Chapter 3

Chapter 3 Discovering the Atom

Essential QuestionsHow was the idea of the atom developed historically?

What important experiments were performed to change our view of atoms?

What are Subatomic Particles?

What is the Modern View of the atom?

What is Atomic Mass?

Historical View – The 4 Elements

Democritus’ Atoms

Changes in The Way We View MatterThe ___________view of __________was based on

__________and not on ______________data.

In 1661, _____________published a proposal that a substance was not an ___________if it was made of two or more _________________.

Changes in The Way We View Matter1760’s - _____________defines the compound.

Experiments That Changed The Way We View Matter

The Law of ____________of __________.(1774)

Dalton’s Atomic Theory1. Elements are made of _______particles

called __________.

2. All _________of a given element are ___________.

3. The _________of a given element are ___________from those of any other __________.

Dalton’s Atomic Theory4. Atoms of _____element can combine

with atoms of _______elements to form _____________. A given __________always has the _______relative _________and ________of atoms.

Dalton’s Atomic Theory5. Atoms are ____________in

_______processes. That is, atoms are not _________or __________in chemical reactions. A chemical reaction simply __________the way the atoms are ___________together.

Law of Constant CompositionIF A given __________always has the

_______relative ______and _____of atoms,

THEN a given _________always ______the _______proportion (by _____) of the elements.

An ExampleWater always contains ____times as much oxygen (by mass)

as hydrogen.

9 grams of water contains ____grams of oxygen and ___gram of hydrogen.

27 g of water has _____g of oxygen and ___g of hydrogen.

What about 100 g of water?

From the other direction8.00 g of oxygen will react with 1.00 g of hydrogen to form

______g of water.

If you mix 24 g of oxygen with 6 g of hydrogen and react them, how much water can you form?

Lab on Constant CompositionPotassium chlorate contains 31.9% potassium, 29.0 %

chlorine, and 39.2% oxygen (by mass).

This should be _____for all samples of _____potassium chlorate.

Lab on Constant CompositionIf you heat potassium ________you get potassium

_______and _______:

2 KC1O3 → 2 KCl+ 3 O2

We will carry out this _____________and measure how much _______we gave off (by difference).

Review of Chemical Formulas1. Each atom present is represented by its _________symbol.

2. The _________of each type of atom is indicated by a ____________written to the right of the element symbol.

3. When only _______atom of an element is present, the subscript ____is not written.

Some FormulasKClO3

H2O

CH4

C12H22O11

S8

The Structure of the AtomUntil the work of ______________, scientists believed that

atoms were the _________possible ___________.

Cathode ray tube – led to the ___________of the ___________by _____________.

Plum Pudding

Rutherford’s Experiment

MODERN ATOMIC STRUCTURE

The _____________charge is found in the nucleus. Therefore, _____________are located in the nucleus. The number of __________held by the nucleus is called ATOMIC _______.

_____________move about the ____________and account for most of the _____________of the atom.

DISCOVERING NEW FORMS OF HYDROGEN

In the early 1930’s, a new form of hydrogen was discovered. It accounted for 0.015% of all hydrogen in nature. The only difference was that it was twice as heavy as the most common form of hydrogen(99.985%). It was, therefore, called heavy hydrogen.

Atomic # Atomic Mass # of p # of e

H

Heavy H

Why is heavy hydrogen twice as heavy?

A NEW SUB-ATOMIC PARTICLE

In 1935, an English scientist of the name ___________discovered a new particle. Its characteristics were:

a. Its mass was basically the _________as that of the ______.

b. Its charge was ____________.

______________, therefore, called this a _____________.

ISOTOPESApparently, ___________hydrogen contains a

___________making it twice as ______________.

Mass Number = the sum of the number of ___________and ____________or sum of _____________.

Isotopes – atoms of the _________element that have the _______number of ___________, but a different number of ___________.

– have the same atomic __________, but different ________ number

Neutrons = ________Number – Atomic ___________

ISOTOPES CONTINUED At.# Mass # #p #e #n

32He

42He

168O

178O

188O

ATOMIC MASSThis is the relative mass of an ________based, temporarily,

on _____________as exactly 1.

Hydrogen Chloride – 2.74% H and 97.3%Cl

Water – 11.1%H and 88.9%O

Ammonia – 17.6%H and 82.4%N

Salt – 39.3%Na and 60.7%Cl

ATOMIC MASSESOld system: H-1 = 1.0000…..

C-12 = 11.9987

New system: C-12 = 12.00000……

H-1 = 1.007825

So atomic mass is defined as the __________mass of an atom based on __-12 as exactly _____.

AVERAGE ATOMIC MASS%PRESENT ATOMIC MASS

H-1 99.985% 1.007825

H-2 0.015% 2.01410

Ave. Atomic Mass = 1.00797

TEXT BOOK ATOMIC MASSThis is the the average of the atomic masses of the isotopes of

an element based on C-12 as exactly 12

CALCULATING ATOMIC MASSES% PRESENT ATOMIC MASS

Cl-35 75.77% 34.969

Cl-37 24.23% 36.966

Ave. Atomic Mass = ?

C-12. 98.892% 12.0000…

C-13 1.108% 13.00335

Ave. Atomic Mass = ?

_______________-- are subatomic particles that comprise known matter and anti-matter.

______________--Do not help hold an atom’s nucleus together and are found in known matter. Are neutrinos and electrons

_______________Particles such as the proton or neutron.

Subatomic Particles

QuarksQuarks--Does not help hold an atom’s nucleus

together. Quarks are extremely ___________, classified by the _________and _________of charge

that they hold, are the most ______________particles discovered to

date.

Bosons and Leptons and QUARKS – Oh MY!TYPES OF QUARKS

1. Up +2/3

2. Down -1/3

3. Top (aka Truth)

4. Bottom (aka Beauty)

5. Charm (aka Charmed)

6. Strange (aka Strangeness)

Proton – 2 Ups and 1 down, 2(2/3) + (-1/3)

Neutron – 1 Up and 2 Downs, (2/3) + 2(-1/3)

Atomic Masses and the Law Of Constant Composition

Remember that the Law of Constant Composition states “a given compound always contains the same proportion (by mass) of the elements.”

This now makes perfect sense with what we know about relative masses.

WaterOxygen has an relative mass of ______ compared

to hydrogen’s _____.

______grams of oxygen has as many O atoms as ______ grams of hydrogen has H atoms.

____ grams of hydrogen has twice as many H atoms as _______ grams of oxygen has O atoms.

The mass ratio in water (H2O) is ___:__ or ___:___

Mass RatiosCarbon and hydrogen react in a ___:____ mass ratio to form

methane (CH4).

How many grams of carbon would react with 6.0 grams of hydrogen?18 g

How does this relate to Atomic Masses?

AlH3

What is the mass ratio for AlH3?Al = __________, H = _____Therefore mass ratio =

__________/__ or ___:___

How many grams of hydrogen would react with 18 grams of aluminum?2 g

How many grams of AlH3 would form from the reaction of 18 grams of aluminum and 6 grams of hydrogen?20 g

PERIODIC TABLEThe elements are arranged in the Periodic Table in order of

increasing ______ __________. When elements are arranged this way, the chemical and physical properties re-occur in a __________fashion. (Dimitri Mendeleev)

Horizontal Rows – ___________

Vertical Columns – ___________

Periodic LawWhen the elements are arranged in order of increasing

__________ ___________ there is a periodic repetition of their chemical and physical properties.

The chemical and physical properties of the elements are a _________function of the _________ _____________.