The Atom

1
The Atom

• Chapter 4

2
From Idea to Theory

• Democritus, Greek philosopher, 400 B.C.,
  introduced the concept of an atom, an
  indivisible particle.

3
Daltons Atomic Theory

• All matter is composed of small particles called
  atoms.
• Atoms of the same element are the same physically
  and chemically.

4

• 3. Atoms cant be divided, created, or
  destroyed.
• 4. Atoms of different elements combine in
  whole-number ratios to form cmpds.
• In chemical rxns, atoms are combined, separated,
  or rearranged.
• Section Review p69

5
Structure of Atom

• Atom- smallest particle of an element that
  retains the chemical properties of that element.

6
Cathode Ray Tube

• Cathode Ray tube experiment by JJ Thomson
  discovered the electron (See pg. 70)

7
(No Transcript)
8
(No Transcript)
9

• Conclusions from Experiment
• 1. Rays cast shadow on other end of tube- light
• 2. Rays push paddle along- some form of matter
• 3. Rays deflected by magnet- not light

10

• 4. Rays deflected by negative charge- therefore
  cathode rays are made up of negatively charged
  particles called electrons.

11
Plum Pudding Model of Atom
Cookie Dough Model
12
Discovery of Nucleus

• Robert Millikan determine the mass of an electron
  to be 9.109 X 10-31 kg. Since atoms are neutral,
  atoms must have positive charge.
• Ernest Rutherfords Gold Foil Experiment
  discovered the nucleus. See pg. 73

13
(No Transcript)
14
Gold Foil Experiment
15
Gold Foil Experiment

• Conclusion of Gold Foil Experiment
• 1. Most of the alpha particles passed through
  atom mostly empty space.
• 2. Few deflected and reflected alpha particles
  - small, dense, positive, nucleus in atom
• Note nuclear forces hold neutrons together in
  the nucleus.
• Section Review p74

16

• James Chadwick discovered the neutral subatomic
  particle called the neutron.

17
Components of Atom
18
Counting Atoms

• Atomic number(Z)- number of protons in nucleus
  of an atom. Number of protons in the nucleus
  determines which element it is.
• Ex. Carbon
• Mass number(A)- number of protons and neutrons
  in the nucleus of an isotope

19
(No Transcript)
20
Condensed Form

• OR
• Element - _____

21
Isotopes

• Isotopes- atoms of the same element with
  different number of neutrons, so their masses are
  different. Isotopes of the same element are
  chemically different

22

• Ex. 3 forms of hydrogen. What is the mass number
  of each isotope? Write each using the condensed
  form.
• 1. Protium- one proton, no neutrons 99.985
  in nature
• 2. Deuterium- one proton, one neutron 0.015
  in nature
• 3. Tritium- one proton, two neutron
  radioactive- very little in nature, can be made

23

• 1. Which of the following is not an isotope?
  What is the mass number for each element?
• Calcium-23 Fluorine
• Potassium-20 Carbon-14

24
2. Complete the table.
25
Practice

• 3. How many protons, electrons, and neutrons are
  in chlorine-37?

26
Atomic Mass

• Mass of one atom of carbon-12 is 12 amu (atomic
  mass unit). So all atomic masses use C-12 as
  standard.
• Average atomic mass of an element is the
  weighted average of all the naturally occurring
  isotopes of that element

27
How do you calculate the average if

• Exams (60)
• Labs/Quizzes (25)
• Homework (15)
• Test 90
• Quizzes 85
• Homework 70

28

• The average atomic mass depends on
• the of isotopes
• the mass
• the abundance of each elements isotope.

29
Atomic Mass Calculations

• 4. Calculate the average atomic mass of copper
  given the following abundances and atomic masses
  for each isotope.
• Isotope 1 62.929598 amu and 69.17
• Isotope 2 64.927793 amu and 30.83

30

• 5. Given the data in the table below, calculate
  the average atomic mass of the unknown element.
  Then, identify the element.

31

• 6. Calculate the average atomic mass of
  magnesium. The three magnesium isotopes have
  atomic masses and relative abundances of 23.985
  amus (78.99), 24.986 amus (10.00), and 25.982
  amus (11.01).

32

• 7. Boron has two naturally occurring isotopes
  boron-10 (abundance 19.8, mass 10.013 amu),
  boron-11 (abundance 80.2 , mass 11.009).
  Calculate the atomic mass of boron.

33
Review Questions

• What is the charge on a proton, electron,
  neutron, and the nucleus?
• Which subatomic particles is/are found in the
  nucleus?
• 3. What is an isotope?

34

• 4. Why is the average atomic mass not a whole
  number?
• 5. What is the mass of one aluminum atom? One
  gold atom?
• 6. What is the mass number for aluminum?