Atomic Structure

1
Atomic Structure

• Pasterik
• 2006

2
Atoms

• What is an Atom?
• An atom is the smallest particle of an element.
  Can an atom be separated into smaller parts?
• Yes, they can be separated into
• electrons.
• protons.
• neutrons.

3
Electrons

• Electrons are very light negatively charged
  particles.
• Mass is almost insignificant relative to the mass
  of a proton.
• Surround the nucleus of an atom.
• Exist in orbitals or electron clouds called
  shells.
• Magnetically attracted to protons.

4
Protons

• Protons are positively charged atomic
  particles found in the center, or nucleus, of the
  atom.
• Have an atomic mass of 1.
• All protons have the same mass.
• Exist in the nucleus (small central core) of the
  atom.
• Attracted to electrons magnetically.

5
Neutrons

• Neutrons are particles with no charge that
  exist in the nucleus of atoms.
• Have an atomic mass of 1.
• Atoms of the same element can have different
  numbers of neutrons--those different atoms are
  called isotopes.

6
Atomic Model (Bohr Model)

• A Bohr model of Helium
• 2 protons
• 2 electrons
• 2 neutrons
• Atomic mass of 4.0

7
Atomic Model (Bohr Model)

• A Bohr model of Lithium
• 3 protons
• 3 electrons
• 4 neutrons
• Atomic Mass of 7

8
Atomic Model (Bohr Model)

• A Bohr model of Beryllium
• 4 protons
• 4 electrons
• 5 neutrons
• Atomic Mass of 9

9
Electron Shells

• Electron Shells are the volume of space in an
  atom where the electrons are likely to be.
• the electron occurs randomly within the electron
  shell.
• Neils Bohr is credited for the initial
  development of the electron shell concept. (Bohr
  model, 1913).
• only a certain number of electrons can fit into
  each shell.

10
Electron Cloud Theory

• In 1928, the Electron Cloud Theory was
  developed. (only minor changes).
• Electron cloud is the volume of space around an
  atomic nucleus in which electrons move.
• motion of electrons is less definite than planet
  orbits.
• more like bees moving about the area around their
  hive.

11
Electron Cloud Model

• Electron cloud model represents the possible
  locations for the electrons at any time.
• Electron cloud model of a Beryllium atom

12
The Bohr Model

• The Bohr model is still used to explain how the
  electrons are distributed throughout the atom
  into their shells.
• Another term for shell is electron level.
• the first level can hold only two electrons,
• the second level can hold eight electrons, and
• the third level can hold up to eighteen, but for
  our purposes we will say it can hold only eight
  electrons.

13
The Nucleus

• contains almost all of the mass of the atom
• consists of nucleons
• (particles in the nucleus)
• protons
• neutrons
• The Atomic Number is the number of protons in the
  nucleus of an atom.

14
Mass of the Atom

• Atomic Mass is the sum, expressed in a.m.u., of
  the protons plus the neutrons in an atom.
• electrons not counted in the mass
• 1,837 electrons 1 proton (mass)
• Atomic Mass Unit (amu) is a special unit of
  measure used to express the mass of atomic
  particles and atoms.

15
Atomic Mass Units

• Just how small is an atomic mass unit?
• There are 602 billion trillion atomic mass units
  in a gram
• 6.02 x 1023 a.m.u. in a gram or
• 602,000,000,000,000,000,000,000 a.m.u. in a gram

16
Drawing Bohr Models

• Draw a Bohr model atom for each of the first 20
  elements. Do this in the form (same columns and
  rows) of the periodic table given to you. Use
  your periodic table to help you.
• Hint remember that the atomic number is equal to
  the number of protons the atomic mass minus the
  atomic number equals the number of neutrons and
  there will be the same number of electrons as
  there are protons.

17
Bohr Models 1-20
1 2 13 14
15 16 17 18