Chapter 2 notes
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Date Created: 08/21/16
Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards Chapter 2: Atoms, Molecules, and Ions Atoms First An atom is the smallest quantity of matter that still retains the properties of matter. An element is a substance that cannot be broken down into two or more simpler substances by any means. John Dalton (1803-1807) Modern Atomic Theory 1.) All matter is composed of tiny particles called atoms. 2.) All atoms of a given element have identical chemical properties. 3.) Atoms form chemical compounds by combining in whole-number ratios. 4.) Atoms can change how they are combined but they are neither created nor destroyed in chemical reactions. The Atomic Theory Law of Conservation Mass Happens when there is no detectable change in mass during an ordinary chemical reaction. Law of Composition/ Law of Definite Proportion One chemical sample will be the same as another chemical sample. A chemical compound will always contain the same element in the same proportions by mass. Example: Aspirin C9H8O4 Law of Multiple Proportions When two elements combine with each other to form more than one compound, the mass of one element will react with the mass Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards of a second element so compounds always equal a ratio of small whole numbers. Example: Subatomic Particles and Atomic Structure Background: During the late 1800s, many scientists were doing research involving radiation, the emission and transmissions of energy in the form of waves. They commonly used a cathode ray tube, which consists of two metal plates sealed inside a glass from which most of the air has been evacuated. Electrons Thomson in 1897 discovered the e-: “Cathode rays” Travel from cathode (-) to anode (+) Negative charge (e-) Emitted by cathode metal atoms Electric and magnetic fields deflect the beam −9 Gives mass/charge of e- = −5.60∗10 g/C Coulomb (C)= SI unit Millikan studied electrically charged oil drops (1911). Subatomic Particles and Atomic Structure Researchers discovered the like charges repel each other and opposite charges attract one another. J.J Thomson noted that the rays were repelled by a plate bearing a negative charge, and attracted to a plate bearing a positive charge. Thomson’s contributions: These negatively charged particles are called electrons. Thomson determined the charge-to-mass ratio of 8 electrons to be 1.76∗10 C/g Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards (C is coulomb the derived Si unit of electric charge) He proposed the “plum pudding” model of an atom, where positive & negative charges were squished together like a chocolate chip cookie. Ernest Rutherford Used alpha particles to probe the structure of atoms. He proposed a new model for the atom, a nuclear model o Positive charge is concentrated in the nucleus. o The nucleus accounts for most of an atoms mass and is an extremely dense central core within an atom. 5∗10 −3 o Typical nucleus radius is about pm Atomic Structure Protons- Positively charged particles found in the nucleus. Neutrons- Electronically neutral particles found in a nucleus. Electrons- Negatively charged particles distributed around the nucleus. Atomic Number, Mass Number, and Isotopes All atoms can be identified by the number of protons and neutrons they contain. The Atomic Number (Z) is the number of protons in the nucleus. Atoms are neutral, so it is also the number of electrons. Protons determine the identity of an element. Example: Carbons atomic number is 6, so every Carbon has 6 protons. The Mass Number (A) is the total number of protons and neutrons. Protons and neutrons are collectively referred to as nucleons. Atomic Mass 1 amu= 1 atomic mass unit =1/2 the mass of a single carbon 12 atom Bold & Highligterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards 1 amu= 1.66∗10−24g The Chemical Elements Elements have unique names and symbols. Symbols start with a capital letter. Most symbols are obvious abbreviations Nitrogen-N Hydrogen- H Titanium- TiGermanium- Ge “Old” element symbols come from ancient names. Gold= Au (aurum) Tin= Sn (Stannum) Silver= Ag (argentum) Lead= Pb (plubnum) Atomic Mass & Mass Number The sum of the number p+ and n^0 in an atom is: A= mass number For element X write: a X z (z is constant for a given element) Isotopes Most elements have two or more isotopes. Isotopes of the same element typically have very similar chemical properties. Isotopes are atoms of the same element that have the same atomic number (Z) but different mass numbers (A). 1 H; 2 H ; 3 H 1 1 1 Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards Average Atomic Mass Atomic Mass is the mass of an atom in Atomic mass units (amu). The average atomic mass on the periodic table represents the average mass of the naturally occurring mixture of isotopes. Measuring Atomic Mass The most direct and accurate method for determining atomic and molecular masses is mass spectrometry using a mass spectromete Chapter 2: Covalent bonding and Molecules Molecules A molecule is a combination of at least two atoms in a specific arrangement held together by chemical bonds. A molecule may be an element or a compound. Law of multiple proportions When two elements can form two or more different compounds, the law of multiple proportions tells us that the ratio of masses of one element can combine with a fixed mass of the other element and can be expressed in small whole numbers. Diatomic Molecules Diatomic molecules contain two atoms and may be either (two different) or mononuclear (same two). Polyatomic