Atomic Structure

1
Atomic Structure
2
Mass Number

• Actual masses of atoms are frustrating to work
  with.Therefore we use relative comparisons of the
  masses of atoms.
• We use the atomic mass unit (amu) which is
  one-twelfth the mass of a carbon atom that
  contains six protons and six neutrons.
• Therefore one proton or one neutron weighs one
  (1) amu.
• Hydrogen has a mass number 1,Helium has a mass
  number of 4
• Page 76, Complete Problem 3.

3
Atomic Mass Atomic Number
4
Concept Map
5
Imagine This!

• If an atom were the size of a football stadium,
  the nucleus would be the size of a marble!
• If people were the size of atoms, all the people
  living on the earth today would fit on the head
  of a pin!f

6
Chemistry in the Environment

• The processing of uranium ore for nuclear fuel
  produces large amounts of radioactive mill
  tailings. Until the late 1970s disposal of the
  radioactive tailings was not controlled. As a
  result , millions of tons of these radioactive
  tailings are present in unmarked sites across the
  United States and Canada.

7
Consumer Chemistry

• In the late 1980s, tests showed traces of
  dioxins and furans in paper products such as
  coffee filters, paper towels and disposable
  diapers. These compounds form when pulp paper is
  bleached with chlorine. Dioxins and furans are
  considered potentially dangerous environmental
  pollutants.

8
Consumer Chemistry

• Dioxins and furans have also been identified as
  probable carcinogens and poisons which affect the
  reproductive and immune systems at low doses.
• What is cheaper? Bleached or unbleached?
• Why do we bleach paper products?
• What does this mean to you?

9
Atomic Theory

• John Dalton and His Atomic Theory
• In 1803, John Dalton (17661844) forcefully
  revived the idea of atoms. Dalton linked the
  existence of elements, which cannot be decomposed
  chemically, to the idea of atoms, which are
  indivisible.

10
John Daltons Theory

• Compounds, which can be broken down into two or
  more new substances, must contain two or more
  different kinds of atoms. Dalton went further to
  say that each kind of atom must have its own
  properties,including mass.This idea allowed his
  theory to account quantitatively for the masses
  of different elements that combine chemically to
  form compounds.

11
Electrons

• Electrons are subatomic particles found rotating
  around the nucleus of every atom.The number of
  electrons outside the nucleus is always the same
  as the number of protons in the nucleus. This
  makes the atom electrically neutral.

12
Arrangement

• The electrons which move around the nucleus of an
  atom have different quantities of energy. Those
  restricted to being closest to the nucleus have
  the least energy while those with the ability to
  be furthest away from the nucleus have the most
  energy.

13
Electron Arrangement

• The electrons can therefore be regarded as
  occupying different spherical volumes of
  different sizes, these levels usually being
  referred to as shells.It is worth noting that
  within each shell the electrons are not orbiting
  the nucleus at a fixed distance but can travel
  anywhere within the spherical shape of that
  shell.

14
Neutrons

• Neutrons are subatomic particles found in the
  nucleus of every atom.The number of neutrons in
  the nucleus does not follow a regular pattern.The
  number of neutrons can vary even for atoms of the
  same element.(Isotope)
• Neutrons have no charge.

15
Neutrons

• Discovery
• Neutrons were the last of the three main
  subatomic particles to be discovered, being first
  recorded in 1932.

16
Daltons Theory

• 1. All matter is composed of tiny indivisible
  particles called atoms.
• 2. Atoms of the same element are identical. The
  atoms of any one element are different from those
  of any other element.

17
Daltons Theory

• 3. Atoms of different elements can combine with
  one another in simple whole number ratios to form
  compounds.
• e.g. H2O CO2 HCl
• 4. Chemical reactions occur when atoms are
  separated, joined or rearranged. Atoms of one
  element are not changed into atoms of another by
  a chemical reaction.

18
Protons

• Protons are stable subatomic particles found in
  the nucleus of every atom.
• The number of protons in the nucleus is the
  proton number of that atom, which tells which
  element the atom belongs to.
• The proton number determines the relative
  position of the element on the periodic table.

19
Proton Discovery

• Two scientists, W. Wien in 1898, and J.J.Thomson
  in 1910, concluded that a positive particle
  existed and had a mass equal to that of a
  hydrogen atom.
• In 1919, E.Rutherford demonstrated that particles
  were emitted when nitrogen was bombarded with
  alpha particles. In 1920 he proposed that these
  hydrogen nuclei were fundamental particles and he
  named them PROTONS.

20
Isotopes

• Remembering back to Dalton's atomic theory
• He stated that all atoms of the same element are
  identical.
• That is not true.
• The nuclei of atoms must contain the same number
  of protons in order to maintain the elements
  characteristics.

21
Isotopes

• Symbolizing the composition of an isotope
• The symbol is written.
• The mass number is superscripted to the left.
• The atomic number is subscripted to the left.
• He
• H
• The larger number is always on top.

22
Isotopes

• Atoms that have the same number of protons but
  different numbers of neutrons are called
  isotopes. However, the number of neutrons may
  vary

23
Atomic theory Review

• (1) The idea of atoms was put forward thousands
  of years ago.
• (2) Initially, atoms were considered to be small
  solid spheres.
• (3) Most discoveries about atoms were made in the
  twentieth century.
• (4) Atoms are now known to be made of even
  smaller particles.

24
Atomic Theory Review

• (1) Atoms are too small to be seen.
• (2) Models help to visualise the behaviour of
  atoms.
• (3) The Rutherford/Bohr model of the atom is
  useful to explain some atomic behaviour.
• (4) Modern models are still based on the
  Rutherford/Bohr ideas but electron behaviour is
  represented in a different way.

25
Atomic Theory Review

• (1) Atoms are made of many different particles.
• (2) There are three main particles called
  protons, neutrons and electrons.
• (3) Protons and neutrons form the main part of
  the centre of the atom.
• (4) The centre of the atom is called the nucleus.
• (5) Electrons orbit the nucleus.
• (6) Most of the volume of the atom is empty
  space.
• (7) Most of the mass of the atom is in the
  nucleus.

26
Atomic Theory Review

• There are two types of charge positive and
  negative.
• (3) Protons have a positive charge.
• (4) Electrons have a negative charge exactly
  equal in size, but opposite to the charge of a
  proton.
• (5) Neutrons have no charge they are neutral.
• (6) Atoms are electrically neutral because they
  have the same number of protons and electrons.
• (7) The number of protons gives the proton number
  (atomic number) of the atom.

27
Atomic Theory Review

• (1) Electrons have different amounts of energy.
• (2) The amount of energy of an electron
  determines its movement around the nucleus.
• (3) The different energy levels of the electrons
  are called shells.
• (5) There is a maximum number of electrons that
  fit into each shell.
• (6) One shell does not have to be full before
  electrons appear in a higher shell.
• (7) Atomic mass is determined by the total number
  of protons and neutrons in the nucleus.

28
Atomic Theory Review

• (1) Atoms bond together in different ways to form
  a piece of the element.
• (2) The appearance and properties of the same
  element can be very different depending upon how
  the atoms are joined.
• (3) The different forms of the same element,
  caused by different atomic arrangements, are
  called allotropes.