Revision on the atomic structure
of an atom
Made by :
Dr. Niveen Fawzy
Chemical symbols of elements
Some famous symbols
Element
Symbol
Zinc
Zn
Si
Silver
Ag
Magnesium
Mg
Gold
Au
Ca
Bromine
Br
Copper
Cu
Cl
Lithium
Li
Iron
Fe
Sodium
Na
Potassium
K
Mercury
Hg
Lead
Pb
Element
Symbol
Element
Symbol
Hydrogen
H
Sulphur
S
Helium
He
Silicon
Carbon
C
Calcium
Chlorine
Iodine
I
Nitrogen
N
Argon
Ar
Fluorine
F
Aluminum
Al
Oxygen
O
Phosphorus
P
Neon
Ne
Atomic construction
An atom consists main of two
 parts: 1-NUCLEUS

2-ENERGY LEVELS
 First: Nucleus:




It’s the central core of an atom
The mass of an atom is concentrated in it
Contains: 1-PROTONS  2-NEUTRONS
GR: The nucleus is positively charged
Second: Energy levels:

Level symbol
K
L
M
N
O
P
Q
Level number (n)
1
2
3
4
5
6
7
Second: Energy levels:
They are imaginary regions around the nucleus in which
electrons move according to their energies
The maximum no. of energy levels is 7
Each level has a certain amount of energy increases by
increasing the distance from the nucleus.
Level (k) has the least energy , while level (Q) has the highest
energy
Points of
comparison
proton
neutron
electron
1-Position:
In the nucleus
In the nucleus
Around the
nucleus in energy
levels
2-Charge:
positive
neutral
negative
3-Mass:
v.Large
compared to
electron mass
v.Large
compared to
electron mass
Very small
The no. of protons the no. of electrons, so the atom is
electrically neutral
The no. of neutrons can be equal or more than no. of protons
except in hydrogen it doesn’t contain neutrons
Atomic number & mass number
 Atomic no. no. of protons  no. of electrons
 Mass no. no. of protons  no. of neutrons
 No. of neutrons  mass no.- atomic no.
 REMEMBER:
 The mass of the atom is concentrated in the nucleus


Electronic configuration
Electronic configuration & chemical
activity
 The chemical activity is related to the no. of electrons in
the outer level :
1- If less than 8 electrons in outermost level
active atom , enter chemical reactions, like
active gases
2- If saturated by 8 electrons in the outermost level
inactive atom , don’t enter chemical
reactions , like noble gases
Give reason

Atoms of active elements take part in the chemical
reactions
 To produce stable molecules

Noble gases don’t enter chemical reactions
 Because the outermost energy levels are completely filled
with electrons
 N.B The electrons in the outermost energy level are
responsible for chemical reaction

Comparison between active & noble gases

Active gases
Noble gases
Have less than 8
electrons in the
outermost level
The outermost level is
completely filled with 8
electrons (except He)
Take part in chemical
reactions
Diatomic molecule
Don’t take part in
chemical reactions
Monoatomic molecule