Chapter 9: The Periodic Law Part 2

1
Chapter 9 The Periodic Law Part 2

• Alyssa Jean-Mary

2
Not All Compounds Consist of Molecules

• Elements that are liquids or solids are usually
  assemblies of individual atoms.
• Many compounds that are liquids or solids are
  also assemblies of individual molecules, but some
  are assemblies of ions instead. This is unlike a
  compound that is a gas, which only consists of
  molecules.
• For example, instead of consisting of neutral
  atoms or molecules, sodium chloride (i.e. table
  salt), consists of sodium ions, which are
  positively charged, and chloride ions, which are
  negatively charged. There is one sodium ion,
  Na,, for every chloride ion, Cl-. Thus, they are
  in a fixed ratio. The two ions are also firmly
  held together in a definite pattern. The formula
  for sodium chloride is NaCl. Even though NaCl
  doesnt consist of molecules like other compounds
  such as water, H20, it is still a compound.

3
Metals and Nonmetals

• At room temperature, all metals except for
  mercury, which is a liquid, are solids.
• Most metals have luster.
• Most metals are opaque, meaning that light cannot
  pass through even the thinnest sheet of a metal.
• Most metals are malleable, meaning they can be
  hammered into a specific shape.
• Most metals are ductile, meaning they can be
  drawn into wires.
• Most metals are good conductors of heat and
  electricity.
• Metals are the elements that are to the left of
  the bold staircase on the periodic table.
• There are 5 times more metals than nonmetals.

• At room temperature, nonmetals can be solids
  (carbon, sulfur), liquids (bromine), or gases
  (chlorine, oxygen, nitrogen).
• Most nonmetals dont have luster, i.e. they are
  dull.
• Most nonmetals are transparent when they are in
  thin sheets.
• Most nonmetals arent malleable or ductile
  instead, they are brittle and break, not bend, if
  enough force is applied.
• Most nonmetals are not good conductors of heat
  and electricity instead, they are insulators.
• Nonmetals are the elements that are to the right
  of the bold staircase on the periodic table.

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Identifying Metal and Nonmetal

• Identify the following elements as metal or
  nonmetal
• Sulfur (S) __nonmetal__
• Chlorine (Cl) __nonmetal__
• Carbon (C) __nonmetal__
• Sodium (Na) ___metal___
• Silver (Ag) ___metal___
• Zinc (Zn) ___metal___

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Chemical Activity

• Even though the differences in physical
  properties between metals and nonmetals is quite
  apparent, the differences in their chemical
  properties is not. Some elements are very active,
  which means that they combine readily to form
  compounds, while other elements are inactive,
  which means that they have little tendency to
  react chemically to form compounds.
• For example, sodium is a very active metal. It
  loses its luster through chemical reactions after
  exposure to the open air for a few seconds. It
  combines spectacularly with chlorine to give off
  heat and light. Sodium also reacts with dilute
  acids and even with water.
• On the other hand, gold is an inactive metal. It
  retains its luster even after a lifetime of
  exposure to the air and moisture. It combines
  only sluggishly, and when it does combine, only a
  little bit of energy is released. Gold is also
  only affected by concentrated hydrochloric and
  nitric acids.
• To determine the relative activity of different
  elements, the amount of heat that is given off in
  similar chemical reactions can be measured for
  each element.
• For example, if we measure the amount of heat
  that is given off when sodium and gold each
  combine with the same amount of chlorine, what is
  found is that there is 15 times more heat formed
  when sodium combines with chlorine than when gold
  combines with chlorine. Thus, sodium is much more
  active than gold.
• Another way to determine the relative activity of
  different elements is to start with similar
  compounds and measure how easily they can be
  separated into their component elements.
• For example, if we heat sodium chloride and gold
  chloride, what is found is that gold chloride
  breaks up when it is heated to about 300C and
  sodium chloride doesnt break up until it is
  heated to above 1000C. Thus, sodium chloride is
  considered to be a relatively stable compound,
  while gold chloride is considered to be a
  relatively unstable compound.
• The more active an element is, the more difficult
  it is to decompose its compounds.

