ATOMIC STRUCTURE

ATOMIC STRUCTURE

from Femosky110 on 06/12/2020 01:05 PM

STRUCTURE OF THE ATOM
Matter is anything that has mass and occupies space. Atoms are fundamental building blocks of matter that cannot be further divided by any chemical means. What are elements?

 

Elements are constituents of matter. There are 92 natural elements. Elements like hydrogen, carbon, nitrogen and oxygen are elements that make up the majority of living things. Other groups of element that exist in living things are: magnesium, calcium, phosphorus, sodium, potassium.

Many elements were discovered before the late 1800's. A Russian scientist Dmitri Mendeleev then proposed an arrangement of elements based on their atomic masses. In the modern time, elements are no longer arranged based on their atomic masses but according to their atomic numbers.

The word atom is a derivative of the Greek word atom which means undividable. The Greeks came to a conclusion that matter could be further divided into particles that are too tiny to be seen with the naked eye. These tiny indivisible particles of matter were referred to as atoms.

An atom is made up of three types of particles:

• Protons

• Neutrons, and

• Electron.

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The nucleus of an atom is made up of protons and neutrons. The electron of an atom resolves round the nucleus of an atom in an orbit known as shells.

Neutrons are neutral and have no electrical charge while protons and electrons are electrically charged. While Protons are positively charged and have a relative charge of +1, electrons are negatively charged with a relative charge of -1.

The number of protons in the nucleus of an atom is known as its atomic number. Atoms are arranged in atomic number order in the periodic table while electrons are arranged in energy levels or shells. Each energy level holds a definite numbers of electrons.

The electronic structure of an atom is an explanation of the manner the electrons are arranged, which can be demonstrated in a diagram or through numbers. The position of an element in the periodic table and its electronic structure interrelated.

The atomic mass of an element is greatly determined by the number of protons and neutrons in its nucleus. For instance, in a mass number of 150; 149 lbs which equivalent to 15 oz is protons and neutrons while only 1 oz. is the electron's mass. The mass of an electron is extremely small - 9.108 X 10-28 grams.

It is the number of protons in an atom that establishes the atomic number. For example, Hydrogen is with an atomic number of 1.The number of protons in an element is invariable (example, the number of proton in Hydrogen (H) =1 and that of Uranium (Ur) = 92 but the number of neutron may well differ, therefore the mass number (protons + neutrons) of an element could differ.

A particular element may have differing numbers of neutrons; the different forms of an element with the same number of proton but with differing numbers of neutron are referred to as isotopes. Isotopes have the same chemical properties but the physical properties of a number of isotopes might be different.

Some isotopes are radioactive in nature. This means that give out energy while they decompose and break down to a more stable form. This gives rise to another element.

Half-life of a radioactive element is the time that it takes for half of the atoms of that element to decay into stable form. An example of element that exhibits isotopy is oxygen. The element-Oxygen with an atomic number of 8 may possibly have 8 or 9, or 10 neutrons.

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Atomic Symbols and Isotopes
The atom of every element is composed of electrons, protons and neutrons. Atoms of the same element possess the same number of protons and electrons but the number of neutrons can vary. When the neutrons vary such elements are referred to as isotopes. Due to these isotopes, it got crucial to formulate a notation to differentiate an isotope from the other. This notation is known as the atomic symbol. The atomic symbol is usually denoted with three different letters:

1. The X: This is used to represent the element.

2. The A: This is a symbol that represents the atomic number. This is the number of protons situated on the left side of letter A as a subscript.

3. The Z: This is used to denote the mass no. The mass number is equal to the number of protons and neutrons in the isotope usually placed on top of letter Z as a left superscript.

Relative atomic mass (Ar) of an element is the ratio of the average mass of atoms of that element to 1/12 of the mass of carbon-12 isotope.

IUPAC's definition of Relative atomic mass:
An atomic weight or relative atomic mass of an element is the ratio of the standard mass per atom of the element to 1/12 of the mass of an atom of 12C.

Relative atomic mass scale
The mass of atoms and other tiny particles is calculated on the atomic mass scale as a relative number put side by side the carbon atom. The carbon 12 atom is allocated with the value of exactly 12.0000 on the scale and the whole thing else is calculated with respect to that figure.

Carbon atom Magnesium atom Hydrogen atom
mass = 12 mass = 2 x carbon atom mass = 1/12 x carbon atom
The magnesium atom has double the atomic mass of the carbon atom, so a magnesium atom has a relative mass of 24.

