O Level Chemistry – Atomic Structure

Today’s tip is about the difference between Atomic Number (Z) and Atomic Mass Number (A).

I realised that some students are confused between the? 2 numbers that normally comes together with the Chemical Symbols, in the Periodic Table. It is imperative for Chemistry students to know this topic well, as this is the easiest topic to score in Chemistry exams.

In the periodic table, a symbol is used to designate an element, and each atom is characterized by a value of A and Z. The atomic number (Z) is at the lower left of the symbol, and atomic mass number (A) is at the upper left.

Atomic Number (Z): Its value is equal to the number of protons in the nucleus.

Atomic Mass Number (A): Its value is equal to the number of protons plus the number of neutrons in the nucleus.

Chemically, an atom is made of three species: Neutrons, Protons, and Electrons.

The nucleus of the atom contains the protons and neutrons. For most chemists, they focus their attention on the electrons, which govern the chemical properties and reactivity of any molecule.

Now, let’s check out a couple of questions to see how much you understand.

Question 1:
Which one of the following statements is correct?
Carbon has atomic number 6 and mass number 12. This means that in the nucleus of this atom there are:
a) 12 protons and no neutrons
b) 2 protons for every neutrons
c) 2 neutrons for every proton
d) Equal number of protons and neutrons

Question 2:
Deduce the number of protons, neutrons and electrons in an atom of Antimony-122.

Question 3:
In the Periodic Table, the elements are arranged in order of
a) atomic number
b) mass number
c) number of neutrons
d) number of isotopes

PS: I emphasized again that the best way to learn is to participate.

PPS: Leave down your suggested answers in the “Leave A Reply” section right below this post.

Sean Chua

Winners Education Centre Pte. Ltd.

Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students. If you want to have an enjoyable time learning Chemistry and being motivated to excel in Chemistry, contact me today at 98287357

Comments

sean says
February 7, 2013 at 12:37 pm
Hi Saif,
Thanks for your comment.
Yes, there are many archive blogposts on this topic called Atomic Structure.
Do a search for “Atomic Structure” on the top right hand corner of http://www.SimpleChemConcepts.com and you will be able to see all the archive posts.
All the best to your learning of basic Chemistry.
Sean 🙂
Saif says
February 4, 2013 at 9:03 pm
Hi,
Just wanted to know whether there is a similar topic and lesson on stiochiometry.
Thank you.
sean says
May 5, 2010 at 11:45 pm
Well Done!
Keep Learning! =)
Danyyal Ahmed says
June 7, 2009 at 12:10 am
Question 1:
Which one of the following statements is correct?
Carbon has atomic number 6 and mass number 12. This means that in the nucleus of this atom there are:
a) 12 protons and no neutrons
b) 2 protons for every neutrons
c) 2 neutrons for every proton
d) Equal number of protons and neutrons
Question 2:
Deduce the number of protons, neutrons and electrons in an atom of Antimony-122.
Question 3:
In the Periodic Table, the elements are arranged in order of
a) atomic number
b) mass number
c) number of neutrons
d) number of isotopes
ANSWERS:
D) equal number of protons and neutrons
2) protons: 51
electrons:51
neutrons: 71
3) atomic number
sean says
June 2, 2009 at 1:07 am
Hi Nazneen,
From the Periodic Table, you will find out the Antimony has Atomic Mass Number (A) to be 122 and an Atomic Number (Z) to be 51.
From those information, you can find the answers to be:
No. of Protons = Atomic Number = 51
No. of Electrons = No. of Protons = 51
No. of Neutrons = Atomic Mass Number – No. of Protons = 122 – 51 = 71
(since Atomic Mass Number = No. of Protons + No. of Neutrons)
Hope this explanations helps.
Let me know if you more clarification.
PS: Do check out other questions in this blog and participate to learn.
Cheers,
Sean
Master Trainer @ SimpleChemConcepts.com
Author of UP YOUR CHEMISTRY GRADES NOW! book
nazneen says
May 17, 2009 at 11:50 pm
how did u get the answer for number 2??
sean says
October 13, 2008 at 1:54 am
Hi Michelle,
Well Done!
All the Answers are correct!
Keep up the good work!
Sean
Master Trainer @ SimpleChemConcepts.com
Author of UP YOUR CHEMISTRY GRADES NOW! book
MICHELLE says
October 6, 2008 at 6:26 pm
Question 1:
Which one of the following statements is correct?
Carbon has atomic number 6 and mass number 12. This means that in the nucleus of this atom there are:
d) Equal number of protons and neutrons
Question 2:
Deduce the number of protons, neutrons and electrons in an atom of Antimony-122.
no. of protons: 51
no. of electrons:51
no. of neutrons: 71
Question 3:
In the Periodic Table, the elements are arranged in order of
a) atomic number