Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Isotopes
Take Home Message
• Atoms are the chemical building blocks of all matter
• Structure of atoms (electrons, neutrons, protons and
their arrangement) determine the unique
behavior/attributes of the elements
• Of the above (No. 2), the “place” and “pairing” of the
electrons are the most critical
• Electrons reside in defined shells (orbits) surrounding the
nucleus of the atom and the electrons in the outermost
shell (valence electrons) determine an atom’s chemical
reactivity
• Utility and periodicity of the Periodic Table of Elements is
a function of the valence electrons in the outermost shell
and the mass of the element
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Isotopes
Matter and Elements
• Phases of Matter
– Shape and volume
• Gas (no definite shape nor definite volume)
• Liquid (definite volume but no definite shape)
• Solid (definite shape and definite volume)
Elements
• Substances that can not be broken down
by chemical reaction
• Hierarchy
Compound
Element
Atom
Subatomic Particle
Elements
• Patterns
– 92 naturally occurring elements (e.g., hydrogen, gold, helium,
sulfur, carbon, uranium)
– 26 short-lived or artificially yielded elements
– Total of 118
– 25 of 92 are essential to life (e.g., ?????)
– Earth’s mass is predominantly six elements (oxygen, sulfur,
magnesium, iron, aluminum and calcium)
• Key points
– any element is the same in its chemical structure and physical
properties (~stable over time)
– All elements have their origin in either the big bang (hydrogen
and helium) or the subsequent evolution of the universe
Elements
• Compound
– Elements combine in very precise ways that are
recurrent and predictable
Sodium + Chlorine = Sodium Chloride
Na
+
Cl
=
NaCl
metal +
gas
=
solid
• Key points:
– atom of sodium (Na) remains an atom of sodium (as
for chlorine)
– Emergent property: “creation” of new properties in a
compound that can not be explained by the
summation of the two elements (hierarchy theory)
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Atoms
• Definition: smallest unit of an element that
retains properties of an element (e.g.,
gold, sodium)
• Observations
– Period has 106 atoms (1,000,000)
– Period of sodium (Na) atoms, all Na atoms
have the same identical physical and
chemical properties
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Particles
• Atoms are composed of particles (subatomic particles)
• Most stable particles
– Neutrons
– Protons
– Electrons
• Other less stable particles (quarks, neutrinos, etc.)
• Relationship among the more stable particles
Neutron
Proton
Electron
Charge
neutral
positive
negative
Mass
2*10-24 g
2*10-24 g
5*10-28 g
1 Dalton
1 Dalton
Atomic Structure
• Atoms of the same elements (e.g., hydrogen,
helium, gold) have the same number of
subatomic particles and by convention we
abbreviate as follows:
2
Helium
# of protons
He
4
Abbreviation of element
Atomic mass (g/mole; Daltons)
Hydrogen
• Mass = Protons + Neutrons
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Atomic Structure
• Example of sodium (Na)
11
Na
23
• Mass = Protons + Neutrons
23 = 11
+
?
Protons =
Neutrons =
Electrons =
• If atom is neutral (not charged), # protons always equals # electrons
• If atom is charged (“ionized”), # protons does not equal the #
electrons and atom is charged (ion)
– Positive ion (# protons > # electrons)
– Negative ion (# electrons > # protons)
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Electrons
• Energy “barons” of the atom (motion)
– Energy = ability to do work
– Potential energy = energy stored due to position or
location
• Charge is negative (-) and particle is always in
motion
• Capturing an atom and its orbiting electron
Electrons
• Re-capture the same atom
• Distance of electron from nucleus is always the
same but the location varies (distance is
synonymous with energy)
• Keys
– Nucleus is stationary
– Electron moves constantly with energy (chemical)
– Distance is the same
• Relate to last week’s lecture (Bohr’s atom and
quantum levels)
Electrons
• Re-capture the same atom
• Re-capture to create a “fuzzy orbit” around the
nucleus (1 orbit and 1 electron)
• Example of Lithium ( 37Li)
(3 electrons in 2 orbits)
Key to Electron Structure
• Count the number of electrons (and
compare with abbreviation of element)
• Electrons are negative in charge and in
constant motion
• Electrons are in orbits around the nucleus
• Chemists sometimes refer to orbits as
“shells”
• See word slide + 2
Electrons
• Example of Sulfur (1632S)
(16 electrons in 3 orbits)
Key to Electron Structure: Revised
• Previous slide plus the following
• Shell is function of distance from nucleus (and
energy)
– 1st shell has 1 orbit, is the lowest energy state, and has
maximum of 2 electrons (e.g., H and He)
– 2nd shell has 4 orbits and a maximum of 8 electrons (2
electrons per orbit)
• If electron possess energy, it can loose or gain
that energy
– Loose energy…drops down to a lower shell
– Gains energy…jumps to a higher shell (remember
Bohr and quantum numbers)
Example of Electrons in Shells
• As electrons move between shells, they
change potential energy
– Hot summer day, bright sun and car top
• Light absorption by pigments and electrons “jump”
to higher shell (potential energy); give off energy
when they drop back (kinetic energy)
– Banana, orange juice or bagel this AM?
