Chapter 2 (Atoms, Molecules, Ions) PDF

Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules & Ions  The atomic Theory of matter  The Modern View of atomic structure  Atomic weight  The periodic table  Molecules and Molecular Compounds  Ions and ionic compounds Atoms, M...

Atoms, Molecules, and Ions Chapter 2 Atoms, Molecules & Ions  The atomic Theory of matter  The Modern View of atomic structure  Atomic weight  The periodic table  Molecules and Molecular Compounds  Ions and ionic compounds Atoms, Molecules, and Ions Atomic Theory of Matter Dalton’s Atomic Theory:  Each element is composed of extremely small particles called atoms.  All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements.  Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.  Atoms of more than one element combine in simple whole ratios to form Compounds Atoms, Molecules, and Ions  Atoms, Molecules, and Ions  Dalton’s Theory Explains  Law of Constant Composition (law of definite proportions) In a compound the relative number and kinds of atoms are constant. Ammonia always ! has 3 H and 1 N  Law of Conservation of Mass Total mass of substances before chemical reaction is the same as the mass of substances after the reaction. Atoms, Molecules, and Ions  Law of Multible proportion If two element A and B combine to form more than one compound the mass of B that combine with a given mass of A are in the ratio of small whole number. EXAMPLES!!!!!!! Atoms, Molecules, and Ions  The Structure of Atom According to Rutherford nuclear theory of the atom; Atoms, Molecules, and Ions Atoms are electrically neautral Atoms, Molecules, and Ions  Subatomic Particles Protons and electrons are the only particles that have a charge. Protons and neutrons have essentially the same mass. The mass of an electron is so small we ignore it. 1amu=1.66054x10-23g Atoms, Molecules, and Ions  Atoms are also extremely small in size !  Diameter around 1x10-10 m and 5x10-10 m (100-500 pm)  Non-SI unit used to express atomic dimension is the angastrom (Å) 1 Å = 10-10 m Atoms, Molecules, and Ions  Symbols of Elements Elements are symbolized by one or two letters. Atoms, Molecules, and Ions  Atomic Number All atoms of the same element have the same number of protons: The atomic number (Z) Atoms, Molecules, and Ions  Atomic Mass The mass of an atom in atomic mass units (amu) is approximately the total number of protons and neutrons in the atom. Atoms, Molecules, and Ions  ISOTOPES Atoms with identical atomic numbers but different mass number are called ISOTOPES. Isotopes have different numbers of neutrons. 11 12 13 14 6C 6C 6C 6C # Neutrons 5 6 7 8Atoms, Molecules, and Ions  Atomic Mass (Average Mass) Because in the real world elements exist as mixtures of isotopes. Average mass is calculated from the isotopes of an element weighted by their relative abundances. “Natural abundance” Atoms, Molecules, and Ions Example Isotope Abundance Atomic mass 24Mg 78.99% 23.98504 amu 25Mg 10.00% 24.98584 amu 26Mg 11.01% 25.98259 amu what is the average molecular mass of magnesium (Mg)? ANS: 24.31 Mg (24.31) Atoms, Molecules, and Ions Example: Cooper has two naturally accuring isotopes; Cu-63 with mass of 62.9396 amu and natural abundance of 69.17 % and Cu-65 with mass of 64.9278 amu and a natural abundance of 30.83 %. Calculate the atomic mass of cooper. (ANS:63.55) Atoms, Molecules, and Ions  Periodic Table Elements are arranged in order of atomic number. Atoms, Molecules, and Ions  The rows on the periodic chart are periods. Columns are groups. Elements in the same group have similar chemical Atoms, properties. Molecules, and Ions  Groups These four groups are known by their names. Atoms, Molecules, and Ions  Periodic Table Nonmetals are on the upper right-hand corner of Atoms, the periodic table (with the exception of H). Molecules, and Ions  Periodic Table Metalloids border the stair-step line (with the exceptionAtoms, of Al and Po). Molecules, and Ions  Periodic Table Metals are on the left side of the chart. Atoms, Molecules, and Ions  Elements of life Elements required for living organisms (pretty much all organisms). Red, most abundant blue, next most abundant Green, trace amounts. Atoms, Molecules, and Ions Chemical Formulas The subscript to the right of the symbol of an element tells the number of atoms of that element in one molecule of the compound. Atoms, Molecules, and Ions Molecular Compounds Molecular compounds are composed of molecules and almost always contain only nonmetals. Atoms, Molecules, and Ions  Diatomic Molecules These seven elements occur naturally as molecules containing two atoms. Atoms, Molecules, and Ions  Types of Formulas Empirical formulas give the lowest whole-number ratio of atoms of each element in a compound. Molecular formulas give the exact number of atoms of each element in a compound. Example: Ethane Example: Hydrogen peroxide Empirical formula: CH3 Empirical formula: HO Molecular formula: C2H6 Molecular formula: H2O2 Atoms, Molecules, and Ions  Ions Neutral Atom Cation Anion (+) (-) Atoms, Molecules, and Ions  Ions Often they lose or gain electrons to have the same number of electrons as the nearest noble gas.  Cations are positive and are formed by elements on the left side of the periodic chart.  Anions are negative and are formed by elements on the right side of the periodic chart. Atoms, Molecules, and Ions  Mono-atomic ions metals nonmetals Metals usually become cations (+) Nonmetals usually become anions (-) Atoms, Molecules, and Ions  Polyatomic ions NH4+ Ammonium ion SO42- Sulfate ion NO2- Nitrite HSO-4 bisulfate HPO42- Hydrogen phosphate ClO- hypochlorite ClO2- chlorite Atoms, Molecules, and Ions  Ionic compounds A metal will give up electrons to a nonmetal forming a cation (+) (the metal), and an anion (-) (the nonmetal). Contains both (+) and (-) charged ions. Na + Cl Na+ + Cl- NaCl Mg + 2Cl Mg2++2Cl- MgCl2 Note, everybody gains or loses electrons to be like the nearest noble gas. Compounds are always electrically neutral!! Atoms, Molecules, and Ions  Ionic Bonds Ionic compounds (such as NaCl) are generally formed between metals and nonmetals. Atoms, Molecules, and Ions  Writing Formulas Because compounds are electrically neutral, one can determine the formula of a compound this way:  The charge on the cation becomes the subscript on the anion.  The charge on the anion becomes the subscript on the cation.  If these subscripts are not in the lowest whole- number ratio, divide them by the greatest common factor. Mg2+ O2- MgO Not Mg2O2 Atoms, Molecules, and Ions  Hydrogen H can be cation or anion H- (Hydride) H+ (Hydrogen) Atoms, Molecules, and Ions