For the last few days, we have discussed on the topics of “Acids, Bases & Salts” (Day 2 & Day 3). Today we are going to discuss a very basic but Important Sec 3 Chemistry Topic on “Atomic Structure“.

It is essential that all chemistry students must know this topic very well, in order to handle the rest of chemistry topics. Let’s look at some key points:

Atoms consists of 3 types of particles:

• Protons (+ve charge)
• Neutrons (Neutral)
• Electrons (-ve charge)

Protons and Neutrons are located inside the Nucleus of the atom while Electrons are arranged in Shells surrounding the nucleus. Each shell can hold a maximum number of electrons as shown below:

• Shell 1: 2
• Shell 2: 8
• Shell 3: 8

The electrons that are furthest away from the Nucleus is called the Outermost Shell Electrons or Valence Electrons. These electrons is very important because they are used to form Chemical Bonds.

• Metals tend to fewer outer shell electrons – 1, 2 or 3 electrons
• Non-metals tends to have many outer shell electrons

Number of Protons in an atom is called the PROTON NUMBER.

Number of Protons + Neutrons in an atom is called the NUCLEON NUMBER.

The number of Protons = number of Electrons, and bcos of this, the +ve and -ve charges balance each other are all atoms are Neutral.

Isotopes is another important term you would need to know for GCE O Level Chemistry (also IGCSE, IB and IP Chemistry).

Isotopes are atoms of the Same Element with same number of Protons (and thus Electrons) but different number of Neutrons.

Isotopes have slightly different physical properties but have identical chemical properties because they have the same number and arrangement of Electrons.

Now, let’s try out some O Level Chemistry – type questions:

Question 1: Based on topic “Atomic Structure”

Which element has an isotope that does not contain neutrons?

a) Helium
b) Hydrogen
c) Neon
d) Nitrogen

and

Question 2: Based on topic “Atomic Structure”

An atom of Ne-20 loses two protons and two neutrons from its nucleus and forms the atom X.

a) What would be the number of protons and neutrons in the atom of X formed? (2 mark)
b) What is the symbol for X, including the proton and nucleon number? (1 mark)

and

Question 3: Based on topic “Atomic Structure”

What do the electronic configurations of the alkali metals (Group I elements on the Periodic Table) have in common? (1 mark)

Attempt the above questions and leave your answers and reasonings in the “Leave A Reply” section below.

Look forward to your participation. =)

PS: If you have any burning question that would like us to discuss on this humble chemistry blogsite, please do not hesitate to email us.

Stay tuned for the next post!

In yesterday’s post on “O Levels Chemistry Tips Blog Marathon – Day 1″, i have given you the links to all the O Levels Chemistry Exam-Based Questions that we have discussed in this Chemistry Blogsite for Year 2008 as well as Year 2009. These includes Chemistry Tips and Exam Strategies on the tougher topics in O Levels Chemistry, with numerous participative discussions by readers of this blog.

Let’s continue Day 2 of this O Levels Chemistry Tips Blog Marathon with more O Levels Chemistry Exam-based questions, in order to prepare students for the Mid-Year Examinations

We shall start with a basic but “BIG” topic known collectively as “ACIDS, BASES & SALTS“. Many students hate dislike these chapters because they are very content based (i.e. lots of chemical and physical properties they need to know) and they are lost unsure what is required for them to know in order to score well for O Levels Examinations.

Just like going for soccer competition, the team (and players) would need to know the rules of the game first. As such, it is important that students know the learning objectives (aka what can be tested).

Learning outcomes for Acids, Bases & Salts are:

(Source: http://www.seab.gov.sg/SEAB/oLevel/syllabus/school/2009_GCE_O.html )

Acids and bases

(a) describe the meanings of the terms acid and alkali in terms of the ions they produce in aqueous solution and their effects on Universal Indicator

(b) describe how to test hydrogen ion concentration and hence relative acidity using Universal Indicator and the pH scale

(c) describe qualitatively the difference between strong and weak acids in terms of the extent of ionisation

(d) describe the characteristic properties of acids as in reactions with metals, bases and carbonates

(e) state the uses of sulfuric acid in the manufacture of detergents and fertilisers; and as a battery acid

(f) describe the reaction between hydrogen ions and hydroxide ions to produce water

(g) describe the importance of controlling the pH in soils and how excess acidity can be treated using calcium hydroxide

(h) describe the characteristic properties of bases in reactions with acids and with ammonium salts

(i) classify oxides as acidic, basic, amphoteric or neutral based on metallic / non-metallic character

(j) classify sulfur dioxide as an acidic oxide and state its uses as a bleach, in the manufacture of wood pulp for paper and as a food preservative (by killing bacteria)

Salts

(a) describe the techniques used in the preparation, separation and purification of salts (methods for preparation should include precipitation and titration together with reactions of acids with metals, insoluble bases and insoluble carbonates)

(b) describe the general rules of solubility for common salts to include nitrates, chlorides (including silver and lead), sulfates (including barium, calcium and lead), carbonates, hydroxides, Group I cations and ammonium salts

(c) suggest a method of preparing a given salt from suitable starting materials, given appropriate
information

Let’s check out some O Levels Chemistry-based questions:

Question 1: Based on topic “Acids, Bases & Salts”

Which of the following oxides reacts with an acid to form a salt but does NOT react with an alkali?

A. Aluminium oxide
B. Carbon dioxide
C. Copper (II) oxide
D. Zinc oxide

and

Question 2: Based on topic “Acids, Bases & Salts”

Titrating dilute sulfuric acid with aqueous potassium carbonate can be used to prepare potassium sulfate. Which conclusion can be drawn from this information?

A. Potassium carbonate is insoluble in water
B. Potassium carbonate neutralises sulfuric acid
C. Potassium sulfate is a base
D. Potassium sulfate is insoluble in water

>> Try out the questions and leave your Answers & Reasonings in the “Leave A Reply” section directly below.

The best way of learning is Experiential Learning, which requires 100% Participation! If you want to learn effectively and efficiently, the only way is to participate and not fear “failure” getting answers wrong.

It is only when you see your misconceptions and common errors made, that you can be aware of the common pitfalls, and avoid it in future. This is also how “Up Your Chemistry Grades Now!” chemistry guidebook is all about.

PS: We will come in to give our suggested answers and thought-process very shortly.

PPS: Leave your comments below. I would love to hear from you.