1. Chapter 11
The Atom

2. The Atom
The smallest particle into which an element can be broken down.
size: 3x10-8 cm = cm
3 hundred millionths cm
Structure - Subatomic particles located in the nucleus and the electron cloud

3. Nucleus small, dense, positively charged center of the atom
Contains:
Protons – positively charged particles
Mass: 1amu (atomic mass unit) = 1.7x10-24 g
Neutrons – no charge
Mass: 1 amu
Most of the mass of an atom is found in the nucleus.
The volume is small which is why it is dense.

4. Electron Cloud mostly empty space.
Contains:
Electrons – negatively charged particles
Mass: 0 amu
Can only predict where the electrons can be found around the nucleus.
Most atoms have an equal number of protons and electrons.

5. Forces in the Atom
Electromagnetic force – holds the electrons around the nucleus.
Negative electrons are attracted to the positive protons, opposites charges attract.
Strong force – holds the nucleus together.
Stronger than the electromagnetic force that pushes the protons apart, like charges repel.
Weak Force – plays a key role in radioactive atoms where neutrons turn into protons and electrons

7. Atomic Number Number of protons in the nucleus Determines the elements
Found in each elements square on the periodic table.

8. Isotopes
Atoms of the same element with a different number of neutrons.
You can tell them apart by their mass numbers
Mass number = number of protons plus neutrons

9. Naming Isotopes Element name – mass number Hydrogen – 1
(1 proton + no neutrons =1)
Hydrogen – 2
(1 proton + 1 neutron = 2)

10. Number of Neutrons in an Isotope
# neutrons = mass # – atomic #
p + n – p = n

11. Unstable Isotopes
Some isotopes are unstable making them radioactive (break apart over time)
Carbon – 14
used in carbon dating
Uranium – 238
used in nuclear chain reaction

12. Weight
Mass
Atomic
average of all the known naturally occurring isotopes of an element.

13. Weight Mass Calculating Atomic Copper’s atomic mass = 63.6 amu
Known Isotopes: copper – 63 (69%)
copper – 65 (31%)
Equation:
mass# X percentage + mass# X percentage +.…= atomic mass
63 amu (.69) + 65 amu (.31) = 63.6 amu

14. Try These Chlorine = Chlorine – 35 (76%) Chlorine – 37 (24%)
Thallium =
Thallium – 203 (30%)
Thallium – 205 (70%)
Gallium =
Gallium – 69 (60%)
Gallium – 71 (40%)
35.5 amu
Uranium =
Uranium – 238 (99.284%)
Uranium – 235 (0.711%)
Uranium – 234 (0.005%)
Titanium =
Titanium – 46 (8%)
Titanium – 47 (7.3%)
Titanium – 48 (73.8%)
Titanium – 49 (5.5%)
Titanium – 50 (5.4%)
amu
204.4 amu
47.9 amu
69.8 amu

15. charge = protons – electrons
Ions
Atoms with a charge because they gained or lost an electron.
Have an unequal number of protons and electrons
charge = protons – electrons
Positive Ion Sodium atom has 11 protons
Sodium Ion has 10 electrons
+11 – 10 = +1
Negative Ion Chlorine atom has17 protons
Chlorine Ion has 18 electrons
+17 – 18 = – 1