Part 1 • Atomic Theory
Dec 30, 2015
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