1. Lesson 1: Structure of Atoms
Unit 2: Elements
Lesson 1: Structure of Atoms

2. Bell Work Why do you think it is important to study science?
What would you like to do with Science?

3. Standards
7.P.2.A Conceptual Understanding: All substances are composed of one or more elements. Elements are pure substances which contain only one kind of atom. The periodic table organizes these elements based on similar properties. Compounds are substances composed of two or more elements. Chemical formulas can be used to describe compounds.
7.P.2A.1: Develop and use simple atomic models to illustrate the components of elements (including the relative position and charge of protons, neutrons, and electrons).
S.1A.2: Develop and use models to (1) understand or represent phenomena, processes, and relationships, (2) test devices or solutions, or (3) communicate ideas to others.

4. Learning Objectives
Develop and use simple atomic models to illustrate the components of elements (including the positions of protons, neutrons and electrons).

5. The Beginning 430 BC Democritus proposed that
“matter was made of small pieces that couldn’t be cut”
Coined the term ATOMS
1800’s Dalton’s Atomic Theory
Smooth hard balls that couldn’t be broken down any smaller
In order to try to gain an idea of how small an atom really is, you will complete the following activity.
Cut a strip of 11 in. paper in half.
Discard one half.
Cut the remaining piece in half.
Continue cutting and discarding the strips as many times as you can.
Make all cuts parallel to the first one. When the width gets longer than the length, you may cut off the excess, but that does not count as a cut.

6. Results How many cuts were you able to make?
Do you think you could keep cutting the paper forever? Why or why not?
You would have to cut the paper in half around thirty-one (31) times to get to the size of any atom.

7. Atomic Theories!!! Thomson’s model (1897) Rutherford's Model (1911)
Atoms are made of smaller parts
(Dalton didn’t get it quiet right)
Discovered negatively charged particles
Called them electrons!
Couldn’t figure out what was in the middle
Assumed it had to be positive charges
An atom is like a watermelon full of seed (electron)
Rutherford's Model (1911)
Oh no he challenged his teacher!
Let see what happens when I shoot stuff a gold (pic next slide)
Mostly empty space except in the middle
The nucleus must be positive because like repels like.
Nucleus found at the center of an atom
The nucleus is made of what would later be called protons

8. Thomson’s and Rutherford’s Models

9. Really More Atomic Theories!
Bohr’s Model (1913)
Electrons are found in orbits not random
Look like planets moving around the sun
Cloud Model (1920’s)
Next to last 1
Electrons do not orbit the nucleus like planets
Move rapidly within a cloudlike region around the nucleus
Electrons movement is related to its energy level

10. Bohr’s and Cloud Model

11. Last Model (1932) James Chadwick (1932)
Found something else in nucleus
Discovered the neutron
Has a neutral charge, meaning no charge at all
Nucleus has both protons (positive) and neutrons (neutral)
Most of the volume is made of electrons

12. Short Activity Get a white sheet of paper
Put a line down the middle going long ways
At the beginning put the date 430 at the end put 1932
Now make a time line using drawings of each of the major models.

13. Homework
Do chapter 2 Lesson 1 in the textbook

14. Lesson 1: Structure of Atoms
Day 2
Lesson 1: Structure of Atoms

15. Bell Work
Compare and contrast the major atomic theories from yesterday.

16. Atoms
Smallest possible unit into which matter can be divided, while still maintaining its properties.
Made up of:
protons
neutrons
electrons
The solar system is commonly used as an analogy to describe the structure of an atom - + + - + + - + - -
For example, what is the
smallest possible unit
into which a long essay can be
divided and still have some meaning?

17. + Protons (+) Positively charged particles
Help make up the nucleus of the atom
Help identify the atom (could be considered an atom’s DNA)
Equal to the atomic number of the atom
Contribute to the atomic mass
Equal to the number of electrons + - +

18. Neutrons Neutral particles; have no electric charge+ -
Neutral particles; have no electric charge
Help make up the nucleus of the atom
Contribute to the atomic mass

19. - Electrons (-) Negatively charged particles
Found outside the nucleus of the atom, in the electron orbits/levels; each orbit/level can hold a maximum number of electrons ( 1st = 2, 2nd = 8, 3rd = 8 or 18, etc…)
Move so rapidly around the nucleus that they create an electron cloud
Mass is insignificant when compared to protons and neutrons
Equal to the number of protons
Involved in the formation of chemical bonds + - -

20. Sub-Atomic Particles Weight Comparison (protons, neutrons, electrons)
Neutron = x10-27 kg Proton = x10-27 kg Electron = x10-31 kg - - +
1839 electrons = 1 neutron
1836 electrons = 1 proton +
How do you think the mass of a neutron
compares to that of a proton?
1 neutron ≈ 1 proton

21. What would be the atomic number of this atom?
The number of protons in the nucleus of an atom -
What would be the atomic number of this atom? + - -

22. Isotopes
Atoms that have the same number of protons, but have different numbers of neutrons
Examples
Notice that each of these atoms have one proton; therefore they are all types of hydrogen. They just have a different mass number (# of neutrons). - - + + + -
Hydrogen (Protium)
Hydrogen (Deuterium)
Hydrogen (Tritium)

23. + Mass Number + What would be the mass number of this atom? - - -
The total number of protons and neutrons in an atom’s nucleus
Expressed in Atomic Mass Units (amu)
Each proton or neutron has a mass of 1 amu
What would be the mass number of this atom? - +
 3
 4 + -
3 protons + 4 neutrons = a mass number of 7 amu
Why did we not account for the electrons when calculating the mass number? -

24. Atomic Mass
The weighted average of the masses of all the naturally occurring isotopes of an element
The average considers the percent abundance of each isotope in nature
Found on the periodic table of elements
Example
What would be the atomic mass (≈) of Hydrogen if these three isotopes
were found in the following percentages (99.9, 0.015, 0) respectively? - + + + - -
Hydrogen (Protium)
Mass # = 1 amu
Hydrogen (Deuterium)
Mass # = 2 amu
Hydrogen (Tritium)
Mass # = 3 amu
If you simply average the three, 2 amu (1 amu + 2 amu + 3 amu/3) would be the atomic mass, but since 99.9% of the Hydrogen is Protium, the atomic mass is around 1 amu (.999 x 1 amu)

25. Building Atoms Atoms Protons Neutrons Electrons Carbon 6 Beryllium 4 5
Using the whiteboard and the proton, neutron, and electron pieces, build the following atoms, and determine their atomic and mass numbers.
Atoms
Protons
Neutrons
Electrons
Carbon 6
Beryllium 4 5
Oxygen 8
Lithium 3
Sodium 11 12

26. Atom Builder
Using the interactive website link below, practice building atoms.
Using the classzone.com link below, click on the “Build an Atom” simulation and practice building atoms.