9th Class chemistry notes of unit 4

Atoms of different elements react to attain noble gas configuration, which is stable one.

Chemical bonds may be formed by complete transfer of electrons (ionic); mutual sharing (covalent) or by donation from an atom(coordinate or dative covalent).

Metals have the tendency to lose electrons easily forming cations.

Non-metals have tendency to gain electrons and form anions.

In ionic bonding strong electrostatic force hold ions together.

Ionic compounds are solids with high melting and boiling points.

Covalent bonds among non-metals are weaker than ionic bonds.

Ionic bonds are non-directional, but covalent bonds are formed in a particular direction.

Covalent bonds formed between similar atoms are non-polar while between different atoms are polar.

In covalent bonding single, double or triple covalent bond is formed by sharing of one, two or three electron pairs by the bonded atoms.

Coordinate covalent bond is formed between electron pair donors and electron pair acceptors.

Metallic bond is formed between metal atoms due to free electrons.

In addition to chemical bonds, intermolecular forces of attraction exist between polar molecules.

Hydrogen bonding exists between the hydrogen atom of one molecule and highly electronegative atom of other molecule.

Hydrogen bonds affect the physical properties of the compounds.

Properties of the compounds depend upon the nature of bonding present in the compound.

Ionic compounds are crystalline solid with high melting and boiling points.

Covalent compounds exist in molecular form in three physical states.

Polar and non- polar covalent compounds have different properties.

Metals have shining surface. They are good conductor of electricity and are malleable and ductile.

9th Class notes of chemistry chapter 3

In nineteenth century attempts were made to arrange elements in a systematic manner.

Dobereiner arranged elements in a group of three called triads.

Newlands arranged elements in groups of eight like musical notes.

Mendeleev constructed Periodic Table containing periods and columns, by arranging elements in order of increasing atomic weights.

There are total eighteen groups and seven periods in the modern Periodic Table.

Depending on outermost electrons and electronic configuration, element in periodic table are grouped in s, p, d and f blocks.

Atomic size increases down a group but decreases along the period .

Ionization energy decreases down a group but increases along a period.

Shielding effect is greater in atoms with greater number of electrons.

Electronegativity increases along a period and decreases down the group.

9th Class Chemistry Notes of Chapter 2

Cathode rays were discovered in last decade of nineteen century. The properties of cathode rays were determined and they led to the discovery of electron.

Canal rays were discovered in 1886 by Goldstein . The properties of canal rays resulted in the discovery of proton in the atom.

Neutron in the atom was discovered in 1932 by Chadwick.

First of all structure of an atom was presented by Rutherford in 1911. He proposed that an atom contains nucleus at the center and electrons revolve around this nucleus.

Bohr presented an improved model of an atom in 1913 based upon four postulates. He introduced the concept of circular orbit, in which electrons revolve. As long as electron remains in a particular orbit, it does not radiate energy. Release and gain of energy is because of change of orbit.

The concept of shells and subshells is explained.

A shell consists of subshells.

Isotopes are defined as the atoms of elements that have the same atomic number but different atomic mass.

Hydrogen, carbon and uranium have three isotopes each, whereas chlorine has two isotopes