1. Aim: What is the internal structure of an atom?
DO NOW: Prepare for quiz. Need pen or pencil, and reference tables.

2. Atomic Structure A) Nucleus Proton Neutron B) Electron Cloud

3. The Three Fundamental Subatomic Particles
Name
Symbol
Charge
Mass (amu)
Location
Proton p+ 1+
1.007
Nucleus
Neutron n0
1.009
electron e- 1-
5.486 x 10-28
Outside nucleus

4. Nucleus (Protons and Neutrons)
1) Contains most of the mass of the atom; very dense
2) Has a positive charge (nuclear charge)
Charge from protons
Neutrons have no charge

5. Atomic Number and Atomic Mass
Atomic # = # of protons only
Atomic mass or mass # is both mass of neutron and proton

6. Neutral Atom In a neutral atom, the # of electrons = # of protons
The protons “hold the electrons in the atoms”
The number of protons (atomic #) determines the element you have

7. Sample Problems
1. Lithium has 3 protons and 4 neutron. What is the mass number?
Mass # = # of protons + # of neutrons
Mass # = 3 + 4
Mass # = 7
2. An atom has a mass number of 9 and has 5 neutrons. How many protons does it have?
9 = # of protons + 5
# of protons = 4

8. Electronic Structure
Electrons are found in orbitals (most probable location) outside the nucleus
Electrons are arranged in different shells around the nucleus; each can only hold a certain number of electrons.
The innermost shell is filled first.
Electrons closer to the nucleus have less energy than electrons further away from the nucleus.

9. Electronic Structure Cont.
Green = proton
Blue= neutron
Red= electron
Which element is this? How can we tell?
How many electrons are in the first shell? Second shell?

10. Electronic Structure Cont.
Element
Bohr Structure
Electron Configuration
Electrons
Periodic Table Group
Fluorine (F)
2-7
2 e- in 1st shell
7 e- in 2nd shell 17
Neon (Ne)
2-8
2e- in 1st shell
8 e- in 2nd shell 18
Sodium (Na)
2-8-1
1 e- in 3rd shell 1
Calcium (Ca)
8 e- in 3rd shell
2 e- in 4th shell 2

11. Electron Shells Energy shell Maximum number of electrons First 2
Second 8
Third

12. Sample Problem What is the mass number of Magnesium?
Explain from this diagram why the aluminum atom is neutral.

13. Symbol for Carbon Carbon-12 or 12C:
It tells us that a carbon atom has:
Six protons (because its proton number, at the bottom, is 6)
Six electrons (because the number of protons and electrons in an atom is the same)

14. Isotope of Hydrogen What stays the same in each isotope of hydrogen?
What changes?

15. Isotopes of Hydrogen and Chlorine

16. What is are Isotopes? Atoms of an element that:
Have the same number of protons and electrons
Have different numbers of neutrons, and therefore have different atomic masses

17. Discussion
Why are isotopes of an element still of the same element even though they have different number of neutrons between them?