Atomic Math

24 teachers like this lesson
Print Lesson


SWBAT differentiate between the three subatomic particles in terms of charge and location. SWBAT calculate the mass of an atom using protons, neutrons and atomic number.

Big Idea

Students will practice determining what an atom's mass is in relation to number and type of subatomic particles.


This lesson addresses the NGSS HS-PS1-1, "use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms".  The goal of the lesson is to build on what students learned about the basic structure of the atom in the previous lesson (Modeling the Atomic Structure), and build on it with the understanding of calculate the number of subatomic particles. This is aligned with the NGSS Disciplinary Core Idea (DCI) PS1.A (Structure and Properties of Matter): “each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons”. 

The students explore the atom using two of the NGSS Practices:  (1) Questioning and (2) Mathematical and Computational Thinking.  Students will continue to “Practice” questioning using a method called fact-first questioning.  This process will be teacher-led, but the goal is to advance students towards higher-order thinking.  Mathematical and Computational Thinking will be accomplished when students calculate atomic mass and think about the atoms' mass in relation to their parts.

The NGSS Cross Cutting Concept (CCC) that is illustrated throughout the lesson will be Patterns.  This is illustrated when students see the # of protons and the atomic # of an atom can be used to determine an atom's identity. It’s important to recognize that this is an underlying theme and that students will not be summatively evaluated on this part of the lesson.


10 minutes

As students walk into class they will pick up their graded exit slip from the previous day, this is to provide them with quick feedback.  The first five minutes I have students look at their exit slip and share it with their partners to make any corrections.  I explain to the students that this process needs to be a discussion, not just time to copy down another student’s correct answers. 

The goal is to learn any missed information from their partner, and continue to practice questioning. The questions that students ask show what they are struggling with and how the parts, such as protons and electrons, affect the net charge and identity of an atom.

The last minutes are used to give the whole class the the answers (key1 and key2).  I have students write the answer on the board.


10 minutes

To elicit higher-order thinking about the new topic I use a strategy called fact-first questioning. This is an excellent strategy that can be found in Page Keeley's book Science Formative Assessment:  75 Practical Strategies for linking Assessment, Instruction, and Learning. This type of question is a higher-order questioning technique used to bring out student knowledge beyond the recall level. 

To achieve this I take the question, “what two subatomic parts are used to calculate the mass of an atom?” and give them a version stating the fact first “the atomic mass of an atom is calculated using protons and neutrons” and then ask “why are protons and neutron used to calculate atomic mass?”

This type of divergent questioning gets kids to answer questions with more than a single response by having them apply a deeper understanding of the material.

I follow the question by having students engage in a think-pair-share.  After 1 or 2 minutes of students writing thoughts about the question in their science journals, the students share their thinking in a group of 4. After 3 minutes of group sharing, I take the remaining 5 minutes and have each group share what they have determined by writing it on the board. 

I have students write on the board because it helps students stick to their group thought and not restate what other groups have said.  This is a great way to get a deeper response that describes the involvement and interactions of subatomic parts.  The misconception that charge is involved in mass may surface during this process, but can easily be addressed during the discussion.  

Explanation/Guided practice

20 minutes

The goal here is to engage students in the practice of Mathematical and Computational Thinking and further understand PS1.A.  Students have been exposed to the concept of atomic mass and mass number in lessons 1 and 2 and will now summarize the idea by calculating atomic mass and atomic number using a table with element names, atomic numbers, mass number, number of protons and neutrons.  The explanation and guided practice will all be done on the same Atomic math worksheet

I begin by providing student with a few examples on the worksheet:  One that shows them how to calculate mass, one that shows them how to determine neutrons and one that shows them how to find the element name using protons.

There are a variety to choose from on the worksheet and the important part is that you illustrate one of each.  

The rest of the worksheet will be completed as student practice.  As students complete the assignment I let them look at the Atomic math key at my desk.

As students are practicing the problems I walk around answering questions students might have. Typically they struggle with how to calculate the number of neutrons in an atom using the atomic number and mass number.  If they are struggling with this I simply tell them to subtract the small number (atomic number) from the larger number (mass number) and this usually solves the problem.



10 minutes

I choose random students to write one of the practice problems on the board for the remainder of the period.  This is sufficient to determine whether or not students have mastered the objective of calculating atomic # and mass # (the Practice of Mathematical Computation).  If students have not completed the 5 Atomic math questions at the end of the practice worksheet, it should be completed for homework.