Chem Unit2

The AtomDemocritus

Invisible

Immortal

Indivisible units

Aristotle

Continuous matter

Joseph

Proust

(1754 – 1826)Law of Definite Proportions

Law of Definite

ProportionsCopper Carbonate:

Regardless of the source, a compound always has the same proportion of elements

Law of Definite

Proportions

Copper Carbonate:

CuCO3 -> Copper + Carbon + Oxygen

Law of Definite

ProportionsCopper Carbonate:

CuCO3 -> Copper + Carbon + Oxygen

51.36% 9.72% 38.85%

Antoine Lavoisier

Law of Conservation of Mass

Antoine Lavoisier

Law of Conservation of Mass

Antoine Lavoisier

Accounting for Oxygen gas

John Dalton

Law of MultipleProportions

Law of Multiple Proportions

CO and CO2

H2O and H2O2

NH3 and N2H4

Law of Multiple Proportions

NH3 and N2H4

N2 + 3 H2 ---> NH3

N2 + 2 H2 ----> N2H4

Law of Multiple Proportions

NH3 and N2H4

N2 + 3 H2 ---> NH3

28 g 6 g 34 g

N2 + 2 H2 ----> N2H4

28 g 4 g 32 g

Law of Multiple Proportions

When elements combine to form more than one compound, different masses of one element compared to the mass of the other element are small whole number ratios.

Law of Multiple Proportions

CO and CO2

2 C + O2 ---> 2 CO

24 g 32 g 56 g

C + O2 ----> CO2

12 g 32 g 44 g

Dalton’s Five Principles

Matter is made of atoms

All atoms of one element are the same

Atoms of different elements are different

Atoms combine to form compounds

Atoms are rearranged in chemical reactions but not created nor destroyed

What is an Atom?

Cathode Rays

William Crookes

CRTs

Stream of Charged Particles

How much smaller?

Robert Millikan found that the particles were 1/1840 the size of the Hydrogen atom

Plum Pudding Model

Negatively charged particles embedded in a positively charged ball of matter.

The Discovery of ElectronsJ.J. Thomson found that the cathode ray particles were much smaller than the H atom

Rutherford’s Gold Foil experiment

Ernest Rutherford directed alpha particles at gold foil

Planetary Model

The Discovery of the Neutron

1932

Finds particle with no charge that has a mass of 1 atomic mass unit

Atomic Number

Identification Number

NUMBER

OF PROTONS

Atomic Numbers

Atomic Masses

Number of Protons (ATOMIC NUMBER)

+

Number of Neutrons

ATOMIC MASS

Dalton’s Atoms

Atoms

Atomic Symbols

Mass Number A = Sum of protons and neutrons

Atomic number, Z = # of protons

Atomic Symbols

Mass Number A = Sum of protons and neutrons

Atomic number, Z = # of protons

The number of neutrons for any atom will be the difference between A and Z (A – Z = # neutrons)

Writing Atomic Symbols

Symbol Atomic mass

protons neutrons

22 ???? ?????

????? 20 26

11 ???? 6

???? ????? ??????

€

1022Ne

€

2046Ca

€

511B

€

3064Zn

Writing Atomic Symbols

Symbol Atomic mass

protons neutrons

22 10 12

46 20 26

11 5 6

64 30 34

€

1022Ne

€

2046Ca

€

511B

€

3064Zn

Isotopes

Same atomic number

Different Mass number

Different # neutrons

Isotopes

Relative abundance

Br-79 Br-81

50.697% 49.317%

Bromine:

35 protons

Relative abundance

Br-79 Br-81

50.697% 49.317%

Bromine:

35 protons

(79)(0.50697) + (81)(0.49317) =

40 + 39.9 = 79.9

Listed Atomic Massed areWeighted Averages

Br79.9

35

Same atomic mass??

€

2860Ni

2960Co

What about Electrons?

Why don’t electrons crash into the Nucleus?

Bohr Model of the Atom

Niels Bohr1913

Allowable Energy Transitions

Electromagnetic Spectrum

Properties of Waves

As Wavelength increases, Frequency decreases.

Wavelength x Frequency = λ x ν = velocity of Light = c

Emission Spectra

Atomic Emission Spectra

Schrödinger probability functions

S orbital

P orbitals

3 types of porbitals

D orbitals

5 types of d orbitals

How can electrons be ordered?

Energy Levels

Aufbau (Building up)

Principle

An electron must fill the orbital

With the lowest energy first.

Energy Levels

Orbital Shapes

S orbitals

P orbitals

Orbital Shapes

D orbitals

F orbitals

Quantum Numbers

n Principal Quantum numberEnergy Level

l Angular Momentum Quantum Shapenumber

n Magnetic Quantum numberSpin

Spin States

Pauli exclusion Principle

No two electrons in the same atom may have the same set of four quantum numbers;

Electrons in the same orbital must have opposite spins.

Hund’s Rule

Orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron. All electrons in singly occupied orbitals must have the same spin state

Groups

Dozen

Pair Quartet

The Mole

# of atoms in 12 grams of Carbon-12 atoms

Molar Mass

Mass of one MOLE of pure substance

Helium: 4.00 grams -------> 4 grams per mole

Lithium 6.94 grams ---------> 6.94 grams per mole

Mercury 200.59 grams -------> 200.59 grams per mole

Size of the Atom

Diameter of an atom = 10-10 m

250,000,000 atoms in One Inch

Size of the Atom

1 atomic mass unit = mass of one proton, neutron

= 1.66 x 10-24 grams

Avogadro’s Number

There are 6.02 x 1023 particles in a mole of any substance.