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Families of Elements

• Some elements resemble one another so much that
  they seem to be members of the same natural
  family
• The Halogens are a group of active nonmetals
• The Alkali Metals are a group of active metals
• The Inert Gases are a group of gases that undergo
  almost no chemical reactions

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The Halogens

• The halogens are a group of highly active
  nonmetals. They include the elements fluorine
  (F), chlorine (Cl), bromine (Br), iodine (I), and
  astatine (At), and are in group 7 on the periodic
  table.
• Fluorine is actually the most active of all the
  elements. It is so active that it can corrode
  platinum, which is one of the most stable metals.
• The halogens have some of the worst odors and
  some of the most brilliant colors.
• Halogen means salt former, which is
  appropriate since these elements combine with
  many metals to give white solids that resemble
  table salt.
• At room temperature, fluorine is a pale-yellow
  gas, chlorine is a greenish-yellow gas, bromine
  is a reddish-brown liquid, iodine is a steel-gray
  solid, and astatine is a radioactive solid.
• At ordinary temperatures, the molecules of the
  halogens contain two atoms F2, Cl2, Br2, and I2.
• The compounds that they form with metals have
  similar formulas, since they combine with each
  metal in a specific ratio. For example, when they
  combine with sodium, Na, they form the following
  NaF, NaCl, NaBr, and NaI. Also, when they combine
  with aluminum, Al, they form the following AlF3,
  AlCl3, AlBr3, and AlI3.
• When halogens react with hydrogen, they form the
  following HF, HCl, HBr, and HI. If these
  compounds are dissolved in water, they form
  acids.
• They dissolve readily in a liquid called carbon
  tetrachloride. When they dissolve, the solution
  is colored in the same way as their vapors.
• Halogens are only slightly soluble in water.

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The Alkali Metals

• The alkali metals are a group of soft, very
  active metals. They include the elements lithium
  (Li), sodium (Na), potassium (K), rubidium (Rb),
  cesium (Cs), and francium (Fr), and are in group
  1 on the periodic table.
• The alkali metals lose their luster when they are
  exposed to open air for a few seconds.
• They liberate hydrogen from water and dilute
  acids.
• They combine with active nonmetals to from very
  stable compounds that have similar formulas,
  since they combine with each nonmetal in a
  specific ratio. For example, when they combine
  with bromine, Br, they form the following LiBr,
  NaBr, KBr, RbBr, CsBr, and FrBr. Also, when they
  combine with sulfur, S, they form the
  followingLi2S, Na2S, K2S, Rb2S, Cs2S, and Fr2S.
• The alkali metals have quite low melting points
  for metals. Lithium has the highest melting point
  of the alkali metals, and its melting point is
  only 186C. Cesium actually melts on a really hot
  day.

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The Inert Gases

• The inert gases are so inactive that they form
  only a few compounds with other elements. They
  are actually so inactive that their atoms dont
  join together into molecules like the atoms of
  the other elements that are gases do (i.e. they
  arent like O2 or N2). They include the elements
  helium (He), neon (Ne), argon (Ar), krypton (Kr),
  xenon (Xe), and radon (Rn), and are in group 8 on
  the periodic table.
• They are found in small amounts in the
  atmosphere. Argon makes up about 1 of air, with
  the other inert gases making up much less than
  this.
• Many of the inert gases glow in various colors
  when they are excited by an electric current.
  Thus, they are widely used to make signs.

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The Periodic Table

• The periodic law is a result of checking the
  regularities that occur among the properties of
  all the elements. The periodic law states When
  the elements are listed in order of atomic
  number, elements with similar chemical and
  physical properties appear at regular intervals.
• In 1869, Dmitri Mendeleev, a Russian chemist, was
  the first to formulate the periodic law in
  detail.
• The periodic table is a listing of the elements
  according to their atomic numbers. It is a series
  of rows, so that the elements that have similar
  properties form vertical columns.

