Chemistry Study Guide Chapter 3 - Atomic Theory PDF

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A very concrete and detailed study guide of chapter 3 test that covers everything from the book and class' lecture....

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CHEM 1140: Chapter 3 Study Guide Elements are represented by one or two letter symbols. The first letter is capitalized. (If there is a second letter, it is not capitalized.) Terms Atom: the smallest fundamental particle of an element that has the properties of that element. Molecule: a grouping of two or more atoms held together by covalent bonds Covalent Bond: two atoms in each case are joined and held together by a force that involves the sharing of electrons Molecular Compound: composed of molecules with atoms of two or more different elements Formula: compounds are represented by using the symbols for the elements of which they are composed (Ex/ H2O for water, NaCl for table salt). The number of atoms present is represented as a subscript numeral to the right of the element symbol. No number indicates the present of one atom. Structural formula: show the order and arrangement of specific atoms (diagrams for the compound). When writing structural formulas, the lines connecting the atoms represent chemical bonds. Dalton’s atomic theory: 1. Matter is composed of small indivisible particles called atoms. (Not entirely true. We now know that atoms can be further divided into electrons, protons, and neutrons) 2. Atoms of the same element are identical and have the same properties. (Not entirely true. Isotopes are atoms for the same element that vary in the number of neutrons.) 3. Chemical compounds are composed of atoms of different elements combined in small whole-number ratios. 4. Chemical reactions are merely the rearrangement of atoms into different combinations. Composition of the atom: Atoms are composed of a small central core known as the nucleus, surrounded by a vast, mostly empty, space. The outer region contains the tiny electrons, which carry a charge of -1. The smaller nucleus contains the nucleons: protons (+1) and neutrons (neutral). Neutrons have a slightly larger mass than protons (both are ~1 amu) and are much, much larger than the mass of electrons (~0 amu). The number of electrons and protons are the same in atoms that are neutral. Atoms of a single element that vary in the number of neutrons are called isotopes. For ions: Atoms that have gained an electron, gain a negative charge and are anions (gain of 1 electron is equivalent to a charge of -1, gain of 2 e- is equivalent to a charge of -2, etc). Atoms that have lost an electron, lose a negative charge and are cations (loss of one electron is equivalent to a charge of +1, etc).

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Atomic number: number of protons in the nucleus. Located as a subscript number to the left of the elemental symbol in isotopic notation. (DEFINES THE ELEMENT) Mass number: total number of nucleons (protons + neutrons). Located as a superscript number to the left of the elemental symbol in isotopic notation. (DEFINES THE ISOTOPE) The atomic number is the distinguishing factor for an element. Oxygen (and only oxygen) has an atomic number of 16, but its mass number can vary depending on the isotope of oxygen you are referring to. The mass number is a somewhat imprecise representation of the actual mass for an element because it does not take into account isotopes and estimates protons and neutrons at 1 amu each. The isotopic mass is a better measurement of mass for isotopes because it is determined by comparison to a standard, 12C, which is defined as having a mass of exactly 12 atomic mass units (amu). The atomic mass or weight of an element is obtained from the weighted average of the atomic masses of all isotopes stably present in nature depending on the percentage of each isotope that exists (isotopic mass of the “average atom” for that element). 3 main categories of compounds: 1) intermetallics (all metals), 2) ionic compounds (metal + nonmetal), 3) molecular substances (all nonmetals). Metalloid-containing compounds are much more difficult to categorize without knowing properties of the compound. Ionic Compounds: Atoms can achieve an electrostatic charge. When they become charged, they become ions. Electrostatic forces exist between charges, in which opposite charges attract and like charges repel one another. Ions: atoms with an electrostatic charge (not neutral) -Cations: ions with a positive charge -Anions: ions with a negative charge Ionic compounds: compounds consisting of ions. They are held together by ionic bonds. Ionic bonds: electrostatic forces holding ions together by attraction between + and – charges (strong bond) Ionic charges are represented in superscript to the right of the corresponding element. (Ex: Fe2+) Ions are going to combine in such a way as to form an overall neutral compound. They will combine in the simplest whole-number ratios in order to achieve this neutrality. The simplest whole-number ratio of ions in an ionic compound is referred to as a formula unit or chemical formula. Ex/ Na+ and Cl- form NaCl, Ca2+ and Cl- form CaCl2, Al3+ and N3- form AlN When you write a formula unit for an ionic compound, figure out the charge for each ion and determine the fewest number of atoms that each element would require to reach a neutral compound formed. Your book gives some examples on p 47. Sometimes groups of atoms that are covalently bonded to each other may also be electrostatically charged. These are known as polyatomic ions. When more than one polyatomic ion is in a formula, parentheses are used to keep each covalently bonded group together. Subscript numbers outside of the parentheses can be used to represent the number or

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polyatomic ions in the ionic compound. You will become more familiar with these as we go along. Some are used quite often in chemistry and you will not be able to help learning them. Ex/ NO3-, SO42-, NH4+. Use of parentheses: Mg(NO3)2, NaNO3, Al2(SO4)3, AlPO4 Molecular Substances: form discrete units of specific numbers of nonmetal atoms (S2Cl2 = disulfur dichloride, H2O = water, H2O2 = hydrogen peroxide) This category also contains nonmetals that exist quite stably as atoms (not compounds), like the noble gases (He, Ne, etc.) and diatomic atoms (Cl2, O2) or polyatomic atoms (S4, P8). NOTE: There are a lot of terms here. Make sure you recognize the difference between atomic mass and atomic number. You should be able to look at the isotopic notation for an element and tell me the number of protons, neutrons, electrons, the mass number, and the atomic number for that isotope. How did we come up with the units of amu? Remember that for ions the charge is present because the number of electrons is different from that of the neutral atom. The gain of an electron corresponds to the gain of a negative charge (one negative charge per gain of one electron). The loss of an electron corresponds to the loss of a negative charge (or the gain of a positive charge) (one electron lost = the gain of one positive charge). Charges are never written in formula units!!! To memorize for quizzes/exams: Know the symbols and element names for the first 36 elements in the periodic table plus I, Ag, Sn, Pt, Au, Hg, and Pb. Be able to tell the difference between intermetallics, ionic compounds, and molecular substances. Be able to write formulas for ionic compounds and molecular substances.

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