Chem 141, Chapter 1 Notes
Chem 141, Chapter 1 Notes Chemistry 141
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This 5 page Class Notes was uploaded by Sara Auger on Tuesday October 4, 2016. The Class Notes belongs to Chemistry 141 at Emory University taught by Dr. Egap in Fall 2016. Since its upload, it has received 37 views. For similar materials see Chemistry 141 in Chemistry at Emory University.
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Date Created: 10/04/16
The properties of matter are determined by the structure of the atoms and molecules that compose it. 1.1: A particulate View of the World: Structure Determines Properties o Matter is particulate (composed of particles) o The structure of those particles determines the properties of matter. Matter is anything that has mass and takes up space. Atoms: the basic particles that compose ordinary matter About 91 different types of atoms exist naturally Atoms bind together in specific shapes to form molecules (Ex: water) Two or more atoms chemically arranged in a specific shape Structure of molecules determines properties of substance o Chemistry: the science that seeks to understand the properties of matter by studying the structure of the particles that compose it. 1.2: Classifying Matter: A Particulate View o Substance: a specific instance of matter (Ex: air, water, or sand) o Classifications of Matter: State of Matter-- depends on the relative position of the particles and how strongly they interact with one another (relative to temperature) Composition of Matter-- depends on the types of particles. o States of Matter: Solid, Liquid, and Gas Solid matter particles attract each other more strongly and pack closely to each other in fixed locations. Vibrate, but don't move around. Fixed volume and rigid shape. Liquid matter: pack as closely as solid matter, but weaker attractions allow them to move around. Fixed volume, no fixed shape. Gaseous matter: attract each other very weakly Don't clump together like solids or liquids Particles can move long distance Space between particles makes them compressible, unlike liquids or solids. o Elements, compounds, and mixtures We classify matter based on types of particles compose it and how many different types there are Pure substance: made of only one type of particle (can be atom or molecule) Can be element or compound, depending on whether it can be broken down further. Element: substance that can't be broken down into a simpler substance. Compound: composed of two/more elements in fixed proportions. More common. Mixture: composed of two/more types of particles that can vary in proportions. Heterogeneous: composition varies from one part to another (Ex: water in sand) Homogeneous: same composition throughout. (Ex: sweet tea) 1.3: The Scientific Approach to Knowledge o Based on observation and experiments. Can be qualitative: how a process happens Or quantitative: measuring or quantifying something about the process Observation leads to hypothesis --> tentative explanation or interpretation of the observations Good hypothesis are falsifiable: can be proved true or false Experiments: test hypothesis. Highly controlled procedures designed to generate observations that can dis/prove hypothesis. o Scientific law: a brief statement that summarizes past observations and predicts future ones. Ex: Law of Conservation of Mass: "In a chemical reaction, matter is neither created nor destroyed." Describe how nature behaves. o Scientific theory: model for the way nature is and what it does and why Atomic theory (John Dalton) is basis for particulate view of matter Theories are never proven bc new evidence can prove them wrong o The Importance of Measurement in Science Observations can usually be measured Unit: standard, agreed upon quantity Metric system English System (US) Scientists use SI (based on metric) o Creativity and Subjectivity in Science The Structure of Scientific Revolution Science isn't linear Normal science: scientists ignore small inconsistencies to fit observations with the thought of the time Revolution is when there's too many inconsistencies to ignore Basically scientists aren't always 100 percent real 1.4: Early Ideas about the Building Blocks of Matter o Leucippus and Democritus (460-370 BC) proposed theory of atoms Plato and Aristotle disagreed. Four elements theories o 16th cent. Beginning of modern science Copernicus, earth around sun theory 1.5: Modern Atomic Theory and the laws that surround it o Three important ones: Law of conservation of mass law of definite proportions Law of multiple proportions o LoCoM: in a chemical reaction, matter isn't created or destroyed. Chemical reaction: a process in which one or more substances are converted into one or more different substances. o LoDP: Joseph Proust (1754-1826) made observations on the composition of compounds. Elements composing given compound always occur in fixed proportions. "All samples of a given compound, regardless of their source or how they were prepared, have the same proportion of their constituent elements." o LoMP: when two