1. Notes 4-1
Intro to Atoms

2. What’s an atom?
Smallest particle of an element

3. Atomic Theories
There have been many theories of proposed models of the atom.
Some were completely wrong!
And some were partially correct or close to correct.
We will look at some of the most known theories and models.

4. Dalton’s Atomic Theory
Dalton thought that atoms were like smooth, hard balls that could not be broken into smaller pieces.
He was credited with coming up with the earliest model of the atom
Most of this theory is still accepted today

5. Thomson’s Model
Thomson suggested that atoms had negatively charged electrons embedded in a positive sphere.
This is the first model that included smaller particles of the atom
His model is similar to blueberries in a muffin

6. Rutherford’s Model Developed the first model that included a nucleus
Similar to a peach with a pit, the pit = the heavy mass of protons in the nucleus, the fruit = the empty space made up of electrons

7. Rutherford’s Gold Foil Experiment
Rutherford was surprised that a few particles were deflected strongly. This led him to propose an atomic model with a positively charged nucleus.

8. Bohr’s Model
Said electrons could only have a certain amount of energy, so they must move in certain orbits
Similar to planets orbiting the sun (sun = nucleus), or the rings/layers of an onion

9. Cloud Model
Says Bohr’s model is wrong, electrons do not orbit the nucleus like planets do the sun
Instead, electrons can be found anywhere in a cloud-like region around the nucleus, rapidly orbiting in every direction

10. Later Atomic Models
Through the first part of the twentieth century, atomic models continued to change. REMEMBER: Electrons are the subatomic particles that are lost, gained or shared in chemical reactions.

11. Modern Atomic Model Accepted since the 1930s
At the center of the atom is a massive nucleus, containing positively charged protons and neutrally charged neutrons (no charge)
Surrounding the nucleus is a cloud-like region of moving negatively charged electrons
# protons in atom = # electrons in atom
# neutrons can change

12. Particles in an Atom
An atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

13. Atomic Number
Every atom of a given element has the same number of protons in its nucleus
This is known as the element’s atomic number
For example, Helium’s atomic number is 2, so every atom of helium has 2 protons in its nucleus. If the element has more than 2 protons, it is NOT helium!
Carbon’s atomic number is 6. How many protons does an atom of carbon have?

14. Isotopes: Atoms of elements have same number of protons, but different numbers of neutrons
Atoms of all isotopes of carbon contain six protons and six electrons, but they differ in their number of neutrons. Carbon-12 is the most common isotope.

15. Mass number 6 How do you know? Because if the mass number is 12,
An isotope is identified by its mass number
Mass number = #protons + #neutrons
Example: Carbon-12, the mass number is 12. We know carbon has 6 protons by looking at its atomic number on the periodic table. How many neutrons does carbon-12 have? 6
How do you know?
Because if the mass number is 12,
12 – 6 protons = 6 neutrons

16. Problem: The atomic number of nitrogen is 7.
How many protons, neutrons, and electrons make up Nitrogen-15?
Protons = 7
Neutrons = 8
Electrons = 7

17. Organizing the Elements
4-2, 4-3 and 4-4 Notes
Organizing the Elements

18. Mendeleev’s Periodic Table
1869 Russian scientist who discovered a pattern of the elements
Arranged the elements in order of increasing atomic mass (average mass of all the isotopes of an element)
Then he lined them up in groups of similar properties
Developed the first periodic table of elements
Contained 63 elements

19. The Modern Periodic Table
Changed as new elements were discovered
Contains over 100 elements
Arranged in order of increasing atomic number (not atomic mass like Mendeleev’s)
Atomic number = number of protons in an atom of that element
The properties of an element can be predicted from its location on the periodic table

20. The Periodic Table
Elements are organized into rows and columns based on their atomic number.

21. The Periodic Table
Elements are organized into rows and columns based on their atomic number.

22. The Periodic Table
Elements are organized into rows and columns based on their atomic number.

23. Classes of Elements Open your books to pages 134-135
Each colored region corresponds to a different class of elements
Metals = blue
Semimetals = yellow
Nonmetals = light green
Inert gases = dark green

24. Periods Horizontal rows
There are 7 periods on the table, look how they are labeled on the left side of the table
Properties within each period change in a pattern
Notice the lanthanides and actinides have been taken out of the table and placed underneath it
This is to save space and make the table easier to read
Look at the expanded table on page 136

25. Groups Vertical columns Aka family
Elements within the same groups have similar characteristics

26. Investigation: Define the Following Words and Classify Each (Metal, SemiMetal, Nonmetal or Inert gas)
Ductile
Malleable
Magnetic
Reactive
Noble gas
Lanthanides*
Actinides*
Brittle
Good conductor
Alloy
Semimetal
Alkaline earth metal(Group 2)
Alkali metals(Group 1)
Diatomic molecule
Tracers (radioactive)
Halogen

27. Finding Data on Elements
REVIEW: Each square in the periodic table lists four pieces of information: an element’s atomic number, chemical symbol, name, and atomic mass.

28. Groups (Families) Have Similar Characteristics

29. Notes 4-5
Radioactive Elements

30. Some isotopes are unstable
Reviewing Isotopes
Atoms with same number of protons but different numbers of neutrons
Example:
Carbon-12 (normal carbon) versus Carbon-14
Some isotopes are unstable
Nuclei break down in a process of radioactive decay, releasing particles and energy

31. Radioactivity
Unstable nuclei of an element spontaneously emit radiation
Example: Uranium, Polonium, Radium
There are 3 types of radioactive decay

32. Types of Radioactive Decay
During alpha decay, a nucleus loses an alpha particle, which consists of two protons and two neutrons.
* Decreases atomic # by 2, and mass # by 4

33. Types of Radioactive Decay
During beta decay, a neutron inside an unstable nucleus changes into a negatively charged beta particle and a proton.
* Atomic # increases by 1, mass # remains the same

34. Types of Radioactive Decay
Gamma radiation has no charge and does not cause a change in either the atomic mass or the atomic number.

35. Types of Radioactive Decay
The three types of nuclear radiation were named based on how easily each one could be blocked. Alpha, beta, and gamma are the first three letters of the Greek alphabet.

36. Using Radioactive Isotopes
Cancer treatment
Chemical reactions
Industrial processes
Electricity
Smoke detectors
Pest control
Rock/ fossil dating
Food treatment
Nuclear weapons

37. Risks of Radioactive Isotopes
Burn causing
Cancer causing
Genetic mutations
death

38. Review Nickel-63 Beta Iodine-131 Beta Thorium-234 Radium-226 Alpha
Use your periodic table to predict the element that forms in each case of radioactive decay:
Isotope Type of Decay Element Formed
Uranium Alpha
Nickel Beta
Iodine Beta
Radium Alpha
Thorium-234
Copper-63
Xenon-131
Radon-222