Atoms and atomic theory

English in chemistry 1 – 2017 
TS. Nguyễn Tuyết Phương – TS. Trần Thu Phương 
 
 
1 
Lesson
 1. 
ATOMS AND ATOMIC THEORY
 
1.1 Listening: What is an atom? 
Complete the paragraph by filling the blanks 
 
Atoms make up all of the earth’s matter. …(1)… can be broken down into three basic 
components: positively charged protons, negatively charges electrons, and neutrally charged 
neutrons. The number of these …(2)… and their arrangement determines the atom’s 
elemental properties. Here we have a helium atom. Helium atoms consist of two …(3)…, 
two neutrons, and two electrons. The nucleus at the center of the atom is made up protons 
and neutrons. The nucleus is relatively small in relationship to the rest of the atom. In fact, if 
an atom were the size of a football stadium, the nucleus would only be as big as a pea. The 
remainder of the atom’s volume is made up …(4)… with electrons orbiting around the 
nucleus. While the electrons orbiting the nucleus occupy a relatively vast amount of space 
and comprise most of an atom’s volume, they have virtually zero mass protons and …(5)… 
on the other hand although very small contribute most of the mass of an atom.
Electrons are arranged in the electron cloud by the distance of their orbit from the nucleus. 
These …(6)… layers are also referred to as shells. Each shell can hold only a certain 
number of electrons. The exact number of possible electrons per shell is defined by a rule of 
quantum mechanics stating that each orbit is filled when its electron count equals …(7)… 
times N squared or 2n squared where N is the number of shells away from the nucleus for 
which you are calculating the maximum number of electrons, also known as the principal 
…(8)… number. To calculate the number of electrons in in the first shell, you would use the 
equation 2 times 1 squared which is 2 times 1 or 2 electrons. For the second shell, it would 
be 2 times 2 squared or 2 times 4 to give eight …(9)…. For the third, two times three 
squared or two times nine equals eighteen electrons. And for the fourth shell, it would be 
two times 4 squared or 2 times 16 yielding 32 electrons and so on. …(10)… may have up to 
7 shells though each shell may not have its full allotment of electrons. This formula can be 
used to calculate the theoretical electron capacity for elements having a maximum of seven 
shells.