Here are the key rules for writing electron configurations: 1. Electrons fill the lowest available energy level first. They fill sublevels in the order s, p, d, f. 2. Each orbital in a sublevel can hold a maximum of two electrons, one with spin up and one with spin down. 3. The first energy level (K shell) holds up to 2 electrons. The second energy level (L shell) holds up to 8 electrons. The third energy level (M shell) holds up to 18 electrons. And so on as we go to higher principal quantum numbers. 4. Write the electron configuration with the closest noble gas as a prefix followed by the remaining electrons. For example,

1. Chapter 3 QBA Miguel A. Castro R.
Substances are
made of atoms

2. Natural Philosophy
 Heraclitus versus Parmenides
 Heraclitus– everything is in the
process of change
 Parmenides – Change is impossible

3. Natural Philosophy
 In400 BCE, Democritus stated, All
matter consists of tiny particles called
átomos, which are not created and
cannot be destroyed.
 This was the beginning of the atomism.

4. Natural Philosophy
 The fight wasn’t over. Plato disagreed.
 He thought that the beauty of the world
had to be caused by more than mere
atoms.
 He proposed a system of changing
elements; water, fire, earth, air.

5. Natural Philosophy
 Aristotle
disagreed with both
Democritus and Plato. He proposed a
system called Hylomorphism.
 Hylomorphism is a system of ever
changing states of matter.

6. Natural Philosophy
 Atomism was lost until the 16th Century
 Though it was still not a hard science, it
was part of a belief system called
alchemy.
 Thankfully, Robert Boyle put an end to
the mess when he wrote The Skeptical
Chemyst.

7. “Nature works by means of
bodies unseen.”
Lucretius

8. The Elements

10. Atomic Theory
 Threelaws provide supporting
evidence of atoms.
– Law of Definite Proportions
– Law of Conservation of Mass
– Law of Multiple Proportions

11. Law of Definite Proportions
Every compound is composed of
specific elements and whole-
number ratios of those elements.
Water H20 - 2 Hydrogen: 1 Oxygen

12. Law of Conservation of Mass
Matter cannot be create or
destroyed by normal physical or
chemical processes
i.e.- What goes in, must come
out!

14. Law of Multiple Proportions
The same elements can bond
in differing whole-number ratios
to form different compounds.
Methanol CH3O
Ethanol C2H5O

16. Dalton’s Atomic Theory
 Itcontained five principles based on
current knowledge of atoms.
 We have summarized those principles
in the following statements:

17. Dalton’s Atomic Theory
1. All matter is made up of tiny
indestructible particles called atoms.
2. All atoms of one type (element) have
the same mass and properties.
3. Atoms of different types (elements)
have different masses and properties.

18. Dalton’s Atomic Theory
4. In Chemical reactions, atoms
rearrange, but are not changed,
created, or destroyed.
5. When different elements combine,
they do so in some ratio of whole
numbers.

19. Chapter 3
Structure of Atoms

20. Atomic dessert
 In 1897 J.J. Thomson was able to control
light in a vacuum through the use of
magnets.
 He concluded that the charge of the
beam was negative.
 He also new that the charge was due to
movement of something inside atoms
 He concluded that atoms contain
subatomic particles with + and - charges.

22. Atomic Dessert
 He created the
“plum pudding”
model of the atom
 The Atom was a big
positive charge, with
very small particles
of negative charges
embedded in it.

24. Radioactive Man
 In1907, Ernest
Rutherford performed
“The Gold Foil
Experiment”

25. Radioactive Man
 Conclusion: Atoms have a hard, positively
charged center called a nucleus.
 The center was packed with tiny particles called
PROTONS.
 Most of the atom is empty space, while the tiny,
tiny electrons float around outside.

28. Subatomic Particles
ATOM
ATOM
NUCLEUS
NUCLEUS ELECTRONS
ELECTRONS
PROTONS
PROTONS NEUTRONS
NEUTRONS NNEGATIVE CHARGE
E G A T IV E C H A R G E
P O S IT IV E
POSITIVE NEUTRAL
NEUTRAL
CHARG E
CHARGE CHARG E
CHARGE
Atomic Number equal in a
equals the # of... neutral atom

29. Elephants and Fleas
Today, we believe that the atom has
three subatomic parts:
PROTON – positive charge in the
nucleus
NEUTRON – no charge in the nucleus
ELECTRON – negative charge, orbiting
the nucleus

30. Elephants and Fleas
 Atomic Number – number of protons
 Atomic Mass – number of protons +
number of neutrons
 Whyaren’t electrons added into the
mass of the atom?

31. Isotopes
 ISOTOPE - atoms of the same element
that have a different number of
neutrons
 This happens rather frequently, that is
why the atomic mass on the periodic
table is not a whole number. It is an
average of the different isotopes for
that element.

32. Chapter 3
Electron
Configurations

33. The not so great “greats”
 Dalton, Thomson, and Rutherford were
great men of science, but they had yet
to understand the atom.
 It wasn’t until Niels Bohr began to think
about Hydrogen that were started to
understand how complex an atom
really is.

36. Bohr: What is it good for?!
 Bohr, using a technique called Line
Emission Spectrums, saw that electron
didn’t just fly randomly around the
nucleus. In fact, they are in distinct
orbits called ENERGY LEVELS.

38. Bohr: What is it good for?!
 Ifyou put energy into an electron, it will
change energy level into an EXCITED
STATE. It will eventually drop back
down to it’s GROUND STATE and give
off energy in the form of light.

40. The colors of chemistry
 Electromagnetic Spectrum – radiation
moving at the speed of light ranging
from low-energy radio waves to high-
energy cosmic rays; includes visible
light
 It is often referred to as “light”
 The spectrum is created by the
“jumping” of electrons between orbits

41. Visible Spectrum
 The more energy a wave has, the
higher the frequency
 Red has the lowest frequency,
therefore it has the lowest energy
 The most energetic color is violet
 ROY G BIV

42. Electrons are wavicles.
 Bohr model of the atom shows
electrons orbiting a nucleus.
– Electrons are particles
 When we attempt to observe an
electron, it changes position
– Electrons are waves

43. De Broglie to the rescue
 In 1924, Louis De
Broglie suggested
that electrons do not
travel in perfect
orbits, but rather in
orbitals.
 The resulting image
was an “electron
cloud.”

45. Electron Configuration Rules
 Takenotes on Hog Hilton and work on
board.