TAKS Objective 3

Substances have Chemical and

Physical Properties

The student will demonstrate an understanding of the structures

and properties of matter.

TEKS Science Concepts 7.7 B

The student knows that substances have chemical and physical properties. The student is expected to:

Describe physical properties of elements and identify how they are used to position an element on the periodic table.

What is a property?

Properties are defined as what matter is like and how it behaves.

Properties are divided into two major groups: chemical and physical.

Physical properties

Physical properties are those that describe what the matter is like (what does it look like, feel like, taste like, etc.). They are those properties that can be observed with our senses.

Examples of physical properties

• Color• Size• Shape• Density• State of matter• Odor• Texture

Chemical Properties

• Chemical properties describe how matter behaves (what does it do when one type of matter encounters or reacts with another.

• Those properties can only be observed when matter reacts or doesn’t react.

Examples

• Rusting• Chemical reactivity• Flammability• Combustibility

Physical or Chemical?

A major test of whether or not a property is physical or chemical is whether or not the property may be observed without changing the identity of the substance. Physical properties do not change the identity.

Physical or Chemical?

• Physical – paper is wadded up (it is still paper)

• Chemical – paper is burned (it is no longer paper)

Engage

Demonstration: Choose several objects. Keep them hidden out of view of the students. Describe each one using its physical properties as you observe the object inside a paper bag. Allow students to guess what each object is as you describe it.

Explore

• Activity: Ornamental Properties

• Class Time: 20 minutes• Objective: The student will

demonstrate knowledge of physical properties by making an ornament and listing five physical properties of that ornament.

Explain Physical properties are

things that can be described about an object or material by observing it using the five senses. There are characteristic physical properties, such as density and state of matter, that do not change regardless of how much of the material is present.

Elaborate 1

• Activity: The students will choose 10 of the ornaments that have been made and place them into categories based on their physical properties.

• Class Time: 15 minutes• Objective: The student will

organize ornaments by similar physical properties.

Elaborate 2

• Activity: Density, a Physical Property

• Class Time: 15 minutes• Objective: The student will

demonstrate that density is a characteristic property.

Evaluate• Present students with three items.

You may place them on a table or in a sack to be given to each student. The student must list five physical properties of each item.

• Give each student a density chart and an unknown element. Allow them to identify the element based on its density.

TEKS Science Concepts 7.7 C The student knows that substances have

chemical and physical properties. The student is expected to:

Recognize that compounds are composed of elements.

Periodic Table

The periodic table with which we are familiar was first organized in the 1860’s by a Russian chemist named Dmitri Mendeleev (Men-da-‘le-off).

Organization• He looked at properties such

as density, appearance, atomic mass, melting point, and compounds formed from the element.

• Arranged them by increasing atomic mass in rows and columns and saw a pattern.

Changes made to the periodic table

In 1914, a man named Henry Moseley rearranged the table in order of increasing atomic number.

Organization

• Vertical columns are called groups or families

• Horizontal rows are called periods

Major divisions

• Metals • Nonmetals

Alkali Metals

Group 1 elements all have one electron in their outer shells. This gives them similar properties.

Alkaline Earth Metals

• Group 2 metals are very reactive and cannot be found in nature in pure form.

• Contain 2 electrons in the outer shell

Transition metals

Groups 3-12 possess properties of both metals and nonmetals and are therefore called transition metals.

Halogens

Group 17 elements are prone to form salts with metals and are therefore called “salt formers”.

Noble Gases

• Group 18 elements are all gases and contain 8 electrons in their outer shells.

• They are very stable and nonreactive

Lanthanides and Actinides

The two groups at the bottom of the table have been removed to keep the table from becoming too wide.

Engage

Activity: Group IT! Overview: Students

will group types of transportation based on passenger capacity and mode of transportation.

Explore

• Activity: Periodic Parallels (Blackline Master)

• Class Time: 30 minutes• Objective: The student

will label the periodic table according to groups that contain similar properties.

Explain

The periodic table is organized to show relationships vertically and horizontally. The elements in a vertical column (called group or family) have the same number of electrons in their outer energy levels. Each element in a particular horizontal row (called a period) has the same number of energy levels as every other element in that particular row.

Because elements have the same number of outer level electrons, they exhibit similar properties. Some groups are named because of the properties that they share. For example, the word “halogen” means “salt-former”. The elements in group 17 tend to form salts when combined with other non-metals or metals. They are also poor conductors of electric current, react violently with alkali metals to form salts, and are never found uncombined with other elements in nature.

Explain

For example, the word “halogen” means “salt-former”. The elements in group 17 tend to form salts when combined with other non-metals or metals. They are also poor conductors of electric current, react violently with alkali metals to form salts, and are never found uncombined with other elements in nature.

Explain

Elaborate

Students will do research to find examples of properties shared by each specific group on the periodic table. For example, alkali metals react violently with water and are soft, silvery, and shiny. Elements in the actinide period are all radioactive.

Evaluate

Students will be given a blank copy of the periodic table to fill in with the correct names of the specific groups. (See Blackline Masters – Evaluate – Periodic Parallels)

Elements

Elements are pure substances that cannot be broken down into anything simpler by physical or chemical means.

Compounds

• Elements combine to form compounds.

• Compounds may be made up of only two elements or many.

Engage

• Activity: Marshmallow molecules

• Class Time: 20 minutes• Objective: The student will

construct a model of a water molecule using marshmallows

Explore• Activity: Electrolysis of Water

(Student Worksheet that comes with lab kit)

• Class Time: 50 minutes• Objectives: • The student will conduct a

decomposition reaction in which water is broken down into hydrogen and oxygen and each gas is collected into a separate test tube.

• The student will demonstrate how compounds are composed of elements.

Water molecules are composed of two atoms of hydrogen joined with one atom of oxygen. The bonds formed are covalent bonds in which electrons are shared, but when a substance such as salt is dissolved in the water, the atoms are separated, forming ions (atoms with a positive or negative charge).

Explain

The hydrogen atoms leave their one electron with the oxygen atom resulting in hydrogen now being a positive ion (minus one electron) and oxygen being a negative ion (gaining two electrons, one from each hydrogen atom).

Explain

Once the system is connected to the battery, a current begins to flow. One electrode underneath one test tube becomes positively charged and the other electrode underneath the other test tube becomes negatively charged. The pathway from the negative electrode to the positive electrode is accomplished by an electrolyte solution (a solution which conducts electricity) such as salt water.

Explain

The now positive hydrogen ions are attracted to the negative electrode and the negatively charged oxygen ions are attracted to the positive electrode. As the gases collect on the electrodes, it is very obvious. Large bubbles appear on the + electrode (oxygen) and thousands of very tiny bubbles (hydrogen) appear on the – electrode.

Explain

Elaborate

• Activity: Combining some elements with oxygen. (Activity #7) (Students will use the student worksheet from the lab kit)

• Class Time: 15 minutes• Objective: The students

will synthesize compounds from elements.

Explain

• When elements combine to form compounds they are brand new substances with completely unique properties.

• They no longer possess the properties of the elements that formed them.

Evaluate

The students will journal about what they learned concerning the formation of compounds from elements. They should cite examples learned from the lab experience.