Download Atoms: Building Blocks of Matter

Atoms: Building Blocks
of Matter
Structure of an Atom
• Subatomic particles: 3 particles that make
up an atom (protons, neutrons, electrons)
–Nucleus: made up of protons and
neutrons in center of atom
Proton: positively charged particle
Neutron: particle with no charge
Structure of an Atom
–Electrons: negatively charged
particles around the nucleus
All protons are alike, all neutrons are
alike, and all electrons are alike even
in different substances!
Atomic Models
Greek Model:
original idea of
matter made of
particles
–Atomos:
“not to be cut”
or indivisible
Atomic Models
John Dalton Model: 1803
All elements (gold, silver, hydrogen,
oxygen,…) are made of atoms
Atomic Theory and Models
Dalton thought that atoms were like
smooth, hard spheres that could not be
broken into smaller pieces.
Atomic Models
Dalton Model:
Atoms of the
same element are
exactly alike
Atoms of different
elements are
different
Atomic Models
Dalton Model:
Compounds: formed by the joining
of atoms of 2 or more elements
J.J. Thomson and his cathode
ray experiment 1897
Atomic Theory and Models
•Thomson suggested that atoms had
negatively charged electrons embedded
in a positive sphere.
Also known as the
“plum pudding” model
Ernest Rutherford’s Gold Foil
Experiment 1908
Most of the particles went
directly through the foil!
Atomic Theory and Models
Rutherford was
surprised that only a few
positive particles were
deflected strongly. This
led him to conclude that
atoms had positively
charged particles in the
nucleus.
Atomic Theory and Models
Since many particles
passed right through
the foil sheet, he also
concluded that the
atom must have a lot
of space separating
the nucleus from the
electrons.
Atomic Theory and Models
Through the early twentieth century,
atomic models continued to change.
Niels Bohr Model:
1912
Niels Bohr suggested
that electrons move in
specific orbits around
the nucleus of an atom
Atomic Theory and Models
Cloud Model:
1927
Electrons move
rapidly in every
direction around
the nucleus
Atomic Theory and Models
Modern Atomic Model:
The nucleus, which
contains both protons
and neutrons, is
surrounded by a
cloudlike region of
electrons.
• Let's see what Tim and Moby
have to say about Atomic Models
Design of periodic table
• Periodic Table: A classification system for
elements
Atomic number
79
Au
Gold
196.967
Atomic mass
chemical symbol
common name
Characteristics of Atoms
• Atomic Number: number of protons
in each element
Hydrogen = 1
Oxygen = 8
Helium = 2
Nitrogen = ___
Look at periodic table of elements in
your agenda or on the back cover of
your book
Characteristics of Atoms
• AMU: special unit to measure the
mass of atoms
–One proton = one AMU
–One neutron = one AMU
0.00000000000000000000000167 g
–Electrons have no mass
0.0000000000000000000000000911 g
Using your periodic table, answer the following.
How many protons does Krypton have?
a) 84
b) 36
c) 83
d) 48
How many electrons does Krypton have?
a) 84
b) 36
c) 83
d) 48
How many neutrons does Krypton have?
a) 84
b) 36
c) 83
d) 48
Using your periodic table, answer the following.
How many protons does Silver have?
a) 107
b)61
c) 108
d)47
How many electrons does Silver have?
a) 107
b)61
c) 108
d)47
How many neutrons does Silver have?
a) 107
b)61
c) 108
d)47
Electrons
• Each electron is in an energy level
• The higher the energy level = the farther the
distance from the nucleus
• Inside level holds 2 electrons
• The 2nd level holds 8 electrons
• The 3rd level holds 8 electrons (it CAN hold 18)
• The number of electrons in the outer “shell” or
“orbit” determines how it will act and react to
other substances
Drawing Bohr Models of the Atom
Remember the Bohr Model?
Even though the “Cloud” model is
the most accurate, we cannot
diagram atoms easily in 3-D.
We use Bohr’s model to illustrate which energy levels the
electrons are located in.
Examples of Bohr Diagrams
Sodium
• Build a Bohr Diagram
Which element?
Atom Game
Each person represents a subatomic particle:
Proton = Red
Neutron = Blue
Electron = Yellow
In your group, please construct the following
atoms – help each other!
- Oxygen – O
- Sodium - Na
- Silicon – Si
- Beryllium – Be
- Chromium – Cr
- Titanium - Ti
Valence Electrons and Bonding
Valence electrons are those electrons that have the
highest energy level and are held most loosely.
All elements are most
stable when there are 8
electrons in their valence
shell
The number of valence
electrons in an atom
determines which
elements it can bond
with.
• Isotopes
– Atoms of the same element have the same
number of protons but have different numbers
of neutrons
• Example of isotopes:
– Hydrogen: