1. The Structure of the Atom
Chapter 4
The Structure of the Atom

2. Section 1 – Early ideas about matter

3. The Atomic Theory Daltons Atomic Theory
In 1803 John Dalton proposed a Theory to explain the laws of conservation of matter, definite proportions and multiple proportions.
Theory
Matter is composed of extremely small particles called atoms
Atoms are indivisible and indestructible
Atoms of a given element are identical in size mass and chemical properties
Atoms of a specific element are different from those of another element
Different atoms combine in simple whole-number ratios to form compounds
In a chemical reaction atoms are separated, combined or rearranged

4. Section 2 – Defining the atom

5. The Atom
Atom: The smallest unit of matter that retains the properties of that matter
Imagine a Gold bar
Atoms are very small and cannot be seen by the naked eye, however an instrument called the scanning tunneling microscope (STM) allows individual atoms to be seen
Atom

6. Structure of the Atom
Atoms are made up of 3 particles called sub-atomic particles
Electrons
Neutron
Proton

7. Structure of the Atom Particle Symbol Location Charge Relative Mass
Electron e-
Space surrounding nucleus 1-
1/1840
Proton p
Nucleus 1+ 1
Neutron n
Atoms are spherically shaped
Electrons are located outside the nucleus and are fast moving
Electrons are held in the atom by its (-ve) charge being attracted to the (+ve) charge of the protons in the nucleus

8. Structure of the Atom Cont'd
Particle
Symbol
Location
Charge
Relative Mass
Electron e-
Space surrounding nucleus 1-
1/1840
Proton p
Nucleus 1+ 1
Neutron n
Neutrons are neutral and exists in the nucleus
Protons are positively charged and exist in the nucleus
An atom is neutral (has no charge) this means that the # electrons = # of protons in the atom
Chemical behavior can be explained by an atoms electrons

9. Section 3 – How atoms differ

10. How Atoms differ There are more than 110 different atoms that exists
Atoms of different elements differ in their number of Protons

11. How Atoms differ Cont'd Atomic Number: The # of protons in an atom
Atomic number = # protons = # electrons

12. How Atoms differ Cont'd

13. Examples Symbol Atomic # Protons Electrons
Fill out the following table by determining the element, atomic number, protons and electrons given the following information:
Element Name
Symbol
Atomic #
Protons
Electrons a.
Lead Pb 82 b. 8 c. 30

14. Practice Problems (Page 116 #12, 13, 14, 15)

16. (You must know these for the next exam)
Write out the first 20 Elements (Include their name, symbol and atomic number)
(You must know these for the next exam)
Hydrogen, H
Helium, He
Lithium, Li
Beryllium, Be
Boron, B
Carbon, C
Nitrogen, C
Oxygen, O
Fluorine, F
Neon, Ne
Sodium, Na
Magnesium, Mg
Aluminum, Al
Silicon, Si
Phosphorus, P
Sulfur, S
Chlorine, Cl
Argon, Ar
Potassium, K
Calcium, Ca

17. Isotopes and Mass Number
Elements that have the same number of protons but different numbers of neutrons
These atoms keep the same chemical properties because they have the same number of electrons
We use the number of neutrons or mass number to tell isotopes apart
Mass number or Atomic Mass: Is the total weight of the element
Mass number/ Atomic Mass = # protons + # neutrons
Mass Number is always written as a decimal

18. Atomic Mass of Atoms
Small masses expressed in scientific notation are extremely difficult to work with so scientists developed a method of measuring the mass of an atom relative to the mass of a specific atomic standard.
1 atomic mass unit (amu) = 1/12th the mass of a carbon-12 atom
Carbon has an atomic mass of 12
Almost equal to one proton or one neutron

19. Average Atomic Mass of Elements
The atomic mass of an element is the weighted average mass of the isotopes of that element

20. Isotopes and Average Atomic Mass
(Practice Problems page 118)

21. Isotopes and Average Atomic Mass
(Practice Problems page 121)

22. Isotopes and Average Atomic Mass
(Practice Problems page 121)

23. Section 4 – Unstable nuclei & radioactive decay

24. Radioactivity
In the late 1890’s Scientists noticed some substances spontaneously emitted radiation in a process called radioactivity. This is because their nuclei is unstable
Rays and particles emitted are called radiation
Radioactive atoms undergo changes that alters their identity and allows them to form totally new atoms
Nuclear Reaction: A reaction that involves a change in an atoms nucleus
Nuclear reactions can change one element into another element

25. Radioactive Decay
Unstable nuclei lose energy by emitting radiation is a spontaneous process called radioactive decay.
Unstable atoms undergo radioactive decay until they from stable atoms which are often of a different element.

26. Types of Radiation Alpha Radiation Beta Radiation Gamma Radiation

27. Types of Radiation Alpha (α) Radiation
The radiation that is deflected towards the negatively charged plate is called alpha radiation.
An alpha particle has 2 protons and 2 neutrons and therefore has a 2+ charge (which explains why α particles are attracted to the negatively charged plates)
An alpha particle is equivalent to a helium 4 nucleus and is represented by:

29. Types of Radiation Alpha (α) Radiation
Example: Radioactive Decay of Radioactive Radium-226 into Radon 222

30. Types of Radiation Beta (β) Radiation
The radiation that is deflected towards the positively charged plate is called beta radiation.
A beta particle article is a high speed electron with a 1- charge (which explains why β particles are attracted to the positively charged plates)
An Beta particle is represented by:

32. Types of Radiation Beta Radiation
Example: Radioactive Decay of Carbon 14 to Nitrogen 14
Other ways to write the β particles

33. Types of Radiation Gamma (γ) Radiation
A high energy radiation that possesses no mass and is denoted by the symbol γ.
They are neutral and so are not deflected by in an electric or magnetic field.
They usually accompany α & β radiation
Gamm rays by themselves cannot result in the formation of a new atom.

34. Types of Radiation Gamma (α) Radiation
Example: Radioactive Decay of Uranium-238 into Thorium 222 or Neptunium-237