Chapter 5 Notes – The Periodic Table

 Key Concepts:
 Mendeleev arranged the elements into rows in
order of increasing mass so that elements with similar
properties were in the same column.
· The close match between Mendeleev’s predictions
and the actual properties of new elements showed
how useful his periodic table could be.
 The periodic table is
the most useful tool
in chemistry.
 You get to use it on
quizzes and tests!
 It organizes lots of
information about
all the known
 …was a mess!!!
 No organization of elements.
 Imagine going to a grocery
store with no organization!!
 Difficult to find information.
 Chemistry didn’t make sense.
 Previous attempts to organize known elements
failed to work for all known elements at the time
 Russian Chemist and teacher, Dmitri Mendeleev,
discovered a way
 Found a way to approach the problem when playing
his favorite card game, a version of solitaire
(organization was the key)
 Solitaire…??????
 Put elements in rows by increasing atomic weight.
 Elements with similar properties were in the same
 Put elements in columns by the way they reacted.
 Periodic Table: an arrangement of elements in
columns, based on a set of properties that repeat
from row to row
 Table was not complete, not all elements had yet been
He left gaps/spaces in his table for those elements
He was NOT the first to organize the elements in the
form of a table
He was the FIRST to offer good explanations for how the
properties of an element were related to its location in his
He used the gaps in his tables to predict properties of
undiscovered elements
Other scientists used the predictions to help in their
search for undiscovered elements
 The close match between Mendeleev’s predictions
and the actual properties of new elements
showed how useful his periodic table could be
 With the periodic table, chemists could do more
than predict the properties of new elements –
they could explain the chemical behavior of
different groups of elements!!!
 Mendeleev wasn’t too far off.
 Now the elements are put in rows by increasing
 The horizontal rows are called periods and are
labeled from 1 to 7.
 The vertical columns are called groups are labeled
from 1 to 18.
 Period: A row in a periodic table of elements (left to
 To understand the structure of the table, think what
happens as the atomic number increases:
 Reminder: Atomic Number = Number of Protons
 First energy level has ONLY 1 orbital
 The 1 e- in a hydrogen atom and 2 e- in a helium atom
can fit in this orbital (first energy level)
 This is why H and He are in Period 1
 Lithium, 1st element in Period 2, has one of its the
three electrons in the second energy level
 This is why lithium is the first element in Period 2
 Sodium, 1st element in Period 3, has one e- in its third
energy level
 Potassium, 1st element in Period 4, has 1 e- in its
fourth energy level
 This pattern applies to ALL the elements in the 1st
column on the table
 Columns are also grouped
into families (or groups).
 Families may be one column,
or several columns put
 Families have names (Just
like your family has a
common last name.)
 Group: A column in a periodic table of elements
 Properties of elements repeat in a predictable
way when atomic numbers are used to arrange
elements into groups
 Periodic Law: the pattern of repeating properties
displayed by elements in the periodic table
 Elements within a group have similar properties:
 Similar e- configurations (see example above –
first column of the table)
 Electron configuration determines an elements
chemical properties
 Atomic mass is a value that depends on the
distribution of an element’s isotopes in nature
and the masses of those isotopes.
 Mass of an atom in grams is EXTREMELY small
 Scientists came up with an easier way to talk
about mass
 Chose one isotope to serve as a standard
 Scientists assigned 12 atomic mass units (amu’s) to the
carbon-12 atom (which has 6P and 6N)
 Atomic Mass Unit (amu): 1/12 the mass of a
carbon-12 atom
 Chlorine has an atomic number of 17 and an
atomic mass of 35.453 atomic mass units
 Where does the number 35.453 come from???
 There are two natural isotopes of Chlorine:
 Chlorine-35 which has 17 protons and 18 neutrons
 Chlorine-37 which has 17 protons and 20 neutrons
 Atomic masses come from an average of the
isotopes for a given element that exist in nature
 The value for atomic mass is known as a
“weighted average”
 Cl-35 occurs 3 times as often as Cl-37
 Take an average of those numbers:
(3 × 35) + (1 × 37)
= 35.453
 Elements are classified as metals, nonmetals,
and metalloids.
 Metals: elements that are good conductors of electric
current and heat.
 Properties of Metals:
 Except for mercury, metals are solid at room
 Most metals are malleable
 Many metals are ductile (can be drawn into thin
 Some metals are extremely reactive* (page 135, figure
 *Meaning they easily combine chemically with other
 Transition Metals: metals in groups 3-12, form a
bridge between the elements on the left and right
sides of the tables.
