Composition of the atom (PROTONS, ELECTRON, MASS NUMBER, RELATIVE ATOMIC MASS)

Atoms have a definite structure. this structure determines the chemical and physical properties of matter. the atomic structure was not fully understood until the discovery of the neutron in 1932. the history of the discovery of the atomic structure is one of the most interesting and profound stories in science. in 1910, Rutherford was the first to propose what is accepted today as the basic structure of model of the atom.

Today, the Rutherford model is called the " planetary" model of the atom.

In the planetary model of the atom there exist a nucleus at the centre made up of positively charged particles called " protons" and electrically neutral particles called " neutrons". surrounding or "orbiting" this nucleus are the electrons.

In elements the number of electrons equal the number of protons.

This is a useful fact to remember. If the number of electrons does not equal the number of protons in the nucleus then the atom is an ion:

Cation: number of electron < number of proton

Anion : number of electron > number of proton

the nucleus of an atom is about 100,000 time smaller than the atom.

Nevertheless, the nucleus contains essentially all of the mass of the atom. In other to discuss the mass of an atom we need to define a new unit of mass appropriate to that of an atom. this new unit of mass is called the

" atomic mass unit" or amu (or Dalton). the conversion between the amu and gram is:

1 amu = 1.67 x 10 g. The mass , in amu, of the three particles is given in the table below:

            Properties of the sub-atomic particles

NAMES	SYMBOL	ELECTRICAL CHARGE	MASS (AMU)
Electron	e	-1	0.000549
Proton	p	+1	1.00728
Neutron	n	0	1.00867

Note that the mass of an electron is about 2000 times smaller than that of the proton

and neutron. Also note that the mass of the proton and neutron is close to 1 amu.

ATOMIC NUMBER

Atoms of each element contain an equal number of protons and electrons. The number of protons determines an element's atomic number (Z) and distinguishes one element from another. For example, carbon's atomic number (Z) is 6 because it has 6 protons. The number of neutrons can vary to produce isotopes, which are atoms of the same element that have different number of neutrons. the number of electrons can also vary across atoms of one element.

MASS NUMBER

An element's mass number (A) is the sum of the total number of protons and number of neutrons. the small contribution of mass from electrons is disregarded in calculating the mass number. this approximation of mass can be used to easily calculate how many neutrons an element has by simply subtracting the number of protons from the mass number. protons and neutrons both weigh about one atomic mass unit or amu. isotopes of the same elements will have the same atomic number but different mass number.

ISOTOPES AND RELATIVE ATOMIC MASS

Each chemical elements has its own unique atomic number full stop that means that all the atoms of any particular element must have the same number of protons (and therefore electrons) full stop so any atom of hydrogen has one proton, otherwise it wouldn't be hydrogen if the item has two products, it will be easier.

However, there is no reason why the number of neutrons can't be real. In fact, there are three types of hydrogen atom, each containing a different number of neutrons. We these isotopes of hydrogen. So isotopes are atoms of the same element that have different masses.

ISOTOPES OF HYDROGEN	PROTONS	NEUTRONS	ELECTRONS
HYDROGEN (PROTIUM)	1	0	1
DEUTERIUM	1	1	1
TRITIUM	1	2	1

An isotope is any of two or more forms of a chemical elements, that have the same number of protons in the nucleus, or the same atomic number, but having different number of neutrons in the nucleus, or different atomic weight.
There are 275 isotopes of the 81 Stable elements, in addition to over 800 radioactive isotopes and every element has known isotopic forms. Isotope of a single element possess almost identical properties. The chemical properties of an element are determined by its electronic structure.

Because isotopes have the same number, and therefore arrangement, of electrons, isotopes of an element undergo the same chemical reactions. The only difference is their mass. Isotopes are sometimes the name of the element, followed by the mass number. Thus the three isotopes of hydrogen would be:

RAM = (MASS OF ONE ATOM OF ISOTOPE)/MASS OF ONE ATOM OF CARBON-12

Therefore, the relative atomic mass of H is one, making it the lightest of all atoms. 

However, if you look up the mass elements in the data, you will find that chlorine has a relative atomic mass of 35.5. At first sight this seems a bit strange.
How can you have an atomic mass that is a fraction? After all, you can't get half a proton or half a neutral in an atom but the answer lies in the existence of isotopes. Chlorine exist as two isotopes chlorine 35 and chlorine 37.
When we calculate the relative atomic mass of an element we have to take into account the proportions of each isotope present. In a naturally occurring samples of chlorine, we find that 75% is chlorine 35 atoms and the other 25% is chlorine-37 atoms. Imagine you have 100 atoms of chlorine 75 will have a relative atomic mass
of 35 and 25 will have a relative atomic mass of 37.

Average atomic mass calculations

the average atomic mass of an element is a weighing average of the atomic masses of different isotopes of that element. The atomic weight of all the elements can be found on the periodic table. In order to calculate atomic will you multiply the percentage abundance of each isotope by the atomic mass of that isotope then
add the multiplication products together

RAM = (MASS OF ISOTOPE X % ABUNDANCE)/100

Average atomic mass= (mass number X % of isotope 1 + mass number X % of isotope) /100

carbon has an atomic number of 6, and two stable isotopes with mass numbers of 12 and 13, respectively. Its average atomic mass is 12.11

sample questions

1. What is an atom? what are atoms made of?

2. What are the similarities and differences between a neutron and a proton?

3. What is a “DALTON” how is it you in atomic mass?

4. describe the isotopes of hydrogen

5 .define atomic number, atomic mass and relative atomic mass.

6. Copper is listed on the periodic table as having a relative atomic mass of 63.5. Episode reference books in indicates 2 isotopes of copper, with relative masses of 62.93 and 64.93.Find the percentage abundance of each isotope.

7. magnesium has three isotopes, mg -24, mg -25, and mg -26.and the percentage of each in order is 7870 cent, 10.1 3%, 11.1 7%.
Calculate the relative atomic mass of magnesium