The document explains the concept of matter, atoms, and their structure, detailing the components of an atom including protons, neutrons, and electrons. It discusses the periodic table, developed by Henry Moseley, which organizes elements by atomic number into groups and periods, indicating similarities in chemical properties. Additionally, it categorizes elements into groups such as alkali metals, alkaline earth metals, and halogens based on their reactivity and valence electrons.

1. Periodic Table

2. Fill in the blank
1. Any thing which has mass, occupies space and can be perceive through our senses is called as
___________
Matter
2. Matter is made up of __________.
Atoms

3. • What is this?
 It is the structure of atom.
 At center of the atom there is
nucleus.
 Nucleus consist of positively charged
particles, known as protons and
neutral neutrons.
 It is surrounded by the extra nuclear
region known as Shell or orbits.
 Negatively charged particles known
as electrons revolve around the
nucleus.

4. Proton(s)
 It is situated inside the nucleus.
 It is positively charged.
 It is denoted by p+

5. Electron(s)
 Negatively charged
 Revolves in fixed path known as
orbits.
 Mass in negligible
 Denoted by e-.

6. • Atomic number
 Number of protons or number of electrons in the atom.
Denoted by the letter Z

8. Periodic table:
 Tabular arrangements of elements.

9.  It is given by Henry Moseley.
 Elements are classified according to increasing order of the atomic number.
 Hydrogen is the first element in the table with atomic number 1.
 18 vertical columns known as groups
 7 horizontal rows known as periods.

10. Law: Physical and chemical properties of the
elements are periodic function of their atomic
number.
 Similar properties are repeated after regular interval of time.
 Elements in the same group posses similar chemical properties.
Foe eg
 Li, Na, K belongs to the same group .
 Shows similar chemical properties.
 All are metals.

11. Group 1: Alkali metals
 Highly reactive metals.
 Li,Na, K
 Reacts with water to form hydroxides.
 Have one valence electron in their
outermost orbit.

13. Group 2 : Alkaline Earth metals
 Less reactive than alkali metals
 Eg Be , Mg, Ca
 Reacts with water to form hydroxides.
 Have 2 valence electrons.

15. Group 7 : Halogens
 Highly reactive non metals
 F,Cl,Br
 Have 7 electron in the valence shell.