ICSE Chemistry Class 8 Notes Chapter 5 Language of Chemistry
→ Symbol: Berzelius suggested – a simple approach to represent elements.
→ Symbol is the short form or abbrevated name of element.
→ Atom is the basic unit of element. It may or may not exist independently. Every substance is made up of atoms.
→ Element is a pure substance made up of one kind of atoms only.
e.g. iron, silver, gold, platinum, sodium, potassium, mercury, iodine, bromine, oxygen, hydrogen etc.
→ Symbol of sodium is Na – derived from natrium
Symbol of potassium K – Latin name Kalium
Symbol of iron Fe, latin name Ferrum
Symbol of copper Cu – Latin name Cuprum
Symbol of Pb – Latin name Plumbum
Symbol of Gold Au – Latin name Aurum
Symbol of Silver Ag – Latin name Argentum
Symbol of Merucry Hg – Latin name Hydragyrum
Symbol of Tin Sn – Latin name Stannum
→ Symbol of an element is the first letter or the first letter and another letter of the English name or Latin name of the element.
→ Valency is the number of hydrogen atoms which can combine with [or displace] one atom of the element [or radical] forming compound.
→ Valency of hydrogen is taken 1 (one).
→ H2O : One atom of oxygen has combined with 2 atoms of oxygen.
∴Valency of oxygen atom is 2.
NH3 : Nitrogen combines with 3 atoms of hydrogen to form compound amonia.
∴Valency of nitrogen is 3.
ZnO : Knowing the valency of oxygen 2. Oxygen combines with 1 atom of Zn.
∴Valency of Zn atom is 2.
→ Metals have valency 1, 2 or 3 as they can lose one electron or 2 or 3 from valency shell. Metals have valency +ve and are cations. Non-metals accept electrons to complete the valency shell i.e. 2 or 8 electron in valence shell to become stable. Valency of non-metals is -1, -2 or -3. They are anions. Noble-metals have valency zero.
→ Ions : Charged particles are called ions Al3+, Na+, positively charged ions are cations and Cl–, O2- negatively charged ions are anions.
→ Radical : “Group of atoms of elements that behave like a single unit and show valency.” [NH1+4] is positive radical, [HCO1-3“] is negative radical.
→ Chemical equation : “is a short hand form-representing the result of a chemical change.”
Zn + H2SO4 → ZnSO4 + H2