1. Atomic Structure Notes
Everything is made of atoms. Atoms are the smallest part of matter. Atoms are made up of 3 subatomic particles (particles smaller than the atom itself): electrons, protons, and neutrons.

2. This model of the atom looks like a solar system
This model of the atom looks like a solar system. The nucleus, which contains the protons and neutrons in the center, would represent the sun. The electrons are the planets spinning around the nucleus.

3. Negatively charged particles; outside the nucleus; can be gained or lost to and from other atoms; very small mass: 1/2000th of a proton
Neutral particles in the nucleus; gives mass to the atom, but not charge.

4. Count the protons to find out what element this is: # of Protons:
Positively charged particles; in the nucleus; determines what element an atom is.
Count the protons to find out what element this is:
# of Protons:
Element:
Center of the atom; contains protons and neutrons.
99.9% of mass of an atom

5. John Dalton in 1808 published a theory of the atom that had these important points:
All atoms of a particular element are the same.
Atoms of different elements have different properties, mass, and chemical reactivity.
Atoms are not changed by chemical reactions, just rearranged in order or number.

6. Niels Bohr in 1913 hypothesized that electrons traveled in fixed orbits around the atom’s nucleus.

7. Reading Element Tiles Element Name Atomic Number (number of protons)
Chemical Symbol
Atomic Number
(number of protons)
Atomic Mass

8. When thinking about the small masses of atoms, scientists found that even grams were not small enough to use for measurement. The unit of measurement used for atomic particles is the atomic mass unit (amu). The mass of a proton or a neutron is almost equal to 1 amu.

9. Atomic mass—weighted average mass (of the mixture of an element’s
Atomic mass—weighted average mass (of the mixture of an element’s *isotopes)
Use the atomic mass and the atomic number to find the number of neutrons.
Formula: # of Neutrons = Atomic Mass (Rounded to whole #) – Atomic number

10. The number of protons tells you what type of atom you have and vice versa.
Example: Every carbon atom has six protons and all atoms with six protons are carbon atoms.
Atomic number—the number of protons in an atom

11. # of electrons = # of protons
Bohr’s Model
# of electrons = # of protons
In a neutral atom there is one electron for every proton.

12. Electric charges work just like magnets; opposites attract and like charges repel. Since protons are positive and electrons are negative, protons attract electrons. Protons repel protons; electrons repel electrons.

13. Because of electron-to-electron repulsion, electrons don’t crowd around the nucleus as their number increase. Instead, they fill up orbits. Each orbit can hold a certain number of electrons, then that orbit is full. This is because even though as the number of protons increases (attraction), the number of electrons also increases (repulsion).

14. Electron Distribution: The most inner orbit can hold two electrons
***Electron Distribution: The most inner orbit can hold two electrons. The second orbit can hold up to eight electrons to be considered full. The 3rd orbit, or energy level, can hold eighteen electrons but only needs eight to be considered full.

16. Isotopes
Atoms of the same element will always have the same atomic number, but may have different mass numbers. Atoms of the same element, which differ in mass number, are called isotopes. Their atomic masses differ, however, because they have slightly different number of neutrons. The atomic mass of any element is the average of the weighted sum of the atomic masses of its various isotopes.

17. Example: One isotope of an element—for example, carbon-12—is far more abundant than the others because natural processes favor that particular isotope. These three carbon isotopes all have the same number of protons and thus the same atomic number, 6.

18. Lewis Structure
The Lewis Structure (also called an electron dot diagram) uses the symbol of the element and dots to represent the valence electrons (electrons in the outer energy level).
To make an electron dot diagram:
Write the symbol.
Write a dot to symbolize each electron.
Rule: The electrons will not pair up until they have to. 

20. Ex: Let’s start with Phosphorus – P.
Phosphorus has an Atomic Number of 15 (number of protons), thus, having 15 electrons.
Draw a Bohr’s model of Phosphorus.
How many valence electrons are there? _____

21. Place the first four electrons around the symbol starting at the top.
Then place the remaining electron starting on the top again.

22. Ex: Try Magnesium – Mg.
# of electrons = _____
Bohr’s model of Magnesium:
# of valence electrons = _____
Lewis Structure of Magnesium:

23. – simplest and purest substance that
CANNOT be broken down or changed
into simpler substances.
– smallest particle of an element
– basic building block of matter
are made of
Subatomic particles
located in the
– 99.9 % of mass
– shells or orbitals
= Atomic Number
…has a ___ charge
sum of is
Mass Number
The average of all known isotopes is the
In a neutral atom the # of ____________ equals the # of _____________

24. Atomic Structure Notes - Learning Log
Everything is made of ________.
Atoms are the smallest part of____________.
Atoms are made up of 3 subatomic particles called ____________, ____________, _____________.
The negatively charged particles are called _________________.
The electrons are located _________________ the nucleus.
The electrons can be ____________ or ____________.
Electrons are ( SMALLER or LARGER ) than a proton.
The positively charged particles are in the ____________.
Protons are important because they determine what _______________ an atom is.
The protons and the ______________ are in the nucleus.

25. The neutrons provide _____________, but not ____________.
___________ ____________ published the theory of the atom that had these important points:
___________________________________________________
The atomic number is equal to ___________________________.
The mass number is equal to _____________________________.
Number of Protons is equal to ____________________________.
Opposites charges attract and like repel; therefore, protons __________ electrons but protons ___________ protons; electrons ______________ electrons.

26. Sketch a picture showing how attraction and repulsion work.
Explain the distribution of electrons in their orbits. ____________________________________________________
Attraction
Repulsion
Sketch hydrogen showing the equality of electrons and protons.
Sketch the correct filling of the orbits with the lithium model.

27. Find the missing number of…
Element
Symbol
Atomic Number
Atomic Mass
Number of Protons
Number of Neutrons
Number of Electrons
Hydrogen H 1
1.0
Helium He 2
4.0
Lithium Li 3
6.9
Beryllium Be 4
9.0
Boron B 5
10.8
Carbon C 6
12.0
Nitrogen N 7
14.0
Oxygen O 8
16.0
Fluorine F 9
19.0
Neon Ne 10
20.2
Sodium Na 11
23.0
Chlorine Cl 17
35.5
Lead Pb 82
207.2
Uranium U 92
238.0