mixture solid liquid gas D: element compound mixture solid liquid gas E: element compound mixture solid liquid gas F: element compound mixture solid liquid gas Ex. 2 Match the following substances with the correct molecular-level representation above. B ammonia (NH 3 ) air silver sodium chloride mercury hydrogen Ex. 3: Circle all of the following that are chemical changes: burning condensing dissolving rusting vaporizing melting CHEM161: Chapter 1 page 6 of 7

7 1.8 MAKING MEASUREMENTS AND EXPRESSING THE RESULTS: PRECISION AND ACCURACY accuracy: indicates how close a measurement is to the true value precision: refers to how closely two or more measurements agree with one another Ex. 1: Indicate the accuracy and precision for the targets above: a. accurate inaccurate precise imprecise b. accurate inaccurate precise imprecise c. accurate inaccurate precise imprecise 1.10 TESTING A THEORY: THE BIG BANG REVISITED (100 Greatest Discoveries video) (Why collecting all data matters and how bad data can lead to scientific breakthroughs) In the 1960s, the US launched the first communication satellites, called Echo and Telstar, which were basically reflective spheres that bounced microwave signals from transmitters to receivers back on Earth. Bell Labs in NJ had built an antenna to receive such signals, and two Bell Lab scientists, Robert W. Wilson and Arno A. Penzias, were trying to improve the antenna s reception. But they kept picking up a background signal, no matter where they directed the antenna. Assuming the signal was just an artifact, even attributing it to pigeons roosting on the antenna, the pair continued testing the equipment until they finally realized their original hypothesis must have been wrong, that the nuisance signal was not an artifact but actually significant. Wilson and Penzias learned that a Princeton University physicist named Robert Dicke had predicted residual energy left over from the Big Bang. The nuisance signal matched Professor Dicke s predicted Big Bang microwave echo Wilson and Penzias shared the Nobel Prize in Physics in 1978 for discovering the cosmic microwave background radiation of the universe. CHEM161: Chapter 1 page 7 of 7