class XI atomic str

1. Submitted by
Nihal tyagi
Xi a5

3. 1808 john dalton
 Suggested that all the matter
was made up of tiny spheres
that were able to bounce back
around perfecty with elasticity
 https://www.britannica.com/
video/153020/John-Dalton-
development-atomic-theory
Regarded atom as ultimate particle

4. 1898 JJ thompson
 Carried out cathode ray tube
experiment
 In his studies he founded that:
 Cathode start from cathode
and move toward towards
anode
 rays are not visible
 He named them as electron
Discovered electron

5. Erenest Rutherfofd
 Conducted nuclear scatterind
experiment
 Gave conclution that:
 Most of the space in atom is
empty
 His calculation shows that
nucleus occupy negligble
mass
 He show that positive charge
is not scaterred

6. Neil bohr
 Bohr model of atom
 Dual character of electonic
radiation
 Experiment result regarding
atomic spectra

7. Electron around nucleus

8. What is an atom?
 Atom: the smallest unit of matter that retains
the identity of the substance

9. Atomic Structure
 Atoms have 2 regions
1) Nucleus: the center of the atom that contains
most of the mass of the atom.
2) Electron cloud: surrounds the nucleus & takes up
most of the space of the atom.
Nucleus
Electron
Cloud

10. What’s in the Nucleus?
 In the nucleus we find:
 Protons: positively charged subatomic particles
 Mass of 1 amu
 Neutrons: neutrally charged subatomic particles
 Mass of 1 amu

11. What’s in the Electron Cloud?
 In the electron cloud we find:
 Electrons: the subatomic particle with a negative
charge and relatively no mass
 Mass of ~ 1/1836 amu

12. Subatomic Particles
Particle Charge Mass (g) Location
Electron
(e-) -1 9.11 x 10-28 Electron
cloud
Proton
(p+) +1 1.67 x 10-24 Nucleus
Neutron
(no) 0 1.67 x 10-24 Nucleus

13. How do we know the number of
protons in an atom?
 Atomic number (#)= # of protons in an atom
 Ex: Hydrogen’s atomic # is 1
 hydrogen has 1 proton
 Ex: Carbon’s atomic # is 6
 carbon has 6 protons
**The number of protons identifies the atom-it’s
an atom’s fingerprint.

14. How do we know the number of
neutrons in an atom?
 Mass #: the # of protons plus neutrons in the
nucleus
 # of neutrons = mass # - atomic #
Example
 Li has a mass # of 7 and an atomic # of 3
 Protons = 3 (same as atomic #)
 Neutrons= 7-3 = 4 (mass # - atomic #)

15. Mass # vs. Atomic Mass
Mass # ? = The Atomic mass on the periodic table
rounded either up or down

16. How do we find the number of
electrons in an atom?
 Most atoms are neutral (have no overall
charge)
 Because the only charged subatomic
particles are the protons and electrons…
they must balance each other out in an
electrically neutral atom.
 Therefore..
 # Electrons = # Protons *
* (in a neutral atom..)

17. Examples
 He has a mass # of 4 and an atomic # of 2
 p+ = 2 no = 2 e- = 2
 Cl has a mass # of 35 and an atomic # of 17
 p+ = 17, no = 18, e- = 17

18. How exactly are the particles
arranged?
 Bohr Model of the atom: electron
configurations
All of the
protons and
the neutrons
The 1st ring can
hold up to 2 e-
The 2nd ring can
hold up to 8 e-
The 3rd ring
can hold up
to 8 e-

19. What does carbon look like?
Mass # = 12 atomic # = 6
p+ = 6 no = 6 e- = 6
6 p and 6 n live
in the nucleus

20. Isotopes
Dalton’s 1st postulate was wrong.
Atoms of the same element can
be different (they can have
different # of neutrons)
Thus, different mass numbers.
These are called isotopes.

21. Isotopes
Isotopes are atoms of the same element
having different masses, due to varying numbers
of neutrons.

22. Isotope Protons Electrons Neutrons Nucleus
Hydrogen–1
(protium) 1 1 0
Hydrogen-2
(deuterium) 1 1 1
Hydrogen-3
(tritium)
1 1 2

23. Naming Isotopes
We name the isotope based on
its mass number
carbon-12
carbon-14
uranium-235

24. Isotopes
• Elements
occur in
nature as
mixtures of
isotopes.

25. Atomic Mass
 How heavy is an atom of oxygen?
 It depends.. b/c there are different oxygen
isotopes.
 We are more concerned with the average atomic mass.
 This is determined based on the abundance of each isotope
 We don’t use grams for this mass because the
numbers would be too small.

26. Measuring Atomic Mass
Instead we use the Atomic Mass
Unit (amu)
defined as one-twelfth the mass of a
carbon-12 atom.
Each isotope has its own atomic
mass, thus we determine the
average from percent abundance.

27. Atomic Mass
Isotope Symbol Composition of
the nucleus
% in nature
Carbon-12 12C 6 protons
6 neutrons
98.89%
Carbon-13 13C 6 protons
7 neutrons
1.11%
Carbon-14 14C 6 protons
8 neutrons
<0.01%
Atomic mass is the average of all the
naturally occurring isotopes of that element.
Carbon = 12.011