Bellwork- Classify Matter Identify 5 items that fit each of the following categories. a) Substance b) Homogeneous mixture c) Heterogeneous mixture d) Solution Select one thing from category b and one from category c and outline a method for separating the components.

Lecture 2.3- Elements vs. Compounds 2.33 Lecture 2.3- Elements vs. Compounds Elements and compounds are both pure substances. How are they different?

An element is the simplest form of matter. 2.3 An element is the simplest form of matter. A compound is a substance that contains two or more elements chemically combined in a fixed proportion.

2.3 Compounds can be broken down into simpler substances by chemical means, but elements cannot.

2.3 Breaking Down Compounds A chemical change produces matter with a different composition than the original matter. When table sugar is heated, it goes through a series of chemical changes. When table sugar is heated, it goes through a series of chemical changes. The final products of these changes are solid carbon and water vapor.

2.3 The final products of these chemical changes are solid carbon and water vapor. The following diagram summarizes the process. Because sugar can be chemically broken into more than one element, it is a compound.

Liquid H2O  H2O vapor

Liquid H2O  H2O vapor Physical change because it is still H2O!

Liquid H2O  H2O vapor Physical change because it is still H2O! Glass cup  pile of broken glass

Liquid H2O  H2O vapor Physical change because it is still H2O! Glass cup  pile of broken glass Physical change because it is still glass!

Liquid H2O  H2O vapor Physical change because it is still H2O! Glass cup  pile of broken glass Physical change because it is still glass! H2 + O2  H2O

Liquid H2O  H2O vapor Physical change because it is still H2O! Glass cup  pile of broken glass Physical change because it is still glass! H2 + O2  H2O Chemical change because H2 and O2 become something different.

2.3 Properties of Compounds The properties of compounds are very different from those of their component elements. When the elements sodium and chlorine combine chemically to form sodium chloride, there is a change in composition and a change in properties.

Chlorine is used to kill harmful organisms in swimming pools. 2.3 Chlorine is used to kill harmful organisms in swimming pools. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine.

2.3 Sodium is stored under oil to keep it from reacting with oxygen or water vapor in the air. Sodium vapor produces the light in some street lamps. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine.

2.3 Sodium Chloride (commonly known as table salt) is used to season or preserve food. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine.

2.3 Sodium Chloride (commonly known as table salt) is used to season or preserve food. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine. Cl + Na  NaCl 17

Cl + Na  NaCl Poison explosive food! 2.3 Sodium Chloride (commonly known as table salt) is used to season or preserve food. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine. Cl + Na  NaCl Poison explosive food! 18

element element compound 2.3 Sodium Chloride (commonly known as table salt) is used to season or preserve food. Compounds and the elements from which they form have different properties. Observing Based on the photographs, describe two physical properties of sodium and two of chlorine. Cl + Na  NaCl Poison explosive food! element element compound 19

This flowchart summarizes the process for classifying matter. 2.3 This flowchart summarizes the process for classifying matter. Figure 2.11 on page 50 The flow chart summarizes the process for classifying matter. Any sample of matter is either an element, a compound, or a mixture. Interpreting Diagrams What is the key difference between a substance and a solution?

for Conceptual Problem 2.2

2.3 Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds. These chemical symbols were used in earlier centuries. The symbols used to represent elements have changed over time. Alchemists and the English chemist John Dalton (1766–1844) both used drawings to represent chemical elements. Today, elements are represented by one- or two-letter symbols.

Each element is represented by a one or two-letter chemical symbol. The first letter is always capitalized. The 2nd letter (if applicable) is always lowercase

2.3 Section Quiz compound. mixture. element. solution. 1. Passing an electric current through a certain substance produces oxygen and sulfur. This substance cannot be a(n) compound. mixture. element. solution.

2. Which of the following is a mixture? sodium chloride carbon dioxide 2.3 Section Quiz 2. Which of the following is a mixture? sodium chloride carbon dioxide sucrose air

3. The symbol for the element potassium is 2.3 Section Quiz. 3. The symbol for the element potassium is K. Po. P. Pt.