Chapter 2 A Review of the Chemistry Basics

1. Chapter 2 � A Review of the Chemistry Basics

2. Atoms, Elements, Compounds and Molecules Atoms are the basic building blocks of matter. Atoms are the smallest particle of an element that canenter into a chemical reaction. Elements are comprised of a single kind of atom. An element is defined by its number of protons (Z). Protons have positive charges and a mass of 1 atomic mass unit (amu). One amu = 1.66 x 10-27 kg. Neutrons have no charge (electrically neutral) and a mass of 1 atomic mass unit (amu). Electrons have negative charges and very small (negligible) mass. Some material taken from Chemistry, 7th Edition, Zumdahl & Zumdahl.

3. To Speak the Language Atoms, Elements, Compounds and Molecules Atomic Names Inorganic Nomenclature Ionic Compounds Molecular Compounds Organic Nomenclature

4. Atoms, Elements, Compounds and Molecules Compounds are comprised of more than one kind of atom in a fixed ratio by mass. Molecules (aka molecular compounds) are groups of atoms chemically bonded together (covalent bonds) into a discrete unit. Molecules are electrically neutral (no net charge). A substance is matter that has a definite composition and constant properties. Some material taken from Introductory Chemistry: Concepts and Connections, 5th Edition, C.H. Corwin.

5. Atoms, Elements, Compounds and Molecules Elements cannot be broken down or decomposed into simpler substances by chemical or physical means, whereas compounds can be broken down into elements by chemical processes. Can elements be molecules? Yes, Elements made up of 2 or more equal atoms form a molecule. Example: Oxygen (O2) consists of 2 oxygen atoms bonded together to form an oxygen molecule. Oxygen is an element and a molecule.

6. Atoms, Elements, Compounds, and Molecules Chemical properties are characteristics that describe the chemical reactivity of a substance. Chemical changes result in the formation of chemically different substances (e.g., run an electric current thru water which contains NaSO4, the water will separate into hydrogen gas and oxygen gas). This is a chemical change from one substance (liquid water) into 2 new chemical substances (hydrogen gas and oxygen gas). Physical properties do not describe the chemical reactivity of a substance. A substance can display physical properties without a change in composition. Physical changes occur without changing the chemical make up of the substance (e.g., ice cube melts into water is a physical change from water in the solid form to water in the liquid form but IT IS STILL WATER). Some material taken from General Chemistry: Principles and Modern Applications, 9th Edition, Petrucci, Harwood, Herring, and Madura.

7. Physical Properties A physical property can be observed or measured without changing the chemical makeup of the substance. A physical change occurs without producing a new chemical substance

8. Intensive and Extensive Properties Physical Properties have 2 categories: Intensive properties are integral to the material and do not depend on the quantity of material (e.g., color). Extensive properties depend on the amount of material (volume, mass).

9. Atomic Number and Atomic Weight The atomic number (Z) of an atom is the number of protons in the nucleus (identity of the atom, e.g., carbon has z=6, therefore, all carbons have 6 protons, and all atoms having 6 protons are carbon atoms). The neutron number (N) is the number of neutrons in the nucleus. The mass number (A) of an atom is the sum of the proton number (or atomic number) and the neutron number (N). (A=Z+N). The atomic mass (atomic mass unit or amu) or atomic weight is the average mass of an atom in a natural sample of the element.

10. Atomic Symbols The mass number is frequently written as a superscript and the atomic number as a subscript (the highest number is the atomic mass and the lowest number is the atomic number)