Atomic Structure

1
Atomic Structure

• Chapters 3 4

2
Atomic Theory

• Dalton (1800s)
• All matter is composed of small particles called
  atoms
• Atoms of a given element are identical in size,
  shape, mass and other physical properties
• Atoms can not be created, destroyed or subdivided
  (later proven not true)
• Atoms of different elements combine in simple
  whole-number ratios to form compounds
• (ex. H2O, CO2)
• Atoms in compounds can be combined, separated, or
  re-arranged

3
Atomic Theory

• J.J Thomson (late 1800s)
• .Determined that the atom had negatively
  charged particles (called electrons) within the
  internal structure
• Plum pudding model of the atom
• electrons distributed evenly throughout the
  interior of the atom
• Experimented with Cathode Ray Tube

4
Atomic Theory

• Earnest Rutherford (early 1900s)
• Gold Foil Experiment
• Most of the volume on the atom was empty space
• Most of the mass of the atom is concentrated in
  the nucleus (nucleus positively charged)
• Electrons revolve in orbits around the nucleus

5
Atomic Theory

• Neils Bohr (1913)
• Expanded on Rutherfords Theory
• The electrons could move in energy levels within
  the orbitals.
• Each energy level represents a certain amount of
  energy
• Ex. 1 Ex. 2

6
Bohr model continued

• The lowest energy state is called ground state
  (closest to the nucleus)
• If an atom absorbs energy, electrons from ground
  state can move to a higher energy level
• If an atom loses energy and moves back to a
  lower energy state, light is emitted. (Seen in
  neon lights, stars etc.)

7
Excited state configuration
8
Excited state configuration

• To determine if atom is in the excited state,
  compare Bohr configurations from the Periodic
  table to those given.
• Ex. Sr ?2-8-18-8-2 is the ground state
  configuration
• Excited state configuration could be
• 2-8-18-7-3 (a move from 4th ? 5th)
• 2-8-17-9-2 etc. (a move from 3rd ? 4th)

9
Bright Line Spectrum

• An atom may gain energy and have an electron
  jump into a higher energy level (Excited
  state).
• This is an unstable state.
• Light is emitted from the atom as the electron
  moves back to the ground state.
• This light can be seen in a series of wavelengths
  represented by bright line emission spectrums.

10
Bright Line Spectrum continued
11
Modern (Quantum) Atomic Theory or the Electron
Cloud Theory

• Expanded on Rutherfords Theory
• Electrons and orbitals exhibit both particle-like
  and wave-like properties
• Cannot locate an electron with precision at any
  given time due to wave-like properties

12
Atomic Structure

• Nucleus
• Contains protons () and neutrons (neutral)
• Overall positive () charge
• Mass of proton and neutron are approximately
  equal
• Electrons
• Negatively charged particles
• Mass of electron is much smaller than that of
  Protons and neutrons
• Travel in pathways called orbits

13
Atomic Structure

• Protons and electrons have equal but opposite
  charges (makes atoms neutral)
• Each atom is defined by its atomic number ( of
  protons)
• Mass Number the sum of the protons and neutrons
  in the nucleus
• Atomic Mass weighted average of atomic masses
  of all isotopes of an element

14
Atomic Structure

• Isotopes atoms of the same element with
  different number of neutrons
• Example
• C-12 all three isotopes have 6 protons,
• C-13 but different amounts of neutrons
• C-14 Mass
• Nuclear Notation consist of isotope mass number,
  symbol and sometimes atomic number
• 23 Mass
• atomic 11Na

15
Calculating average Atomic Mass

• ((mass1)( Isotope1)) ((mass2)( Isotope2))
• Must convert percentage into decimal form
• Percentages have an infinite amount of sig figs
• The element Boron has 2 isotopes. Boron-10 has a
  mass of 10.013 amu and an abundance of 19.9.
  Boron-11 has a mass of 11.0093 amu and an
  abundance of 80.1. Calculate the atomic mass
  for this element. (amu atomic mass units)
• (10.013 amu)(0.199) (11.0093 amu)(0.801)
• (1.9925amu) (8.81845amu)
• 10.8110amu

16
Average atomic mass continued

• An element consists of 2 isotopes. Isotope A has
  an abundance of 75 and a mass of 14.000 amu.
  Isotope B has an abundance of 25 and an atomic
  mass of 15.00 amu. What is this elements atomic
  mass?
• (14.000amu)(0.75) (15.00amu)(0.25)
• (10.500amu) (3.750amu)
• 14.250amu

17
Valance Electrons

• Electrons in the outermost energy level of an
  atom
• Important in bonding between atoms
• Group 1 1 valence electron
• Group 2 2 valence electrons
• Group13-18 have valence electrons equal to their
  group number minus 10.
• Ex. Group 16 6 valence electrons
• Ex. Group 13 3 valence electrons

18
Lewis Structures or Electron Dot Diagrams

• Used to identify valence electron arrangement
• Divides an atom into two parts
• Kernal equal to the nucleus and all non-valence
  electrons
• Valence electrons
• To draw the structure
• Kernel is represented by atom symbol
• Valence electrons are represented by series of
  dots surrounding symbol (top fills first, up to
  two electrons, then each remaining side/bottom
  gets one electron before it gets a second)
• Ex.
• Top
• Side X Side
• Bottom

X
19
Lewis Structures or Electron Dot Diagrams

• Possible arrangements for 1-8 electrons