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The Construction of the Periodic Table 1

• The first element in the table is hydrogen (H).
  Hydrogen is unlike most of the other elements
  since it behaves chemically like an active metal,
  but physically, it is a nonmetal.
• After hydrogen comes helium (He), which is one of
  the inert gases, then lithium (Li), one of the
  alkali metals, and then beryllium (Be), a less
  active metal than the alkali metals.
• A series of nonmetals than follow, each with more
  nonmetallic activity than the last boron (B),
  carbon (C), nitrogen (N), oxygen (O), and
  fluorine (F), one of the halogens.
• From lithium (Li) to fluorine (F), there is a
  complete series that goes from a highly active
  metal to a highly active nonmetal.
• After fluorine (F) is neon (Ne), another one of
  the inert gases, and then sodium, again, another
  one of the alkali metals.
• Thus, since the pattern seems to start again, the
  rows are broken off at the inert gases (i.e.
  helium (He) and neon (Ne) for these two rows) and
  the rows are started with the alkali metals (i.e.
  lithium (Li) and sodium (Na).
• The seven elements that follow neon (Ne) again
  start with an active metal and go to an active
  nonmetal, before another inert gas is present,
  just like the seven elements that followed helium
  (He).

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The Construction of the Periodic Table 2

• After calcium (Ca), the twentieth element in the
  periodic table, located in the fourth row, there
  are complications.
• Scandium (Sc) is the element after calcium (Ca),
  and although it has some properties in common
  with aluminum (Al) (i.e. the element it should
  fall under) it has other properties that are
  different from aluminum (Al).
• After Scandium (Sc) comes titanium (Ti), which
  has even less properties in common with silicon
  (Si) than scandium (Sc) did with aluminum (Al).
• Ten more metals come after titanium (Ti) that are
  quite similar to each other, but quite different
  from the nonmetals that are above them.
• After these ten metals, three nonmetals that have
  similar properties to these nonmetals that the
  metals dont resemble appear arsenic (As),
  selenium (Se), and bromine (Br).
• Thus, in the first two rows of the periodic
  table, between two inert gases (i.e. between
  helium (He) and neon (Ne) for the first row and
  between neon (Ne) and argon (Ar) for the second
  row), there is a sequence of 8 elements.
• After the first two rows, for the next two rows,
  between two inert gases (for example, between
  argon (Ar) and krypton (Kr) for the third row),
  there is a sequence of 18 elements.
• The row following these four rows, between the
  two inert gases xenon (Xe) and radon (Rn), there
  is a sequence of 32 elements.

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Groups and Periods 1

• On the periodic table, families of similar
  elements occur in the vertical columns, which are
  called groups.
• The horizontal rows, which are called periods,
  have elements all with different properties. Each
  period goes from an very active metal, to a
  series of weakly active metals, to a series of
  weakly active nonmetals, to an active nonmetal,
  and finally, to an inert gas.
• Each column, like each row, also has a steady
  change in properties. For the alkali metal family
  in group 1, the activity of the elements
  increases as you go down the column. For the
  halogen family in group 7, however, the activity
  of the elements decreases as you go down the
  column.
• On the periodic table, 8 of the columns are
  numbered. The inert gases are group 8, the last
  group on the periodic table, after the other
  nonmetals. Each period is broken after the second
  numbered column in order to keep the similar
  elements in the same columns. For the first two
  periods, there are no elements between this
  separation, but for the other periods, there are.

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Groups and Periods 2

• The transition metals are the elements that are
  located on the periodic table in a group that is
  not numbered. These elements are similar in
  chemical behavior to each other, but they dont
  resemble to elements in the numbered groups that
  much. The transition metals are less reactive
  then the metals in groups 1 and 2.
• In the row that has 32 elements between two inert
  gases (i.e. xenon (Xe) and radon (Rn)), 14
  elements of the 32 are brought out to a separate
  box. These elements are called the rare-earth
  metals or lanthanides. These metals are so much
  alike that they are hard to separate chemically.
  In the next row, there are another 14 elements
  that appear in the same position in the periodic
  table as the rare-earth metals. These elements
  are also brought out to a separate box that is
  immediately under the box of the rare-earth
  metals. These elements are referred to as
  actinides.
• In some places on the periodic table, the
  relationships between elements are a little
  vague. As a whole, however, the periodic table
  brings similar elements together with great
  accuracy. The achievement of Mendeleev (i.e. the
  periodic law) is so much more remarkable since in
  1869 there were only 1869 elements known and the
  idea of the atomic number had not yet been
  discovered. Mendeleev actually used average
  atomic mass, not atomic number to arrange the
  elements in the periodic table. When atomic
  numbers were discovered, it was found that they
  fit the sequence in the periodic table perfectly.

