Daily science- pg. 30

1
Daily science- pg. 30

• Create a table like the following on page 30 in
  your notebook. Label this page History of the
  Atom. Leave a few lines for each scientist.

Scientist/Philosopher Theory Year Model/Experiment
Democritus
Aristotle
John Dalton
J. J. Thompson
Ernest Rutherford
Niels Bohr
James Chadwick
New Atomic Theory
2
The Structure of atoms

• Pg. 29

3
What makes up an atom?

• Atom- smallest unit of an element that still
  retains that elements properties
• Atoms are made of subatomic particles.
• The three subatomic particles are the proton,
  electron, and neutron.

4
Structure of an atom

• The nucleus is located at the center of the atom.
• It contains positively charged particles, called
  protons, and neutral particles, called neutrons.
• Most of the mass is located here.

5
Structure of an atom

• Electrons, or negatively charged particles, exist
  outside of the nucleus in the electron cloud.

6
Subatomic Particles chart
Particle Charge Mass Location
Proton 1 1.67 x 10 -27 In the nucleus
Neutron 0 1.67 x 10 -27 In the nucleus
Electron -1 9.11 X 10 -31 Outside the nucleus
7
Atomic Number

• The periodic table can be used to find the number
  of protons, electrons, and neutrons.
• The atomic number of an element (labeled Z) tells
  you how many protons there are.
• On the periodic table, the elements are listed as
  neutral elements so the number of electronsthe
  number of protons.

8
Atomic number
Z
9
Mass Number

• The mass number (labeled A) is the number of
  neutrons protons.
• Mass number (if neutrons is unknown)atomic
  mass rounded to the nearest whole number
• The atomic mass is located under the element
  symbol.
• You can find the number of neutrons by
  subtracting the Atomic number (Z) from the Mass
  number (A)
• A-Z of neutrons

10
Mass Number
11
Writing Atomic number and mass number

• There is a way to represent atomic mass and
  number
• Steps
• 1-start with the element symbol
• 2- place the mass number on the top left side of
  the symbol
• 3-place the atomic number on the bottom left side
  of the symbol

12
Symbol
Al
27
13
13
Isotopes

• An isotope is an element that has the same number
  of protons but a different number of neutrons.
• Ex. Carbon has 2 common isotopes
• Carbon-12 Carbon-14
• The numbers represent the mass number

14
Determining the number of neutrons

• Ex. Carbon 12 and Carbon 14

15
Counting Atoms

• Pg. 31

16
Atomic Mass

• Atomic mass units (amu) are used to express an
  atoms mass
• Atomic mass units are based off the element
  Carbon
• Found under the element symbol

17
Average atomic mass

• Average atomic mass is a weighted average of the
  isotopes of a given element.
• More common isotopes have a greater effect on the
  average atomic mass than do less common isotopes.
• Ex. Chlorine- 37 and Chlorine- 35 (average atomic
  mass is 35.45)

18
Percent Abundance

• The atomic mass can be calculated by summing the
  products of each isotopes percent abundance and
  that isotopes atomic mass.
• Mass contribution tells how much of each isotope
  contributes to the total atomic mass.
• Mass contribution ( abundance) x (atomic mass)

19
Percent Abundance example

• Chlorine 35 has an atomic mass of 34.969 amu and
  its percent abundance 75.770. What is its mass
  contribution?
• Chlorine 37 has an atomic mass of 36.966 amu and
  its percent abundance is 24.230. What is its
  mass contribution.
• Using the two previous answers, what is the
  average atomic mass of Chlorine?