Atomic Structure (18/1/13)

In yesterday's theory lesson, I learnt about the atomic structure and the subatomic particles that make up an atom.

Atoms are the smallest particle that retain an element's chemical properties but they can be divided into smaller particles known as subatomic particles. When looking at the subatomic particles, elements are no longer identifiable.

We were given an analogy in class to better understand this statement:
(YAY analogies again I love analogies!)

There are two coin banks, A and B. One has only ten cent coins while the other has only twenty cent coins. When all the coins are crushed into smaller pieces and put together, you can no longer tell if the crushed pieces belong to Bank A or Bank B.

So it's the same for elements. When you put the subatomic particles together, you cannot tell which element it is from. The subatomic particles are namely:
-Protons (p)
-Neutrons (n)
-Electrons (e)

Protons and neutrons are known collectively as nucleons as they make up the nucleus of the atom. Electrons are found in shells that circle around the nucleus. Actually, I learnt that electrons don't circle really obediently. In fact, they move about randomly but for the purpose of studying them, we take them as orbiting around the nucleus.

PROTONS
-have an electrical charge of 1
-have a relative mass* of 1
-attract electrons
-found in the nucleus of an atom

NEUTRONS
-have no electrical charge (electrically neutral)
-have a relative mass* of 1
-found in the nucleus of an atom

ELECTRONS
-have an electrical charge of -1
-have a negligible mass of ¹⁄₁₈₄₀ 
-are attracted to protons
-circle the nucleus

Acronym: PEN

*Relative mass:
All the subatomic particles are very light that it is inappropriate to express them in grams or kilograms. Instead, they are measured against a standard unit, called the atomic mass unit (amu).
1 amu = 1.67 × 10^-27

Protons and electrons attract each other because of their opposite charges. That's why the electrons "circle" around the nucleus. All atoms are electrically neutral as the number of protons and electrons in an atom are equal.

Next, I learnt about what atomic number and mass number are.

ATOMIC NUMBER (Z)
-also known as proton number
-is the number of protons in an atom (since the number of electrons are the same in an atom, it also represents the number of electrons an atom has)
-is unique to every element; no two elements have the same atomic number

MASS NUMBER (A)
-also known as nucleon number*
-is the total mass of an atom in amu (electrons are left out of the calculation as their mass are negligible)
-is basically the number of protons and neutrons in an atom

*Mass number and nucleon number are actually two different things, although they have the same value. Mass number is the total mass of an atom in amu while nucleon number is the total number of nucleons.
For example, carbon has an atomic number of 6 and a mass number of 12. That means that there are 6 neutrons and 6 protons. The nucleon number is therefore 6 + 6 = 12. As each nucleon has a relative mass of 1, the mass number will be (1 × 6) + (1 × 6) = 12.

I used to think that these two terms meant the exact same thing, and I'm glad I've learnt otherwise!

You can find out the number of protons and electrons by looking at the atomic number. To find the number of neutrons in an atom, you take A − Z.

This is how we represent elements with the atomic and mass numbers.

(taken from Google Images)

That's so fast we are almost (or maybe already) done with this topic. It's so interesting to discover the smallest particles that make up everything around us! :) 

To end off this post, here's a lame joke taken from the internet relevant (or maybe not) to this topic:


A proton and a neutron are walking down the street.
The proton says, "Wait, I dropped an electron help me look for it."
The neutron says "Are you sure?" The proton replies "I'm positive."

Okay not very funny. Bye.

Practical: Comparing Element, Compound and Mixture

This is my first Chemistry practical lesson since I was absent during last week's practical. So I was actually very excited for the session!

-Focus Question: What are some common characteristics of mixtures and compounds that can be used to distinguish them?

-Hypothesis: Mixtures can be separated by physical means but compounds cannot be separated by physical means.

-Conclusion: My hypothesis is correct! (but not complete)
To add on, the substances in a mixture can be mixed in any proportion. No energy change takes place when a mixture is formed. A mixture has the properties of its constituent substances.
On the other hand, properties of a compound have different physical properties from its constituent substances. A compound cannot be separated by physical means. A chemical reaction takes place when a compound is formed when there is energy change.

