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2. • Matter is anything that takes up space and
has mass.
•All matter is made of atoms
•Atoms are the building blocks of matter
•E.G: bricks are the building blocks of houses.

3. •Democritus thought that atoms are tiny,
uncuttable, solid particles that are surrounded
by empty space and constantly moving at
random.
•A Greek philospher Democritus firstly gave
idea of atom.

4. All matter is made up of atoms.
Each element has different atoms.
Atoms can engage in a chemical reactions.
Atoms can neither be created nor be
destroyed, Atoms are indivisible.
JHON DALTON BELONGS TO ENGLAND.

5. •Nucleus - center of the atom of Protons and Neutrons
• Proton Has a positive (+VE) charge
• *Determines the atomic number *inside the nucleus
•Neutron has no (0) charge *inside the nucleus
•'Electron *Has a negative (-) charge *outside the nucleus
Electrons are in specific energy levels called shell of
matter.
•E.G: bricks are the building blocks of houses.

6. •The number of proton in an atom is equal to
number of electrons revolving around it.
•number of proton=number of electrons

7. •Although electrons and protons in an atom have charges,
• but atom as a whole has no charge.
• In an atom, the number of protons is equal to the number of
electrons.
• As a result, the total positive charge of protons balances the
total negative charge of electrons.
• Because of it, the atom is neutral.

8. •The atomic number of an atom is equal to the number of
protons in the nucleus of an atom.
atomic number=number of protons
Z=number of protons
•It is represented by ‘Z’

9. •The mass number is defined as the total number of protons
and neutrons in an atom.
•It can be calculated by adding the number of neutrons and
the number of protons (atomic number) together.
•It is denoted by ‘A’
Mass number=number of neutrons+number of protons
A=number of neutrons+Z

14. A=
Z=

15. •Tungsten is an element with 74 protons and
109 neutrons.
•i) What is tungsten’satomic number?
•ii)How many electrons does tungsten have?

16. •Calculate the number of protons, electrons
and neutrons in a sodium atom? (11
23
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17. atomic number=number of protons
Z=number of protons
atomic number=74
Electrons=?
as we know, No. of P=No. of E
so, 74=No. of E

18. •Z=number of protons
•Z=11 SO, number of protons=11
•No. of P=No. of E
•11=No. of E
•mass no=no of proton + no of neutron
•23=11+no of neutron
•no of neutron=23-11=12

19. •Atoms combine with other atoms but they
stop reacting with other atoms (become
stable)
Two hydrogen atoms combine to form a
hydrogen molecule (H2) by sharing electrons.

20. •Valancy is the combining capacity of
an atom. The valency of an element
is related to how many electrons are
in the orbitals of the outermost shell
(also called valence shell).

21. • an atom or group of atoms that
carries a positive or negative electric
charge as a result of having lost or
gained one or more electrons

23. •Ions are charged substances that are
formed through the gain or loss of
electrons.
•Cations form from the loss of
electrons and have a positive charge
•Anions form through the gain of
electrons and have a negative
charge.

24. • After losing one electron, sodium + atom becomes
sodium ion (Na+).
•The chlorine atom gains one electron to become
chloride ion (Cl-).
•Chloride ion Sodium ion Negative and positive ions
attract each other to
•form sodium chloride (NaCl).
•Sodium chloride is (table salt).

27. •When a glass rod is rubbed with silk,
the rod becomes positively charged.
•What type of particle in the atoms in
the rod has been removed?

28. •When a glass rod is rubbed with silk, the
glass rod loses electrons to the silk piece.
The glass rod has free electrons which
are less tightly bound so get transferred
to the silk cloth. The glass rod has a
deficiency of electrons and acquired a
positive charge while the silk cloth
acquires a negative charge.

29. •When you are rubbing the glass rod
with the silk cloth, electrons are
stripped away from the atoms in the
glass and transferred to the silk
cloth. This leaves the glass rod with
more positive than negative charge,
so you get a net positive charge.

30. 1 0
0 2
2 0
0 1

31. •Atoms with the same number of
protons but different numbers of
neutrons are called isotopes.
•P=P N≠N

34. •Some isotopes release radiation all the time. These
isotopes are called radioisotopes.
•Radioisotopes can be used for human welfare. Food
irradiation is a method to make food safer for a long
time.
•The radiation from a radioisotope kills microorganisms
(bacteria, etc.) present in the food.
•Find some more uses of radioisotopes.