elements form two different compounds, the masses of element B that combine with 1 g of element A can be expressed as a ratio of small whole numbers. " AB1 AB2 AB3 etc. 1.6: The discovery of the Electron o Cathode Rays Late 1800s (1856-1940) JJ Thomson experimented with properties of cathode rays Cathode Rays: a stream of electrons produced when a high electrical voltage is applied between two electrodes within a partially evacuated tube. Travel from the negatively charged electrode (cathode) to the positively charged one (anode) Particles composing cathode ray have the following properties: Travel in straight lines. They're independent of the composition of the cathode (where they come from) They carry a negative electrical charge Electrical charge: results in attractive and repellent forces (electrostatic forces) The area around a particle where these forms exist is called an electric field. Cathode ray tube: partially evacuated glass tube He had discovered the electron: a negatively charged, low mass particle present within all atoms. Millikan's Oil Drop Experiment Millikan figured out the charge of each drop by measuring the strength of the electric field required to stop the drop from falling and figuring out the masses of the drops (from the radius and density) The charge of each drop is a whole number multiple of a single electron's charge. Charge x Mass = mass charge Charge of an electron is important because it determines how strongly an atom holds its electrons. 1.7: The Structure of the Atom o JJ Thomson proposed that the particles are evenly spaced Known as "plum pudding model" o Radioactivity Emission of small energetic particles from the core of certain unstable atoms Becquerel and Curie Allowed researchers to probe the structure of the atom Three different types: Alpha, Beta, and Gamma Alpha particles are positively charged and they are by far the most massive of the three o Rutherford's Experiment The mass and positive charge of an atom must be concentrated in a space much smaller than the size of the atom itself On this, he built nuclear theory: Most of the atom's mass and all of its positive charges are contained in a small core called the nucleus. Most of the volume pf the atom is empty space, throughout which tiny, negatively charged electrons are dispersed. There are as many negatively charged particles as there are positive ones (because atom is neutral) o There were questions as to why elements with proportionate numbers of electrons didn't have proportionate masses. Neutrons were discovered. That answered that. o Nucleus contains over 99.9% of the atom's mass but very little volume. o Revolutionary part of Rutherford's theory: matter is much less uniform than it appears. 1.8: Subatomic Particles: Protons, Neutrons, and Electrons o Protons and neutrons have nearly identical masses, electrons have tiny masses. o Atomic Mass Unit (AMU): 1/12 the mass of a carbon atom containing 6 protons and 6 neutrons One p/n mass basically Mass of 1 P/N is 1 AMU,., Electron is 0.00055 AMU o In relative units, the electron has a -1 charge and the proton has a +1 charge. Equal strength, opposite sign. o Most matter is charge neutral Numbers of each particle determines the identity of that particle. o Number of protons/neutrons an atom has is the Atomic Mass Number on the periodic table. (symbol is Z) o Atomic Mass Numbers of known particles range from 1-116 o Chemical Symbol: abbreviation of the elemental atom (on periodic table) o Chemical symbol and AMN always go together o Elements are named for English word, Latin word, place of origin, or founder. All atoms of a certain element have same number of protons, but not necessarily neutrons. o Isotopes: atoms with the name number of protons but different number of neutrons o Roughly constant percentage of different isotopes in a sample of the element is called natural abundance. Each element has its own characteristic natural abundance o Sum of the number of neutrons and protons in an atom is its mass number. o Isotopes are symbolized by: (see page 20) During chemical changes, atoms can lose/share/gain electrons and become charged particles called ions. o Positively charged ions are cations o Negatively charged ions are anions 1.9: Atomic Mass: The Average Mass of an Element's Atoms o Dalton theorized that every atom of a given element had the same mass. He was wrong bc neutrons o But we can calculate average mass for each element called atomic mass o Mass Spectrometry: technique that separates particles according to their mass Used to measure masses and percent isotopes 1.10: The Origins of Atoms and Elements o Big Bang Theory: asserts the universe began as a hot, dense collection of matter and energy that expanded rapidly. Subatomic particles formed the first atomic nuclei: hydrogen and helium Most abundant in the universe Stars are fueled by nuclear fusion In the core or the star, hydrogen nuclei fuse to form helium. This gives off a lot of energy (why stars are bright and hot) Fusion process ends with iron.
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