ATOMIC STRUCTURE

ATOMIC STRUCTURE

The atom consists of two important parts or zones: the internal zone and the external zone.

1. Internal Zone
 In the Internal Zone is the nucleus, which is the central part of the atom. Here we find almost the entire mass of the atom. In this part, the most stable atom particles are located, we are talking about the protons which have a positive charge, and neutrons that are particles that have no electric charge, it means they are neutral.

Protons

They are positive electric charge particles. Its charge is relative and it is represented by (+1) and its absolute charge is +1,6.10 ^-19 Coulomb.

The mass of a proton is 1,672.10 ^-24g. Note that its mass is taken as the atomic mass unit (AMU), which is equivalent to 1/12 of the mass of carbon-12. The mass of a proton is approximately equal to the mass of a neutron.All atoms of the same chemical element have the same number of protons in the nucleus. This number, which characterizes each element and distinguishes it from others, is called the atomic number and is represented by the letter Z.

Neutrons

A neutron is a subatomic particle, which is also found in the atomic nucleus.

The mass of a neutron is 1,675.10^-24g, which is approximately equal to a mass of a Protron.

The neutron has no net electrical charge unlike the positive electric charge of a proton. Its relative charge is represented by (0).

The neutron is characterized for being a good disintegrator agent. The number of neutrons in an atomic nucleus determines the isotope of the element.

The neutron consists of three quarks, one up quark  and two down quarks.

Mesons

These particles are also found in the nucleus and avoid the repulsive force that is caused by the protons.This particle is produced from certain nuclear reactions or cosmic ray bombardment.

 Its mass is intermediate between the proton and electron. Although it has equal charge to the charge of the electron, its mass is 207 times higher.

Mesons are unstable particles which are characterized by rapidly disintegrate, it means about two millionths (0.000002) os a second, after which other subatomic particles as the positron and neutrino are produced.

*Positron
  
Its electrical charge is equal to the one with the electron but positive; and its mass is identical to the electron. In that sense, it is said that the positron is the antiparticle of the electron. It is also known as antielectron.

In the called antiparticles, we find the positrons. That is, the antiparticles are the counterpart of the particles; and although their masses are identical, the electrical charges are reversed (positive / negative, negative / positive).

Antiparticles as, in this case positrons, form a type of matter called antimatter, as well as the particles belongs to the ordinary matter. 

The reaction e + + e- → γ + γ is known as positron-electron annihilation. In this nuclear annihilation process they become gamma rays, which is energy.

*Neutrino

 Elementary particle that has no electric charge, ie it is neutral and its mass is zero, at rest. Its mass is lower than 0.05% the electron.

Nowadays, it is believed that the mass of neutrinos is below a billionth of the mass of a hydrogen atom and its conclusion is based on the analysis of the distribution of galaxies in the universe whereby it is stated, is the measure far more accurate of the neutrino's mass.

The neutrino is an elementary particle belonging to the family of the electron. Neutrinos are particles produced in large quantities in the thermonuclear processes that take place inside stars like our sun. It is estimated that we receive from our Sun a flow equivalent to ten billion per cm² per second.

The determination of the mass and other physical characteristics of the neturinos come to be a big problem for students of subatomic particles as they interact very weakly with matter and are therefore difficult to determine. Its interaction with other particles is minimal, because they pass through the ordinary matter without hardly disturbing. 
These subatomic particles are fermionic type, without charge and spin 1/2. The mass of the neutrino has consequences for important consideration in the standard model, as this implies the possibility of transformations between the three types of neutrinos in a phenomenon known as neutrino oscillation.

Apparently, neutrinos are not affected by strong electromagnetic or nuclear forces, but by the weak nuclear force and gravity.


2. External Zone
 In this part of the atom we find the electrons, which orbit the nucleus and form an electron cloud that surrounds it.

Electrons

The relative charge of an electron is -1 and the total charge is -1,6.10 ^-19 Coulombs. They have a charge equal to the proton, but opposite sign, that is, negatively charged. If you are given the value a.m.u. mass is given the value of 0, however this does not mean that its value fully acquire this value, but is negligible compared to the proton. The absolute mass of an electron is 9,1.10^-28g and the mass of an electron is 1846 times lower than that of a proton (mean = 1/1846 mp +). Here, they arranged on different levels, orbit the nucleus.


