Salts and halides

We learnt that the neutralisation process of an acid and a base produces only salt and water. The definition of salt here are ionic compounds that result from neutralisation and are composed of a cation and anion, and is thus electrically neutral. The cation is usually a metal from the acid, while the anion is usually a non-metal base. There are different types of salts formed,  such as nitrite salts, base salts, acid salts etc. But the one specific one I am talking about today would be halides. Most salts are halides.The definition of halides would be a compound consisting of a halogen atom and another which is less electronegative than the halogen. The latter is usually a metal also. Examples of these would be sodium chloride, silver bromide etc. Like all salts, the cation is placed at the front of the chemical name. The halogen in this case is called the halide ions, which are negative. Thus these are usually called metal halides, which can be used in energy-efficient lamps. I came across this term in the powerpoint for revision and because it seemed interesting , I went to find out more on it. These has greatly improved my overall understanding on salts and I am glad that I learnt something more out of this.

Strength of acid and alkali

Today's Science lesson we covered about acids(produces H+ ions in water) and bases(produces OH- ions in water), and were given a worksheet to do.  There was a question about the meaning of strong and weak acids or alkalis. We were told to answer that strong acids or alkalis form more H+ or OH- ions when dissolved in water. However, I think that this answer is rather vague and seek for a definition or measurement of "strong". I found out that one way to determine this could be through  obtaining the enthalpy change of the substance. This is the amount of heat energy given out or taken in during a chemical reaction. When the acid or alkali molecules dissolve in water, they break up into different ions. A acid is usually made up of a non-metal(usually halides or halogens) and hydrogen ions, while an alkali is made up of a metal and hydroxide ions. For example, when hydrochloric acid dissolves in water, H+ and Cl- ions are formed. During this process, heat is needed to break the ionic bonds between the elements, and more heat would thus be used to break down the molecules completely into more H+ or OH- ions.Thus, it can be deduced that the greater the enthalpy change of an acid or alkali, the stronger it is. For example, the enthalpy change of a strong acid, hydrochloric acid is -74.84 kJ, while that of acetic acid is- 1.51kJ.  Ammonia, a weak alkali has a change of -30.50kJ, while potassium hydroxide's is -57.61kJ. The heat of reaction is either positive or negative, depending on whether it is exothermic or endothermic. I am glad that my own questioning has allowed me to learn out of the box, and I hope to continue doing so in future.


Blueprint for this topic:

Strong Acids= More H+ ions , Weak Acids= Less H+ ions
Strong Alkali=More OH- ions,  Strong Alkali=Less OH- ions
Acid+Metal=Salt+Hydrogen
Acid+Carbonate=Salt+Water+Carbon dioxide
Neutralisation: Acid+Base=Salt+Water
Base+Acid=Salt+Water
Base+Ammonium Salt=Salt+Ammonia+Water


Basic Information:

Thoughts on my Term 1 Test Performance.

To improve ourselves we must always review on ourself and what we have done. To do better for the upcoming next term, I would like to comment about my performance in this Term 1 Test 1. Scoring 34/40, or 85 marks, I am still behind many of my fellow classmates who scored around 35-38. In fact, around half of the class has passed this test with flying colors,and this indeed let me feel kind of left out and lagging. Anyway, it has been generally thought that this test was rather easy, and as long as you put in some effort, you will definitely soar high in this test. I think that the reason behind this score was that I had not put enough effort in my Science revision this term, largely due to the lack of time. I am rather weak in Maths, and had to spend more time on it as the test was on the day after the Science test. Thus I did not really had a comprehensive revision, and besides, I thought that I was rather relax on those few days before the tests. Luckily, I had prepared for my Science a few months ago., and have largely based on my memory and impression during the test.And that was when I did not memorise much content.Thus, I would say that my achievement this time round contained much of  the element of luck.Maybe I had to work on my management of my time. But looking at the score of my friends, I realized that importance of perseverance and diligence which would always prove worthwhile.Given the status quo I was in, I am really satisfied that I had obtained this result. However, I promise to strive harder for next term for greater heights and would do my best. Most importantly, out of all this test, I have realized what are the aspects I am weak in so as to allow me to upgrade myself, not the score of it.

Formation of Xenon Flouride

Regarding to the formation of compounds and bonds, I have discovered a interesting,additional fact and would like to share it here,which I also did it for my ACE too.The compound name xenon flouride certainly looks difficult but cool. Let us understand it then.As we know, xenon is an unreactive, stable noble gas,with the electronic configuration of 2.8.8, while flourine is a halogen with the configuration of 2.7. It is widely regarded that noble gases will not combine with other elements to form compounds. Why can this compound still form a covalent compound with the electronic configuration of XeF2(xenon flouride can still exist in many other forms). First of all, it would be due to the structure of the xenon atom. As xenon is located at the foot of its group, it has a large number of shells and are thus heavier than the lighter ones.Hence, the outermost electrons experience a shielding effect from the inner electrons that makes them more easily ionised, since they are less strongly attracted to the positively-charged nucleus. This results in an ionization energy low enough to form stable compounds with the most electronegative elements, fluorine and oxygen, and even with less electronegative elements such as nitrogen and carbon under certain circumstances. Ionisation energy is the force or energy needed for an atom to give up and remove its electrons. Electronegativity would then mean an atom's ability or tendency to attract electrons to itself to form a anion. Each element's has its own electronegativity represented by a value. It is classified that elements that have the electronegativity difference of 0.2-0.5 would form non-polar covalent bonds(where there is equal sharing of electrons), 0.5-1.6(polar covalent bonds,unequal sharing) and above which will belong to ionic bonds. Xenon's electronegativity is 2.60, while flourine's is 3.98. The difference would thus mean a non-polar covalent bond formed. For those who don't quite understand what I am discussing about, you can refer to the electronegativity table online. Nonetheless, after all this, you will find this extremely interesting.


                                      

Reflection on Term 1 Syllabus

After the end of Term 1 , I would like to reflect on my Science experiences this term. Basically ,we have been focusing on the study of the Periodic Table this term. As all of us know, the Periodic Table is also closely related to the study of electrons,atoms and properties of elements etc. Firstly, we would have to know the properties of an basic atom,what it contains etc.From the Periodic Table,we can deduce the proton and neutron numbers of an element and also its electronic configuration.  After knowing how to interpret the Periodic Table ,we will go into the more profound study of chemical bonds. In Sec 2,we are only introduced to two types of bonds formed between elements when they react, that is the ionic bonding and covalent bonding, formed dependently on the chemical properties of the elements,and thus we know the formation of compounds around us. I would like to say that the topic taught this term is extremely integral in our journey of learning Science as it lays the foundation of the study of chemical reactions in the coming years. By understanding this topic well, we will be able to predict easily what chemicals ,or reactants,we should combine to achieve a certain product. Through this topic,I am also be able to marvel at the infinite posibillities of Science as the different number of reactions between the 100 plus elements ranging from the common elements to the lanthanides, from the halogens to the alkali metals, are countless and unique. I also felt my interest in Science was piqued even more as this topic allows me to remove the qualms that I had last year about chemicals and elements. Last but not least, this topic is interactive and is thus interesting and easy to learn. For example, I found that I could easily remember the electronic configuration of elements easily without even memorising the periodic table like my friends. That makes it fun too.