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The Structure of an Atom
4.2
The Element Song http://
www.youtube.com/watch?v=DYW50F42ss8
Three Types of Subatomic Particles Protons – Positive Charge (+1) Neutrons – Neutral (no charge, 0) Electrons – Negative Charge (-1)
Locations Protons & Neutrons:
Nucleus of Atom Electrons:
Found in the space outside the nucleus
Mass of Subatomic Particles When we measure the mass of protons,
neutrons and electrons, we consider RELATIVE masses That means we compare the mass of protons and
neutrons to the mass of electrons
Masses Proton = 1 amu (or Atomic Mass Units) Neutron = 1 amu Electron = 0 amu
What makes each atom different? John Dalton predicted that atoms of any
element are different from the atoms of all other elements
Atoms of any given element always have the same number of PROTONS
Atoms of different elements have different numbers of protons
Atomic Number Equals the number of protons in an atom
Found on the Periodic Table of Elements
Number of Electrons Each positive charge in an atom is balanced
by a negative charge because atoms are neutral What does neutral mean?
The atomic numbers gives the number of protons AND the number of electrons in a neutral atom of an element
Practice How many protons does Sulfur have?
How many electrons does Sulfur have?
Additional Practice On white boards
How many protons does hydrogen have?
How many electrons does oxygen have?
How many protons does Magnesium have?
How many electrons does Neon have?
How many electrons does Lithium have?
Mass Number To find the number of neutrons in an atom,
you have to do some simple math…
The mass number of an atom is the sum of the number of protons and neutrons in an atom
Protons have a mass of one, neutrons have a mass of one If we add them together we can find the total
massFormula for Finding # of NeutronsNumber of Neutrons = Mass Number – Atomic
Number
Practice A carbon atom has a mass number of 14
How many protons does it have? How many neutrons does it have?
Steps Look on the Periodic Table Elements to find the
Atomic Number of Carbon Subtract the number of protons from the mass
number. This is the number of neutrons.
Finding Mass Number If an atom has 2 protons and 2 neutrons…
What is the name of the element? How many electrons does it have in a neutral
atom? What is the mass number?
If an atom has 11 protons and 12 neutrons… What is the name of the element? How many electrons does it have in a neutral
atom? What is the mass number?
Isotopes Atoms of the same element that have
different numbers of neutrons, and, therefore, different mass numbers
For example How many protons does Oxygen have? Sometimes Oxygen has 9 neutrons, sometimes it
has 10 neutrons What is the mass number of an atom of oxygen that has
9 neutrons? What is the mass number of an atom of oxygen that has
10 neutrons?
Identifying Isotopes
Oxygen - 18
Mass Number
Element Name
Practice Nitrogen – 14
How many protons? What is the mass number? How many neutrons? How many electrons?
Neon – 20 How many protons? What is the mass number? How many neutrons? How many electrons?
Modern Atomic Theory
4.3
Bohr Model Looks almost like a diagram of a solar system
with planets orbiting around the Sun
Describes the arrangement of electrons in atoms
Energy Levels or Shells (Bohr Model) Electrons move in fixed orbits around the
nucleus
Each electron has a certain amount of energy that determines the energy level that it is in Electrons can NOT exist between energy levels
Electron Cloud Model This model was an improvement on Bohr’s
model Bohr assumed electrons moved like planets in a
solar system, but this is actually not the case
Electron Cloud Visual model of the most likely locations for
electrons in an atom Describes the POSSIBLE locations of electrons
around the nucleus At any moment in time we cannot pinpoint the
location of an electron
Atomic Orbitals A region of space around the nucleus where
an electron is most likely to be found
Each energy level contains a certain number of atomic orbitals Each orbital can contain a MAXIMUM of 2
electrons Each Energy has a certain number of atomic
orbitals
Energy Levels, Orbitals & Electrons
Energy Level Number of Orbitals
Maximum Number of Electrons
1 1 2
2 4 8
3 9 18
4 16 32
Creating a Model of an Atom We can use the energy level and atomic
orbital information in order to create a model of an atom
Each energy level can contain a certain number of electrons.
Steps for Making Models of Atoms
Step 1 Find the number of electrons in a neutral atom of
the element
Step 2 Draw concentric circles to represent the energy
levels
Step 3 Fill up the energy levels from the inside out
with the correct number of electrons. REMEMBER: Only 2 electrons will fit in the
first level (or circle), 8 in the second, 18 in the third, etc.
Practice Create atomic models for the following
elements: Helium Argon Magnesium Carbon