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Mendeleevs Predictions

• Since so few elements were known in Mendeleevs
  time, when he created his table, he had to leave
  gaps in order to have the similar elements fall
  into the same columns. He was so sure that his
  classification was correct, that he proposed that
  these gaps represented undiscovered elements. He
  then predicted the properties of these unknown
  elements. He did this by using the position of
  each gap, the properties of the elements around
  each gap, and the variation of these properties
  across the periods and down the columns. His
  property predictions included general chemical
  activity as well as numerical values for boiling
  points and melting points.
• When the unknown elements were discovered, one by
  one, their properties were found to agree with
  the predictions made by Mendeleev. Thus, the
  validity and usefulness of the periodic table was
  firmly established. Perhaps the greatest triumph
  is when the inert gases were discovered at the
  end of the nineteenth century. Mendeleev was not
  aware of the existence of these six new elements,
  but they actually fitted perfectly into the
  periodic table as one more family of similar
  elements.
• Thus, the history of the periodic table is an
  excellent example of the scientific method in
  action.

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The Periodic Table
17
Ionic Bonds and Covalent Bonds

• In compounds, there are two types of chemical
  bonds
• Ionic Bond
• Formed by the attraction of oppositely charged
  ions
• The ions were created by one element (a metal)
  losing electrons to the other element (a
  non-metal)
• Covalent Bond
• Formed when electrons are shared between the
  elements in a compound
• All the elements are non-metals in a covalent bond

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Identify Ionic and Covalent Compounds

• Problem Identify whether the following compounds
  are ionic or covalent.
• NaCl Na (sodium) is a metal and Cl (chlorine)
  is a nonmetal, so it is an ionic compound
• CH4 C (carbon) is a nonmetal and H (hydrogen) is
  a nonmetal, so it is a covalent compound

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Formulas for Ionic Compounds

• Ionic Compounds
• The total number of electrons lost by the metal
  must equal the total number of electrons gained
  by the non-metal i.e. the total charge on the
  compound must be zero
• If the charges on each ion are equal, one of each
  combine to form the compound
• If the charges on each ion are not equal, more
  than just one of each combine to form the
  compound subscripts are used to show how many
  of each ion combine (subscript 1 is not shown)
  the formula found needs to be the simplest ratio
  of the ions

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Steps for Identifying Formulas for Ionic Compounds

• Steps in identifying formulas
• First, identify the charge of each ion from the
  periodic table and place the positive charged ion
  first
• Second, cross the ionic charges to give the ratio
  of the elements in the compound only charges
  are crossed, not the positive and negative signs
• Lastly, make sure that the subscripts represent
  the simplest whole number ratios

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Examples of Identifying Formulas for Ionic
Compounds

• Example 1 Write the formula for Al (aluminum)
  combining with Cl (chlorine)
• Identify charges
• Al is in group 3, so it forms a 3 ion
• Cl is in group 7, so it forms a -1 ion
• Cross charges
• AlCl3
• Subscripts are the simplest whole number ratios

• Example 2 Write the formula for K (potassium)
  combining with P (phosphorous)
• Identify charges
• K is in group 1, so it forms a 1 ion
• P is in group 5, so it forms a -3 ion
• Cross charges
• K3P
• Subscripts are the simplest whole number ratios

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Naming Ionic Compounds

• When naming ionic compounds, the positive metal
  ion is named first, and then the negative
  non-metal ion is named, with the end of its name
  changed to ide

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Naming Covalent Compounds

• When naming covalent compounds, the central atom
  is named first, and then the other atom is named,
  with the end of its name changed to ide, just
  like when naming ionic compounds
• If more than one atom of the central atom is
  present, then a prefix is used to indicate how
  many atoms are present
• For the second atom, a prefix is used to indicate
  how many of the second atom are present, even if
  only one is present
• If the name of the atom starts with a vowel, the
  prefixes that end in a or o drop the a or the
  o

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Examples of Naming Compounds

• Ionic Compounds
• Example 1 CaS
• Ca metal calcium
• S nonmetal sulfide
• Name calcium slufide
• Example 2 BeCl2
• Be metal beryllium
• Cl nonmetal chloride
• Name beryllium chloride

• Covalent Compounds
• Example 1 SCl2
• S central atom 1 sulfur
• Cl chloride 2 dichloride
• Name sulfur dichloride
• Example 2 CCl4
• C central atom 1 carbon
• Cl chloride 4 tetrachloride
• Name carbon tetrachloride