Download File

A Neutron walked into a bar and asked how
much for a drink. The bartender replied, “for
you, no charge.”
-Jaime- Internet Chemistry Jokes
Chapter 3
Atoms: The Building Blocks of Matter
Section 1 - The Structure of the Atom
-Objectives:
– Define atom
– List the properties of subatomic particles
– Determine the number of protons, neutrons,
electrons found in different elements from the
periodic table
What is an atom?
-Atom: the smallest
particle of an element
that retains the
chemical properties of
that element
-Named by Democritus
-Means “indivisible”
What is an atom made of?
-Discoveries made by people like Dalton,
Thomson, Millikan, Rutherford, and Bohr
-Subatomic particles:
– Protons
– Neutrons
– Electrons
Subatomic Particles
-Nucleus
– Protons and neutrons
– Majority of the mass
– Strong nuclear force
holds it together
-Electron shells or orbitals
– Electrons
– Most of the volume
Subatomic Particles
-Electron:
– Negative charge
– Tiny, very light particles
– Electron cloud
-Proton:
– Positive charge
– At least one in every atom
– Much greater in size and
mass than electrons
– Nucleus
-Neutron:
– Neutral (no) charge
– About the same size and
mass as protons
– Nucleus
How do we measure an atom’s size?
-Atomic Number - #protons
-
Atomic Number
Atomic Symbol
Atomic Mass
-Atomic Mass (or mass number) =
#protons + #neutrons
What about the electrons?
-If an atom is electrically neutral, then #protons
= #_________
Practice:
-Determine the number of protons, neutrons,
and electrons in the following neutral atoms:
– Sodium
– Carbon
– Chlorine
– Helium
– Arsenic
Practice:
-Determine the number of protons, neutrons, and
electrons in the following atoms:
–
–
–
–
–
Sodium (Na): p+:11 e-:11, n0:12
Carbon (C ): p+:6 e-:6, n0:6
Chlorine (Cl): p+:17 e-:17, n0:18
Helium (He): p+:2 e-:2, n0:2
Arsenic (As): p+:33 e-:33, n0:42
Isotopes
-Isotopes: atoms of the same element that have
different masses.
– Same # of protons and electrons, but differ in # of
neutrons
• Different ways to depict which isotope you
have:
mass number
(p + n)
A
Z
atomic number
(p)
X
element symbol
Isotopes
6p+
8nº
Mass of Atoms
- Mass of atom determined by protons and
neutrons
- Actual Mass of:
- Proton: 1.673 X 10-27 kg
- Neutron: 1.675 X 10-27 kg
- Electron: 9.109 X 10-31 kg
- Mass of oxygen-16 atom= 2.657 X10-23 g
Relative Atomic Mass
- Instead of using EXACT mass of an atom in kg,
scientists use the relative atomic mass
- Relative Atomic mass measured in atomic mass units
(amu)
- Proton= 1.007276 amu
- Neutron= 1.008665 amu
- Electron= 0.0005486 amu
Calculating atomic mass
• Average atomic mass = Σ (mass of isotope ×
relative abundance)
• Carbon-12 is the isotope this formula was
based upon
• Ex: One type of copper atoms weighs in
at 62.93 amu, the other has a mass of 64.94
amu. The lighter isotope is more common
with 69.09% occurrence.
Calculating atomic mass
• Average atomic mass of copper = (62.93 amu
× 0.6909) + (64.94 amu × 0.3091)= 63.55
A certain atom has a nucleus containing six protons and eight
neutrons and has six electrons orbiting the nucleus. This
atom is a form of the elementA) silicon
B) carbon
C) magnesium
D) calcium
Ch 3: Section 2 – History of Subatomic
particles
Objectives:
1. Identify and describe the discoveries and
research of Democritus, Dalton, Rutherford,
Thomson, Bohr, Mosley, Mendeleev and
Schrodinger
2. Describe the law of conservation of mass and
law of multiple proportions
3. Describe the atomic theory and its individual
components
Timeline of Events:
370 BC- Democritus - Coined term atom
1803- Dalton - Atomic Theory
1871- Mendeleev – Created periodic table
1897- Thomson - Discovered electron
1911- Rutherford - Discovered proton and nucleus
1911- Mosley- Rearranged periodic table
1915- Bohr- Discovered neutron and made Bohr model
1925- Shrodinger – Quantum theory
Democritus vs. Aristotle
 Greek Philosophers
 Aristotle- viewed the entire known universe as being
made up of five distinct “elements” (earth, fire, air, water,
and ether) which mixed to form anything of substance
 Democritus asked- If you break a piece of matter in half
again and again, how many breaks will you have to make
before you can break it no more? Democritus thought
that it ended at some point, a smallest possible bit of
matter. He called these particles atoms. (370 BC)
 People believed Aristotle for almost 2000 years
John Dalton’s Research
Dalton- English chemist, meteorologist, and
physicist
He studied the atomic mass of elements by
studying water and carbon dioxide and
decided atoms are tiny, hard spheres
He used ideas made by scientists before himDemocritus, Lavoisier , and Proust- to come up
with his atomic theory
Timeline of Events:
1803: Dalton- Created the Atomic Theory
Atomic Theory:
1) All matter is composed of atoms
2) Atoms of a given element are identical in size, mass, and
other properties
3) Atoms can not be subdivided, created, or destroyed ( law of
conservation of mass) (Subdivided part has been disproven)
4) Atoms of different elements combine in simple wholenumber ratios to form compounds (law of multiple
proportions)
5) In reactions, atoms are combined, separated, or rearranged
Law of multiple proportions
- Atoms of different elements combine in
simple whole- number ratios to form
compounds
- Examples:
- NaCl
- H2O
Law of conservation of mass
Atoms can not be created or destroyed
• Example:
How can you explain chemical reactions?
*Atoms are rearranged, separated, combined
2H2O + O2 --> 2H2O2
Dalton’s Theory update
• Dalton proposed that atoms cannot be divided
– Nuclear fission- a nuclear reaction in which the
nucleus of an atom splits into two smaller parts,
releasing tremendous amounts of energy
• Nuclear power plants
Dalton 1803
• Many scientists agreed on this theory and it
stayed unchanged until 1890
– Scientists that followed used Dalton’s theory and
expanded on it
Dmitri Mendeleev (1871)
• Dmitri Mendeleev – first to organize
elements according to their properties
and mass
–Predicted the existence and properties
of elements not yet discovered
–Left blank spots
–Father of the modern periodic table
because he created the first one
J.J. Thomson’s Research (1897)
Discovered electron using cathode ray
 Thomson studied cathode rays and found that they were
negatively charged because they were deflected in magnetic
fields.
 Came up with “Plum pudding” model

