1. CONCURRENT ENROLLMENT CHEMISTRY
CHAPTER 2
CONCURRENT ENROLLMENT CHEMISTRY

2. ATOMS
ELECTRONS
Thomson found a charge to mass ratio of an electron to be x 108 C/g
This figure shows a typical cathode ray tube.

3. MILLIKAN Defining the Atom
SECTION4.2
Defining the Atom
MILLIKAN
In the early 1910s, Robert Millikan used the oil-drop apparatus shown below to determine the charge of an electron.
Millikan’s oil drop experiment determined the electron mass to be 9.11 x kg

4. RADIOACTIVITY
When a nucleus breaks apart, if there are too many or too few neutrons or too many protons.
When a nuclei becomes unstable it loses energy which is called RADIOACTIVE DECAY
This will occur until the nuclei forms a stable nucleus

5. RADIATION Becquerel discovered radioactivity Three type of radiation
Gamma (γ) rays are high-energy “light”
00γ
A high-energy ray that is like an X ray, but is not a particle
Beta (β) particles are high-speed electrons
-10β or -10e-
Identical to an electron but is produced when a nucleus becomes unstable, a neutron changes into a proton by releasing an electron
Alpha (α) particles are a 2+ charged He nucleus
42α or 42He 2+
Identical to the helium nucleus, has two protons and two neutrons

6. RUTHERFORD Defining the Atom
SECTION4.2
Defining the Atom
RUTHERFORD
In 1911, Ernest Rutherford studied how positively charged alpha particles interacted with solid matter.
By aiming the particles at a thin sheet of gold foil, Rutherford expected the paths of the alpha particles to be only slightly altered by a collision with an electron.

7. Defining the Atom The Nucleus (cont.)
SECTION4.2
Defining the Atom
The Nucleus (cont.)
Although most of the alpha particles went through the gold foil, a few of them bounced back, some at large angles.

8. Defining the Atom The Nucleus (cont.)
SECTION4.2
Defining the Atom
The Nucleus (cont.)
The repulsive force between the positively charged nucleus and positive alpha particles caused the deflections.

9. COMPONENTS Rutherford’s gold foil experiment Atoms have a nucleus
Atoms are made up mostly of space
Protons exist in the nucleus with a + charge
Electrons mass is 9.11 x kg, the charge is -
Protons mass is 1.66 x kg, the charge is +
Neutrons mass is 1.67 x kg, there is no charge
AMU means x kg, so a proton and neutron are 1 AMU each
Atoms are small
Diameters between 1 x 10-10m to 5 x 10-10m, Ǻ = 1 x m so it is 1A to 5A
Isotopes have the same number of protons but different number of neutrons

10. Isotopes and Mass Number (Cont.)
SECTION4.3
How Atoms Differ
Isotopes and Mass Number (Cont.)
The mass number is the sum of the protons and neutrons in the nucleus.

11. COMPOUNDS AND ELEMENTS
Compounds are made up of elements and the number of each element
H2O
Atomic weights are an average of all the isotopes for that element
Atomic weight = (% isotope#1)(mass)+(% isotope#2)(mass)
100

12. How Atoms Differ Mass of Atoms (cont.)
SECTION4.3
How Atoms Differ
Mass of Atoms (cont.)
The atomic mass of an element is the weighted average mass of the isotopes of that element.

13. MOLES An amount of a substance, similar to dozen.
One dozen eggs would not weigh the same as one dozen horses, the same is true in atoms
One mole of anything is 6.02 x 1023 particles of that substance. This is known as Avogadro’s number
If you times magnesium atoms mass to this number, you will get 24.3 g per one mole. This is the atomic mass of magnesium.
One atom of magnesium weighs X g, how much would one mole of magnesium weigh?

14. CHEMICAL FORMULAS
All compounds have constant ratios. This means that the number of elements in a compound remain constant
One mole of water would then contain, two moles of hydrogen and one mole of oxygen
One molecule of water would contain, two atoms of hydrogen and one atom of oxygen
Because of this law you can find mass percentage of any element in any given compound

15. Elements and Compounds
SECTION3.4
Elements and Compounds
Law of Definite Proportions
The law of definite proportions states that a compound is always composed of the same elements in the same proportion by mass, no matter how large or small the sample.
Ex. Water is always composed of 2 Hydrogen to 1 Oxygen
The relative amounts are expressed as percent by mass, the ratio of the mass of each element to the total mass of the compound expressed as a percentage.

16. Elements and Compounds
SECTION3.4
Elements and Compounds
Law of Multiple Proportions
The law of multiple proportions states that when different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in whole number ratios.
Ex. Peroxide, H2O2, and water, H2O.
Different compounds formed from the same elements.
Hydrogen mass the same in both compounds but oxygen mass is a 2:1 ratio in peroxide to water.

17. Early Ideas About Matter
SECTION4.1
Early Ideas About Matter
Greek Philosophers
John Dalton revived the idea of the atom in the early 1800s based on numerous chemical reactions.
Dalton’s atomic theory easily explained conservation of mass in a reaction as the result of the combination, separation, or rearrangement of atoms.