Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Chapter Two 1.Dalton’s Atomic TheoryDalton’s Atomic Theory 2.Discovery of atomic structureDiscovery of atomic structure 3.Modern view of atomic theoryModern view of atomic theory 4.Atomic WeightsAtomic Weights 5.The Periodic TableThe Periodic Table 6.Molecules and Molecular CompoundsMolecules and Molecular Compounds 7. lons and ionic compoundslons and ionic compounds 8. Naming inorganic compoundsNaming inorganic compounds

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Atomic Theory Between 1803 and 1807, John Dalton proposed his Atomic Theory to explain experimental observations about gases and chemical reactions occurring in the gas phase. Each element is composed of extremely small particles called atoms. All atoms of a given element are identical; atoms of different elements are different and have different properties.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Atomic Theory Between 1803 and 1807, John Dalton proposed his Atomic Theory to explain experimental observations about gases and chemical reactions occurring in the gas phase. Atoms are not changed into different atoms; atoms are neither created nor destroyed. Compounds are formed when atoms of at least two different elements combine; a given compound always has the same kind and ratio of atoms.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Experimental Evidence In the late 19th and early 20th century, experimental evidence began to accumulate that contradicted some of Dalton's basic ideas

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Experimental Evidence In the late 19th and early 20th century, experimental evidence began to accumulate that contradicted some of Dalton's basic ideas

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Experimental Evidence In the late 19th and early 20th century, experimental evidence began to accumulate that contradicted some of Dalton's basic ideas

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Modern View of the Atom The experiments of the early 20th century dispelled the myth of the indestructible atom. Instead, we now believe that the atom is itself composed of simpler particles. It is convenient for chemists to focus on protons, neutrons and electrons.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Atomic Number & Mass Atoms are identified by the atomic number (Z), which is the number of protons ( ) in the nucleus. The atomic mass is,approximately, the sum of the atom's protons and the neutrons ( ). For example, all Mg atoms have 12 protons.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – Atomic Number & Mass Because atoms are electrically neutral, the number of electrons = the number of proton. Ions are atoms that have more (anions) or less (cations) electrons than protons. Symbol Protons NeutonsElectronsName

Department of Chemistry and Biochemistry CHM Reeves The atomic mass unit is defined by assigning the mass of one atom of is exactly 12 amu. This leads to the relationship CHM 101 – Average Atomic Mass However, the mass of carbon in the Periodic Table is amu

Department of Chemistry and Biochemistry CHM Reeves Although carbon-12 is its most common isotope (98.93%), carbon also contains 1.03% of the isotope C-13, with an atomic mass of amu. Thus, the average atomic weight of Carbon is: CHM 101 – Average Atomic Mass

Department of Chemistry and Biochemistry CHM Reeves Copper has two important isotopes, 63 Cu and 65 Cu. Based on the atomic weight reported in the Periodic Table, what are the approximate abundances of the two isotopes? CHM 101 – Average Atomic Mass 90% 63 Cu 10% 65 Cu 75% 63 Cu 25% 65 Cu 50% 63 Cu 50% 65 Cu 25% 63 Cu 75% 65 Cu

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – The Periodic Table When the elements are arranged in the order of increasing atomic number, their properties are observed to vary in a repeating or periodic pattern. The Periodic Table arranges atoms in order of increasing atomic number such that elements with similar chemical and physical properties appear in the same column (group) of the table.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 – The Periodic Table

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Molecules and Molecular Compounds Most atoms are metals at room temperature. Metallic character increases as you go to the left and down the Table. Nonmetals are concentrated to the right and top of the Table. Metalloids are between metals and nonmetals. Nonmetals combine together to form molecules by sharing some of their valence electrons. Seven nonmetal elements are most commonly found in nature as diatomic molecules. When two or more different nonmetals combine, a molecular compound is formed.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Molecules and Molecular Compounds Compounds are represented by a variety of formulae that present different types of information: Space-filling model: represents the molecule's actual spatial arrangement of atoms Structural formula: shows how atoms are connected, using symbols to represent atoms.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Molecules and Molecular Compounds Molecular formula: provides number and symbol for each atom in the compound Empirical formula: provides smallest whole-number ratio of atoms in the compound. Binary molecular compounds are named using a prefix before each atom to indicate how many there are in the molecule. (cf pg 66 & Table 2.6)

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Molecules and Molecular Compounds Compounds are represented by a variety of formulae that present different types of information: Sulfur trioxide Dinitrogen tetraoxide

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds Positive ions (cations) form when atoms loose electrons.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds A-group metals form only one kind of cation, consistent with their position in the Periodic Table. Cations have the same name as the atoms from which they are derived.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds Cations form when atoms loose electrons. A-group metals form only one kind of cation, consistent with their position in the Periodic Table. Cations have the same name as the atoms from which they are derived. B-group (transition) metals can form two or more different ions. To name them, a Roman Numeral following the symbol is used to indicate the charge on the ion. Cr 3+ : Fe 2+ : Ag + :

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds Negative ions (anions) form when atoms gain electrons. Nonmetals consistently form anions.

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds A-group elements form only one kind of monatomic ion, consistent with their position in the Periodic Table. They are named by replacing the last syllable with "ide"

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds Anions may also be polyatomic, consisting of two or more atoms covalently bonded together, with one or more extra electrons. Some common polyatomic anions have names ending in “ide” Oxyanions are polyatomic ions that contain one or more oxygen atoms. Their names end in “ite” or “ate”. See rules on p. 62 regarding naming conventions. Memorize common ions in Tables 2.4 & 2.5

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds All stable materials are electrically neutral. Ionic compounds are formed through the attraction of anions and cations and are named by combining the cation and anion names sodium chloride

Department of Chemistry and Biochemistry CHM Reeves CHM 101 Ions and Ionic Compounds To be electrically neutral, the ions are combined so that the total positive charge = total negative charge CationAnionName Formula