Atom:
1. Building blocks of all matter are called atoms.
2. Atoms are extremely small, they are smaller than anything that we can imagine or compare with.
3. For example – more than millions of atoms when stacked would make a layer as thick as any sheet of paper.
4. Atomic radius is measured in nanometres
1/10 9 m = 1 nm
1 m = 10 9 nm
5. Some examples of an atom – Oxygen (O), Hydrogen (H), Nitrogen (N), etc.
The naming of Atoms or Elements and Their Symbols :
1. Symbols for elements in a very specific sense was first proposed by Dalton.
2. Berzelius suggested using one or two letters of the name of the element for its symbol.
3. Earlier, the names of elements were derived from the name of the place where they were found for the first time, for example, the name copper was taken from Cyprus.
4. Some names were also taken from specific colors. For example, gold was taken from the English word meaning yellow.
5. IUPAC (International Union of Pure and Applied Chemistry) approves the names of elements.
6. The abbreviation used for the lengthy names of elements are termed as their symbols.
7. The symbol of an element is formed by writing only the first letter or first letter followed by second and some other letter of the name of that element.
For example – Nitrogen (N)
Iron (Fe)
Magnesium (Mg)
Argon (Ar)
8. While writing the symbol of an element, the first letter of a symbol is always capital (uppercase) and the second letter is smaller (lowercase).
For example – Chlorine (Cl)
Lead (Pb)
Zinc (Zn)
9. Symbols have been taken from the names of elements in Latin, German or Greek.
For example – Iron (Fe) – Latin name (Ferrum)
Sodium (Na) – Latin name (Natrium)
Atomic Mass :
1. According to the concept of Dalton's Atomic Theory, each element had a characteristic atomic mass which prompt scientists to measure the atomic mass of an atom.
2. The mass of an atom of an element is called its Atomic Mass.
3. Earlier 1/16 of the mass of an oxygen atom was used as a standard for calculating the mass of other elements.
4. However, in 1961 for a universally accepted atomic mass unit (u), carbon-12 isotope was chosen as the standard reference for measuring the atomic and molecular mass of elements and compounds.
· The Atomic Mass unit is defined as the quantity of mass equal to 1/12 of mass of an atom of carbon-12.
· 1 amu or u = 1/12 × Mass of an atom of c12
· 1 u = 1.66 × 10-27 k
· For example –
1. Hydrogen – 1 u
2. Carbon – 12 u
3. Nitrogen – 14 u
4. Oxygen – 16 u
5. Sodium – 23 u
6. Magnesium – 24 u
7. Sulfur – 32 u
8. Chlorine – 35.5 u
9. Calcium – 40 u
Atoms Existence:
Atoms of most of the elements are very reactive and hence, do not exist independently.
Noble gases are the only atoms (such as He, Ne, Kr, Xe, and Rn) are unreactive and can exist independently as a single atom.
Atoms form molecules and ion, that aggregate in large numbers to form the matter that we can see, feel, or touch.