Summary of the book : Democritus was the first that talk about the atom but as it seems obvious that anybody had believe him, but with the time many people start to believe and to prove that it was real. Democritus was named also as the " Laughing Philosopher " He then reasoned that changes occur when the many atoms in an object were reconnected or recombined in different ways. And also he said that the atoms have different shapes, sizes, etc.Many scientists start proving the theory of Democritus at the time that they prove the reason as an answer. And they create a " Thinker " that represents how much the scientist think about an answer.



John Dalton: Talk about the particles like Oxygen, Hydrogen and carbon. Example: If 1 gram of substance a reacts with 8 grams of substance b 2 grams of substance a reacts with 16 grams of substance b, etc...
The law of definitive proportions applies when the elements reacting together on the same product. He has an experimenter and thinker. Dalton was experimenting with several reactions Question of Dalton: If you could make a with 3 grams of carbon and 4 grams of oxygen to make b also you need 3 grams of carbon but 8 of oxygen instead. Dalton asked himself: Why does b require twice more oxygen than a does? Why not can be 1.21 or, 0,97 of oxygen? Why a hole number like 2 ?? But as we know Dalton starts investigating the topic and he add more substances like c, d or e, but the difference continue being of 2, and he proposed a rule: When two elements react to from more than one substance and the same amount of one element ( like oxygen ) is use in each substance then the ratio of the masses used for the other element ( like nitrogen ) will be in small hole numbers.

Laws of Dalton:

Matter is made of tiny particles called atoms

Atoms are invisible. During a chemical reaction, atoms are rearranged, but they do not break apart, not are they created or destroyed.

All atoms of a given element are identical in mass and other properties.

The atoms with different elements differ in mass and other properties.

Atoms with one element can combine with atoms of another element to form compounds, in a given compound, however, the different types of atoms are always present in the same relatives numbers. 

Isotopes

I am gone to teach you about the isotopes:  Arsenic 76; Cobalto -60; Yodo 131; Radio 226 .
These is the basic information about Arsenic 76.
                           

 Name: Arsenic 
Symbol: As 
Atomic Number: 33 
Atomic Mass: 74.9216 amu 
Melting Point: 817.0 °C (1090.15 K, 1502.6 °F) 
Boiling Point: 613.0 °C (886.15 K, 1135.4 °F) 
Number of Protons/Electrons: 33 
Number of Neutrons: 42 
Classification: Metalloid 
Crystal Structure: Rhombohedral 
Density @ 293 K: 5.72 g/cm³ 
Color: Gray   

information of: http://www.chemicalelements.com/elements/as.html         

Cobalt 60 is a metal that is characterized by emitting energy in the form of rays called gamma when decaying radioactively. It is obtained from the Cobalt in its natural state, called Cobalt 59, exposing it to a neutron flux. These neutrons can be produced in large quantities in nuclear reactors.

information of: http://caebis.cnea.gov.ar/IdEN/CONOC_LA_ENERGIA_NUCX/CAPITULO_4_Difusion/LA_TECNOLOGIA_NUCLEAR/Cobalto_60.htm

Non-metallic element, symbol I, atomic number 53, relative atomic mass 126,904, heavier halogen (halide) found in nature. Under normal conditions, iodine is a black, lustrous, and volatile solid; Receives its name by its vapor of violet color.

Read more: http://www.lenntech.com/periodica/elementos/i.htm#ixzz4ZSaOTHIs
Also y find a new about the iodine 131: 
 In mid-January, scientists in France and Finland detected a slight increase in the radioactive iodine-131 isotope in Earth's atmosphere, but that amount did not pose a danger to human health.

The first country that detected this increase was Norway, although it did not publish any information on this. Subsequently, measurements were also altered in Poland, Czech Republic, Germany and Spain

New taken from: https://actualidad.rt.com/actualidad/231636-europa-atmosfera-nivel-yodo131-aumentar

Chemical element, symbol Ra, of atomic number 88. Radium is a rare radioactive element, found in uranium minerals in proportion of one part for approximately 3 million parts of uranium. From the chemical point of view, the radium is an alkaline earth metal and has properties very similar to those of barium

Read more: http://www.lenntech.es/periodica/elementos/ra.htm#ixzz4ZSbnvQ8f.