Reading: Properties of protons, neutrons and electrons

English in chemistry 1 – 2017 
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 
 
 
2 
neutral. The total number of protons and neutrons in an atom is called the mass number, A. 
The number of neutrons, the neutron number, is A-Z. 
An electron carries an atomic unit of negative charge, a proton carries an atomic unit of 
positive charge, and a neutron is electrically neutral. The table below presents the charges 
and masses of protons, neutrons, and electrons in two ways. To present the composition of 
any particular atom, we need to specify its number of protons (p), neutrons (n) and electrons 
(e). 
The atomic mass unit is defined as exactly of the mass of the atom known as carbon-12 
(read as carbon twelve). An atomic mass unit is abbreviated as amu and denoted by the 
symbol u. As we see from the table, the proton and neutron masses are just slightly greater 
than 1 u. By comparison, the mass of an electron is only about 1/2000th the mass of the 
proton or neutron. 
Atoms that have the same atomic number (Z) but different mass numbers (A) are called 
isotopes. The percentage of each isotope is the percent natural abundances. Some elements, 
as they exist in nature, consist of just a single type of atom and therefore do not have 
naturally occurring isotopes. Aluminum, for example, consists only of aluminum-27 atoms.
Table: Properties of three fundamental particles 
Electric charge 
Mass 
SI (C) 
Atomic
SI (g) 
Atomic (u)
*
Electron 
-1.6022 × 10
-19
-1
9.1094 × 10
-28
0.00054858 
Proton 
+1.6022 × 10
-19
+1
1.6726 × 10
-24
1.0073 
Neutron 
0 
0
1.6749 × 10
-24
1.0087 
*u is the SI symbol for atomic mass unit (abbreviated as amu) 

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