Transcript Chapter 3

Of Atoms and Elements
Historical and Modern Perspectives
1831: Michael Faraday
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Discovery of ions
Anion : negatively-charged particles
 Cation : positively-charged particles
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Science of electrolysis: splitting substances using
electricity
Determined that atoms were electrical in nature
1895: Wilhelm Roentgen
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Studying glow produced from cathode rays
Noticed that the glow could be transmitted to
chemically-treated paper
X-rays discovered, but not fully understood
1895: Antoine Bequerel
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Photographic film fogged when placed close to
samples of uranium
Required no input of energy
Graduate student Marie Curie and later her
husband Pierre continued to study the
phenomenon
Marie coined the term “radioactivity”
1897: Joseph John Thomson
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Showed that the beam created in a cathode-ray
tube was attracted to a positive plate and
repelled by a negative plate
The particles were the same regardless of the
material from which the ray was generated
Coined the term “electrons” for the negative
particles
Thomson’s Experiment
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Thomson’s Model
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Realized that the negatively-charged particles
had to be balanced by a positively-charged
substance
“Plum Pudding Model”
1909: Robert Millikan
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Received Nobel Prize in 1923 for work
Calculated mass and charge of electrons
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Mass = 0.000 000 000 000 000 000 000 000 000 000 911 kg
Millikan’s Experiment
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Sprayed oil droplets into a chamber
Calculated mass of droplets by how fast they
fall (gravity)
Charge 2 plates-one positive, one negative
Oil droplets acquire extra electron by friction
or x-ray irradiation
Oil falls between 2 plates until it stops falling:
positive charge counteracts gravity
How much energy necessary in charged plates?
1910: Ernest Rutherford
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Gold foil experiment
Rutherford Model
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The atom had to have something very dense
and positively-charged that was repelling the
positive alpha particles
1913: Neils Bohr
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Built on discoveries of James Chadwick (the
neutron) and Henry Moseley (atomic number
= number of protons in nucleus)
Proposed an atom with distinct energy shells
occupied by electrons around nucleus
Erwin Schrodinger: Current Model
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Less structured, more uncertainty
“Electron cloud” representing where electrons
are most likely to be found
What Do We Know Now?
What Do We Know Now?
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Structure of atoms
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Nucleus: dense cluster, nearly all the atomic mass
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Electron cloud surrounding nucleus
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Protons: positive charge
Neutrons: no charge
Negative charge, in distinct patterns of arrangement
Description of elements
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Atomic number: number of protons
Mass number: number of protons + neutrons
Atomic symbol: one or two letters
What Do We Know Now?
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Organization of elements
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Isotopes = atoms with the same number of protons,
but different numbers of neutrons
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Atomic mass = average of the masses of all
isotopes of an element
What Do We Know Now?
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Notation
What Do We Know Now?
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Electrons orbit the nucleus in discrete energy levels
Principal quantum numbers represent energy levels
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Lowest numbers closest to nucleus
Electrons CANNOT
park between
energy levels!
What Do We Know Now?
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Light behaves as both waves and particles, and
its behavior is due to atomic structure
Atoms in ground state can absorb energy and kick
an electron up to a higher energy level
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Excited state
An electron can ONLY change state if there is
an available higher quantum level
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Otherwise, incoming energy will not be absorbed
What Do We Know Now?
• Energy needed to excite an electron to a higher quantum
level is very
specific
• Falling electrons
emit photons with
wavelengths equal
to the amount of
energy absorbed
For Example…
Organization of the Atom
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Levels
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Principal quantum number (n)
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Higher number = electron energy increases
Number of electrons allowed
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2n2
Organization of the Atom
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Sublevels
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The number of sublevels in an energy level is equal to
the principal quantum number
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s
p
d
f
Increasing energy
Organization of the Atom
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Orbitals
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Theoretical 3-D regions of probability
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Where an electron is most likely to exist
Orbital shapes
s-orbitals: spherical
 p-orbitals: dumbbell shaped (2 lobes)
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All orbitals of the same type (e.g. s-orbital)
have the same shape, but volume depends on
energy level
 Hold 2 electrons
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1s
2s
2p
3p
Organization of the Atom
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Farther from the nucleus = higher energy
electrons
Filling order depends on energy
Organization of Elements
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Read from left to right = order of filling
Remember: large atoms will fill an s orbital of
the next higher energy level before filling a d
orbital
Review: Atomic Organization
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Atomic spectra give us clues about the organization of
electrons around the nucleus
Type of energy given off corresponds to energy levels,
sublevels and orbitals of electrons
Organization of Elements
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Electron configuration of oxygen?
Organization of Elements
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Alkali Metals
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Group 1 (1A) on the
Periodic Table
Except hydrogen, soft
shiny metals with low
melting points
Good conductors
React vigorously with
water
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Organization of Elements
 Alkaline
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Earth Metals
Group 2 (2A) on the Periodic Table
Shiny metals
Not as reactive with water as Group 1
elements
Organization of Elements
 Halogens
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Group 17 (7A) on the Periodic Table
Strongly reactive
Form compounds with most of the
elements
Organization of Elements
 Noble
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Gases
Group 8 (8A) on the Periodic Table
All gas
Highly non-reactive, seldom in
combination with other elements
Organization of Elements
Metals, Metalloids, Non-metals
Quiz Yourself
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Convert 116.3 kg into mg. Record the number in regular and
scientific notation.
Refer to the periodic table and name at least one element that is:
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Noble gas
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Alkali metal
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Alkaline earth metal
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Halogen
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Non-metal
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Metalloid
Write the full and abbreviated electron configuration of:
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Silicon
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Manganese
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Potassium
What is the density of a piece of molybdenum that has a mass of
13.2g and a volume of 9.43mL?
Quiz Answers
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116,300,000
1.163 x 108
Noble gas = any element in group 18 (8A) on the Periodic Table
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Alkali metal = any element in group 1 (1A)
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Alkaline earth metal = any element in group 2 (2A)
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Halogen = any element in group 17 (7A)
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Non-metal = any noble gas, halogen and O, N, C, P, S, Se, I
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Metalloid = B, Si, Ge, As, Sb, Te, Po, At
Full electron configuration of:
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Silicon = 1s22s22p63s23p2
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Manganese = 1s22s22p63s23p64s23d5
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Potassium = 1s22s22p63s23p64s1
1.40 g/mL