Chapter 2: How Atoms Are Combined J.F. Thompson, Ph.D.

Physical States of Matter  Recall that matter can exist in different states or phases  The physical state of matter is based on its molecular energy (usually measured by temperature)  Solid Liquid Gas

Chemical States of Matter  A pure substance cannot be separated into different subcomponents by physical or mechanical means  is homogeneous, i.e., has uniform composition, throughout the whole sample  has constant physical and chemical properties throughout the whole sample

Chemical States of Matter  A pure substance may be a group of atoms of a single element, or  A pure substance may be a group of molecules of a single more complex chemical material

How Atoms Are Combined  Molecule - two or more atoms held together by chemical bonds (they may be the of the same element or not)  Molecules can be broken down into their two or more elements by chemical reactions H 2, N 2, O 2, H 2 O, NH 3, CO 2, HCl, C 6 H 12 O 6  Compound - atoms of two or more different elements held together by chemical bonds H 2 O, NH 3, CO 2, HCl, C 6 H 12 O 6, but not H 2, N 2, O 2

Molecules And Compounds  Molecules demonstrate new characteristics of the combined atoms which may be quite different that the characteristics of the individual elements  For Example: Hydrogen (H 2 ) and Oxygen (O 2 ) are colorless odorless gases at temperatures at which water (H 2 O) is a pale blue liquid or a white solid

Mixtures  Most substances found in nature, living or non-living, are not pure substances  Most substances are composed of two or more components physically intermixed  These mixtures may be in a gas, a liquid or a solid phase. e.g., the atmosphere, the ocean, the earth, blood, muscle, and bone tissues, etc.

3 Different Kinds of Mixtures  Solutions: salt water, air, blood plasma, etc. Homogeneous mixtures with each molecule a separate entity in the mix  Solvent – the medium in which the other materials are mixed; the major component of the mixture, e.g., water  Solutes – the various other minor components in the mixture  Colloids: gelatin, milk, and cell cytoplasm, etc.  heterogeneous mixtures that appear translucent or milky  smaller particles, clumps of molecules, which scatter light  the particles will not settle out due to gravity  Suspensions: whole blood (red and white blood cells suspended in plasma)  heterogeneous opaque mixtures with larger, often visible particles  these larger particles will settle out due to gravity if the suspension is not in motion

Different Kinds of Mixtures

Taking Measurements  Recall: Density is one measure of the amount of matter occupying a particular space, specifically all the matter present, regardless of composition. Measures include kilograms, grams, pounds, ounces, etc. Relative density is in reference to a standard, such as water (the “specific gravity” of urine or plasma relative to pure water)

Taking Measurements  Concentration – A measure of the amount of an individual solute dissolved in a solvent  Measures include grams/liter (g/l), milligrams/deciliter (mg/dl), moles/liter (mol/l) = Molarity (M), etc.  A mole is the total atomic weight of a molecule in grams  Example:  The atomic weight of glucose (C 6 H 12 O 6 ) is  A 1M solution of glucose would contain g of glucose in 1 L of solvent

End CH 2: How Atoms Are Combined