Chapter 7

Atomic Theory – Inside the Invisible

7.1 Development of A Modern Atomic Theory

Dalton’s Theory

○ Dalton envisioned the atom as the smallest piece of any element, as a smooth, solid sphere, without an electrical charge

Thompson’s Model of the Atom

○ A new model was needed as Michael Faraday discovered atoms contained electric charges

○ Thompson proposed that an atom was mostly positively charged matter, with small negatively charged electrons scattered throughout.

○ Sometimes referred to as the raisin bun model.

Rutherford’s Gold Foil Experiment

Rutherford’s Model

○ Most of the mass of the atom and all the positive charge is concentrated in the centre.

○ The nucleus contains protons and neutrons.

○ Electrons are orbiting the nucleus.

Assignment

○ P. 208 #4-5, 7-10, 12

7.2 Bohr Model of the Atom

Bohr Model of the Atom

○ Electrons are restricted to specific “allowed” orbits, or shells around the nucleus.

○ The amount of energy an electron has is related to how far it is from the nucleus.

○ The periodic law states that the properties of elements are a periodic or regularly repeating function of their atomic number

○ The atomic number is the number of protons in the nucleus of an atom

○ The mass number is the total number of protons and neutrons in the nucleus of an atom

17 protons, 17 electrons, 18 neutrons

Standard Atomic Notation

35Cl17

SymbolMass number

Atomic number

○ In an atom, the number of electrons equals the number of protons

○ In an ion, the number of electrons does not equal the number of protons. Electrons have been added or removed.

Assignment

○ Subatomic Particles Worksheet

7.2 Structure of an Atom

Subatomic Particles

Particle Charge Mass Location

Proton 1+ 1 Nucleus

Neutron 0 1 Nucleus

Electron 1- 1/1800 Outside nucleus

○ Ions are charged atoms ○ A positive ion has had electrons

removed. There are more protons than electrons

○ A negative ion has had electrons added. There are more electrons than protons.

35Cl-17

o Protons

o Neutrons

o Electrons

17

18

18

24Mg2+

o Protons

o Neutrons

o Electrons

12

12

10

12

Assignment

○ P. 212 #2, 5, 6-7, 10-11

7.3 Modern Periodic Table

○ The atomic mass is the average of all the naturally occurring isotopes

○ Isotopes are atoms with the same atomic number, but different mass number (protons are the same but neutrons are different).

Assignment

○ P. 217 #1-18

7.4 Bohr Models

Drawing Bohr Diagrams

○ Each atom can have 2 electrons in the inner most shell, 8 in the second and 8 in the third

○ Shells are filled in the order of inner to outer

○ Electrons in the outer shell are involved in chemical reactions

○ Electrons in full shells do not take part in chemical reactions

Assignment

○ Bohr Diagrams Worksheet

7.4 Formation of Ions

○ Li+ ion is held to F- ion by electrical forces

○ A molecular compound has two or more atoms joined together. Electrons are shared.

○ Ionic compounds are not made of molecules. Ions are attracted to one another due to their charges. Electrons have been transferred.

Assignment

○ P. 223 #1, 5, 11-13

Review Assignment

○ P. 230 #1-5, 7-8, 12, 13 ○ Atoms and Their Electrons Video