Basic Atomic Structure

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Basic Atomic Structure
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Atoms are not solid spheres, they are composed of
. . . Subatomic particles

• Electron e-
• found outside the nucleus in orbitals
• Proton p
• found inside nucleus
• Neutron n0
• found inside nucleus

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Atomic Number
The number of protons defines the element

• Each element has a different atomic number 1, 2,
  3, 4, 5, 6, 7, 8, 9, 10 . . .
• The atomic number is equal to the number of
  protons

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Mass Numbera.k.a. Atomic Mass

• the mass of the atom is contained in the nucleus
• Masses of electrons are negligible
• it takes 1836 e- to equal the mass of 1p
  or 1no

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• atomic mass p no
• 1 p 1 amu or 1/12 the mass of C atom
• 1 no 1 amu or 1/12 the mass of C atom

Carbon - 12 is the standard that all masses are
compared to. All other elements have relative
masses
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• How do you determine the number of neutrons in an
  atom?
• How do your determine the number of electrons in
  an atom?

Atoms are neutral
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Atoms of the same element are not necessarily
alike . . .
Same atomic number different mass number
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Isotopic Notation

• How many protons?
• How many neutrons?

a.k.a. H-1
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Isotopic Notation

• How many protons?
• How many neutrons?

a.k.a. H-2
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Isotopic Notation

• How many protons?
• How many neutrons?

a.k.a. H-3
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How is atomic mass of an element calculated?

• Atomic Mass of an Atom p no
• BUT since the number of neutrons in an atom can
  vary . . .
• Mass H 1 Mass H 2 Mass H 3
• The atomic mass is an AVERAGE mass of the
  isotopes
• BUT!!!!!! Is the mass of Hydrogen is 1.00794 and
  not 2???????

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Weighted average

• Test grades 50
• HW 10
• Labs 40

• Test avg 85
• HW avg 90
• Lab avg 75

What is your MP average?
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Weighted Average of H

• H-1 99.99
• H-2 .01

• 1amu x .9999 .9999
• 2amu x .0001 .0002

1.0001
Do NOT use division in a weighted average!!!!
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Electron Configurationsby principal E level
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Different E levels hold different s of e-

• E level 1 2 e-
• E level 2 8 e-
• E level 3 18 e-
• E level 4 32 e-

But NEVER more than 8 outermost
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e- in higher E levels have more E
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You can tell how many e- an atom hasAND which
energy level is being filled based on its
location in the periodic table
Number of electrons atomic number (p) of an
ATOM Period number where the outermost
electrons are
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Practice Problems

• What is the electron configuration of potassium?
• How many electrons does Phosphorus have in its
  2nd E level?
• How many e- does sodium have in its first
  orbital?
• How many e- does iron have in its 3rd E shell?

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Valence electrons

• Outermost number of electrons
• Never more than eight

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How many valence electrons?

• hydrogen
• potassium
• Sodium
• Lithium
• Magnesium
• Calcuim
• Barium

• Fluorine
• chlorine
• Neon
• Argon
• Krypton

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Notice anything?

• Elements (atoms) in the same group have the
  same number of valence e-
• The of valence e- corresponds to the last digit
  of the group number

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Lewis Dot Structure

• Method of showing valence electrons
• Never more than 8 total

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Draw Lewis Dot diagrams

• lithium
• beryllium
• fluorine
• argon

• phosphorus
• sodium
• helium

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Electron Orbital Notation

• e- dont actually zoom around the nucleus on
  little electron highways as seen in the Bohr
  Model of the Atom.
• THEREFORE
• true electron configuration isnt that easy!

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• Each principle orbital 1, 2, 3, 4 . . . is
  divided into suborbitals s,p,d f
• These are some shapes of the orbitals

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• s can hold 2 electrons
• p can hold 6 electrons
• d can hold 10 electrons
• The size of the suborbital is the same for any
  one energy level
• 3s, 3p, 3d are the same size
• 4s, 4p 4d are the same size but larger than the
  3s

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• When writing orbital notation
• Orbital Suborbital of electrons
• or
• level sublevel number (oh my!)

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Ions
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Ions are particles that carry a charge

• The charge an ion carries is the DIFFERENCE
  between the p and e-

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• Ions form because atoms want to have a full outer
  energy level.
• They will do this the easiest way possible.
• Na loses 1 electron Na1
• Cl gains 1 electron Cl-1
• Be?
• O?
• B?

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Practice Problems

• What is the charge on an ion with 7p and 5e- ?
• What is the charge on an ion with an atomic
  number of 8 and 5e-?
• What is the charge on an ion with an atomic mass
  of 35 if this atom has 18 neutrons and 18
  electrons?

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Lewis Dot Structure

• Method of showing valence electrons
• Never more than 8 total
• For an ion CHARGE must be shown

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Draw Lewis Dot diagramsfor these ions
Dont show dots on the positive ions. All of
your negatives will have full dots. Always show a
charge.

• chloride
• phosphide
• fluoride
• calcium
• potassium
• aluminum

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Ground State vs. Excited state

• So far weve discussed e- in their ground state

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Ground State e-

• Definition e- occupy lowest possible energy
  levels
• Most stable electron configuration
• The electron configurations on your periodic
  table show e- in their ground state
• ex. 2 - 8 - 6

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Excited State e-

• Definition e- of an atom occupy higher E levels
  when lower E levels are still vacant
• ex. 2 - 7 - 7
• ex. 2 - 3 - 1

Can hold up to 8 here.
Can hold up to 8 here.
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Ground state 2 - 6Excited state 2 - 5 - 1
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Ground State to Excited State
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Excited State to Ground State
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Spectroscopy

• Emission lines of elements
• Bright line spectra

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• If you hold a prism to light you will see a
  continuous spectrum of color.
• ROYGBIV

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Emission lines

• Visible light produced by electrons are confined
  to narrow lines of color called bright line
  spectra.
• These emission lines are used to identify
  elements
• fingerprints

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Spectra of some elements
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THE END