Grade 8 Science: UNIT 3: Matter

04/19/16

Matter is the substance of which all material is made. That means objects which have mass. More specifically, they must have rest mass, which is a form of energy that matter has even when it is not moving (it has no kinetic energy), is extremely cold (it has no thermal energy), etc. Matter is a word that is sometimes used in varying ways in everyday life, whereas mass is a well-defined concept and quantity at least in physics. They are not the same thing, though they are related.

Activity 1: Which is Matter and which isn’t?

Describe common properties of matter

Sample	Matter
Sugar	Solid	Has powdery appearance which appears to have packed molecules.
Water	Liquid	Has fluid-like appearance which appears to have separated molecules.
Compressed Air	Gas	Is invisible which appears to have separated molecules.
Stone	Solid	Has aggregate appearance which appears to have strictly packed molecules.
Leaf	Solid	Has soft appearance which appears to have fairly packed molecules.
Smoke	Gas	Is visible but appears to have separated molecules.

Matter can have different properties. You measured the mass of each sample of matter using a balance or a weighing scale. The mass of an object is a measure of the amount of matter the object has. You observed that the mass of each sample of matter in Activity 1 is different from the mass of the other samples. You also found out that each sample of matter occupies space. The measure of the space occupied by an object is called volume. All matter has mass and volume. There are other properties of matter such as hardness, texture, color, flexibility, malleability, and electrical conductivity which vary from one sample to another.

Activity 2: What is matter made of?

Explain how these observed situations or events give evidence that matter is made up of tiny particles.

·         Mixing different molecules would affect their taste, appearance, and texture.

Studying about what matter is made of involves dealing with very small “particles” beyond what your eyes can see. In fact, the ancient Greek philosophers proposed ideas about what matter was made of. Almost 2,500 years ago, Leucippus and his disciple, Democritus believed that nature consisted of two things, “atoms and the void that surrounds them” (Knieram, 1995-2013). They believed that “atoms are physically, but not geometrically, indivisible.” For Democritus, atoms are indestructible and completely full, so there is no empty space. Both Leucippus and Democritus had the idea that there are many different kinds of atoms and each of them had specific shape and size and that all atoms move randomly around in space. However they did not give an explanation for the motion of atoms (Knieram, 1995-2013).

The idea of the atom was not further explored until a little over two centuries ago when John Dalton presented concrete evidence that all matter is made of very small particles called atoms. An atom is the smallest particle of an element that has all the properties of the element. Today, we know that although atoms are very small, they are not indivisible as Democritus thought, rather they consist of still smaller particles, Democritus was right in one aspect of his belief, that is, atoms are the smallest particles of which substances are made.

Activity 3: Are the particles of matter moving? What is between them?

·         Infer from observations that particles of matter move.

o   Using a syringe to compress the air inside is possible by blocking the end of the syringe and pushing its plunger. This would cause the air to force its way out, only to be compressed by the plunger.

o   The compressed air would feel hard because of the resistance and pressure applied to it.

04/26/16

Activity 4: What changes take place when water is kept in a container?

Describe the changes of water particles stored in a container with varying temperature.

Keeping water overnight inside a sealed container will cause the water to evaporate if the temperature is high enough.

Keeping water overnight inside a sealed container will most likely change the taste or nothing at all if the temperature is cold enough.

Changes between Liquid and Gas

The molecules have kinetic energies that differ from each other. Some particles are moving faster than others and therefore have higher kinetic energy and some are moving slower.

So, even at room temperature, some molecules of water have enough kinetic energy to overcome the attraction of neighboring molecules and escape from the surface of the liquid and eventually move into the air. To break away from the surface of the liquid, the molecules must have at least some minimum kinetic energy.

The process by which the molecules on the surface of a liquid break and change into gas is called evaporation.

Usually, it is described as the process where a liquid is changed into a gas. As evaporation takes place, the water molecules which did not escape and were left in the liquid have a lower average kinetic energy than the molecules that escaped. The effect of this is the decrease in the temperature of the liquid water. Evaporation is a cooling process.

Activity 5: What changes happen when water is heated?

Part 1

Heating the water up to 100c would make the liquid produce bubbles.

The bubbles have vapor inside.

The water evaporates as heat increases overtime

Part 2

Sealing the remaining water in place of lower temperature would cool down the liquid.

Condensation is the changing of gas to water.

Activity 6: What happens when ice turns to water?
Physical change is changing the appearance and state of the object. It does not change the chemical substance when physical change is being applied alone.

Example:

     Freezing water is physical change. Despite the change of the liquid state, it didn’t change the chemical substance of the liquid. Ice is still water and can be frozen or heated.

05/03/16

ATOMS: INSIDE OUT

Scientists have proven, however, that the atom is composed of even smaller particles. From experiments conducted in the latter part of the 19th century to the early half of the 20th century, scientists collected evidence that atoms are composed of three types of particles, namely, (1) protons, (2) electrons and (3) neutrons.

These components of the atom are collectively referred to as subatomic particles. In recent years, scientists have discovered that protons and neutrons consist of even smaller particles.

There are still many things about the atom and what is inside it that scientists are discovering. These extremely small particles are being studied using an extremely big structure that serves as their instrument.

Activity 1: “Charge” it to experience!

·         observe that objects may attract or repel each other,

·         infer that objects may carry positive and negative charges

o   Using objects of the same type of charges may cause the objects to repel each other.

o   Using objects of different types of charges may cause the objects to attract each other.

