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  • Write and interpret symbols that depict the atomic number, mass number, and charge of an atom or ion.

What is an atom?

Quiz – Build an Atom / Element / Ion

As we know, an atom is the smallest building block of everything that exists. It is composed of three sub-atomic particles: the proton, neutron, and electron. Protons and neutrons make up the nucleus of the atom, a dense and positively charged core, while the negatively charged electrons can be found around the nucleus in an electron cloud.

  • Atoms can be different by having different numbers of protons, neutrons and electrons. All atoms with the same atomic number behave in the same way chemically and are classified as the same chemical element. Elements are the substances consisting of one type of atoms.
  • Atoms are the units of chemical change.
  • A chemical symbol is an abbreviation that we use to indicate an element or an atom of an element. For example, the symbol for carbon is C.

Read –

Law of Conservation of Mass

Problems based on Law of Conservation of Mass

Law of Definite Proportions / Constant Composition

Dalton Atomic Theory

Problems based on law of Definite Proportions / Constant Compositions

Representation of  Atoms of different Elements by a Symbol

A symbol signifies a shorthand representation of an atom of an element. Dalton was the first scientist to use the symbols for elements in a very specific sense. Dalton’s symbols for elements were difficult to draw and inconvenient to use. Later, Berzilius suggested the modern symbols of elements.

Modern symbols of elements

The symbol of any element is based on the English name or Latin name (written in English alphabets) and is represented by using only its first letter or the first letter and another the symbols .

(a) The first letter is written in capital and the second letter in small.
For example- hydrogen- H; aluminium – Al not AL; cobalt – Co not CO.

(b) The second letter can be any letter in the name of the element, which is internationally accepted.

The names of the elements had originated from different sources in different ways.
For example-

(i) Hydrogen – It was named by Lavoisier using the Greek words ‘Hydro’ ie., water and ‘Genes’
meaning forming.

(ii) Halogens (Chlorine, Bromine, Iodine ..) – Chlorine has its origin from Greek word – ‘Chloros’ – meaning greenish yellow, ‘Bromos’ means stench in Greek and ‘Iodes’ in Greek means violet.

(iii) Nickel – The word nickel has originated from a German word meaning ‘Satan’ or ‘Old nick’.
(iv) Cobalt – It comes from a German word – ‘Globlin’ or ‘Evil Spirit’.

(v) Argon – It comes from a Greek word meaning ‘Inactive’.

(vi) Gold – It is an English word – ‘Aurum’ means yellow.
(vii) Iron(Fe)-derived from latin name ferrum; sodium (Na) from natrium; potassium (K) from kalium.

(vii) Elements Named After Places

Scandium (Sc) – found in Scandinavia ;Thulium (Tm) – named after Thule ; Polonium (Po) – named after Poland

(viii) Elements Named After Planets

Selenium (Se)-‘Seles’ Greek name for the moon ; Mercury was named after a planet but derives its symbol Hg from the Latin word ‘Hydragyrum’ meaning liquid silver ; Copper-it was taken from Cyprus.

(ix) Elements Named After Scientists

Curium (Cm) after Pierre and Marie Curie ; Fermium (Fm) after Enrico Fermi ; Einsteinium (Es) after Albert Einstein ; Mendelevium (Md) after Dimitri Mendeleev

  Significance of a Symbol of an Element

(a) It shows the name of a specific element.

(b) It represents one atom of that specific element.
(c) It gives atomic mass of the element.

For example, ‘C’ denotes one atom of carbon element and the symbol for calcium is Ca.


What is the atomic symbol for bromine, and what is its atomic number? Why isn’t the symbol for bromine just the the letter B? What other element pre-empts the symbol B?                           (Refer to the periodic table)

Solution – Bromine’s atomic number is 35, and its symbol is Br; B is the symbol for boron.

Element        Symbol        

Hydrogen             H
Helium                 He
Lithium                Li
Beryllium             Be
Boron                    B
Carbon                  C
Nitrogen               N
Oxygen                 O
Fluorine               F
Neon                     Ne
Sodium                Na
Magnesium         Mg
Aluminium          Al
Silicon                  Si
Phosphorus         P
Sulphur                S
Chlorine              Cl
Argon                  Ar
Calcium              Ca
Zinc                     Zn
Silver                  Ag

Next –

Atom – Its Size (Atomic Radius)

Quiz – Build an Atom / Element / Ion

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