Transcript Chapter 4

CHAPTER 4
The Structure of the Atom
SECTION 1 – EARLY IDEAS ABOUT MATTER
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
SECTION 2 – DEFINING THE ATOM
The Atom
 Atom: The smallest unit of matter that retains the properties of that
matter
 Imagine a Gold bar
Atom
 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
 https://m.youtube.com/watch?v=NWWkZ2ILNmA
Structure of the Atom
 Atoms are made up of 3 particles called sub-atomic particles
 Electrons
 Neutron
 Proton
Structure of the Atom
Particle
Electron
Proton
Neutron
Symbol
Location
eSpace surrounding nucleus
p
n
Charge Relative Mass
11/1840
Nucleus
Nucleus
1+
0
 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
1
1
Structure of the Atom Cont'd
Particle
Electron
Proton
Neutron
Symbol
Location
eSpace surrounding nucleus
p
n
Charge Relative Mass
11/1840
Nucleus
Nucleus
1+
0
 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
1
1
SECTION 3 – HOW ATOMS DIFFER
How Atoms differ
 There are more than 110 different atoms that exists
 Atoms of different elements differ in their number of Protons
How Atoms differ Cont'd
 Atomic Number: The # of protons in an atom
 Atomic number = # protons = # electrons
How Atoms differ Cont'd
Examples
Fill out the following table by determining the element, atomic number, protons and electrons given
the following information:
Element Name
a.
b.
c.
Lead
Symbol
Atomic #
Pb
82
Protons
Electrons
8
30
Practice Problems (Page 116 #12, 13, 14, 15)
Write out the first 20 Elements (Include their name, symbol and atomic number)
(You must know these for the next exam)
1
Hydrogen, H
13. Aluminum, Al
2
Helium, He
14. Silicon, Si
3
Lithium, Li
15. Phosphorus, P
4
Beryllium, Be
16. Sulfur, S
5
Boron, B
17. Chlorine, Cl
6
Carbon, C
18. Argon, Ar
7
Nitrogen, C
19. Potassium, K
8
Oxygen, O
20. Calcium, Ca
9
Fluorine, F
10 Neon, Ne
11 Sodium, Na
12 Magnesium, Mg
Isotopes and Mass Number
Isotopes
■ 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
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
Average Atomic Mass of Elements
■ The atomic mass of an element is the weighted average mass of the
isotopes of that element
Isotopes and Average Atomic Mass
(Practice Problems 16-17 page 118)
Isotopes and Average Atomic Mass
(Practice Problems 18-19 page 121)
Isotopes and Average Atomic Mass
(Practice Problems 18-19 page 121)
SECTION 4 – UNSTABLE NUCLEI & RADIOACTIVE
DECAY
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
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.
https://www.youtube.com/watch?v=TJgc28csgV0
Types of Radiation
 Alpha Radiation
 Beta Radiation
 Gamma Radiation
https://www.youtube.com/watch?v=VTHQYjkCqV0
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:
https://www.youtube.com/watch?v=MMQ87r7fd24
Types of Radiation
Alpha (α) Radiation
 Example: Radioactive Decay of Radioactive Radium-226 into Radon 222
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:
https://www.youtube.com/watch?v=xVS-dYazXuw
Types of Radiation
Beta Radiation
 Example: Radioactive Decay of Carbon 14 to Nitrogen 14
 Other ways to write the β particles
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.
https://www.youtube.com/watch?v=5oUagoF_viQ
Types of Radiation
Gamma (α) Radiation
 Example: Radioactive Decay of Uranium-238 into Thorium 222 or
Neptunium-237