1. ATOMIC STRUCTURE

2. Bohr’s Atom
electrons in orbits
nucleus

3. HELIUM ATOM + - + - Shell proton neutron electron
What do these particles consist of?

4. ATOMIC STRUCTURE
Particle
Charge
Mass
proton
+ charge 1
neutron
No charge 1
electron
- charge
nil

5. * * number of electrons = number of protons
ATOMIC STRUCTURE He 2
Atomic number
the number of protons in an atom 4
Atomic mass *
The atom’s mass –
A Weighted average of the
isotopes – (protons + neutrons)
* *
* * number of electrons = number of protons

6. Atomic Number This carbon atom’s atomic number is 6.
Atomic Number -- is the number of protons in the nucleus of the atom.
This carbon atom’s
atomic number is 6.
The number of protons (atomic number) determine the identity of an element.

7. ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.
first shell a maximum of 2 electrons
second shell a maximum of 8 electrons
third shell a maximum of 8 electrons

8. Atoms have NO overall electrical charge so, an atom must have as many
electrons as there are protons
in its nucleus.
# of electrons = # of protons

9. Isotopes
&
Ions

10. Isotopes
Isotopes are atoms of an element that have the SAME number of protons,
but a DIFFERENT number of neutrons.
Isotopes remain the same element, because the number of protons doesn’t change.
The mass changes, but the element doesn’t!

11. Identified by the mass # -Number of protons + neutrons
Two Common Isotopes
Carbon has 6 protons
6 neutrons
7 neutrons
8 neutrons
Identified by the mass # -Number of protons + neutrons

12. Properties of Isotopes
Isotopes of an element share most of the same properties – both chemical and physical!
However -- Some isotopes of an element have special properties because they are “unstable” (the nucleus will change over time).
This would be a radioactive isotope that will spontaneously “fall apart” over time, giving off small particles/ energy as they do.

13. Identifying Isotopes Isotopes are identified by their mass number
Mass number is the sum of the protons and neutrons (electrons not included – too small to have an effect on mass)
Boron - 10
Boron - 11

15. All atoms which contain 17 protons are called chlorine atoms
Chlorine (Cl) has 24 isotopes
Examples: Chlorine-35 and Chlorine-37 are both
isotopes of the element chlorine
Chlorine contains 18 neutrons
(17 protons + 18 neutrons = 35 particles in the nucleus)
Chlorine - 37 contains 20 neutrons
(17 protons + 20 neutrons = 37 particles in the nucleus).

16. Atomic Mass
The atomic mass of an element is the weighted average of the masses of all of the naturally occurring isotopes of that element.
Chlorine – 35: 76% of all chlorine in nature
Chlorine – 37: 24% of all chlorine in nature
35 x .76 =
37 x .24 =
35.48 amu

17. Ions Ion – An atom that LOSES or GAINS an electron
Loses an electron: + Positively charged ion
Gains an electron: – Negative ion
Missing an electron
A lower energy
Attractive to ions with
a negative charge

18. SUMMARY The Atomic Number of an atom = number of
protons in the nucleus. Id’s the element!
The Mass Number of an atom = number of
Protons + Neutrons in the nucleus.
3. The Atomic Mass = the weighted average of isotopes
4. The number of Protons = Number of Electrons –
Atoms have NO overall electrical charge
5. Electrons orbit the nucleus in shells.
6. Each shell can only carry a set number of electrons.

19. 7. Ion – An atom that loses or gains an electron
8. Isotopes are atoms of an element that have the
SAME number of protons, but a DIFFERENT
number of neutrons.
9. Isotopes are identified by their mass number;
Mass number is the sum of the protons and neutrons
10. The atomic mass of an element is the weighted
average of the masses of all of the naturally
occurring isotopes of that element.