Structure of the atom Isotopes | CHAPTER 7 | Basic Science

Structure of the atom Isotopes – Introduction to fundamental concepts of Biological Science including the organization and common characteristics of living matters, cell structures and functions, food production by photosynthesis, harvesting energy, mechanism of cells reproduction, genetics, evolutions, and Human Biology. Introduction to general chemistry including basic concepts about matter, atomic structure, chemical bonds, gases, liquid, and solids, solutions, chemical reactions, acid, bases, and salt;

organic and biochemistry including hydrocarbons and their derivatives, carbohydrates, lipids, proteins, enzymes, vitamins, and minerals, nucleic acids; principles of physics and applications to nursing including gravity and mechanics, pressure, heat and electricity; nuclear chemistry and nuclear physics, effects of radiation on human beings, and protection and disposal. The aim of the course is to acquire knowledge and skills in general biological science, general chemistry and physics.

Structure of the atom Isotopes

Atomic Structure of Matter:

Atoms are made up of tiny parts known as sub-atomic particles. In the center of an atom is a nucleus made up of protons (positively charged) and neutrons (no charge). Outside the nucleus is a cloud of tiny electrons (negatively charged) that are much smaller than any of the other sub- atomic particles.

Electrons
The electron is by far the smallest out of these three particles. At 9.11 x 10-31 kg, carrying a negative electrical charge, the electron is too small in size to be measured using the current techniques. Usually, the electrons are bound to the positively charged nucleus due to the attraction created from the opposite electric charges. If the electrons carried by an atom are more or fewer than its atomic number then the atom becomes respectively negatively or positively charged as a whole. A charged atom is known as an ion.

Protons
The protons carry a positive charge and at 1.6726 x 10-27 kg, have a mass 1836 times that of the electron. The atomic number represents the number of protons in an atom.

Neutrons
At 1.6929 x 10-27 kg, neutrons are the heaviest of the three constituent particles of an atom. The neutrons carry no electrical charge and have a free mass of 1839 times the mass of the electron.

Neutrons and protons have comparable dimensions although the surface of these particles is not clearly defined. The electrons are truly elementary particles with no internal structure. However, both protons and neutrons are composite particles composed of elementary particles called quarks. There are two types of quarks in atoms, each having a fractional electric charge. Protons are composed of two up quarks (each with charge +2/3) and one down quark (with a charge -1/3). Neutrons consist of one up quark and two down quarks.

Properties of Atoms and Molecules:

Atomic number:
One of the most important characteristic of an atom is its atomic number (usually denoted by the letter Z), which is defined as the number of units of positive charge (protons) in the nucleus. It is the number of protons in the nucleus that determines the chemical properties of an atom.

Atomic mass:
Atomic mass of an atom is the sum of the mass of protons and neutrons. The mass number is denoted by A.

Electric Charge:
Normally an atom is electrically neutral. But it can gain or lose electrons. Those atoms that gain or lose electrons are called ions. They have an electric charge. Atoms that lose electrons become positive ions and the ones that gain electrons become negative ions.

Radioactivity:
In some atoms, the nucleus can change naturally. Such an atom is radioactive. In nature, there are some elements that are radioactive, like uranium or radium. In labs, scientists can produce radioactivity by bombarding atoms with smaller particles.

Relative atomic mass:
Relative atomic mass of the atom of an element is defined as the average masses of the atom, as compared to 1/12th the mass of one carbon-12 atom.

Formula unit mass:
The formula unit mass of a substance is a sum of the atomic masses of all atoms in a formula unit of a compound.

Molecular mass:
The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance. It is therefore the relative mass of molecule expressed in atomic mass units (u).

Dalton’s Atomic Theory:

Dalton’s atomic theory states:-

• Matter consists of definite particles called atoms.
• Atoms are indestructible.
• An element’s atoms are all alike.
• Atoms of different elements have different masses.
• When forming a chemical compound, atoms of the reacting elements combine in a definite ratio, (i.e., law of multiple proportions).

Atomic Number

According to Rutherford.
The proton as the nuclear particle of unit positive charge. An atom’s number of nuclear protons is called its atomic number. All atoms of an element have the same number of protons, i.e.

• Nuclear charge = number of protons = atomic number

The mass number of an atom is its number of protons and neutrons in the nucleus, i.e.,

• Mass number = number of protons + number of neutrons

Isotopes:

Isotopes are atoms that have the same number of protons and electrons but different numbers of neutrons and therefore have different physical properties

or

All atoms of an element are alike in that they each contain the same number of protons. Isotopes are atoms of the same element that differ in their number of neutrons.

Isotope Examples

Carbon 12 and Carbon 14 are isotopes of carbon, one with 6 neutrons and one with 8 neutrons (both with 6 protons). Carbon-12 is a stable isotope, while carbon-14 is a radioactive isotope (radioisotope).

Atomic Weight:

Atomic weight is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. It is the weighted average of the masses of naturally-occurring isotopes.

The table provides a list of chemical elements and their atomic weights

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