Chemistry lesson scenario

Lesson plan elaborated by: Krzysztof Błaszczak

Target group:

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

I. Internal structure of the matter. Student:

2) describes the composition of the atom (nucleus: protons and neutrons, electrons); based on the location of the element in the periodic table, determines the number of electron shells in the atom and the number of electrons on the outer electron shell for the elements of groups 1 and 2 and 13‑18; determines the location of the element in the periodic table (group number, period number);

3) determines the number of protons, electrons and neutrons in an atom based on atomic and mass numbers; apply the A ZE notation.

Abstract title:

2.2. Electrons in atom

Link to lesson:

https://www.epodreczniki.pl/reader/c/153030/v/43/t/student‑canon/m/iDP5Qw3ExP

Topic: Electrons in atom

Time: 45 min

Aim of the lesson:

The student draws a simplified model of the atom of the indicated chemical element and provides electron configurations

Criteria for success:

• you will specify the number of electron shells in an atom

• you will determine the maximum number of electrons located the individual atomic electron shells

• you will describe the distribution of electrons in an atom

• you will indicate valence electrons

Key competences:

• communicating in the mother tongue

• communicating in foreign languages

• mathematical competences and basic scientific and technical competences

• IT competences

• learning to learn

Acquired and improved skills:

• using the digital textbook

• communication

• computer literacy

• research and investigation

• creative thinking and acting

• cooperation

Teaching aids:

• computers with speakers and internet access

• multimedia resources contained in the abstract and e‑textbook

• interactive whiteboard / blackboard and chalk

• Methodology Guide or green, yellow and red sheets of paper

• active periodic table of elements

Methods / techniques:

• exposing: presentation

• programmed: using the computer, using an e‑textbook

• giving: elements of the lecture

• stoplight technique for student self‑assessment, and thus determining the level of mastery of the discussed issue on an ongoing basis

Forms of work:

• collective activity

• individual activity

Lesson plan overview:

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on stoplight technique. He presents the aims of the lesson on a multimedia presentation in the student's language and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determine the topic- based on the previously presented lesson aims – and then write it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety - before experiments, the teacher familiarise students with the characteristics of the substances to be used during the lesson. He indicates the need to be careful when handling them.

Realization

1. The teacher, recalling the information from the last lesson, asks questions, and volunteers answer them, e.g. what the atom is, what properties the atom has, what is the structure of the atom, which elementary particles are located in the atomic nucleus, how to calculate the number of neutrons in the nucleus, what are electric charges of proton, neutron and electron.

2. The teacher, still referring to the information presented in previous classes, points out that electrons occupy the space around the nucleus in the atom. He discusses the concepts of electron clouds and electron shells in the context of electron motion. The number of electron shells in atoms varies and depends on the number of electrons. The largest known atoms have seven shells, and the smallest - one.

3. The teacher explains students the rules how to number the electron shells and how to mark them with symbols. He presents the table „Electron shells” from the abstract on the interactive whiteboard.

4. The teacher discusses the principle of the maximum number of electrons on electron shells, quotes the 2nIndeks górny 2² formula and discusses its use (where n denotes the next number of the electron shell). The teacher informs that this formula is used in calculations only for the fourth electron shell - the maximum number of electrons on the electron shell is 32. He acknowledges how the number of electrons on the penultimate electron shell is calculated and what determines the number of electrons on the last electron shell - based on periodic table of elements. He emphasizes the role of valence electrons.

5. The teacher explains how the electron configuration works. He discusses the ways of its presentation based on a table from abstract, which he displays on interactive whiteboard. Then he presents the animation „Stages of drawing a simplified model of the atom of a chemical element”.

6. The teacher quotes examples of elements and volunteers draw simplified atomic models on the board.

7. At the end of the lesson the teacher asks students to perform interactive exercises – individual activity.

Summary

1. In the summary of the lesson, the teacher asks students to expand following sentences:

• It was interesting for me…

• I got to know…

• It was easy for me…

• It was difficult for me…

He can use an interactive whiteboard in abstract or instruct students to work on it.

Multimedia:

I. Interactive exercises – single choice, memory

II. Response forms

III. Presentation “Stages of drawing a simplified model of the atom of a chemical element”

IV. Interactive whiteboard for lesson evaluation and self‑assessment of the student's knowledge

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Electrons in atom

Bohr proposed that the electrons are arranged in concentric circular orbits around the nucleus. The Bohr model was modeled on the solar system, known as the planetary model.
Generally, the Bohr model can be summed up with the following principles:

1. Electrons occupy only some orbits around the nucleus. These orbits are stable (stationary orbits).

2. Each orbit has associated energy. The orbit nearest the nucleus has the energy E1, the next orbits in the order from the nucleus have the energies E2, E3, etc.

3. Energy is absorbed when the electron jumps from a lower orbit to a higher one and energy is emitted when the electron drops from a higher orbit to a lower orbit.

