A SIMPLE VIEW OF ATOMIC STRUCTURE

A SIMPLE VIEW OF ATOMIC STRUCTURE

Hello  everyone today we are going  to  discuss ideals  about  atomic structure that  you may  have seen  back in  your chemistry  class rooms .

The sub-atomic particles

We have 3 sub-atomic particles Protons, neutrons and electrons.

Remark : Beyond A-level:  Protons and neutrons don’t in fact have exactly the same mass – neither of them has a mass of exactly 1 on the carbon-12 scale (the scale on which the relative masses of atoms are measured). On the carbon-12 scale, a proton has a mass of 1.0073, and a neutron a mass of 1.0087

The behavior of protons, neutrons and electrons in electric fields:

One  way to  distinguish between these particles is their behavior in the electric field .

Protons are positively charged and so would be deflected on a curving path towards the negative plate.

Electrons are negatively charged and so would be deflected on a curving path towards the positive plate.

Neutrons don’t have a charge, and so would continue on in a straight line.

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The nucleus

The nucleus is at the center of the atom and contains the protons and neutrons. Protons and neutrons are collectively known as nucleons.

Virtually all the mass of the atom is concentrated in the nucleus, because the electrons weigh so little.

TAKE Note from  here !!

Working out the numbers of protons and neutrons

Number  of protons  = ATOMIC NUMBER of the atom

The atomic number is also given the more descriptive name of proton number.

Number of protons  + number of neutrons  = Mass number of an atom

The mass number is also called the nucleon number.

This information can be given simply in the form:

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For the example above can you give me the proton number, neutrons number , atomic number and mass number ?

Solution

For the proton number  is easy  we just count   = 2 ( which is the same as atomic number )

For the neutron number will do some little math, we know that mass number =  protons + neutrons , right ?

Then from  there we can say   that  mass number – protons = neutrons

Therefore neutrons  = 4 -2 = 2,

For the  mass number you can just  read it above  🙂 .

NB: is to  note that the  neutron  number is not always the same as the proton number is just a coincidences that  it happened to be the same .

The atomic number is tied to the position of the element in the Periodic Table and therefore the number of protons defines what sort of element you are talking about. So if an atom has 8 protons (atomic number = 8), it must be oxygen. If an atom has 12 protons (atomic number = 12), it must be magnesium.

Similarly, every chlorine atom (atomic number = 17) has 17 protons; every uranium atom (atomic number = 92) has 92 protons.

Isotopes And Isotopy.

It can happened  that  the number of neutron can vary within small  limits , and  this is called isotopy . Isotopy is a phenomenon whereby atoms of an element have the same atomic number but different mass number. The difference in mass number is due to the different number of neutrons. Since we are talking about isotopy  we can’t  leave out isotopes which the simplest  form can be define as  “Isotopes are the elements that have the same atomic number (number of protons) and different mass number (number of neutrons)”.

NB:  we shall  take the calculation part later

Examples of isotopes

The electrons

Working out the number of electrons

Atoms are electrically neutral, and the positiveness of the protons is balanced by the negativeness of the electrons. It follows that in a neutral atom:

Number of electrons = number  of protons

So, if an oxygen atom (atomic number = 8) has 8 protons, it must also have 8 electrons; if a chlorine atom (atomic number = 17) has 17 protons, it must also have 17 electrons.

The arrangement of the electrons

The electrons are found at considerable distances from the nucleus in a series of levels called energy levels. Each energy level can only hold a certain number of electrons. The first level (nearest the nucleus) will only hold 2 electrons, the second holds 8, and the third also seems to be full when it has 8 electrons and so on .

To work out the electronic arrangement of an atom

• Look up the atomic number in the Periodic Table – making sure that you choose the right number if two numbers are given. The atomic number will always be the smaller one.
• This tells you the number of protons, and hence the number of electrons.
• Arrange the electrons in levels, always filling up an inner level before you go to an outer one.

e.g. to find the electronic arrangement in chlorine

• The Periodic Table gives you the atomic number of 17.
• Therefore there are 17 protons and 17 electrons.
• The arrangement of the electrons will be 2, 8, 7 (i.e. 2 in the first level, 8 in the second, and 7 in the third).

So  to summaries  what  we saw today,

We see that  the different  part  of the atom  are really  important  in O and A level  chemistry  , please everyone  should try  to  understand these before going ahead  .

If  you liked the  notes please say  thanks below  to encourage us 🙂

Special Thanks to chemguide