1. Atomic Structure

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

3. What is an element? Elements are types of atoms
An atom of sodium is different from an atom of sulfur (different identities), but they both are the smallest unit of each substance

4. Atomic Structure Atoms are composed of 2 regions:
Nucleus: the center of the atom that contains the mass of the atom
Electron cloud: region that surrounds the nucleus that contains most of the space in the atom
Nucleus
Electron
Cloud

5. What’s in the Nucleus?
The nucleus contains 2 of the 3 subatomic particles:
Protons: positively charged particles
Neutrons: neutral particles (no charge)
Protons and Neutrons make up the mass of the atom

6. What’s in the Electron Cloud?
The 3rd subatomic particle resides outside of the nucleus in the electron cloud
Electron: negatively charged particle with almost no mass
The Electron Cloud is most of the atom’s volume

7. How do the subatomic particles balance each other?
When atoms are NEUTRAL….
The # protons = the # electrons
If there are 20 protons in an atom then there has to be 20 electrons balance the overall charge of the atom—when the atom is neutral
The neutrons have no charge; therefore they do not have to equal the number of protons or electrons

8. How do we know what’s in an atom?
Atomic number = Number of PROTONS
Ex: Hydrogen’s atomic number is 1. How many protons does hydrogen have?
hydrogen has 1 proton
Ex: Carbon’s atomic number is 6. How many protons does carbon have?
carbon has 6 protons
**The number of protons identifies the atom.
Which element has 2 protons?
Which element has 29 protons?

9. How do we know what’s in an atom?
Mass number: the number of protons and neutrons in the nucleus
(electrons are so small they’re not counted)
Ex: hydrogen can have a mass of 3.
Since it has 1 proton it must have 2 neutrons
# of neutrons = mass # - atomic #

10. What’s the units?

11. Determining the number of protons and neutrons
Li has a mass number of 7 and an atomic number of 3
How many Protons? = 3
How many Neutrons? = 4 (mass # - atomic #)
Ne has a mass number of 20 and an atomic number of 10
How many Protons? = 10
How many Neutrons? = = 10

12. Why are mass numbers on my table not whole numbers?
ISOTOPES: atoms with the same atomic number but different # neutrons.
This doesn’t affect the identity
This doesn’t affect the charge
This gives the atom a different mass number
The periodic table mass numbers are averages
Round to the nearest whole number to do calculations

13. What about the electrons?
To be neutral the # electrons must be equal to the # protons
So e- = p+ = atomic #
Ex: He has a mass # of 4 and an atomic # of 2
p+ = 2
no = 2
e- = 2

14. Determine the number of subatomic particles in the following:
Cl has a mass # of 35 and an atomic # of 17
p+ = 17, no = 18, e- = 17
K has a mass # of 39 and an atomic # of 19
P+ = 19, no = 20, e- = 19

15. Preview: How exactly are the particles arranged?
Bohr Model of the atom:
Nucleus: all of the protons and the neutrons
The 3rd ring can hold up to 8 e-
The 1st ring can hold up to 2 e-
The 4th and 5th rings can hold up to 16 e-
The 2nd ring can hold up to 8 e-

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

17. Color code your periodic table Make sure you draw a dark line to separate metals from nonmetals
Noble Gases