Chemistry is the study of matter and the changes it undergoes. Reading Assignments:

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1 Reading Assignments: Chapter 1& 2 in R. Chang, Chemistry, 8th Ed., McGraw-Hill, 2005 Or Related topics in other textbooks. Consultation outside lecture room: Office Hours: Tuesday & Thursday 10 am -12 pm Wednesday or by appointment Chemistry is the study of matter and the changes it undergoes. 1. Matter is anything that occupies space and has mass. 2. A substance is a form of matter that has a definite composition and distinct properties. water, ammonia, sucrose, gold, oxygen A mixture is a combination of two or more substances in which the substances retain their distinct identities. Physical means can be used to separate a mixture into its pure components. 1. Homogenous mixture composition of the mixture is the same throughout. 2. Heterogeneous mixture composition is not uniform throughout. iron filings in sand distillation magnet

2 An element is a substance that cannot be separated into simpler substances by chemical means. elements have been identified 83 elements occur naturally on Earth lead, oxygen, carbon 32 elements have been created by scientists technetium, americium, seaborgium Periodic Table of Elements 1.4 A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions. Compounds can only be separated into their pure components (elements) by chemical means. Water (H 2 O) Glucose (C 6 H 12 O 6 ) Ammonia (NH 3 )

3 Physical or Chemical Change? A physical change does not alter the composition or identity of a substance. Three States of Matter physical change A chemical change alters the composition or identity of the substance(s) involved. hydrogen gas burns in oxygen gas to form water Temperature Atoms, Molecules and Ions Dalton s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 2. Compounds are composed of atoms of more than one element. The relative number of atoms of each element in a given compound is always the same. 3. Chemical reactions only involve the rearrangement of atoms. Atoms are not created or destroyed in chemical reactions. 2.1

4 Atomic model (+) (-) J.J. Thomson: measured Robert Millikan: measured Thomson s model Rutherford s model 2.2 e - charge = x C Thomson s charge/mass of e - = x 10 8 C/g e - mass = 9.10 x g

5 (1908 Nobel Prize in Chemistry) Rutherford s Model of the Atom α particle velocity ~ 1.4 x 10 7 m/s (~5% speed of light) 1. atoms positive charge is concentrated in the nucleus 2. proton (p) has opposite (+) charge of electron (-) 3. mass of p is 1840 x mass of e - (1.67 x g) atomic radius ~ 100 pm = 1 x m nuclear radius ~ 5 x 10-3 pm = 5 x m Subatomic Particles Mass Number Atomic Number A ZX Element Symbol Particle Mass (g) Charge (Coulombs) Electron (e - ) 9.1 x x Proton (p + ) 1.67 x x Neutron (n) 1.67 x Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons Isotopes are atoms of the same element (X) with different numbers of neutrons in their nuclei 1 H 2 1 1H (D) 1H (T) U 92 U

6 Do You Understand Isotopes? How many protons, neutrons, and electrons are in 14 6 C? How many protons, neutrons, and electrons are in 11 6 C? An ion is an atom, or group of atoms, that has a net positive or negative charge. Alkali Metal Alkali Earth Metal Period Group Halogen Noble Gas cation ion with a positive charge If a neutral atom loses one or more electrons it becomes a cation. Na 11 protons 11 electrons Na + 11 protons 10 electrons anion ion with a negative charge If a neutral atom gains one or more electrons it becomes an anion. Cl 17 protons 17 electrons Cl - 17 protons 18 electrons

7 Atoms, Isotope, and Ions 22 Na 11 Na Na + 11 Na +, Cl -, Ca 2+, O 2-, Al 3+, A monatomic ion contains only one atom Na +, Cl -, Ca 2+, O 2-, Al 3+, N 3- A polyatomic ion contains more than one atom OH -, CN -, NH 4+, NO Do You Understand Ions? Al How many protons and electrons are in ? How many protons and electrons are in Se 2-?

8 + NH 4 2- CO 3 - HCO 3 - ClO 3 2- Cr 2 O 7 CrO 4 2- Some Polyatomic Ions ammonium 2- SO 4 sulfate carbonate 2- SO 3 sulfite bicarbonate - NO 3 nitrate chlorate - NO 2 nitrite dichromate SCN - thiocyanate chromate OH - hydroxide Ionic compounds consist of a combination of cations and an anions held together by ionic interaction the sum of the charges on the cation(s) and anion(s) in each formula unit must equal zero. The ionic compound NaCl Formula of Ionic Compounds 2 x +3 = +6 3 x -2 = -6 Al 2 O 3 Al 3+ O 2-1 x +2 = +2 2 x -1 = -2 CaBr 2 Ca 2+ Br - 1 x +2 = +2 1 x -2 = -2 Na 2 CO 3 Na + CO

9 Molecule A molecule is an aggregate of two or more atoms in a definite arrangement held together by. Molecules A molecule consists of at least two atoms in a definite arrangement held together by chemical forces (or chemical bonds). H 2 H 2 O NH 3 CH 4 H 2 H 2 O NH 3 CH nonmetals + nonmetals or nonmetals + metalloids Chemical Nomenclature Ionic Compounds often a metal + nonmetal anion (nonmetal), add -ide to element name K 2 O Mg(OH) 2 barium chloride potassium oxide magnesium hydroxide potassium nitrate Molecular compounds nonmetals or nonmetals+metalloids common names H 2 O, NH 3, CH 4, C 60 element further left in periodic table is 1 st element closest to bottom of group is 1 st if more than one compound can be formed from the same elements, use prefixes to indicate number of each kind of atom last element ends in -ide

10 Molecular Compounds HI hydrogen iodide nitrogen trifluoride SO 2 sulfur dioxide dinitrogen tetrachloride NO 2 nitrogen dioxide TOXIC! dinitrogen monoxide Laughing Gas 2.7