Atoms Molecules Ions Chemical Symbols Z protons A

Atoms, Molecules, & Ions

Chemical Symbols • Z = protons • A – Z = neutrons – Isotopes will have the same atomic numbers but different mass numbers, therefore a different number of neutrons. • Charge – Generally indicated in the top right hand corner – A positive charge indicates the loss of electrons – A negative charge indicates the gaining of electrons

A Covalent Bond

Naming Covalent Compounds – Name the first element an change the ending of the second to –ide. – Must use prefixes to indicate the # of atoms of an element in the molecule. – Never use mono- when there is only one of the 1 st element.

Naming Covalent Compounds Practice Give the correct name: • PCl 5 • CS 2 • N 2 O 4 • Xe. F 4 • SO 3 * Know the common name: H 2 O NH 3 N 2 H 4 Give the correct formula: • Silicon dioxide • Dinitrogen monoxide • Selenium hexaflouride • Hydrogen fluoride • ammonia

An Ionic Bond

Naming Ionic Compounds • Alkali, alkaline, & silver, zinc, aluminum metals bonded to non-metals: – Name the metal (no roman numerals are necessary) and change the ending of the second element to –ide (names of polyatomic ions do not change). • Transition & Post-Transition metals to nonmetals: – Name the metal, need to include a roman numeral representing the charge of that metal and the ending of the second element changes to –ide. – Using a t-chart helps determine the charge on the metal.

Common Transition Metal Ions

Ionic Bond Strength

Ionic Naming Practice Give the correct name: • Fe(Cl. O 4)2 • Sn. Cl 4 • Cr 2(SO 4)3 • Pb. O • Cu. Cl 2 Give the correct formula: • Manganese II nitrate • Ammonium sulfite • Copper I chromate • Lead II iodide • Mercury II oxide

Naming Acids • Binary Acids • Oxy-acids – The prefix hydro- is never used. Always begin with the polyatomic ion name and change the ending as follows: • -ate in the anion becomes -ic in the acid • -ite in the anion becomes -ous in the acid

Naming Acids Practice Give the correct name: • H 3 N • HCN • HI • HC 7 H 5 O 2 • H 2 CO 3 Give the correct formula: • Nitrous acid • Hypochlorous acid • Hydrochloric acid • Sulfuric acid • Phosphorous acid

Hydrates • Ionic compounds called hydrates have a specific number of water molecules associated with each formula unit. • In their formulas, this number is shown after a centered dot. – Epsom salt has the formula Mg. SO 4· 7 H 2 O and the name magnesium sulfate heptahydrate. – The mineral gypsum has the formula Ca. SO 4· 2 H 2 O and the name calcium sulfate dihydrate. • Heating can remove some or all of them, leading to a different substance. – For example, when heated strongly, blue copper(II) sulfate pentahydrate (Cu. SO 4· 5 H 2 O) is converted to white copper(II) sulfate (Cu. SO 4).

Naming Hydrates Practice • Cupric nitrate trihydrate • Barium hydroxide octahydrate PROBLEM Something is wrong with the second part of each statement. Provide the correct name or formula. (a) (b) (c) (d) Ba(C 2 H 3 O 2)2 is called barium diacetate. Sodium sulfide has the formula (Na)2 SO 3. Iron(II) sulfate has the formula Fe 2(SO 4)3. Cesium carbonate has the formula Cs 2(CO 3).

Covalent vs Ionic

J. J. Thompson

Robert Millikan

Ernest Rutherford

Mass Conservation • The most fundamental chemical observation of the 18 th century was the law of mass conservation: – the total mass of substances does not change during a chemical reaction. The number of substances may change and, by definition, their properties must, but the total amount of matter remains constant. • Even in a complex biochemical change, such as the metabolism of the sugar glucose, which involves many reactions, mass is conserved:

Constant Composition • Another fundamental chemical observation is summarized as the law of definite (or constant) composition: – no matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass. • The fraction by mass (mass fraction) is that part of the compound’s mass that each element contributes. It is obtained by dividing the mass of each element by the total mass of compound. • The percent by mass (mass percent, mass %) is the fraction by mass expressed as a percentage.

Law of Constant Composition

Law of Multiple Proportions • Dalton’s law of multiple proportions: – if elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers. • Consider two compounds that form from carbon and oxygen; for now, let’s call them carbon oxides I and II. They have very different properties. For example, measured at the same temperature and pressure, the density of carbon oxide I is 1. 25 g/L, whereas that of II is 1. 98 g/L. Moreover, I is poisonous and flammable, but II is not. Analysis shows that their compositions by mass are:

MC 1 • Which of the following represents a pair of isotopes? Atomic # (Z) Mass # (A) A I. II. 6 7 14 14 B I. II. 6 14 7 14 C I. II. 6 14 14 28 D I. II. 7 7 13 14 E I. II. 8 16 16 20

MC #2 Which of the following characteristics is common to elemental sulfur, chlorine, nitrogen, and carbon? • (A) They are gaseous elements at room temperature. (B) They have oxides that are acid anhydrides. (C) They have perceptible color at room temperature. (D) They form ionic oxides. (E) They react readily with hydrogen at room temperature.

MC #3 Use these answers for questions 11 -13 (A) Pb (B) Ca (C) Zn (D) As (E) Na 11. Utilized as a coating to protect Fe from corrosion 12. Is added to silicon to enhance its properties as a semiconductor 13. Utilized as a shield from sources of radiation

MC #4 Which of the following is a correct interpretation of the results of Rutherford's experiments in which gold atoms were bombarded with alpha particles? (A) Atoms have equal numbers of positive and negative charges. (B) Electrons in atoms are arranged in shells. (C) Neutrons are at the center of an atom. (D) Neutrons and protons in atoms have nearly equal mass. (E) The positive charge of an atom is concentrated in a small region.

FRQ #1 The postulates of the Bohr model of the hydrogen atom can be stated as follows: (I) The electron can exist only in discrete states each with a definite energy. (II) The electron can exist only in certain circular orbits. (III) The angular momentum of the electron is nh/2 where n is any positive integer. (IV) Radiation is emitted by the atom only when an electron makes a transition from a state of higher energy to one of lower energy. (a) State whether each of these postulates is currently considered to be correct, according to the wave mechanical description of the hydrogen atom. (b) Give the wave mechanical description that has replaced one of the postulates now considered to be incorrect.

Sources • Graphics and tables courtesy of: (Silberberg, Martin S. . Chemistry: The Molecular Nature of Matter and Change, 5 th Edition. Mc. Graw-Hill, 012009. 2. 6. 3).