ATOMIC NUMBER (Z) OR CHARGE NUMBER

It is the number of protons found in the atomic nucleus of an element.

  Z = number of protons = # P⁺

When an atom is electrically neutral, then:

  Z = number of protons= # P⁺ = # e^-


 Where:

 Z = # P⁺    :   Number of protons

# e^-            :   Number of electrons

Note that Z has a unique value for each element of the Periodic Table, so that if Z is known, then we have the identity of the element.

For example:

Element	Z	# P	# e-
Carbon	6	6	6
Hydrogen	1	1	1
Oxygen	8	8	8

 
MASS NUMBER (A) OR NUCLEON NUMBER

This indicates the sum of the number of protons and neutrons that are in the atomic nucleus of an element.

                      A = # P⁺ + # n^º
Where:
 
-    A                  :    Mass number or nucleon number 

-   # P⁺   =  Z   :   Atomic number or number of protons 

-   # n^º    =  N  :   Number of neutrons  

So:

                        N = A - Z
                                                                                                    A> Z
 It should be noted that atoms are electrically neutral, because they have equal numbers of protons and electrons. Thus, the atomic number also matches the number of electrons.


CHEMICAL ELEMENT

A chemical element or element is a set of atoms that have the same number of protons in their nucleus, which means that they have the same atomic number (Z).

                                                   

Element	Symbol
Carbon	C
Hydrogen	H
Oxygen	O
Iron	Fe
Gold	Au

SYMBOLIC REPRESENTATION OF ATOMS

Where:
 
  E    :  Chemical element
  A    :  Mass number or nucleon number
  Z    :  Atomic number or number of protons
  N   :   Number of neutrons

N = A – Z

 A > Z

# n^º  =  N  = 12

ION

An ion is an atom or molecule with a net positive or negative electrical charge.

Anion.- It is formed when the atom gains electrons, then it is negatively charged.

* Example:

Z = # P⁺ :  16

    ^{# e-   = 16 + 3}                         
   
∴  # e^-  : 19

Cation.- It is formed when the atom loses electrons, then it is positively charged.

* Example:

Z = # P⁺ :  26

    ^{# e-   = 26 - 3}                         
   
∴  # e^-  :  23


Illustrative examples:

1. The mass number of an atom is three times its atomic number. If this atom has 48 neutrons, determine the number of electrons.

Solution:

Given an atom whose identity is unknown, we will represent it by "E".

According to the data that the problem gives us:

   A = 3Z

# n^º  = 48

We must remember that:

    # n^º = A – Z
→ 48 = 3Z – Z = 2Z
     48=2Z 
∴    Z=24

Due to the fact that this is a neutral atom, the number of protons and electrons are equal.

 Z = # P⁺ = # e^-  = 24                         
   
∴The number of electrons is 24

2. The species A^-1, B^-2, C⁺⁴, D⁺⁵ altogether have 132 electrons ¿How many electrons will the species A⁺¹, B, C^-3, D jointly have?

According to the problem the ions A^-1, B^-2, C⁺⁴, D⁺⁵ altogether have 132 electrons, then the Z of each species we assing the value of its corresponding lowercase letter, as shown below.

→ #e_T1 = (a+1) + (b+2) + (c-4) + (d-5) = 132

When we operate the variables we have:

a + b + c + d = 138..........(*)

But because the species modify their charges, we must adapt our solution to this. Furthermore, the problem asks us the number of electrons that they jointly have.

                               #e_T2 = (a-1) + b + (c+3) + d

                              #e_T2 =  a + b + c + d + 2 

But according to (*): a + b + c + d = 138

#e_T2 =   138 + 2 

Therefore, the total amount of electrons of the species with modified charges is 140. 

3.The difference of squares of the atomic mass and atomic number is equal to the sum of the atomic mass and atomic number. Find the number of neutrons. 

Solution:

They ask us N

Remember that N= A-Z

According to the data of the problem

 A²-Z² = A+Z

→(A-Z)(A+Z)=A+Z

    (A-Z)=A+Z/(A+Z)

    A-Z= 1
    A-Z=N

∴  N=1