4. The energy and frequency of the emitted or absorbed light can be calculated using the difference between the two orbital energies.

The Bohr model concerned mainly the hydrogen atom model and did not explain the structure of atoms more complex than hydrogen. It was not until 1926 that a new, more complete atomic theory was developed - a modern atomic theory.

During the 10 years since the discovery of the Bohr atom model, there has been a great development in this field of science. In 1921 Louis de Brogllie introduced the wave/particle duality of matter. Werner Heisenberg elucidated the Uncertainty Principle in 1923. In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr atom model one step further. He developed the equation which is used today to understand atoms and molecules - the Schrodinger Equation.

Schrödinger used mathematical equations to describe the probability of finding an electron in a particular position. This atomic model is known as the quantum‑mechanical atom model. In contrast to the Bohr model, the quantum‑mechanical model does not specify the exact path of the electron, but rather predicts the chances of locating the electron. The model is presented as a nucleus surrounded by an electron cloud. Where the cloud is the most dense, the probability of finding an electron is greatest, and vice versa, the electron is less likely in a less dense cloud area. In 1932, James Chadwick discovered that the atomic nucleus consists of positively charged protons and neutron neutral electric charge particles. From 1932, through continuous experiments, many additional particles were discovered in the atom. The atomic theory has been further enhanced by the idea that protons and neutrons even form smaller units called quarks. The quarks themselves are in turn made of vibrating energy strings. The atomic composition theory is a continuous and exciting adventure.

In a quantum (wave) mechanical model, an electron is seen as a standing wave. This is related to a series of wave functions (orbitals) that describe the possible energies and spatial distributions available for the electron. According to Heisenberg's uncertainty principle, the model can not specify detailed electron movements. Instead, it represents the probability distribution of the electron on this orbital. Thanks to this, the image of orbitals is possible due to the probability distribution of electron density maps.

The electrons occupy the space around the nucleus in the atom. They move there at high speed and in different directions. They are said to create an electron cloud.

The space in the atom occupied by electrons is enormous in relation to the volume occupied by the atomic nucleus. However, this does not mean that each of the electrons moves freely in every point of this space. It turns out that electrons move only in limited areas. These areas are named electron shells. Within them, electrons move at high speed and in all directions. The number of electron shells in atoms varies and depends on the number of electrons. The largest atoms we know have seven shells, and the smallest ones – one.

Electrons moving on different shells differ in energy. The closer the electron is to the atomic nucleus, the lower its energy is. And on the contrary – the farther away from the atomic nucleus electron is, the higher its energy is.

Electron shells are not physically reflected in the structure of the atom. It is primarily the energy of a given electron and the presence of other electrons that determine in which area around the nucleus it will move. There are no physical barriers in the space around the nucleus that would hold the electron on a given shell.

An electron shell around a given atom is considered a set of atomic orbitals having the same major quantum number n. The next n values are assigned to subsequent shells: K, L, M, N, O, P and Q. The shells consist of different numbers of electron subcoatings, corresponding to certain types of atomic orbitals.

Electron shells in the atom have been given letter symbols from K to Q. The shell closest to the nucleus (the first one) is marked with the letter K. Next are: L, M, N, O, P, Q.

A specified number of electrons can be found on each shell. For example, the first shell holds only two electrons, and the third one can hold only eight of them. The further away from the nucleus of the atom is the shell, the more electrons it can hold. The maximum number of electrons that can be found on the shell is described by the formula 2nIndeks górny 2², where n means the number of the shell.

The arrangement of electrons on individual shells is called electron configuration. Presentation of the electron configuration of the atom will start with a helium atom that has two electrons. These two electrons can be located on the first K shell. This information can be presented in several ways. These are presented in the table below.

Writing in the form of the scheme

We draw a diagram on which we mark the nucleus of the atom and all shell filled with electrons. We note down the symbols of the shells and the number of electrons assigned to them.

Electron configurations of elements on shells and orbitals

Electron configuration of the silicon atom ${}_{14}\mathrm{Si}$

Write down using square brackets [2,8,4]

Write down using shell symbols K Indeks górny 2²L Indeks górny 8⁸M Indeks górny 4⁴

Writing in the form of the scheme

The electrons farthest from the atomic nucleus are the least attracted by the nucleus and often affect the electrons of other atoms. It can be said that these represent an atom outside. These determine the properties of the atom. As the only one of all of the electrons, these have their own name – valence electrons, and the shell on which these are located is called valence shell. Atoms can have a different number of valence electrons (from one to eight).

• The electrons in the atom circulate in a strictly defined space around the nucleus (in areas known as electron shells).

• Each shell can accommodate a limited number of electrons (2nIndeks górny 2², n – shell number).

• The arrangement of electrons in an atom is called electron configuration.

• The last shell in the atom is called the valence shell, and the electrons moving in its space are valence electrons.

Valence electrons, electron configuration, valence shell