Recaps.

Atomic Structure.
1)Matter is built up from small individual particles called atoms.

2)An atom iis made up 3 basic particles:
-Protons
-Neutrons
-Electrons

3)The properties of these three sub-atomic particles are shown below:
ELEMENTS--->RELATIVE MASS--->CHARGE--->REST MASS--->FOUND IN:
Protons(p)---> 1 ---> +1 ---> 1.67 x 10^-27 kg ---> Nucleus
Neutrons(n)---> 1 ---> 0 ---> 1.67 x 10^-27 kg ---> Nucleus
Electrons(e)--->1/1840---> -1 --->9.11 x 10^-31 kg--> Around Nucleus

4)The protons and neutrons are found in the nuleus of the atoms.These 2 types of particles that make up the nucleus are known as Nucleons.The protons and neutrons make up the dense core of the atom.

5)The electrons move around the nucleus in definite energy levels or electron "shells".

6)Te composition of protons ,neutrons and electrons in an atom can be determined from its proton number(atomic number)and nucleon number(mass number).

7)The proton number is the number of protons in an atom.

8)The nucleon number is the total number of nucleons(p+n)in the nucleus of an atom.

9)Since an atom is electrically neutral,the number of protons is the same as the number of electrons.

Therefore,
Number of neutrons=Nucleon number - Proton number

ELEMENTS
1)An elements is a pure substance that cannot be decomposed into anything simpler by a chemical reaction.

ISOTOPES
1)Isotopes are different atoms of an element with the same proton number but different nucleon numbers.

Isotopes of a particular element have the same:
i)Atomic number(proton number)
ii)Number of electrons in a neutral atom
iii)Electronic Configuration(same number of electrons)
iv)Chemical properties(same number of valence electrons)

Isotopes of a particular element have different:
a)Number of neutrons in an atom
b)Mass numbers
c)Relative isotopic mass
d)Physical properties

ELECTRON CONFIGURATION
1)The way in which the electrons are distributed among the various energy levels or shells.

2)Each energy level can accommodate a definite number of electrons.

3)The energy levels must be filled in order of increasing energy.The first level is filled first before going to the second level and subsequent higher levels.

4)The outermost shell is the highest energy level that is occupied by electrons.

5)Electrons in outermost shell are called valence electron.

6)When the outermost shell is completely filled,the atom would have achieved a stable noble gas configuration.

7)Atoms of other element also try to achieve a noble gas configuration by forming chemical bonds with other atoms.

8)The types of chemical bonds formed between atoms are:
a)Ionic (or electrovalent) bond
b)Simple covalent bond
c)Metallic bond