Objectives

1. Distinguish between the early schools of thought on the nature of the atom.

2. Know the effects of politics on the development of the atomic theory

3. Know and understand Dalton’s atomic theory

4. Know the subatomic particles and their characteristics

5. Know and understand the modern model of the atom

Objectives (cont.)6. Describe the behavior of light and

carry out calculations.7. Define and describe isotopes and

calculate the weighted atomic mass of an element.

8. Understand the atomic emission spectra.

9. Write electron configurations.

The Development

Electron First subatomic particle discovered 1897- JJ Thomson Method of discovery- cathode ray tube Passed electricity through glass tubes with

most of the air removed The ray attracted to the positive charge and

deflected by the negative charge In 1897 he realized:

Electron is negative Mass 1/1800 of proton

Plum Pudding model JJ Thomson proposed this model Uniformly distributed individual

electrons on a positive charge sphere

Ernest Rutherford Rutherford’s Gold Foil Experiment

(1910) Tested the plum pudding model Discovered:

That most of the mass of atom is in the core, named the nucleus

The nucleus is positively charged (protons)

Most of the volume of the atom is empty space

James Chadwick In 1932, he discovered the neutron

They have no charge and the mass equal to that of a proton

The Periodic Table

Development of the Periodic Table In the 1700s, Lavoisier compiled a list of

all the known elements of the time In the 1800s, John Newlands proposed

an arrangement where elements were ordered by increasing atomic mass

Newlands noticed when the elements were arranged by increasing atomic mass, their properties repeated every eighth element

Part 2

Development of the Periodic Table Mendeleev realized there was a

connection between atomic mass and elemental properties

Mendeleev noticed that as atomic mass increased the properties of elements repeated periodically

Mendeleev made predictions about the gaps in the table of the undiscovered elements

Development of the Periodic Table A few problems arose

with Mendeleev’s organization by atomic mass

Moseley arrange the elements by atomic number

This is the periodic table we use today

Periodic Table Columns of elements are called groups Rows of elements are called periods

Elements Most symbols are

formed from the first letter of the element’s name (and sometimes the second letter or third letter) There are exceptions Examples:

First letter is always uppercase and the second is always lowercase

Metals

Metalloids Properties between metals and

nonmetals

Groups and Families alkali metal family(but does not

include H)

alkaline earth metal family

Transition metals Rare earth metals

Nonmetals

halogens

noble gases (or inert gases)

Chemical Formulas Formulas show the elements and

number of atoms of each in a compound Subscripts show the number of atoms Example:

  Symbol Charge

Location Relative mass

Electron e- -1 In the space surrounding the nucleus

0 amu

Proton P+ +1 In the nucleus

1 amu

Neutron n 0 In the nucleus

1 amu

SUBATOMIC PARTICLES

Reading the Periodic Table

For gold: Z:

A:

# protons:

# electrons:

# neutrons:

Isotopic symbol:

Family:

Isotopes Atoms of the same element that have different

masses Many elements have only one stable form, while

other elements have different “versions” of their atoms

Isotopes of the same element have:

Atomic Mass Weighted average of the atomic masses of the

naturally occurring isotopes of an element Example: Calculate the atomic mass of nitrogen.

Given: 99.63% of nitrogen is nitrogen-14 and 0.37% of nitrogen is nitrogen-15.

Example: Determine the weighted atomic mass.

Isotope Mass of one atom

% abundance

Silicon- 28 27.98 amu 92.21

Silicon- 29 28.98 amu 4.70

Silicon- 30 29.97 amu 3.08

Isotope Mass Abundance

Gold- 92 92.09 21%

Gold- 91 91.20 71%

Gold- 90 90.08 8%

Review QuestionWhich isotope of Argon is most likely to be in the highest percentage? Ar- 36 Ar- 38 Ar- 40