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.
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
Reply
sean Reply:
October 13th, 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
Reply
how did u get the answer for number 2??
Reply
sean Reply:
June 2nd, 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
Reply
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
Reply
sean Reply:
May 5th, 2010 at 11:45 pm
Well Done!
Keep Learning! =)
Reply
[...] we have discussed on the atomic number (Z) and atomic mass (A) that are related to a chemical [...]