Activity 2:  The big difference

·         Compare subatomic masses and particle contribution

Particle	Charge	Mass (g)	Mass (amu)
Proton	+1	1.6727 x 10-24 g	1.007316
Neutron	0	1.6750 x 10-24 g	1.008701
Electron	-1	9.110 x 10-28 g	0.000549

Activity 3: Small but terrible

·         When the idea of the atom was first proposed by the ancient Greeks, they thought it was a particle with no parts. However, towards the 19th century, J.J. Thomson was able to discover that atoms have negatively-charged particles, which he called electrons. It led him to propose a new model for the atom, which he called the plum pudding model.

·         Thomson proposed that the negatively-charged electrons were embedded in a kind of cloud or soup of positive charge, as shown in the figure on the right. Since plums and puddings are not commonly known in the Philippines, it may work better for you that we use the other name for the model, the raisin bread model. In science, models, based on observations from experiments are tested further, sometimes by other scientists, to determine their validity. A group of scientists composed of Ernest Rutherford, Johannes "Hans" Wilhelm Geiger and Ernest Marsden tested Thomson’s model by bombarding a very thin sheet of gold foil with positively-charged alpha particles. Their experiment is referred to as the alpha particle scattering experiment.

05/24/16

    The other puzzle about the atom concerns the electrons. Imagine again the atom as 100 meters in diameter, the nucleus, around one millimeter in diameter at the center and the electrons are in this vast space around the nucleus. Where in this vast space are the electrons? Are they moving? How do they move? How fast do they move? One of the models of the electrons in atoms is the planetary model where the electrons were thought to move in orbits around the nucleus similar to the way planets like the earth move around the sun. This has since been found to be incorrect.

    The behavior of electrons in the space around the nucleus is not simple to describe. What we do know, however, are the following: The electron although it is negatively charged does not collapse into the positively charged nucleus; There is attraction between the nucleus and the electron, evidence of which is that energy is required to remove an electron from the atom. Notwithstanding the complex behavior of electrons in atoms, we continue to use a model of electronic structure (or the way electrons are “arranged” in the atom) to help us understand and study the way atoms combine to form the millions of compounds discovered to date.

    So far, you have learned about the three subatomic particles — protons, electrons and neutrons — and how they are arranged in the currently accepted model of the atom. Among these subatomic particles, it is the number of protons that identify the atoms of an element. All atoms of an element contain the same number of protons in their nuclei. This number is the element’s atomic number. In the next activity, you will refer to the periodic table in determining the atomic number. Notice that no two elements have the same atomic number.

05/31/16

  

  The Development of the Periodic Table

    The development of the Periodic table could be traced back in 1817 to the work of Johann Dobereiner, a German chemist who formed the triads of elements with similar properties like the triad of calcium, barium and strontium. In 1863, John Newlands, an English chemist proposed the Law of Octaves. He based his classification of elements on the fact that similar properties could be noted for every eight element when they are arranged in order of increasing atomic masses.

     Around 1869 two scientists determined a way to put the elements in order. Lothar Meyer and Dmitri Mendeleev both came up with periodic tables that showed how elements should be grouped. It is interesting to note that these two scientists did not personally know each other, yet they came up with the same conclusions. Both scientists were teachers living and working in different places. Meyer lived and worked in Germany while Mendeleev in Russia. Both arranged the elements in order of increasing atomic mass while putting in groups those with similar properties. Both of them also left blank spaces in their tables, believing that these spaces would be filled later with elements yet to be discovered.

  Modern Periodic Law

      Later, in 1914, Henry Moseley, an English physicist observed that the order of the X-ray frequencies emitted by elements follows the ordering of the elements by atomic number. This observation led to the development of the modern periodic law which states that the properties of elements vary periodically with atomic number. Recall what you learned in Module 2 that atomic number is equal to the number of protons in the nucleus of an atom. The atomic number is a common characteristic of all atoms of an element. The modern periodic table organizes elements in such a way that information about the elements and their compounds are easily revealed. The vertical columns of the periodic table, called groups, identify the principal families of elements. Some families have their special names.

 06/07/16

  How chemicals in the Periodic Table Work

 The elements are grouped into blocks or series in the periodic table. In the later grades, you will learn how elements were grouped in blocks. Refer to the figure above; Group 3 to Group 12 constitutes one block wherein elements in this block are referred as the transition elements.

 The lanthanides and actinides are special series of elements but are also part of the transition block; they are also called the inner transition elements. Elements from the taller columns (groups 1, 2, and 13 through 18) are called the representative elements or main groups of the periodic table.

 This arrangement allows us to study systematically the way properties vary with the element’s position in the table. Similarities and differences among the elements are easier to understand and remember.

  Reaction of Metal to Acid

  With respect to position in the periodic table of the representative elements, metallic character increases from top to bottom and decreases from left to right; while nonmetallic character decreases from top to bottom and increases from left to right, as seen in the figure on the right. Metallic property relates to how easy it is for an atom to lose an electron. On the other hand, nonmetallic property relates to how easy it is for an atom to gain an electron. Why do metals tend to lose electrons while nonmetals tend to gain electrons? In Module 2, you learned that the behavior of electrons is complicated to describe. However, we use a model of electronic structure which presents a picture where electrons occupy regions around the nucleus called electron shells.

  These are also called energy levels because each electron shell corresponds to a particular energy. Each electron shell can hold only a certain number of electrons. The way the electrons of an atom are distributed in the various energy levels or electron shells is called electronic configuration. The lowest energy level is the one nearest to the nucleus. This is the energy level that electrons occupy first. It can accommodate a maximum of 2 electrons. If there are more than 2 electrons, they occupy the succeeding higher energy levels. The highest energy level that an electron occupies is referred to as the outermost shell or valence shell. The electrons in the valence shells are called valence electrons. These electrons are the ones involved in chemical reactions. The chemical properties of an element depend on the number of valence electrons.