Henry Mosley (1911)
• British Scientist 1911
• Re-ordered the periodic table in order of
increasing atomic number instead of mass.
• Problems with the Mendeleev table
disappeared.
Ernest Rutherford’s Research (1911)
Discovered proton and a nucleus by hitting gold foil with
helium (alpha) particles
 Discovered much of the atom is “empty space”
 He hit gold foil with fast-moving helium (alpha) particles
(positively charged particles)
 Expected particles to pass through because the mass and

charge were uniformly distributed, were deflected into all
directions
 Concluded that a very small, dense area in the center was
positively charged the rest is empty space.
Gold Foil Experiment
Bohr’s Research (1915)
Discovered the neutron and thus was able to
calculate the atomic mass
Studying gamma rays pointed at hydrogencontaining compounds, found that something
was in the nucleus besides protons
It had no charge
Created Bohr model
Erwin Schrödinger (1925)
• Studied electrons and their behavior
• Determined electrons have dual properties
• They act like matter because they have mass
and volume BUT they also act like light
because they can be bent or diffracted
• Became known as quantum theory
and helped to predict the location and
shape of the electron cloud
Timeline of Events:
370 BC- Democritus - Coined term atom
1803- Dalton - Atomic Theory
1871- Mendeleev – Created periodic table
1897- Thomson - Discovered electron
1911- Rutherford - Discovered proton and nucleus
1911- Mosley- Rearranged periodic table
1915- Bohr- Discovered neutron and made Bohr model
1925- Shrodinger – Quantum theory