Chapter 17 Composition of Matter

Objectives Objective: Define substances and mixtures. Objective: Identify elements and compounds. Objective: Compare and contrast solutions, colloids, and suspensions. CLE 3202.1.5 Evaluate pure substance and mixtures.

The study of matter, its properties, and changes. Chemistry The study of matter, its properties, and changes.

The basic unit that makes up all matter. Atom The basic unit that makes up all matter.

A. Pure Substances A pure substance is made of only 1 type of matter.

Either an element or a compound. A. Substance Either an element or a compound.

1. Elements Matter with identical atoms (only 1 type of atom) All the atoms in a substance are the same

Elements 118 total elements known (as of 2011, but this is changing? As research continues, so do the findings)

2. Compounds A compound is a substance with two or more elements chemically combined in a fixed proportion

Compounds

Compounds Different atoms (elements) are always combined in the same ratio.

b. Compounds can only be separated (broken apart) into different elements by chemical or electrical processes.

c. Common Compounds H2O = water NaCl = salt C6H12O6 = sugar / glucose

Substance Element Hydrogen Compound Water Salt

B. Mixture Two or more substances that are NOT chemically combined Can be easily separated by physical means

1. Homogeneous Homogeneous mixture contains two or more gaseous, liquid or solid substances blended evenly; you can not easily see the parts.

a. Solutions Liquid homogeneous mixtures with particles so small they can not be seen without a microscope.

Solutions salt-water) The particles remain constantly and uniformly mixed. (Kool-aid, tea, salt-water)

Homogeneous Solution

Mixture Homogeneous Heterogeneous

Homogeneous

2. Heterogeneous Mixtures Mixture of different materials that can be easily seen and separated. Mixtures of materials that are not evenly blended.

Heterogeneous

3. Colloid Heterogeneous mixture with larger particles that never settle.

Colloid Colloids scatter light in the Tyndall effect. Particles in the colloid are large enough to scatter light, but those in the solution are not.

Tyndall effect Colloid

Colloids Examples: jello, milk, smoke, fog, whipped cream

4. Suspension A heterogeneous mixture containing a liquid in which visible particles that settle out on standing.

Suspensions One material is denser than the other so a substance will float and never mix with the other. Examples: oil and water, muddy water, vegetable soup

Suspension

Heterogeneous Suspension Muddy Water Colloid Milk, fog

Composition of Matter 1 Suspensions The table summarizes the properties of different types of mixtures.

A _______ is a type of matter with a fixed composition. Section Check 1 Question 1 A _______ is a type of matter with a fixed composition. A. colloid B. mixture C. substance D. solution

Section Check 1 Answer The answer is C. A substance can be either an element or a compound.

Question 2 How many elements are found on Earth? A. 5 B. 10 C. 30 Section Check 1 Question 2 How many elements are found on Earth? A. 5 B. 10 C. 30 D. 90

Section Check 1 Answer The answer is D. About 90 elements are found on Earth, and more than 20 have been made in laboratories.

How are compounds different from mixtures? Section Check 1 Question 3 How are compounds different from mixtures?

Section Check 1 Answer The atoms in compounds are combined in fixed proportions and cannot be separated by physical means. A mixture is made of two or more substances that can be easily separated by physical means.

Question 4 How can a solution be distinguished from a colloid?

Answer Use the Tyndall effect to observe that colloids scatter light.

Objectives Objective: Define substances and mixtures. Objective: Identify elements and compounds. Objective: Compare and contrast solutions, colloids, and suspensions. CLE 3202.1.5 Evaluate pure substance and mixtures.