TEKS Addressed: 8.1A, 8.1B, 8.2A, 8.2B, 8.2C, 8.2D, 8.2E, 8.3A, 8.3B, 8.3C, 8.3D, 8.4A, 8.4B, 8.1A, 8.2A, 8.2C, 8.2E, 8.3A, 8.3B, 8.3C, 8.3D, 8.4A, 8.5A, 8.5B, 8.5C 

Introduction

This unit bundles Student Expectations that address the structure of atoms and the arrangement of the Periodic Table. Matter is composed of atoms that are made up of subatomic particles and are distinguished by their individual properties. The Periodic Table has recurring trends that are seen in the properties of elements. The historic scientific discoveries of the nature of the atom have fundamentally changed the scientific understanding of the nature of matter.

Prior to this Unit

• Grade 6

  • 6.5A – Know that an element is a pure substance represented by a chemical symbol and that a compound is a pure substance represented by a chemical formula.

  • 6.5B – Recognize that a limited number of the many known elements comprise the largest portion of solid Earth, living matter, oceans, and the atmosphere.

  • 6.6A – Compare metals, nonmetals, and metalloids using physical properties such as luster, conductivity, or malleability.

During this Unit

Students describe the structure of an atom including mass / size comparisons, electrical charges, and locations of subatomic particles. Additionally, students determine the electrical charge of a nucleus, based on the presence and number of positively charged protons. Students use scientific practices and a variety of tools to investigate and interpret the relationship between the information on the Periodic Table and the atomic structure of atoms / elements for the purpose of drawing, constructing, and decoding models. They calculate the number of neutrons in the nucleus by subtracting the atomic number from the mass number on the Periodic Table and identify elements based on the number of protons in an atom. Furthermore, students examine patterns in physical and chemical properties to understand the organization and placement of elements into periods and groups / families on the Periodic Table. They analyze and interpret information on the Periodic Table to ascertain why elements are arranged into groups / families. Additionally, students identify that valence electrons determine an element’s chemical properties including reactivity, and students relate an element’s structure to its placement on the Periodic Table. Students view the Periodic Table as a model and learn how the arrangement of the Periodic Table allows for the prediction of undiscovered elements and their properties. Additionally, students communicate and discuss their observations and record and organize data in their notebooks. Students continue to demonstrate safe practices as outlined in the Texas Education Agency-approved safety standards and consider environmentally appropriate and ethical practices with resources during investigations. Finally, students identify the advantages and limitations of atomic models and relate the research and development of atomic models and the Periodic Table to their impact on scientific thought and society.

Note: Although students are not expected to understand or define isotopes in Grade 8, it is appropriate for students to understand that the atomic mass on the Periodic Table represents the average mass of atoms of an element that have a variety of mass numbers.

After this Unit

In Unit 02, students will study chemical formulas and evidence of chemical reactions, as well as the concept of conservation of mass. In high school, students will study atomic structure and the Periodic Table in more detail.

Additional Notes

STAAR Note

The Student Expectations in this unit support the understandings that will be assessed on the Grade 8 Science STAAR under the following Reporting Categories:

• Reporting Category 1: Matter and Energy

  • 8.5A – Readiness Standard

  • 8.5B – Readiness Standard

  • 8.5C – Readiness Standard

Research

“By the end of 8th grade, students should know that:

• All matter is made up of atoms, which are far too small to see directly through a microscope. 4D/M1a

• The atoms of any element are like other atoms of the same element, but are different from the atoms of other elements. 4D/M1b*

• Chemical elements are those substances that do not break down during normal laboratory reactions involving such treatments as heating, exposure to electric current, or reaction with acids. All substances from living and nonliving things can be broken down to a set of about 100 elements, but since most elements tend to combine with others, few elements are found in their pure form. 4D/M5*

• There are groups of elements that have similar properties, including highly reactive metals, less-reactive metals, highly reactive nonmetals (such as chlorine, fluorine, and oxygen), and some almost completely nonreactive gases (such as helium and neon). 4D/M6a

• Carbon and hydrogen are common elements of living matter. 4D/M6c*

• Most substances can exist as a solid, liquid, or gas depending on temperature. 4D/M8** (SFAA)"