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Matter, Energy, and Measurement Scientific Method - Chemistry is the study of the structure of matter. - An experiment is the process by which scientific ideas are tested. - A Hypothesis is a reasonable and testable explanation for observations. - A Variable is a factor that could affect the results of an experiment. - A Theory is a well-tested explanation of observations. Units of Measurement - Matter is anything that has mass and volume. - Mass is the quantity of matter in an object measured in grams. - Volume is the space an object occupies measured in liters. - Weight is the force produced by gravity acting on a mass - The density of an object is the mass if the object divided by volume of the object - Know how to convert using conversion factors (deci, kilo, centi…) - Know how to use significant figures and scientific notation. - The Accuracy of a measurement is how close the measurement is to the true or actual value - Precision is the exactness of a measurement Energy, Heat, and Temperature - Heat is the energy transferred between objects that are different temperatures. - Temperature is a measure of the average heat or thermal energy of the particles in a substance. - Energy is the capacity to do work, such as moving an object, forming a new compound, or generating light. - The energy of the motion of particles is called kinetic energy. - The Law of Conservation of Energy is that energy cannot be created nor destroyed. - Energy can be absorbed (Endothermic) by the surroundings or released (exothermic) to the surroundings, but it cannot be created or destroyed. Physical and Chemical Changes and Properties - Physical Changes are changes in which the identity of a substance doesn’t change (Changes of state are physical changes) - A chemical change DOES change the substance, it cannot be undone. - Chemical Changes occur when the identities of substances change and new substances form. - Evidence of a chemical change o the evolution of a gas o the formation of a precipitate (solid substance forms and typically sinks to the bottom) o the release or absorption of energy o a change in temperature or the giving off of light o a color change in the reaction system - A chemical property is a property of matter that describes a substance’s ability to participate in chemical reactions Elements, Molecules, Compounds, and Mixtures - Elements are pure substances that only contain one kind of matter (atoms). They cannot be separated or broken down into simpler substances. A molecule is the smallest unit of a substance that keeps all of the physical and chemical properties of that substance. A molecule usually consists of two or more atoms combined in a definite ratio A mixture is a combination of two or more substances that are NOT chemically combined A homogenous mixture describes something that has a uniform structure or composition throughout. A heterogeneous mixture describes something that is composed of dissimilar components An alloy is a solid mixture Atomic Theory and Atomic Structure Atomic Theory - The Law of Definite Proportions states that a chemical compound always contains the same elements in exactly the same proportions by weight or mass and that every molecule of a substance is made of the same number and types of elements. - The law of conservation of mass states that mass cannot be created nor destroyed in ordinary chemical and physical changes. The mass of the reactants is equal to the mass of the products. - Dalton’s Theory Contains Five Principles o All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed. o Atoms of a given element are identical in their physical and chemical properties. o Atoms of different elements differ in their physical and chemical properties. o Atoms of different elements combine in simple, whole number ratios to form compounds. o In chemical reactions, atoms are combined, separated, or rearranged but never created, destroyed, or changed. - JJ Thomson proposed that the electrons of an atom were embedded in a positively charged ball of matter. His model of an atom was named the plum-pudding model, or chocolate chip cookie model. - Ernest Rutherford performed the gold foil experiment, which discovered the nucleus of an atom. He concluded that an atom is made up of mostly space, with a dense nucleus that is positively charged. Rutherford suggested that electrons, revolve around the nucleus in circular or elliptical orbits. We call this the planetary model of the atom. - Neils Bohr’s model confines electrons to energy levels. Electrons can be only certain distances from the nucleus. Each distance corresponds to a certain quantity of energy that an electron can have. We call this the quantum energy model of an atom. - De Broglie suggested that electrons could be considered waves confined to the space around the nucleus. - The present-day model of the atom is known as the Quantum Model Atomic Structure - The three subatomic particles that are most important for chemistry are the electron, proton, and neutron. - The nucleus is the dense, central portion of the atom. It is made up of protons and neutrons. - Protons are the