1. The Atom

2. What is an Atom? Atom: Smallest unit of all matter 3 Main Parts:
1) Proton (+ charge)
2) Neutron (No charge)
3) Electron (- charge)
Protons & Electrons usually equal in number
Elements (substance made of only 1 type of atom) are identified on the Periodic Table (page R36)

3. Reading the Periodic Table
Atomic Number: Number of protons (+) the atom contains
Usually # of electrons also
Atomic Mass: Combined # of protons and neutrons inside the nucleus
Electrons too small to affect mass
How many protons, electrons, and neutrons does Carbon contain?
Protons = ______
Electrons = ______
Neutrons = ______ 6 6 6

4. What’s the: Atomic number of Beryllium? B) Atomic mass of Beryllium? 4
C) How many protons?
D) How many electrons?
E) How many neutrons? 4 9 4 4 5

5. Electron Cloud Electrons orbit the nucleus in “energy levels”
1st level:
closest to nucleus
stable w/ 2 electrons
2nd level:
stable w/ 8 electrons
3rd level:
Atoms are stable when the outermost level is “full”
Examine Carbon below. It has 2 electrons in the first level and 4 electrons in the 2nd level. Is Carbon stable?

6. Molecules Molecule: 2 or more atoms held together by a covalent bond
Form when atoms are unstable
Covalent Bond: Chemical bond where atoms share electrons
Ex: Oxygen atom
Why unstable? Only 6 electrons in outer energy level
What happens? Each oxygen atom will share two electrons with the other oxygen
End result? Both will have 8 electrons in its outer level (O2 is created)
Molecules

7. Ionic Bonds Ionic bond: chemical bond where electrons are gained/lost
sodium
chlorine
Ionic bond: chemical bond where electrons are gained/lost
Creates Ions (atoms with + or – charge)
Held together by magnetic attraction
Cause: 1 atom steals an electron(s) from another atom
Ex: Sodium + Chlorine = Sodium Chloride

8. Ionic Bonds 11+ 17+ 11+ 17+ 10- 18- 11- 17- +1 -1 Na Cl Na Cl e e e e
sodium e e e e e e
chlorine e e e e e e e e e
After bonding
Before bonding Na Cl
Protons (+)
Electrons (-)
Net charge Na Cl
Protons (+)
Electrons (-)
Net charge
11+
17+
11+
17+
10-
18-
11-
17- +1 -1

9. Quick Review
Atoms become stable when their outer electron level is “full”
Molecules created when 2 or more atoms combine together
Covalent Molecules: share electrons
Ions: lose and gain electrons