Chapter 3 Atoms and the Periodic Table

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Chapter 3Atoms and the Periodic Table

• Periodically, we need to review our atomic
  knowledge...

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3.1 Atomic Structure

• Atoms - tiny units that determine the property of
  all materials. Derived from atomos (Greek for
  unable to be divided).
• Democritus (Greek guy, 4th century B.C.) said
  that the universe was made up of invisible tiny
  units called atoms. Good idea, but he was unable
  to give evidence for his ideas.
• 1808, John Dalton proposed a theory (3pts)
• Every element made of tiny, unique, indivisible
  particles called atoms.
• Atoms of the same element are exactly alike
• Atoms of different elements an join into
  molecules.

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• At the center of an atom is a small dense
  nucleus, made up of protons () and neutrons (no
  charge).
• A protons or a neutrons mass is 1.67X10-27 kg
• Electrons are - charged, very small,
  9.11X10-31kg, and move around the nucleus in a
  cloud with differing energy levels.
• Note the overall charge of a complete atom is
  0the proton electron charges cancel out.

Protons in nucleus, charge, atomic mass of 1
Neutrons in nucleus, no charge, at.mss of 1
-
-



-
Electrons little mass, -charge, in cloud around
nucleus
Nucleus small,dense center of atom containing
protons and neutrons
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• Atoms - thought of by Democritus and Dalton as
  not divisible. When particles of atoms were
  discovered -- it was proven wrong.
• Neils Bohr - electrons move in set paths (energy
  levels). Electrons can only be in these energy
  levels. They must gain energy to move to a
  higher energy level and lose energy to be in
  lower levels. Higher energy levels are closer
  together
• Modern model - electrons move like waves on a
  stringposition,speed,direction cant be seen
  easily (like fan), so shown as electron cloud.

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Electrons can only be at partic. energy levels
gain energy as move to higher levels, lose e. as
go lower level
Higher energy--
3rd energy level. Each level becomes
closer together...
2nd energy level floor Holds 8 electrons
Energy level any of the possible energies an
electron may have in an atom.
e-
Lower energy--
1st energy level floor Holds 2 electrons
Nucleus
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• Energy levels may indicate the level of energy an
  electron is found at.
• Orbitals are the region (actual place) an
  electron is found. There are four kinds
• s orbitals-spherical lowest energy level (see
  p.75)
• p orbitals-dumbbell-shaped, oriented on x,y,z
  axis in 3-D space. Slightly higher energy level.
• d orbitals - 5 types possible, complex. High en.
• f orbitals - 7 types poss., complex, highest
  energy level.
• Electrons occupy lowest orbital or energy level
  available and fill outward as needed.
• Shown as an electron cloud with fuzzy shading
  indicating where an electron is likely to be
  found.

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Electron clouds and the modern atomic model are
similar to the prop below. It isnt possible to
predict the speed or location of any particular
blade, but it is known that the blades rotate
within the fuzzy region pictured (and anything
intruding within that space will most certainly
prove that something is there!).
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• Electrons in energy levels are important
  indicators of how that element will behave when
  interacting with other elements.
• Particularly important, the outermost electrons
  in the outermost shell.
• These electrons are called valence electrons.
• In a neon atom at right, neon contains 10
  electrons (atomic 10). Electrons fill lowest
  shells first, so two electrons go in the

1st energy level. That is all the shell will
hold, so the remaining 8 go in the 2nd shell
level (filling it). There are 8 valence electrons
(8 electrons in the outer shell).
10P
Neon
10N
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Intermission
(Wake up, everyone!)
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• Periodic Table -organized table of the elements
  that groups elements that are similar, and
  organizes them by properties.
• Periodic Law - properties of elements tend to
  change in a regular pattern when elements are
  arranged (as in the P.Table) in order of
  increasing atomic number.
• Atomic number number of protons
• Horizontal rows are called periods, as the atomic
  number ( protons) increases across a period
  (left to right) so does the number of electrons.
  
• You can tell how an elements electrons are
  arranged by where it is in a period.

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Hydrogen, atomic number 1, has 1proton and 1
electron (in 1s orbital)
Helium, at.2, has 2P, and is in the space to the
right. It has 2 electrons, both in the 1st s
orbital.
Lithium, 3, has 3P, 3e. The first 2 are in the
1st s shell The 3rd e is in the 2nd s orbital
(b/c its on the 2nd row).
s - orbitals lowest en.
d -orbitals high en.
p - orbitals low energy
f - orbitals highest en.
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• Horizontal rows show numbers of protons and
  electrons increasing with atomic number, left to
  right.
• Vertical columns are called groups or families.
  Elements in the same group have properties in
  common. This is b/c elements in the same group
  have the same number of valence electrons.
• This doesnt mean these group elements are the
  same, but b/c of their similar valences, they
  have properties in common.

