Ariana Garcia-Minsal

Dalton's Atomic Theory - (1808)

His atomic theory could be summarized as:

1) Matter is composed of tiny and indivisible particles called atoms.

2) All atoms of a particular element are identical in size and in mass. Atoms of different elements are different in size and in mass.

Dalton's Atomic Theory - (1808)

His atomic theory could be summarized as:

3) Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.4) Chemical reactions occur when atoms are separated from each other, joined, or rearranged in a different combination. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.

Discovery of the Electron

In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle.

Cathode ray tubes pass electricity through a gas that is contained at a very low pressure.

In the years between approximately 1860 and 1935 the internal structure of the atom was elucidated: see video

J.J. Thomson: In 1904, J. J. Thomson proposed an atomic model best known as the “raisin-pudding model”. He described the atom as a uniformly positive sphere of matter in which electrons were embedded somewhat like raisins in a pudding.

ATOMIC MODELS

See videoThe Nuclear Atom

Rutherford’s major conclusions from the -particle scattering experiment

1. The atom is mostly empty space.

2. It contains a very small, dense center called the nucleus.

3. Nearly all of the atom’s mass is in the nucleus.

4. The nuclear diameter is 1/10,000 to 1/100,000 times less than atom’s radius.

The Nuclear Atom

The atom is mostly empty space.

Two regions

Nucleus contains protons and neutrons.

Electron cloud- region where you might find an electron.

The Nuclear Atom

NUCLEAR MODEL:

In 1911, Ernest Rutherford proposed the first nuclear model. The atoms consisted of a very tiny center, or nucleus, that contains all the positively charged particles and nearly all the mass of the atom. The electrons were distributed throughout the extra nuclear part of the atom. According to this model “the volume” of the atom is largely an empty space.

Particle Mass (amu) Charge

Electron (e-) 0.00054858 -1

Proton (p,p+) 1.0073 +1

Neutron(n,n0) 1.0087 0

Sub-atomic Particles Z - atomic number = number of protons

determines type of atom. A - mass number = number of protons +

neutrons. Number of protons = number of electrons if

neutral.

Symbols

XA

Z

Na23

11

11 protons11 electrons12 neutrons

Isotopes: Atoms with the same number of protons, but different number of neutrons

O OO16 17 188 8 8

H HH1 2 31 1 1

99.762% 0.038% 0.200%

# protons

# electrons

# neutrons Atomic number Z

Mass number A

Isotopic symbol

Hydrogen-3 1 1 2 1 3 3 1

Copper-65 29 29 36 29 65 6529

Beryllium-9 4 4 5 4 9 94

Carbon-14 6 6 8 6 14 14 6

Phosphorus-31

15 15 16 15 31 3115

Nitrogen-14 7 7 7 7 14 147

H

Cu

Be

C

P

N

Mass Spectroscopy

The spectrum obtained from this technique allows us to know the abundance of each isotope in a sample.

63 650

20

40

60

80Percent abundance

Atomic mass

The atomic weight of an element is the weighted average of the masses of its stable isotopes

Example: Naturally occurring Cu consists of 2 isotopes. It is 69.1% 63Cu with a mass of 62.9 amu, and 30.9% 65Cu, which has a mass of 64.9 amu. Calculate the atomic weight of Cu to one decimal place.

copperfor amu 63.5 weight atomic

100

9)(30.9)(64. 9)(69.1)(62. weight atomic