WHAT WE DID
(here I took pictures of our investigation in progress with my lousy camera phone! :P)

Here are some of the materials we used for the whole investigation.

Shown in the picture on the left are iron fillings, sulfur powder, thongs, test tubes, crucibles, filter paper, magnets and bunsen burner.

We also used a tripod stand for heating and a stirrer for stirring the mixture and compound with water.

Of course, we had to put on our safety goggles (shown in picture) as a safety measure.





PART A:
We recorded our observations of the two substances, iron fillings and sulfur powder after putting them on a piece of filter paper.
The iron fillings appeared silvery-grey while the sulfur powder appeared bright yellow.
Then, we mixed the two substances together.
We then felt the bottom of the filter paper to feel if it was warm but it was just cold.
Next, we tried to separate the iron fillings from the mixture using a magnet and it worked!
We then put the mixture into a test tube filled with water. What we observed was that both substances were insoluble in water and that the sulfur powder is suspended near the surface of the water while the iron fillings sank to the bottom of the test tube. This was because the density of iron fillings is higher than that of sulfur powder.

Sulfur and iron.

Mixing them! 

Iron fillings being attracted by the magnet at the bottom of the filter paper.

PART B:

We mixed one spatula of sulfur powder and half a spatula of iron fillings in a crucible. Then, we set up the bunsen burner and left the crucible covered with a lid to heat for 10 minutes under a strong flame. As I missed last week's practical, I did not know how to use a bunsen burner at all and I was pretty lost. Luckily my partner patiently explained to me the steps involved in setting it up, making me feel much more confident of using it. 

After heating, we allowed it to cool, and we got a black hard solid substance in the crucible. 

The compound did not separate iron from sulfur when we used a magnet. Neither did the two constituent substances separate when placed into the test tube with water. The black compound was also insoluble in water. 

Heating up the mixture under a strong flame

After 10 mins of heating

Along the lesson, I came to learn that this compound is known as iron sulphide and I actually googled for it's chemical formula, just out of curiosity. So it's FeS. Then I got really confused. I came across another term, iron sulphate. I have not the slightest idea which is which and how they are different but I think I will probably find out soon. 

Extra stuff I've learnt also include that adding too much iron will cause the final compound to have excess iron fillings. 

Some reflections I have for the day...

I feel that reading instructions carefully is very important. Another group in class added one spatula of iron fillings into the crucible instead of the half spatula which was specified. Although it was good that everyone could learn something out from their mistake (about how the final compound would be affected if there were more iron fillings), it could be really dangerous if there was a harmful chemical reaction that would take place whenever there were excess substances. I also think that I should be more accurate and alert while doing the experiment. While setting the crucible to heat, I did not take note of the time we started heating but luckily, we quickly realised that we forgot to watch the time and tried to start counting from where we left off. I think it's always better to be accurate and precise.

I've learnt so much from such a simple science practical and I could finally try it out for myself to make compounds and mixtures. I'm looking forward to the next science practical! 

Theory Lesson on 14/1/13

Today in class I learnt about what elements, atoms and compounds are. 

Elements are made up of only one type of atom while atoms are the smallest particle that retains the chemical properties of the substance. Compounds are made up of two or more atoms chemically bonded together. 

In addition, I learnt that the Periodic Table is classified into groups and periods. Groups are the vertical columns and they number from I to 0/VIII. Periods are the horizontal rows that number from 1 to 7. 

Actually, although I've heard of what elements, atoms and compounds are, I was really confused at the start. I was not sure of what exactly was the difference between the elements and atoms, since both have got to do with atoms, I would mix the two up, thinking that they are almost the same thing. However, after being given an analogy in class today, all my confusion were cleared at once.

The analogy was that each paperclip is an "atom". When they are connected together, the string of paperclips is an "element". 

I find this analogy really helpful, and I feel that by using analogies, I can understand much better. So I hope that there will be more interesting analogies in class to aid my understanding in Chemistry.

Introducing Me

Hello I am Eleanor from Class 203 :D
Welcome to my Chemistry journal where I record down my reflections and what I've learnt.

Taken from Google Images.

There, here's a funny meme. I think it's funny. I hope Chemistry is fun. I find Chemistry interesting :D I'm looking forward to learn more stuff about Chemistry!