1. Ch. 3 - Atomic Structure
Subatomic Particles

3. Development of the Atom
1st Model: Dalton’s Theory 1. All matter is made of indivisible atoms. 2. All atoms of a given element are identical.
2nd Model: Thomson’s model “Plum-pudding” model. Discovered electron (negative charges) through Cathode Ray Tube Experiment.
3rd Model: Rutherford’s Model, Discovered the nucleus made of protons through Gold Foil Experiment.

4. Development of the Atom
4th Model: Bohr’s Model “Planetary” model: Electrons orbit the nucleus on specific paths.
Chadwick: Discovered the neutrons in the nucleus. Neutrons are the “glue” of the atom, or strong nuclear force.

5. Development of the Atom
5th Model: Electron Cloud Model, the current model of the atom. Developed by Schrodinger. Electrons are in “clouds” or regions of space outside the nucleus. Also called orbitals or energy levels.

6. Subatomic Particles Atoms Size Most of the atom’s mass. ATOM NUCLEUS
Smallest particle that retains the chemical identity of an element
ATOM
NUCLEUS
ELECTRON CLOUD
PROTONS
NEUTRONS
ELECTRONS
NEGATIVE CHARGE
POSITIVE CHARGE
NEUTRAL CHARGE
Most of the atom’s mass.
Atoms Size

7. Subatomic particles
In a neutral atom, the # of protons equals the # of electrons.
A proton is more massive than an electron: 1 proton equals approx electrons!

8. Subatomic particles
Atomic Number (Moseley): the # of protons in the nucleus of an atom
Unique to each element
For example:
Oxygen: Atomic # 8
8 protons
8 electrons
Positive charge = Negative charge in a neutral atom

9. Subatomic particles Mn (manganese) # of protons: # of electrons:
Kr (Krypton) 25 36

10. Subatomic particles Charge (c) Mass (g) Mass (amu) Proton +
1.67 x 1
Neutron
Electron -
9.11 x

11. Mass Number mass # (atomic mass or atomic weight)= protons + neutrons
round the atomic mass to the 2nd decimal when calculating
© Addison-Wesley Publishing Company, Inc.

12. Mass Number Mass # Atomic # Nuclear symbol: Hyphen notation: carbon-12
Mass number – the atomic mass (weight) rounded to the nearest whole number when displayed like this.
Nuclear symbol:
Mass #
Atomic #
Hyphen notation: carbon-12

13. Ions
Ions – atoms with a net electrical charge (lose or gain one or more elctrons - # of protons is unchanged)
Oxygen O –2 gains 2e-
Hydrogen H + loses 1e-
Magnesium Mg or Mg 2+

14. Ions Write the symbol: 9 protons, 10 electrons (anion)
13 protons, 10 electrons (cation)
S –2 has how many protons and electrons?
F-1 or F1- or F-
Al+3 or Al3+
16 p+ and 18 e-

15. Ions Fe Iron has how many protons, electrons and neutrons?
Fe+2 has how many protons, electrons, and neutrons? 56
26 protons, 26 electrons, neutrons Fe 26
26 protons, 24 electrons, 30 neutrons (h.o.)

16. Isotopes … …don’t have to be radioactive.
1. Atoms of the same element with different mass numbers (diff. # of neutrons )
…don’t have to be radioactive.
Some isotopes are unstable and decay
But, there are many stable isotopes
that don’t decay.

17. Isotopes
2.The periodic table gives the average atomic mass of all the naturally occurring isotopes according to how abundant the isotope is.
3.If the avg. atomic mass is rounded to the nearest whole number it will tell the most abundant isotope.
Carbon: amu so……
Hydrogen: amu so….

18. Isotopes Chlorine-37 atomic #: mass #: # of protons: # of electrons:
# of neutrons:
(Is this the most abundant isotope?) 17 37 20

19. Average Atomic Mass Avg. Atomic Mass weighted average of all isotopes
on the Periodic Table (write this on p.t.)
round to 2 decimal places
Avg.
Atomic
Mass

20. Average Atomic Mass
EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O.
Avg.
Atomic
Mass
16.00
amu

21. Average Atomic Mass Find the average atomic mass of neon if :
90.48 % Neon amu, 0.27 % Neon amu, 9.25 % Neon amu.
= amu

22. D. Average Atomic Mass
EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37.
Avg.
Atomic
Mass
35.40 amu