chemistry - fundamental chemistry and atoms C1.1

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Elements are made from only one type of atom. Atoms are the smallest indivisible particle.The periodic table is a chart of all the elements arranged in increasing atomic number.

Atoms contain

-nucleus ( this contains protons and neutrons)
-Electron cloud ( contains electrons


These are called sub-atomic particles

Protons - found in nucleus and are POSITIVELY charged

Neutrons - found in nucleus and have NO charge

Electrons - found in Electron cloud and are NEGATIVELY charged

Atomic number in an element contains the number of protons in the nucleus

Atomic Mass number in an element contains the number of protons and neutrons altogether

find the total amount of protons, neutrons and electrons you need to add the atomic number and mass number before subtracting to find protons and neutrons and the remainder of electrons

Chlorine 35 square from the periodic table. The mass number (35) is top-left. The atomic number (17) is bottom-left. (

In this example the atomic number is 17 and the mass number is 35. This means that each of these atoms has:

17 protons

35 protons and neutrons = 18 neutrons

17 electrons

There are the same amount of protons and electrons because their charge cancel each other out so the amount has to be equal

arrangement of electrons

Electrons are found in the electron cloud on orbits or shells

The maximum of electrons in the 1st shell = 2

the maximum of electrons in the 2nd shell = 8

maximum of electrons in the 3rd shell = 8


The amount of electrons in the outer shell represents the elements group in the periodic table


Beryllium has 2 electrons in its outer shell so it is in Group 2

The amount of shells in an atom represents its period in the periodic table


Chlorine has 3 shells therefore it


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