Bowen_Chpt 3

Atoms: The Building Block of

Matter

Atom: from idea to theory 3-1

The structure 3-2

I. Idea to Theory

A. Democritus, 400 B.C. proposed that the world

was made up of two things:

1. Empty space

2. Small particles he called atomos (translates to

tiny invisible particles)

B. i. A theory is valid as long as there is no evidence to dispute it.

ii. A law generalizes a body of observations. At the time it is made, no exceptions have been found to a law. Scientific laws explain things, but they do not describe them.

C. Law of Conservation of Mass = matter cannot be

created nor destroyed, only chemically altered. A + B 

AB.

D. Law of Definite Proportions = specific substances always contain elements in the same ratio by mass.

(DNW Example, mass of sodium 60.66% to the mass of chlorine 39.34% in salt is always the same.)

E. Law of Multiple Proportions = the ratio of masses of

elements that form more than one compound with each other are represented with a small whole number ratio.

DNW Isaac Newton and Robert Boyle

in the 17

century published articles

stating their belief in atomic structure

.

•

John Dalton in the

early 1800s offered

the first logical

quantitative (#)

explanation of atomic

structure.

•

He use the previous

F. Dalton’s Atomic Theory

i. All matter is composed of tiny particles called atoms. ii. These particles could not be broken down into

smaller substances.

iii. Atoms of the same element are all exactly alike and atoms of different elements are not alike.

iv. Atoms combine in simple ratios to form compounds. (law of definite and multiple proportions)

v. Atoms can not be destroyed (only rearranged during a chemical reaction)

II. Research and Revisions of Dalton’s

Atomic Theory3-2

A. JJ Thomson proposed

the Plum Pudding

Model in which the

negative electrons were

held in place by a

II. Research and Revisions of Dalton’s Atomic

Theory

i. (DNW)Thomson work with the cathode ray tube led to the discovery that cathode rays consisted of electrons. By exposing the ray to a magnetic field and measuring the bending of the ray, he was able to calculate the ratio of an electron’s charge to its mass.

ii. High voltage electricity is passed into the cathode (negative end). A ray is generated toward the anode (positive end). When a magnet is placed near the ray, the negative end of magnet would cause the ray to bend in the opposite direction and the positive end would bend the ray towards the magnet.

• _{http://www.chem.uiuc.edu/clcwebsite}

II. Research and Revisions of Dalton’s Atomic Theory

B. Robert Millikan obtained the first accurate measurement of the electron charge

c.

i. Rutherford's Gold Foil experiment. ii. Alpha particle is a form of radiation.

Most of the alpha particles are

Results of Gold Foil Experiment

1. The atom contains a tiny dense center called the nucleus

the volume is about 1/10 trillionth the volume of the atom . Ex. If a marble was in the center of a FB field.

2. The nucleus is essentially the entire mass of the atom 3. The nucleus is positively charged

the amount of positive charge of the nucleus balances the negative charge of the electrons

4. The electrons move around in the empty space of the atom surrounding the nucleus

III. Atomic Structure

A. Electrons = negatively charged particles i. Smallest of the subatomic particles (e-)

ii. Found on the outside of the central mass (nucleus) in a cloud type structure.

B. Protons = positively charged subatomic particles

i. Largest (along with the neutron) of the subatomic particles (p+).

ii. Found in the dense central mass called nucleus. C. Neutrons - neutral, no charge

i. Equal to the size of the proton(no).

III. Atomic Structure

D. Particle mass

i. amu – An atomic mass unit ii.

Particle Mass

# Relative Mass (amu) Actual Mass (kg)

Electron 0 .0005486 9.109 x10-31

Proton 1 1.007276 1.673 x 10-27

IV. Counting Atoms 3-3

b.

Atomic Mass

vs. Mass Number

•

Mass of protons and

neutrons.

•

If in decimal form is

an average of the mass

of all isotopes.

•

Mass of protons and

neutrons.

•

Always expressed as a

whole number.

•

Can obtain by rounding

atomic mass.

19

K

39.0983

c. The number of neutrons in an atom determines

an isotope

i. Isotope- atoms of an element that have the same numbers of protons but differ in the number of neutrons.

D. Average Atomic Mass

(On Your Test!!!!!)

ii. Use the weighted averages to include how frequently atoms are found in certain isotopes.

iii. Example: 90% of the time, neon is found as Neon-20 with a mass of 19.992 amu. 10% of the time, it is found as Neon-22 with a mass of 21.991 amu.

a. First isotope: 90%

i. .90(90%) x 19.992 amu = 17.992 amu b. Second isotope : 10%

i. .10(10%) x 21.991 amu = 2.1991 amu c. Add these together

E. Mole

A. Mole (mol) – the amount of a substance that contains as many particles as there are in exactly 12g of carbon-12.

i. just a counting unit or label ii. Have out you Mole

Calculation Hand out

F. Avogadro's Number

A. is the accepted value for how many particles are in 1 mol of a pure substance.

i. 6.0221367 x 1023 atoms of _____

G. Molar Mass

A. The mass of 1mol of a pure substance is called the molar mass of that substance.

i. the unit is g/mol or mol/g (it is a conversion factor, they can be reciprocals)

ii. Molar mass is equal to the atomic mass of an element.

a. 1mol (element) = ____ g (=amu of that element)

b. ____ g (=amu of that element) = 1mol (element)

iii. YES THIS IS WHY I HAD YOU MEMORIZE THEM!!!!!!!!!  (DNW)

H. Grams / mole conversion & calculation.

A. How many grams are in 3.50 mol of Cu? Steps

3.50 mol Cu x ____g of Cu = 1 1 mol of Cu

3.50 mol Cu x 63.55g of Cu = 1 1 mol of Cu

VII. Conversion with Avogadro’s Number

A. Used to Calculate the number of atoms from its molar amount and vice versa.

B. It is done the same way as the other

C. 1 mol of ____ or 6.022 x 1023 atoms of

6.022 x 1023 atoms of 1 mol of ____

11.9 g Al x 1

1 mol of Al = _____g of Al

How many mole in 11.9g of Al?

11.9 g Al x 1 mol of Al

How many mol of Silver(Ag) are in 3.01 x 1023 atoms of Ag?

=.51 mol Ag

How many atoms are 3.75 mol of H ???

= 2.26 x 10 24 atoms of H

3.01 x 1023 atoms of Ag 1

x 1 mol of Ag = 6.022 x 1023 _{atoms of Ag}

6.022 x 1023 atoms of H 1 mol H