2 He
This group, the Noble gases (group 18) is
usually very unreactive. This is b/c they all
have full valence electron shells. He has 2e
in the 1st shell (holds 2), Ne has 2e in the lst
shell, and 8e in the 2nd shell (full).
10 Ne
18 Ar
36 Kr
54 Xe
86 Rn
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• Atoms without full electron shells (ex. grp.1)
  are very reactive and often undergo a process
  called ionizationthe process of adding electrons
  to, or removing electrons from an atom or a group
  of atoms.
• Atoms do this to get an electron shell that is
  fullthat is if they have 1 valence electron,
  they would tend to lose it, so as to have a
  complete shell (the previous shell level).
• When electrons are gained or lost, they no longer
  are the same as the number of protons (protons do
  not change), so they develop a (lost electrons)
  or - (gained more electrons) charge.

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• An atom with a charge (b/c of changed numbers of
  electrons) is called an ion.
• Ions that are - charged are called anions.
• Ions that are charged are called cations.

Li
Fluorines 7 valence electrons tend to gain
an additional electron to make a full shell of
8 electrons (2s and 6p). It then has an extra
-charge, b/c of gaining an extra electron.
Lithiums valence electron is removed, leaving a
full shell of two s electrons. Thus, Li has now
2e, and a charge of 1, b/c it lost a -charged
electron.
F
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Atomic number - indicates the number of protons
in an atom. Since the protons and electrons are
equal, it also indicates the number of
electronsunless its an ion.
Atomic symbol
6 C Carbon 12.011
Element name
Average atomic mass - tells us the mass of the
atom. Since an electrons mass is
insignificant, this tells us (round the number)
the number of protons and neutrons together.
To find the number of protons, see the atomic
number. To find the number of electrons (not an
ion) see the atomic number also. To find the
number of neutrons, subtract the atomic number
from the atomic mass. Atomic
mass -- 12 Atomic - -
6 6 neutrons are in
carbon.
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• Isotopes of an element - have different numbers
  of neutrons than the usual atoms.
• Ex. Hydrogen has 1 proton and 1 electron.
  Deuterium (an isotope of hydrogen) also has 1
  proton and 1 electron, but has an additional
  neutron (raising the atomic mass to 2).
  Tritium,3rd isotope, has 2N--raising the atomic
  mass to 3.
• Isotopes have different mass. They are the same
  element, but differ a bit in some mass related
  properties. Isotopes are usually quite a bit
  less common than most normal atoms. On earth,
  they are 1 in 6000, in the sun 1 in 50000.
• Atomic mass unit (amu) 1/12 of mass of a
  carbon-12.

Elements are often symbolized this way. Atomic
mass number is the top number, atomic is
the bottom. Note that the normal isotope is at
left, the other at right.
35
37
Cl
Cl
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17
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Families of Elements...

• Nonmetals (except H) are found on the right side
  (in green).
• Nonmetals may be solid, liquid or gassolid ones
  are usually dull,brittle and poor conductors.
• Some nonmetals, those boxed in on page 86, are
  able to conduct under certain conditions and are
  called semiconductors or considered to be
  metalloids.

• See page 86. All elements in red to the left of
  the chart are in the general category of metals.
• Metals are usually shiny solids that can be
  stretched and shaped (they are ductile and
  malleable). They are also good conductors of
  heat and electricity.

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Alkali Metals - Group 1

• Soft, shiny metals that react violently with
  water and other stuff.
• 1 valence electron in this groupvery reactive.
  Will give up an electron.
• Found in nature as a compounds (b/c of
  reactivity). Form 1 ion
• Ex. Sodium reacts violently with Cl to give up
  an electron to it and become NaCl, salt.

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Alkaline Earth Metals- Group 2

• Two valence electrons, not as reactive as alkali
  metals, but still reactive enough to form 2 ions
  and react to form compounds.
• Calcium forms many hard compounds used to
  strengthen organic structures shells become
  limestone and marble, coral and bones and teeth.
• Magnesium- light structural material, milk of
  magnesia and Epsom salts, and flares.

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Transition metals - Groups 3-12
Mercury- liquid at room temp useful in
thermometers and switches Au, Ag, Pt- very
shinyjewelry use.

• Much less reactive, but still can forms ions, and
  hence compounds. Transition metals often have
  more than one cation that can be formed (Au,
  Au3, Fe2, Fe3) due to their complex d shell
  electron arrangements.
• Gold - valuable b/c free rare metal, doesnt
  corrode and very shapeable and shiny.
• Copper-electrical stuff, tungsten-light bulbs,
  Fe, Co, Mn- body chemistry

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Rare Earth/Synthetic elements - (those two
separate bottom rows).

