Chapter 3Atoms and Moles

Atomic Theory

All matter is made of atoms

Law of definite proportions Water is 88.8 % oxygen and 11.2 %

hydrogen Law of conservation of mass

Mass cannot be created or destroyed Law of multiple proportions

CO , CO2 / C6H12O6 , C12H22O11 / H2O , H2O2

Dalton’s Atomic Theory

1. All matter is made of extremely small particles called atoms.

2. Atoms of a given element are identical in their properties.

3. Atoms cannot be created, destroyed, or subdivided.

4. Atoms of different elements combine in simple whole-number ratios to form compounds.

5. In chemical reactions, atoms are combined, separated, or rearranged.

Discovery of the electron

Electrons were discovered in a Cathode Ray Tube

Electrons are very small particles that have a negative charge

Original model of an atom

“Plum pudding” model

Electrons were embedded in a positively charged ball of matter

Discovery of the nucleus

Rutherford shot a stream of positive particles at a piece of gold foil and expectedthe particles to go right through the atoms of gold.

Rutherford’s gold foil experiment

He expected most of the particles to go straight through but some ofthe particles bounced straight back. Something very dense and positivelycharged had to be the reason it bounced back.

New model of the atom

Old model

New and improved model

The atom is very large compared to the size of the nucleus

Atomic Nucleus

Protons are positively charged particles Neutrons have no charge - neutral

Counting Subatomic Particles

Atomic number = number of protons

Protons = electrons

Atomic mass = protons + neutrons

Isotope – atoms of a certain element that have a different mass because it has a different number of neutrons.

Where are the electrons

Electrons are found in 3-dimensional spaces around the nucleus called orbitals.

We use 4 quantum numbers to tell:1. The distance from the nucleus2. The shape of the orbital3. The relationship of the orbitals with the

x,y,z axes4. The spin of the electrons

Principal Quantum Number

Indicates the main energy level Values = 1 – 7

This shows how far the orbital is from the nucleus.

Orbital Quantum Number

Indicates the shape of the orbital 4 shapes

s, p, d, f

Orbital shapes

P orbital

Magnetic Quantum Number

Indicates the orientation of the orbitals on the x, y, and z axes.

How many orbitals there are s – 1 p – 3 d – 5 f – 7

Spin Quantum Number

Electrons spin in opposite direction (+1/2, -1/2)

2 electrons can fit in each orbital

Order of orbital filling

Electron Configuration

Oxygen – 8 electrons 1s22s22p4

Sodium – 11 electrons 1s22s22p63s1

Argon – 18 electrons 1s22s22p63s23p6

Arsenic – 33 electrons 1s22s22p63s23p64s23d104p3

Mole

1 mole of any substance has 6.02 x 1023 atoms (Avogadro’s number)

1 mole of any substance is equal to it’s mass on the periodic table in grams. (Molar mass)