3 helium atoms have atomic mass equivalent to the mass of a carbon atom. This means that each of the 3 helium atoms has a relative atomic mass of 4. The relative atomic mass of an element can either be written as Ar or RAM for short.

Relative molecular mass

Molecules are merely groups of atoms. Therefore they are as well measured on the relative mass scale with carbon 12 just like in relative atomic mass.

Hydrogen atom Oxygen atom water molecule
mass = 1 mass = 16 mass = (2 x 1) + 16 = 18
A water molecule for example has a mass of 3/2 times relative that of a carbon 12 atoms, consequently the relative molecular mass of water is equal to 18.

The relative molecular mass of a substance is obtained by adding up the relative masses of all the atoms that make up a molecule of that substance.

All masses are calculated relative to the mass of a 12C isotope = 12.0000 atomic mass units.

Since relative molecular mass is a comparative calculation, it is not denoted with any unit.

For instance: Benzene has the molecular formula C6H6

A benzene molecule contains 6 carbon atoms and 6 hydrogen atoms.

The relative molecular mass = (6 x relative atomic mass of carbon) + (6 x relative atomic mass of hydrogen)

The relative molecular mass of benzene = (6 x 12) + (6 x 1) = 78

The relative molecular mass of an element can either be written as RMM or Mr for short.

Mole:
The mole is the amount of substance that contains as many "elemental particles - atoms, molecules, ions, electrons as the number of atoms in 12g of carbon-12 isotope.

1 mole of a substance is equal to 6.022 x 1023 items

Subatomic Particles of an atom and their properties

All atoms are composed of three subatomic particles: Protons, neutron and electrons.

The properties of these three sub atomic particles are tabulated below:

Particle Charge Mass (g) Mass (amu)

Proton +1 1.6727 x 10-24 g 1.007316
Neutron 0 1.6750 x 10-24 g 1.008701
Electron -1 9.110 x 10-28 g 0.000549
What we have used in the above table is a unit of mass called the atomic mass unit (amu). This is a better unit to use than grams when discussing masses of atoms. It is defined with the intention that both protons and neutrons have a mass of just about 1 amu. The significant points to remember are bulleted below:

• Protons and neutrons have roughly the same mass, while the electron is more or less 2000 times less heavy.

• Protons and electrons bear charges of equivalent size, but opposite charge. Neutrons have no charge ie they are neutral.

It was at one time believed that protons, neutrons and electrons were spread out in a somewhat uniform fashion to form the atom according to J.J. Thompson's plum pudding model of the atom but in reality the actual arrangement of the atom is rather different.

Electrons move about rapidly just about the nucleus and make up almost the whole volume of the atom. The quantum mechanics are essential to give details of the motion of an electron about the nucleus, but we can say that the sharing of electrons round an atom is in a spherical form.

The force that holds an atom together
The electron which is negatively charged is attracted to the nucleus which is positively charged by a Columbic attraction.

The protons and neutrons are mutually bonded in the nucleus by the strong nuclear force.

The relationship between the structures of an atom with its properties

Chemical reactions occur when there is either a transfer or a sharing of electrons between atoms of same or different elements. What this means is that the chemical properties of an element is for the most part reliant on the number of electrons in one atom of that element. Protons as well play a noteworthy role for the reason that the propensity of an atom to either lose, gain or share electron is reliant on the electrical charge of the nucleus.

Therefore, it is right to conclude that the chemical properties of an atom is reliant on the number of electrons and protons of the atom and the number of neutrons does not add to the chemical properties of that atom.

On the other hand, the mass and radioactive properties of an atom are reliant on the number of protons and neutrons in the nucleus.

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Atomic Number (Z) -The no of protons

Mass Number (A) - The no of protons] + [the no of neutrons]

The number of protons, neutrons and electrons in an atom are uniquely specified by the following symbol

ASyC, where:

• Sy = The symbol of an element like C, N, Cr) -defines the no of protons

• A = The mass number-[the no of protons] + [the no of neutrons]

• C = The net charge- [the no of protons] – [ the no of electrons]

For instance: A neutral boron 10 atom with 10B

A boron atom according to the periodic table has 5 protons in the nucleus Z = 5.

Since the boron atom is a neutral atom, the number of electrons ought to be equal to the number of protons, 5 electrons.

The mass number of Boron is 10. Therefore, the number of neutrons is A - Z = 10 - 5 = 5 neutrons.