• Rare earth elements are very heavy. Since more
  particles means its harder to hold together, they
  often come apart radioactive.
• Synthetic elements are man-made. Pm, Tc, and all
  elements above 92 are syn.
• Last 2 periods are by themselves to keep the
  periodic table shorter and easier to read.

Tc-99 used to diagnose cancer, etc. Pm-147 is
used in glow-in-dark paints Am-241 used in
smoke-detectors
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Various nonmetal specifics...

• Carbon - 3 pure forms - graphite, diamond,
  fullerenes. Fullerenes are clusters of carbons
  bonded in a spherical hollow ball like a geodesic
  dome.
• Carbon-very useful in millions of organic
  struct./compounds from sugars and fats to
  plastics.
• O,N,S are common nonmetals. Form -ides with
  -ions. O2-oxide, S2-sulfide, and N3-nitride.

• Nonmetals make up common gases (nitrogen, oxygen)
  Sulfur compounds can make strong odors.

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Halogens - Group 17
Iodine - poisonous purple solid iodide compounds
are used in medical antiseptics and to
make iodized salt (a dietary thyroid cpd)

• Valence electrons are 1 electron short of a full
  shell, so very reactive trying to gain 1
  electron.
• Chlorine - kill bacteria in pools, etc.,
  poisonous green gas, reacts with Na to gain one
  electron and make NaCl.
• Fluorine - poisonous yellow gas, fluoride
  compounds are added to toothpaste and water to
  stop tooth decay.

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Nobles gases - Group 18

• All gases. Different from most elements, because
  they are very unreactive and exist as single
  atoms.
• Have full valence electron shells, so dont want
  to form any ions or compounds.
• Neon - used in neon signs (mixed with other
  elements gives other colors).
• He is very light (blimps, balloons).
• Argon is used in light bulbs to prevent filaments
  from burning up (b/c unreactive).

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Semiconductors/metalloids - boron, silicon,
germanium, arsenic, antimony, and tellurium
Semiconductors conduct according to how charged.
They can store electrical charge too
computer memory.

• Classified as nonmetals, but have some properties
  of metals. Conduct heat and electricity under
  correct conditions.
• Boron - very hard, often used to harden steel or
  make glass heat resistant.
• Antimony - fire retardant
• Tellurium - conducts better when exposed to
  light.
• Silicon - sand (very common) and used in computer
  chips.

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3.4 Using Moles to Count Atoms

• When counting large numbers, we use counting
  units. Ie., a dozen eggs, a ream of paper, a
  bushel of peaches. large number with less
  trouble.
• You can use mass to count something when you know
  theyre all the same. Ex. pennies are often
  weighed instead of counted, then the weight is
  divided by the weight of a penny to tell how many
  pennies there are.
• Chemists use a large counting unit to count
  molecules. This is called a mole, a measure of
  602,213,670,000,000,000,000,000 atoms.
• Usually written 6.022 X 1023/mol

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• 6.022 X 1023/mol is also called Avogadros
  constant. Its the number of particles in 1 mol
  of a pure substance.
• A mole of popcorn kernels would cover the United
  States to a depth of about 500km (310 miles)
  its a very large unit, but useful for counting
  atoms.
• The mass in grams of 1 mol of a substance is
  called its molar mass.
• The molar mass of a substance is its average
  atomic mass in grams.
• Ex. Carbons atomic mass is 12.011. 1 mole of
  pure carbon would be 12.011g of it.

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• Relating mass and numbers can make conversion
  factors.
• Ex Suppose 10gumballs masses 21.4g on your
  balance. This can be used to predict increase in
  mass with greater numbers (see diagram, p.97).
• Ex Given the above, how much would 50gumballs
  mass?
• 50 gmblls X 21.4g ?
  10gmblls
• cancelling 50 X 21.4g 107g
  10
• You can also do this same exercise with moles and
  grams.

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• Ex. Determine the mass in grams of 5.50mol of
  iron.
• Given amount of Fe 5.50 mol. Molar mass
  55.85g/mol Fe (find as atomic mass in
  P.Table)
• 5.50 mol Fe X 55.85 g Fe ? 1 mol
  Fe
• Cancelling. 5.50 X 55.85g Fe 307 g Fe
  1
• There now that wasnt too painful!

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You can find the amount of an element (in moles)
from a mass, too.

• Determine the amount of iron present in 352 g of
  iron.
• Given mass of iron 353 g Fe molar
  mass 55.85 g/mol Fe
• 352 g Fe X 1 mol Fe ?
  55.85g Fe
• Cancelling 352 X 1mol Fe 352 6.30mol
  Fe 55.85 55.85

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The End
SShhhhhh.. you can hear the moles digging...