Atoms and the Periodic Table

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Atoms and the Periodic Table

• Chapter 4

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Atomic Structure

• Atoms are the simplest unit of a substance that
  still maintain the properties of the substance.
• John Dalton proposed that atoms could not be
  divided.
• Dalton also stated that atoms of different
  elements could join to form compounds.

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Parts of an Atom

• Atoms are composed of subatomic particles.
• Protons and neutrons are found in the nucleus of
  the atom.
• Electrons are found in orbitals around the
  nucleus of the atom.

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Protons

• Protons have a positive charge.
• Protons have the mass of one amu (atomic mass
  unit).
• The number of protons in an atom is
  characteristic of that element.
• Each element has different number of protons.

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Neutrons

• Neutrons have no charge.
• Neutrons have the mass of one amu.
• Neutrons add to the mass of an atom.
• Atoms of the same element with different number
  of neutrons have different masses (isotopes).

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Electrons

• Electrons have a negative charge.
• Electrons have the mass of 1/2000 the mass of a
  proton.
• The mass of an electron is insignificant.
• The outer most electrons determine how elements
  combined in chemical compounds.

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Quarks

• A quark (IPA /kw?rk/) is a generic type of
  physical particle that forms one of the two basic
  constituents of matter, the other being the
  lepton.
• Various species of quarks combine in specific
  ways to form protons and neutrons, in each case
  taking exactly three quarks to make the composite
  particle in question.

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Models of Atoms

• Niels Bohr suggested that electrons in an atom
  move in set paths around the nucleus.
• Electrons can only be in certain energy levels.
• Number of electrons2n2

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Electron Cloud Model

• This model suggest that electrons orbit the
  nucleus in a cloud.
• The regions in an atom where electrons are likely
  to be found are called orbitals.
• The four different kinds of orbitals are the s,
  p, d and f orbitals.

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Valence Electrons

• An electron in the outermost energy level of an
  atom is called a valence electron.
• Valence electrons determine an atoms chemical
  properties and its ability to form bonds.

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Periodic Table

• The Periodic Law states that when elements are
  arranged this way, similarities in their
  properties will occur in a regular pattern.

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Structure of the Periodic Table

• Horizontal rows in the periodic table are called
  periods.
• Atoms of elements in the same group, or column,
  have the same number of valence electrons, so
  these elements have similar properties.

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Ions Formation

• Atoms that gain or lose electrons form ions.
• Elements that lose electrons have a positive
  charge (cation).
• Elements that gain electrons have a negative
  charge (anion).

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Periodic Information

• The atomic number is the number of protons in an
  element.
• The mass number of an atom equals the number of
  protons plus the number of neutrons.

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Isotopes

• Isotopes are atoms of the same element that have
  different number of neutrons.
• Isotopes of the same element have different
  atomic masses.
• The three isotopes of hydrogen are protium,
  deuterium tritium.

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Mass of Atoms

• An atomic mass unit (amu) is equal to one-twelfth
  of the mass of a carbon 12 atom.
• The average atomic mass for an element is a
  weighted average, so the more commonly found
  isotopes have a greater effect on the average
  than rare isotopes.

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Squares on the Periodic Table

• The chemical symbol is abbreviation of the
  chemical name.
• The first letter of the chemical symbol is
  capitalized.
• If there is more than one letter, the other
  letters are lower case.
• Atomic number.
• Average atomic mass.

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Classifications of Elements

• Metals are on the left side of the periodic
  table.
• Nonmetals are on the right side of the periodic
  table.
• Metalloids are located between the metals and
  nonmetals.

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Alkali Metals

• This is the most reactive group of metals.
• Has only 1 valence electrons.
• Reacts violently with water.
• Elements include Li, Na, K, Rb, Cs Fr.

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Alkaline Earth Metals

• Not as reactive as Alkali Metals.
• Has two valence electrons.
• Members include Be, Mg, Ca, Sr, Ba Ra.

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Transition Metals

• Members have a wide variety of properties.
• Has 1, 2 or 3 valence electrons.
• Contain the coin metals gold, silver copper.
• Contain the iron triad of Fe, Co Ni.

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Halogens

• The most reactive group of nonmetals.
• Has 7 valence electrons.
• All members are poisonous.
• Members include F, Cl, Br, I At.

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Noble Gases

• Members contain a stable octet with 8 valence
  electrons.
• These elements do not react with other elements.
  Dont form compounds.
• Members include He, Ne, Ar, Kr, Xe Rn.

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Semiconductors

• Have the properties of both metals nonmetals.
• Used in the electronic industry.

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Using Moles to Count Atoms

• A mole is a collection of a very large number of
  particles.
• Avagadros constant is the number of particles in
  a mole of a pure substance.
• Avagadros constant is 6.022 x 1023/mol.

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Molar Mass

• Molar mass is the mass in grams of 1 mol of a
  substance.
• The molar mass of an element in grams is the same
  as its average atomic mass in amu on the periodic
  table.

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Converting Moles to Grams

• Amount(mol) x molar mass of element/1 mol of
  element mass(g)
• Amount(mol)1 mole of element/molar mass of
  element x mass(g)

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Converting Amount to Mass

• Determine the mass in grams of 5.50 mol of iron.
• Given amount of iron5.50 mol mol Fe
• molar mass of iron55.85 g/mol Fe
• Unknown mass of iron?g Fe
• 55.85 g Fe/1 mol Fe
• 5.50 mol Fe x 55.85 g Fe/1 mol Fe307 g Fe

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Converting Mass to Amount

• Determine the amount of iron present in 352 g of
  iron.
• Given mass of iron352 g Fe
• molar mass of iron55.85 g/mol Fe
• Unknown amount of iron? mol Fe
• 1 mol Fe/55.85 g Fe
• 352 g Fe x 1 mol Fe/55.85 g Fe6.30 mol Fe

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Sample Problem 1

• A chemical reaction requires 5.00 mol of sulfur
  as a reactant. What is the mass of this sulfur
  in grams?
• 160.4 g S

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Sample Problem 2

• For an experiment you have been asked to do, you
  need 1.5 g of iron. How many moles of iron do
  you need?
• 0.027 mol Fe

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Sample Problem 3

• James is holding a balloon that contains 0.54 g
  of helium gas. What amount of helium is this?
• 0.14 mol He

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Sample Problem 4

• A pure gold bar is made of 19.55 mol of gold.
  What is the mass of the bar in grams?
• 3851 g Au

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Sample Problem 5

• Robyn recycled 15.1 mol of aluminum last month.
  What mass of aluminum in grams did she recycle?
• 407 g Al