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