Tuesday!!!!!11/1/11Bell Ringer

1) Get out your Ch. 5 book pages and your notes we started.

Schedule1. Bell Ringer

2. CH. 5 Notes

3. Flame Test Pre-lab

HOMEWORK: Print Ch. 5 Notes

PAP Chemistry

Teachers open the door, but you must enter by yourself.

I CAN……solve chemistry problems by being an independent, creative thinker.

Dalton• Proposed model for atom• Dalton’s Atomic Theory

– Elements composed of atoms– Atoms of same elements are alike in mass and size***– Atoms of different elements have different mass and size– Chemical compounds are formed by the union of two or

more atoms of the different elements– Atoms combine to form compounds in simple numeric

ratios– Atoms of two elements may combine in different ratios to

form more than one compound• Modifications to Dalton’s original theory:

– Atoms are composed of subatomic particles– ***Not all atoms of same element have the same mass– Under certain circumstances, atoms can decompose

Use of Models• Models are used to explain behavior• Dalton’s Atomic Model:

– Explains behavior of atoms, compounds and molecules

• Modifications made when new information arises

Law of Definite Composition• Compounds contain two or more elements

chemically combined in definite proportions by mass

• Water is always a 1 : 2 ratio, oxygen to hydrogen

• Hydrogen peroxide is always a 2 : 2 ratio, oxygen to hydrogen

Law of Multiple Proportions• Atoms of two or more elements may

combine in different ratios to produce more than one compound

• CuCl CuCl2• CH4 C8H18

Significance of the two Laws…why are they so important???

• Composition of a substance will ALWAYS be the same

• Composition of different compounds formed from the same elements will be unique

Law v. Model• Law

– Summary of observed behavior– Remain constant

• Model (theory)– Attempt to explain the observed

behavior– Can be modified

Electric Charge

• Positive• Negative• Unlike charges attract• Like charges repel• Charge may transfer form one object to

another: induction or contact– Induction: influence of a charged object,

NOT BY CONTACT

Force, charge and distance

F = kq1q2 r2

Ions ( Faraday and Arrhenius)

• Positive = cations• Negative = anions• Gain or transfer of electrons

(Stoney / Thomson)

Subatomic Particles• Electron (Thomson) e-

– Negative charge– Mass 9.11 x 10-28 g

• Proton (Goldstein, Thomson) p+ – 1.637 x10 -24 g – Positive charge

• Neutron (Chadwick) n°– Neutral charge– 1.675 x10 -24 g

Rutherford and the Nucleus of the Atom

• Gold Foil ExperimentTop: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge. Note that the image is not to scale; in reality the nucleus is vastly smaller than the electron shell.

Atomic Arrangement• What makes

an atom neutral?

• Same number of protons and electrons

What do the numbers mean?

• Atomic # = # p+

• Whole number increasing from left to right on the periodic table

• # p+ = # e- • Mass number = n° + p+

Isotopes • Atom with same atomic number and different numbers of neutrons in nucleus of atom

Isotopes• Most elements occur in nature as

mixtures of isotopes• Not all are stable• Radioactive isotopes• Decompose

Atomic Mass• Atomic mass or atomic weight• Measured in atomic mass units or amu• Atomic mass is average relative mass

of all naturally occurring isotopes of that element

• The atomic mass of an element is compared to the atomic mass of carbon-12 (12.00 amu)