Atoms, Moles, Formulae and Equations

Atom is the smallest particle of an element, which can take part in chemical reaction. Molecule is the smallest particle of an element which can exist on its own and still retain the chemical properties of that element.  Ion is an atom or group of atoms which are either positively or negatively charged due to loss or gain of electrons. First 20 elements Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Flourine Neon Sodium Magnesium Aluminum Silicon Phosphorus Sulphur Chlorine Argon Potassium Calcium Relative atomic mass of an element is the number of times the average mass of one atom of an element is greater than one twelfth of the mass of carbon 12. Relative Molecular mass of a compound is the number of times the average mass of one Molecule of the substance is greater than one-twelfth of the mass of carbon 12. Mole One mole of a substance is the amount containing as many elementary entities as the number of atoms in exactly 12 grams of carbon 12.  Note: Avogadro

Detailed Explanation of Atomic Structure and it's components

  Atomic Structure:

This refers to the way an atom is made up of which includes protons, electrons and neutrons

Proton: this is the part of an atom that is positively charged.

Neutrons; this is the part of an atom that is neutrally charged

Electrons: this is the part of an atom that is negatively charged.

Below is a simplification of the popular John Dalton's atomic theory which was propounded in the year 1808.

Fun question: ask your friend if he/she knows John Dalton.

Alright, below is Dalton's atomic Structure theory

  1. All elements are made up of small visible particles called atoms.
  2. Atoms can neither be created nor destroyed
  3. Atoms of a particular element are exactly alike and differ from atoms of all other elements.
  4. When atoms combine, they do so in simple ratios.
  5. All chemical changes from separation or combination of atoms.
But after critical investigation of John Dalton's atomic Structure theory, it was found out that not all of his theories were true, rather this is why it never became a law.

Below are some of the criticisms of John Dalton's atomic Structure theory

  1. The discovery of sub-particles like proton, electrons and neutrons, led to the nullification of the first theory and hence atom is divisible.
  2. Physical reaction disapproves the second theory since atoms can be created or destroyed in physical reactions.
  3. Isotopy also nullifies the third theory. some scientists like JJ Thomson, Rutherford, Niel Bohr, worked very hard through their various experiments to describe the structure and arrangements of the atoms.
        Structure of an Atom
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The picture above describes the structure of an atom in details but if their is any question or confusion, feel free to comment and you will get your reply within 24 hours.

Quantum Number

There are four main quantum numbers, which are

1. Principal Quantum number: it is denoted by'n'and determines the energy levels of the atoms. The shells are K,L,M,N,O and Q, which mean 1,2,3,4,5,6,7, respectively.

2. The subsidiary- it is also called azimuthal quantum number. It shows the energy sub levels in each shell. It ranges from O to (n-1). It is represented by L.

3. Magnetic- it is represented by 'm' and shows the orientation of the shells. It ranges from-L through O to L.

4. Spin- it shows the spinning of the electrons. It is represented by 's' and has value-- ½ and ½.

Take away: maximum possible number of of electrons in a shell is 2n².


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 Arrangement of Electrons in an Atom

It is governed by two rules

1. Hund's rule- it states that electrons filling an orbital will first exist singly before pairing.

2. Pauli exclusion principal- it states that not more than two electrons will occupy an orbital and these two electrons must spin in opposite direction.

Example: the example below contains both an example and the modern electronic configuration

Moving on,

Atomic number- is the number of proton in the nucleus of an atom. Z represents it.

Mass Number- is the sum of proton and neutron present in the necleus of an Atom. A represents it.

Isotopy- isotope is a phenomenon in which atoms of an element possesses the same atomic number but different mass numbers due to differences in the number of nuetrons

E.g 16 O 8 and 17 O 8

The O there means Oxygen

The 16 and 17 are the mass Numbers

The 8 and 8 are the atomic numbers which are the same.

In the example above, 16and17 are the mass numbers, while 8and8 are the atomic numbers.

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Periodic table: The latest periodic table was the arrangement of Elements in the increasing order of their relative atomic mass.

Modern periodic law states that the property of an element is the periodic function of it's atomic number.

What are transition elements

They are elements found between elements in group two and three.

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Characteristics of transition elements

1. They have variable valencies


They have high melting point

3. They are paramagnetic

4. they change color in solution. Thanks


  1. Wow thanks I actually got my periodic table today, thanks.


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