ATOMS AND MOLECULES
1. There are two laws of chemical combinations.
2. They are conservation of mass states that mass can neither be created nor destroyed in a chemical reaction.
3. Law of constant proportions states that in a chemical reaction chemical substance the elements are always present in definite proportions by mass.
4. All matter is made of very tiny particles called atoms.
5. Atoms of different elements have different masses and chemical properties
6. Berzelius suggested that symbols of elements from one or two letters of the name of the element.
7. IUPAC approves names of elements and also mass of atoms as u-unified mass equal to mass of carbon atom.
8. A molecule is the smallest particle of an element or compound that is capable of an independent existence and shows all the properties of that substance.
9. Atoms of same or different elements combine to form molecules.
10. Molecules of elements are constituted by the same type of atoms.
11. Atoms of different elements join together in definite proportions to form molecules of compounds.
12. Iron is charged particles. Negative charged particle is anion, positive charge is cation.
13. A group of atoms carrying a charge is called polyatomic atom.
14. The chemical formula of a compound ¡s a symbolic representation of its composition.
15. Chemical formula of a molecular compound is determined by valency of each element.
16. In atomic compounds, the charge on each ion is used to determine chemical formula.
17. The molecular mass of a substance is the sum of atomic mass of all atoms in a molecule.
18. Formula unit mass of a substance is a sum of atomic masses of all atoms in a formula unit of a compound.
19. The Avogadro constant 6.022 * 1023 is defined as the number of atoms in exactly 12g of carbon 12.
20. MoIe is the amount of substances that contain same no.of (molecules, atoms, ions or particles) that quantity in number having a mass equal to its atomic or molecular mass in grams.
21. The mass of 1 mole of a substance is equal to its relative atoms or molecular mass in grams.
