Engineering Materials – Atomic Structure Introduction

All material things are made from atoms. There are different types of atom called elements. Well, as you know, an atom consists of electrons protons and neutrons. The number of electrons in outer shell gives us number of atom. Similarly, number of protons and neutrons are associated with atomic number and mass number of atoms. In this article, we will learn more about Atomic structure.

What is Atomic Structure?

Atoms are composed of electrons, protons and neutrons. Electron and protons are negative and positives charges of same magnitude 1.6 x  coulombs. Neutrons are electrically neutral. Every atom is made of nucleus consisting of protons and neutrons. This nucleus is surrounded by electrons. Read about Engineering Material – Normalizing

Protons and electrons are oppositely charges and neutrons have no charge. This means nucleus of an atom is always positively charged. An atom has neutral overall charge because it has same number of electrons as protons. Protons and neutrons have same mass. Electrons have such small mass that this can be taken as zero.

Proton and neutron are nucleons bounded by nuclear forces into atomic nuclei. However, neutron atom has same number of electrons and protons and neutrons and protons have very similar masses equal to 1 a.m.u each. On other hand, protons are positively charges particles of equal magnitude. Neutrons are neutral particles having no charge.

Following are basis terms related to character of an atom

Atomic Number

Atomic number also called proton number and this number of protons in an atom. This atomic number determines identity of an element and many of its chemical properties. In other words, each element has unique number that identifies how many protons are in one atom of that element. In fact, this number is how you can distinguish one element from another.

Atomic number is simply number of protons in an atom. For this reason it is sometimes call proton number. But in calculations, it is denoted by capital letter Z. Atoms of different elements have different atomic numbers. However, atomic number ranges in integral units from 1 for hydrogen to 92 for uranium and this is highest naturally occurring elements.

Atomic Mass Unit

Atomic mass is characteristic of an atom that is measure of its size. It plays major role in chemical properties of elements. Atomic mass is total mass of protons and neutrons in an individual atom or isotope. Mass Number also called nucleon number is total number of protons and neutrons in an atom. Atomic mass of an element is expressed in atomic mass units.

Atomic mass units are described as unit of measurement for atoms and molecules just like mass of person may be expressed in ponds or kilograms. Atomic mass unit is equal to 1.6605 x . One mol of an atom is amount of mass in grams equal to atomic mass of atoms. Thus, one mole of carbon has mass of 12g and it is unit of mass used to express atomic masses and molecular masses. AMU is used to differentiate between isotopes.

Atomic weight

Atomic weight is average mass of atoms of an element, based on abundance of isotopes. And atomic weight can change because it depends on our understanding of how much each isotope of an element exists. Check Engineering Materials – Desirable Bearing Materials Properties

Atomic weight is given in terms of atomic mass units and indicates mass of atom in units of 1/12 mass of carbon isotope with 6 protons and 6 neutrons.  Atomic weights are normally weighted according to natural abundance of isotopes.

Avogadro’s Number

Avogadro’s Number is number of particles found in one mole of substance. It is number of atoms in 12 grams of carbon 12. Note, Avogadro’s number on its own is dimensionless quantity. Avogadro’s number may be designated using symbol L or

Avogadro’s number refers to quantity of atoms molecules, or ions, but it can be applied to any particles. Thus, it is reciprocal of atomic mass unit. Number of atoms in one mole of substance is called Avogadro’s number.

= 1/ (1.6605 x)

= 6.0223 x  / k.mole

=6.0223 x  / mole

If number of electrons in an atom varies, element remain same but new ions produced. Protons are found together with neutrons in atomic nuclear. See atomic weight and periodic table of the elements. In 1 mole of a substance there is Avogadro’s number (NA) of atoms or molecules.