subatomic particles that have a positive charge and that is found in the nucleus of an atom. - Neutrons are the subatomic particles that have no charge and that are found in the nucleus of an atom. - The number of protons that an atom has is known as the atomic number. - The mass number is the sum of the number of protons and neutrons of an atom. - Isotopes are atoms of the same element that have different numbers of neutrons. - Ions are formed when electrons are gained or lost. - Orbitals are regions where electrons are likely to be found. - A single orbital can hold a maximum of two electrons, which must have opposite spins. - There are 4 orbitals: o S: 1 shape, can hold a max of 2 electrons. o P: 3 shapes, can hold a max of 6 electrons. (shaped like dumbbells) o D: 5 shapes, can hold a max of 10 electrons. o F: 7 shapes, can hold a max of 14 electrons. - Know how to write electron configurations! Periodic Table and Trends - John Newlands arranged the known elements according to their properties and in order of increasing atomic mass. He placed the elements in a table. He noticed in a given row had similar chemical and physical properties. Because these properties seemed to repeat every eight elements, Newlands called this pattern the Law of Octaves. - Dmitri Mendeleev invented the first periodic table. - Elements in each column have the same number of electrons in their outer shell. - The electrons in the outer shell are called Valence Electrons. - A vertical column on the periodic table is called a group. - Elements in a group share chemical properties. - A horizontal row on the periodic table is called a period. - Elements in groups 1,2 and 13-18 are known as the main-group elements. - Four groups within the main-group elements have special names. These are: o Alkali metals- 1 valence electron, very reactive (group 1) o Alkaline-earth metals- 2 valence electrons, very reactive (Group 2) o Halogens- 7 valence electrons, very reactive (Group 7 or 17) o Noble gases- 8 valence electrons, nonreactive (Group 8 or 18) - Metals are located left of the staircase or zig-zag - Nonmetals are located right of the staircase or zig-zag - An alloy is a solid or liquid mixture of two or more metals. - Ductile- draw into a wire, stretch it - Malleable- bendable, folded 1) The transition metals are located in the D Block The ionization energy required removing an electron from an atom or ion. Know the Periodic Trends Atomic Radius- distance from the nucleus to the edge of the electron cloud increases decreases Electron cloud 2) 3) 4) 5) -Bond Radius – half the distance between bonding atoms (nucleii) Electronegativity- the measure of the ability of an atom in a compound to attract electrons decreases increases Ionic Size- the increase or decrease in the size of an atom when it gains or loses electrons (ion- an atom with a charge) Ionization Energy- the energy required to remove an electron from an atom or ion BP/MP(boiling point/melting point)- changes in state due to energy changes Mol, %Composition, Empirical Formula - 1 mole = 6.02x1023 = Avogadro’s Number - The mole is defined as the number of atoms in exactly 12 grams of the carbon isotope-12 - Know how to calculate molar mass - Know how to calculate moles, grams, or liters with givens. - Know how to calculate the percent composition - An empirical formula is chemical formula that shows the simplest ratio of the relative numbers and kinds of atoms in a compound. - Molecular Formula (actual formula) is a whole number multiple of the Empirical Formula. Chemical Equations - Reactants yields Products - A coefficient is the number before the element or compound 2H2O - A subscript in the little number on the bottom after the element or compound - (s)(l)(g)- physical state - (aq)- (aqueous) dissolved in water - Know how to balance chemical equations. - When balancing chemical equations, you may ONLY change the coefficients - Due to the Law of Conservation of Mass, chemical equations must be balanced. - Types of Chemical Reactions Single Displacement Rxn- one element displaces (or replaces) another in a compound Ex: A + BC=B + AC Ex: 2Al(s) + 3CuCl2(aq)3Cu(s) + 1AlCl3(aq) Double Displacement Rxn- positive and negative portions of 2 compounds are interchanged. Ex: AB + CD AD + CB Ex: HCl + NaOH HOH + NaCl (or H2O) Decomposition Rxn- substances break up into simpler substances when energy is applied. Ex: ABA + B Ex: 2H2O electricity 2H2 + O2 Synthesis Rxn- Two or more substances combine to form a new substance. Ex: A + B AB Ex: C + O2 CO2 Combustion Rxn- Oxidation reaction of an organic compound in which energy is released. Every combustion has O2, CO2, and H2O. Ex: + O2 CO2 + H2O + energy Ex: C3H8 + 5O23CO2 + 4H2O + energy Stoichiometry - Given a reaction, know how to calculate: o Number of moles when given moles o Number of grams given moles o Number of moles given grams o Molar ratio Labs - Know lab procedures (what to do first, second…last) - Know lab safety procedures - Know the difference and what they look like: a beaker, test tube, graduated cylinder, flask, evaporating dish, crucible and cover, and funnel. - Know how to read measurements off the above. - Density = mass/volume