ASTRONOMICAL CHEMISTRY

 

Name of teacher:           

Week:                                                                   Date:                                                     Time:

Period:                                 Duration: 1 HR 20 MIN.                                                  Average age of learners: 16YEARS

Subject:                               CHEMISTRY                                                                         Class: SS THREE

Topic:                                    ASTRONOMICAL CHEMISTRY

Sub topic:

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials: beaker, beam balance

Entry behavior: The students have been taught density.

Objective: At the end of the lesson the students should be able to:

1.       State the composition of earth.

2.       List the layers of atmosphere

3.       Explain solar planet

CONTENT

ASTRONOMICAL CHEMISTRY

Chemical analysis of earth and space.  

-The age of the earth as determined by radioactive decay.

Scientists are able to calculate the age of the earth from the decay rates of the radioactive element  (which are known), and the ratio of the parent and daughter element.

The radioactive isotopes most commonly used for these studies include carbon-14, rubidium-87, potassium-40, uranium-235, uranium-238 and thorium-232. The method is not exact and the ages obtained may vary as much as several hundred million years. Studies shows that the oldest known rock on Earth was formed nearly 4.0x10⁹ years ago. Based on this, we can say that Earth is between 4.5x10⁹ to 5.0x 10⁹ years old.

Structure and composition of the earth

The earth is made up of three parts:

 (i) atmosphere:- this is the layer of air that surrounds the planet. It contains the gaseous layer that surround the earth. It is composed of 78% nitrogen, 21% oxygen and 1 % other gases including carbon (iv) oxide.

Layers of Atmosphere

I.                    Troposphere- the lower layer of about 10km – 17km at the equator above the Earth’s surface

II.                  Stratosphere-  about 17km -45km above the surface of the Earth.

III.                Mesosphere- from about 45km – 75km..The  temperature varies from 0oC at the altitude of about 45km to -90oC at about 75km.

IV.                Thermosphere (ionosphere)- the region of atmosphere extending from about 75km to about 400km. The air in the thermosphere is thin.

V.                  Exosphere – region beyond  400km.

(ii) hydrosphere:- this is the part composed of water. It covers nearly 71% of the Earth’s surface.

(iii) Lithosphere:- this is the solid part of Earth. It is made up of  a crust, mantle and core. The crust is composed of  less dense materials, which are compounds of  oxygen and silicon, while the mantle  and the core are composed of more dense materials like iron and nickel.

Planetary data

The solar system consists of the Sun, the nine planets together with their moons and the asteroids, comets and meteoroids in it. Spectroscopy is used to study the chemical composition of planets and stars. The sun is a star composed mainly of hydrogen, helium and small of other elements found on Earth. It gives out energy which is liberated by the fusion of hydrogen atoms to form helium atoms.

The Moon is Earth’s natural satellite and is composed of rocks, which look like those on Earth but have different chemical composition.

Mercury, Venus, Earth, and Mars are rocky planet composed of dense elements. Jupiter, Saturn, Uranus and Neptune are gaseous planets composed mainly of gases such as hydrogen, helium, ammonia and methane. Pluto is the smallest planet as well as the furthest planet from the sun. it has a low density and so is probably composed of frozen methane.

Stars are self-luminous bodies, shining by radiation obtained from energy sources within themselves. Stars vary in size, age, luminosity, colour, temperature and chemical composition. Stars can be grouped into classes O, B, A, F, G, K and M according to their spectral information and belong to the main sequence. They are arranged in order of increasing temperature which also corresponds to a colour sequence, which range from bluish-white to yellow to red. The stars in the main sequence are composed mainly of hydrogen and helium.

Star may be small, medium-sized or large when they are formed. Their life histories vary according to their sizes at formation. The smallest stars have the longest life span, while the largest have the shortest. A medium-sized star has a life span of about 10000 million years. The sun, which was medium sized at birth, is a G type yellow star. It is in the middle age now.

Space travel was made possible by the launching of artificial satellites. Astronauts have landed on the Moon stations are in orbit round Earth. Unmanned probes have been sent to study the inner and outer planets.

PRESENTATION

Step I: The teacher explains the age of the earth.

Step II: The teacher explains structure and composition of the earth.

Step III: The students chorus the layers of the atmosphere.

Step IV: The teacher explains solar system.

Step V: The teacher allows the students to ask questions.

EVALUATION

The teacher asks the following questions:

1.       State the composition of earth.

2.       List the layers of atmosphere

3.       Explain solar planet