• Excited electron is “capture” by chlorophyll in leaf
and shuffled to a sugar molecule in its excited state
(potential energy) until you release the energy via
digestion/respiration by allowing the electron to
“drop back” to a lower level (kinetic energy)
Key to Electron Structure: Revised
Again
• Electrons reside in shells as a function of
quantum mechanics (1-4 orbits per shell)
• Never more than 2 electrons per orbit (Pauli
Exclusion Principle)
• Distribution of electrons is key to understanding
why elements behave the way they do and why
the Periodic Table “works”
• Outermost electrons are called the valence
electrons: special significance
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Periodic Table of Elements
• Concept: most stable state for an atom is
one in which the outer shell is filled with
the maximum number of electrons
• 1st Shell (1 orbit; 2 electrons)
– Hydrogen (11H; 1 electron; stable ?)
– Helium (24He; 2 electrons; stable ?)
• Periodic Table’s 1st Row
– Hydrogen and Helium
Periodic Table of Elements
• 2nd shell has 4 orbits with 2 electrons
(maximum) per orbit (total of 8 electrons)
• Most stable configuration is the following:
– 1st shell filled with 2 electrons
– 2nd shell filled with 8 electrons
– Total of 10 electrons (1020Ne)
• 2nd row of Periodic Table
– 8 elements (list and relate to the above)
Periodic Table of Elements
• 3nd shell has 4 orbits with 2 electrons
maximum per orbit (total of 8 electrons)
• Most stable configuration is the following:
– 1st shell filled with 2 electrons
– 2nd shell filled with 8 electrons
– 3rd shell filled with 8 electrons
– Total of ___ electrons (1840Ar)
• 3nd row of Periodic Table
– 8 elements (list and relate to the above)
Periodic Table of Elements
• Rows
– Number of elements in a row is not chance
but reflects the maximum number of electrons
in a shell
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Row 1 = 2
Row 2 = 8
Row 3 = 8
Row 4 = 18
etc
Periodic Table of Elements
Columns
– Elements in a given column have similar
chemical properties
– All elements in column have the same
number of valence electrons
– Column IA has 1 electron in outer shell
– Column IIA has 2 electrons in outer shell
– Column IIIB has 3 electrons in outer shell
– Column VA has 5 electrons in outer shell
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Valence Electrons
• Outermost electrons in a shell (can be in multiple orbits
within that shell)
• Most stable (2nd Law TD) is one in which valence shell is
completely filled with electrons
– Helium: 2 electrons in the 1st shell
– Neon: 2 electrons in 1st shell and 8 electrons in 2nd shell (N=10)
– Argon: 2 electrons in 1st shell, 8 electrons in 2nd shell, and 8 in
the 3rd shell (N= 18)
– Krypton: 3 (1st), 8 (2nd), 8 (3rd) and 18 (4th shell)
– Pattern with respect to the Periodic Table?
• All other elements are less stable since outermost shell
is not filled
Atoms and Elements
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Matter and Elements
Atoms
Particles
Atomic Structure
Electrons
Periodic Table
Electrons in Shells
Valence Electrons
Isotopes
Isotopes
• Key to behavior of an atom gleaned from the number of
electrons and protons (e.g., 24He (# protons =___;
neutrons = __)
• Hypothetical: Add 1 additional neutron (25He)
– Electrons = ____
– Protons = ____
– Chemical behavior of atom changed or unchanged?
• Isotope: each element has
–
–
–
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Fixed number of protons (Periodic Table)
Fixed number of electrons (Periodic Table)
Number of neutrons may vary
Atoms of same element with same number of protons but
different number of neutrons are called stable isotopes
– Not radioactive isotopes
Isotopes
• Carbon twelve is 612C
– 6 protons, 6 electrons and 6 neutrons
• Carbon thirteen is 613C
– 6 protons, 6 electrons and 7 neutrons
• Carbon fourteen is 614C
– 6 protons, 6 electrons and 8 neutrons
• Oxygen sixteen is 816O
• Oxygen eighteen is 818O
– 8 protons, 8 electrons and 10 neutrons
Take Home Message
• Atoms are the chemical building blocks of all matter
• Structure of atoms (electrons, neutrons, protons and their
arrangement) determine the unique behavior/attributes of
the elements
• Of the above (No. 2), the “place” and “pairing” of the
electrons are the most critical
• Electrons reside in defined shells (orbits) surrounding the
nucleus of the atom and the electrons in the outermost
shell (valence electrons) determine an atom’s chemical
reactivity
• Utility and periodicity of the Periodic Table of Elements is a
function of the distribution of all electrons in shells, the
valence electrons in the outermost shell, and the mass of
the element
Frequency
Grade Distribution First Test
16
14
12
10
8
6
4
2
0
47.5 52.5 57.5 62.5 67.5 72.5 78.5 82.5 87.5 92.5 97.5
Midpoint of Grade