The atomic number and mass number of an element are 15 and 31. a. What is the number of valence electrons in this atom? b. How many neutrons are present in this atom? c. Draw the orbit electron configuration of this atom.
Answer (1)
To answer this question, let's break it down into parts:
a. What is the number of valence electrons in this atom?
The element with an atomic number of 15 is phosphorus (P).
The atomic number tells us the number of protons, and in a neutral atom, it also equals the number of electrons.
Phosphorus has 15 electrons. The electron configuration for phosphorus can be determined by distributing these electrons in its atomic orbitals.
The electron configuration is: 1 s 2 2 s 2 2 p 6 3 s 2 3 p 3
The electrons in the outermost shell (third shell in this case) are the valence electrons. For phosphorus, this shell has two electrons in the 3 s orbital and three electrons in the 3 p orbital, making a total of 5 valence electrons.
b. How many neutrons are present in this atom?
The mass number of phosphorus is 31. The mass number is the sum of protons and neutrons.
Number of protons = Atomic number = 15
Mass number = 31
Therefore, number of neutrons = Mass number - Number of protons = 31 - 15 = 16
c. Draw the orbit electron configuration of this atom.
The orbit electron configuration shows the distribution of electrons around the nucleus in different shells:
1st shell: 2 electrons in the 1s orbital ( 1 s 2 )
2nd shell:
2 electrons in the 2s orbital ( 2 s 2 )
6 electrons in the 2p orbitals ( 2 p 6 )
3rd shell:
2 electrons in the 3s orbital ( 3 s 2 )
3 electrons in the 3p orbitals ( 3 p 3 )
Thus, the complete orbit electron configuration for phosphorus is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 3 , which is consistent with having 5 valence electrons in the 3rd shell.