molecules contain more than two atoms. Types of Formulas A chemical formula denotes the composition of the substance. Example:H20 A molecular formula shows the exact number of atoms of each element in a molecule. Example: H:O:H Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards o Some elements have 2 or more distinct forms known as allotropes. A structural formula shows the general arrangement of the atoms and the elemental composition. Molecular substances can also be represented by using empirical formulas, the whole number ratio of elements. (simplest form of a compound) Example: Molecular Formula: N2H4 Empirical Formula: NH2 How did I get the empirical formula from the molecular formula? I just saw that N2 and H4 had a subscript of 2 in common so I simplified it by dividing each by 2 which left me with NH2. The Periodic Table The periodic table is a chart in which elements having similar chemical and physical properties are grouped together. On the periodic table, elements are arranged in periods. Periods are the horizontal rows in order of increasing atomic number. Metals, Non-metals, metalloids Metals are good conductors of heat and electricity o Characteristics- Solids (except mercury- a liquid), ductile, malleable. Nonmetals- poor conductors of heat o Characteristics- Occur in all physical states (solid, liquid, gas), does not conduct electricity. With the exception of Graphite. Metalloids- can have metal or nonmetal properties o Characteristics- They look like metals (shiny) and they are semiconductors. o There are six metalloids: Boron(B), Silicon(Si), germanium(Ge), arsenic(As), antimony(Sb), tellurium(Te) Composing the Periodic Table Groups- vertical columns on the periodic table. Group 1A: Li, Na, K, Rb, Cs, Fr; called Alkali metals Group 2A: Be, Mg, Ca, Sr, Ba, Ra; are called Alkaline earth metals Group 6A: O, S, Se, Te, Po; are called Chalcogens Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards Group 7a: F, Cl, Br, I, Ar; are called Halogens Group 8a: He, Ne, Ar, Kr, Xe, Rn; are Noble gasses The groups 1B, 3B-8B are called transitional elements/ transitional metals Ionic Charge Patterns in the Periodic Table Groups 1A- +1 charge 2A- +2 charge 5A- +3 charge 6A- +/- 4 charge 7A- -3 charge 8A- -2 charge Noble Gasses- 0 charge Naming Ions & Ionic Compounds Ionic compounds are electronically neutral. In order for ionic compounds to be electronically neutral, the sum of the charges on the cation (positively charged ion) and the anion (negatively charge ion) in each formula have to be zero. Example: Aluminum Oxide: Al3+ & O2- = Al2O3 How did I get Al subscript 2 O subscript 3? Basically, all you have to do is cross the charges so that the 3 is cancelled out by the 2 and the 2 is cancelled out by the 3 when you add them together. Naming Ions and Ionic Compounds To name ionic compounds: Name the cation an example would be K+ (potassium) it is a cation because it has a positive charge. o Use a roman numeral if the cation has more than one charge such as Iron II (Fe 2+). Bold & Highlight=terms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards Name the anion by replacing the ending with -ide of the second ion. Example: K+N- the name would be Potassium Nitride. Polyatomic Ions Consist of a combination of two or more atoms. Formulas are determined following the same rule as for ionic compounds containing only monatomic ions: ions must combine in a ratio that give a neutral formula overall. perchlorate ClO4 chlorate ClO 3 chlorite ClO 2 hypochlorite ClO nitrate NO 3 nitrite NO 2 3 phosphate PO4 3 phosphite PO3 sulfate SO 2 4 Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards 2 sulfite SO 3 *I will have flashcards available for these also. Oxyanions Oxyanions are polyatomic anions that contain one or more oxygen atoms and one atom (the central atom) of another element. Naming Molecular Compounds Use when both elements are non-metals Naming rules: o Name the first element that appears in the formula o Name the second element that appears in the formula, changing its ending to -ide. o Add Greek prefixes to elements (skip the mono- on the first element) Greek Prefixes PrefixMeaning PrefixMeaning Mono- 1 Hexa- 6 Di- 2 Hepta- 7 Tri- 3 Octa- 8 Tetra-4 Nona-9 Penta- 5 Deca- 10 The prefix mono- is generally omitted for the first element. Compounds containing Hydrogen The names of molecular compounds containing hydrogen do not usually conform to the systematic naming rules. Many are called by the common names that do not indicate explicitly the number of H atoms present. Bold & Highlighterms to be familiar with Bold ONLY=Examples & formulas Italic= Important people & terminology *=Flash Cards Example: B2H6 Diaborane Acids An acid is a substance that produces hydrogen ions(H+) when dissolved in water. HCL is an example of a binary compound that is an acid when dissolved in water. Naming Acids: Remove the -gen ending from hydrogen Change the -ide ending to the second element to -ic hydrogen chloride- hydrochloric acid A compound must have at least one ionizable hydrogen atom to be an acid upon dissolving. Oxoacids Oxoacids, when dissolved in water, produce hydrogen ions and the corresponding oxoacids. o An acid based on an -ate ion is called…ic acid o An acid based on -ite ion is called….ous acid o Prefixes in oxoacids names are for naming oxoacids Hydrates A hydrate is a compound that has a specific number of water molecules. Example: BaCl2* 2H2O Anhydrous compounds have been heated and the water has been driven out of the compound so they are no longer associated with the compound.
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