part 1 atomic theory. chemistry warm-up: why do you think we have to learn about chemistry in a...

Part 1

• Atomic Theory

Chemistry

Warm-up:

Why do you think we have to learn about Chemistry in a

Biology class?

A Brief History:

• Democritus (Fourth Century BC)– First named the “atom”– Lacked evidence

• John Dalton (1766-1844)– Performed experiments to discover:

• Dalton’s Atomic Theory

Dalton’s Atomic Theory

1. All elements composed of tiny indivisible particles called atoms.

2. Atoms of the same element are identical

It sure is nice hanging out with you, Carbon.

Tell me about it, Carbon!

Um, who is this? He looks

pretty different from you and me, Carbon.

I’m Oxygen. I am different from you, but I’m sure we could find

some way to bond!

Atoms of Element A

Atoms of Element B

What happens when they mix?

Still more of Dalton’s Atomic Theory…

3. Atoms of different elements can physically mix together or can chemically combine to form compounds.

4. Chemical reactions occur when: – atoms are separated, joined or rearranged; – however, they are never changed into atoms

of another element.

Reflecting on Dalton’s Theory

Most of Dalton’s theory is still accepted. Which part do you think has been rejected?

The Atom is Divisible!

The three kinds of subatomic particles

1. Electrons (e-)– Discovered by J.J. Thomson in 1897.– He used a cathode ray tube– In 1916, Robert Millikan discovered the

mass was 1/1840 H, and the charge was one unit of negative charge.

– Actual mass: 9.11 x 10-28 __________grams

2. Protons (p+)– Discovered in 1886, Eugen Goldstein saw

cathode rays traveling against the flow.– What do you think the proton’s mass is in

relation to the electron? ________________– Actual mass = 1.67 x 10-24 grams– One unit of positive charge

3. Neutrons (n0)– Discovered by James Chadwick in 1932.– Actual mass = 1.67 x 10-24 grams– No charge

The three kinds of subatomic particles

1,840 times as big

In 1911, Rutherford performed an experiment:

So how are all these parts put together?

Thin sheet of gold foil

Source of alpha particles

What did this prove?

Atoms are mostly empty space

• Rutherford proposed that the atomic structure was like “planets around the sun”– This did not account for very specific traits

that atoms possessed.

The Bohr Model

• In 1915, Neils Bohr modified Rutherford’s “planetary” model of the atom and added the new discovery of Quantum Theory:

High energy orbital

Low energy orbital

What makes atoms different from each other, if they have the same basic parts?

The Atomic NumberDefinition: The number of protons in the nucleus

of an atom of that element.

Why protons?Why not neutrons?

Or electrons?

• Oxygen’s Atomic Number is 8.– How many protons does it have? _______– How many neutrons does it have? ________– How many electrons does it have? ________

• Wait a minute, how do we know we have that many of each atomic component?

888

Mass Number

• The total number of protons and neutrons is called the mass number.

+ +

Based on this nucleus, what is the mass number?

What element is it?

4

Helium

What about those special cases?

• Sometimes there are more or less neutrons in a nucleus, these are called isotopes.

Do page 30 now

BP = _____

N = _____

E = _____

5

6

5

5The Atomic Number

Element’s Name Boron

Atomic Mass 10.81

B

Bohr Diagram

Lewis Structure

Part 2

• Bonding with activities

Bond with your classmate! (page 37)

• Each of you will have an element.

• The charge – or oxidation number – is on the element.

• Your goal is to bond with as many of your classmates as possible.

• Balance your equations!– i.e., Magnesium (Mg) and Bromine (Br) must

make MgBr2

Bond!

Bonding and Chemical Reactions

• Chemical Bonding:

Combining Atoms of Elements to form Chemical Compounds

Hi there!I’m Nitrogen.

Am I an atom or a

compound?

Greetings, Nitrogen. We are Hydrogen

atoms. Perhaps we will change the way

you think about yourself.

You were right! I am now

Ammonia! But, am I an atom

or a compound now?

Oh, you can’t be serious!

Bonding

Ionic Bonds:A bond that involves a transfer of electrons

To achieve stability, an atom will either gain, lose or share electrons.

Ionic Bonds

Sodium ChlorineIon (+1) Ion (-1)

ChlorideSodium Chloride = Salt!

Covalent Bonds

• A covalent bond is a chemical bond formed by sharing electrons.

Can you guess which element I am?

What will complete my valence shell?

Different types of Covalent Bonds

Single Bond: One pair of shared electrons

Double Bond: Two pairs of shared electrons

Triple Bond: Three pairs of shared electrons

Hydrogen Cyanide (HCN) can form this.

Can you?

= H – H

CO=C=OLone pairs: Electron pairs not shared between atoms

N H

H

H

Practice ExercisesHow many Bonds and Lone Pairs?

1. Write Lewis structure for F2.

2. Write Lewis structure for O2.

3. Write Lewis structure for N2.

4. Write Lewis structure for ammonia, NH3.

5. Write Lewis structure for CO2.

Time for more Practice

• Page 34-35 Making Ionic Bond

Chemical Reactions

• Any process in which a chemical change takes place.– Slow occurring (i.e., Iron and Oxygen Rust)– Quickly occurring (i.e., Combustion Reaction)

Time to Practice

Page 36 Balancing Act

Bonding Basics Practice Answers (page 33)

Ionic Bonds

1. Mg + Br

2. Pb + S

3. Al + Cl

Mg BrBr

1- 1-2+

MgBr2

PbS2Pb SS

4+ 2-2-

Al Cl

Cl

Cl3+ 1-1-

AlCl3

1-

Bonding Basics Practice Answers (page 33)

Covalent Bonds

1. H + Cl

2. C + Cl

3. Si + O

H Cl H – Cl HCl

CCl4 C Cl

Cl

Cl

Cl

C Cl

Cl

Cl

Cl

Si OO O = Si = O

SiO2