Download Atom

Objective 1
 Describe the structure of the atom
including: protons, electrons, and
neutrons.
Atoms and Atomic Theory
 Atom - the smallest particle of a given type
of matter.
 Atomic Theory – the idea that all matter is
made up of particles called atoms.
Scale of the Universe website:
http://www.youtube.com/watch?v=fUAFqkS7y9M&feature=relate
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Early Ideas About Matter
Democritus
400 B.C.
atomos = “indivisible”
Modern Atomic Theory
Lavoisier
Law of conservation of matterWhen a chemical reaction occurs,
matter is neither created nor
destroyed, but only changed.
John Dalton – Father of the Modern
Atom
1.) All matter is made of atoms.
2.) All atoms are indestructible and
cannot be divided into smaller
particles.
3.) All atoms of one element are exactly
alike, but they are different from all
other elements.
Subatomic Particles
 Electrons
 Protons
 Neutrons
Electrons
 J.J. Thomson – Discovered the electron
using a cathode ray tube.
 Symbol: e Mass = 1/1837 amu
 1 amu ~ the mass of a hydrogen atom
 Charge = (-1)
Protons
 Symbol: +p
 Mass = 1 amu
 Charge = (+1)
Thomson’s Model
 Put both the electron
and proton together
and proposed the
“Plum Pudding”
model of the atom.
Neutrons
 Symbol: n0
 Mass = 1 amu
 No charge
Nucleus
Discovered by Ernest Rutherford.
 Using the “Gold Foil” experiment,
Rutherford determined:
1. An atom is mostly empty space.
2. There is a nucleus in the middle of the
atom containing the protons.
3. The electrons orbit a large distance away
from the nucleus.
 Proposed the nuclear model of the atom.

Let’s Review
 http://www.brainpop.com/science/mattera
ndchemistry/atomicmodel/
 http://www.youtube.com/watch?v=xqNSQ3
OQMGI
Atomic Number
 Designates the number of protons in a
nucleus of an atom.
 Each element has a characteristic atomic
number.
 The number of electrons equals the atomic
number in a neutral atom.
Practice (Lab Notebook)
 How many protons do each of the following
elements have?
C
 Ne
K
Mass Number
 Designates the total number of protons and
neutrons in an atom.
 Number of neutrons = mass number -
atomic number.
 Atoms of the same element can have
different mass numbers.
Practice (Lab Notebook)
 How many neutrons do each of the
following elements have?
 C (Mass number 12)
 Ne (Mass number 22)
 K (Mass number 40)
Objective 2
 Explain why isotopes differ.
Isotopes
 Atoms with the same number of protons,
but different numbers of neutrons.
 Isotopes of an element have the same atomic
number, but different mass numbers.
Describing Isotopes
 Nuclear Symbol or isotopic
symbol – shows number of
protons, neutrons and electrons in
an atom.
 Isotopes may also be described by labeling
the name following by the mass number
(Example: carbon-12).
Practice
 Diagram the nuclear symbols for Lithium –
7
 Helium – 4
 Titanium – 48
Average Atomic Mass
 Weighted average mass of the atoms in
naturally occurring sample of an
element.
 On periodic table.
 Ex: For Xenon-124, Xenon-126
& Xenon- 134
Atomic Mass Example
 In nature carbon is composed of 98.89% 12C
atoms and 1.11% 13C atoms. 12C has a mass of
12 amu and 13C has a mass of 13.0034 amu.
What is the average atomic mass of carbon?
Objective 3
 Diagram the Bohr Model of the atom.
Bohr Model
 Niels Bohr (1913) – Created the Bohr Model stating
electrons travel around nucleus in energy levels.
 Uses rings to show the energy levels.
 The number of rings should match the row the
element is in on the periodic table.
http://www.youtube.com/watch?v=ydPzEZTd-98]
Bohr Model Diagram
 The protons in the nucleus = the atomic number.
 The neutrons in the nucleus = mass number atomic number.
 Electrons = number of protons. Fill the shells from
low to high until the correct number of electrons
are added.
 This model works for the first 20 elements.
Diagram Lithium-7
Diagram Nitrogen-14
Diagram Aluminum-27
Diagram Calcium-40
Valence Electrons
 Electrons in the outermost energy
level.
 Ex: Li = 1, F = 7
 Corresponds with the group number
for Groups 1-2, 13-18.
Lewis Dot Structures
 Show valence electrons.
 Look at the group number. This is how many dots you
draw for each atom.
Ex:
Potassium
Fluorine
Sulfur
Phosporous
Aluminum Beryllium
Silicon
Xenon