 Examples: copper and silver
 Some of the first elements discovered
 Ability to form compounds with distinctive colors
(page 137  production of colored glass)
 Includes the lanthanide and actinide series (at the
bottom of the table)
 Nonmetals: elements that are poor conductors of heat
and electric current
 Properties opposite those of metals
 Low boiling points
 Most are gases at room temperature
 Nonmetals that are solid at room temperature tend
to be brittle (will shatter)
 Some very reactive, some not at all, some fall
somewhere in between
 Fluorine (in Group 17) is the most reactive nonmetal
(found in toothpaste)
 Metalloids: elements with properties that fall
between those of metals and nonmetals
 Ability to conduct electric current varies with
 Pure silicon (Si) and germanium (Ge) are good
insulators at low temperatures and good
conductors at high temps.
 Across a period from left to right, the elements
become less metallic and more nonmetallic in their
 Most reactive metals on left side
 Most reactive nonmetals on the right side (in Group
 Period 3 elements (left to right) provide an example
of this (page 138, Figure 13)
 Why is hydrogen (H)
on the left side of the
table with the active
 Hydrogen’s location
is related to its
configuration, not its
 Wonder why there are 2 numbering schemes on the
periodic table?
 When the ‘A’ groups are numbered 1-8, they provide
a reminder about the electron configurations of the
elements in those groups
 The number of an ‘A’ group matches the number of
valance electrons in an electron configuration for an
element in that group
 Valence Electron: an electron that is in the highest
occupied energy level of an atom
 Valence electrons play a key role in chemical reactions
 Properties vary across a period because the number of
valence electrons increases from left to right
 Elements in a group have similar properties because
they have the same number of valence electron
 Hydrogen is on far left of table because it has one
valence electron, just like the rest of the elements in
that column
 Hydrogen belongs to a
family of its own.
Hydrogen is a diatomic,
reactive gas.
Hydrogen was involved
in the explosion of the
Hydrogen is promising
as an alternative fuel
source for automobiles.
 1st column on the periodic table (Group 1
/1A) not including hydrogen.
 Very reactive metals, always combined
with something else in nature (like in
 Single valence electron
 Soft enough to cut with a butter knife.
 The reactivity of alkali metals
increases from the
top of Group 1A to the bottom
 Lithium (Li) down through Francium (Fr)
 Group 2 / 2A on the periodic table.
 Reactive metals that are always
combined with nonmetals in
 Several of these elements are
important mineral nutrients (such
as Mg and Ca).
 2 valence electrons
 Harder than metals in Group 1A
 Higher melting point than Group 1A
 Differences in reactivity among the alkaline
earth metals are shown by the ways they react
with water
 Calcium, strontium, and barium react easily with
cold water
 Magnesium reacts with hot water
 No change with beryllium and water
 Elements in groups
 Less reactive, harder
 Includes metals used
in jewelry and
 Most are hard and
 Elements in group 13 (3A)
 Aluminum:
 Metal was once rare and
expensive, not a “disposable
 Most abundant metal in Earth’s
 Less reactive than sodium and
 strong, lightweight, malleable,
and good conductor of electric
 3 valence electrons
 Boron is used in
glassware like flasks
because it doesn’t
shatter when it
undergoes a rapid
temperature change
 Elements in group 14 (4A)
 Group 4A contains one nonmetal (C), 2
metalloids (Si, Ge), and 2 metals (Sn,
 Contains elements important to life
and computers.
 Carbon is the basis for an entire branch
of chemistry.
 Coal and oil are mostly made of
 4 valence electrons
 Metallic nature increases from top to bottom (Ge
is better conductor than Si)
 Life would not exist without carbon (except for
water, most of the compounds in your body
contain carbon)
 Reactions in your body controlled by carbon
 Si is 2nd most abundant element in Earth’s crust
(found in rocks, sand, and glass)
 Elements in group 15 (5A)
 Nitrogen makes up over ¾ of the
 Nitrogen and phosphorus are
both important in living things.
 The red stuff on the tip of
matches is phosphorus.
 5 valence electrons
 2 nonmetals, 2
metalloids, and 1 metal
 Contain a wide range of
physical properties
 Elements in group 16 (6A)
 Oxygen is necessary for respiration.
 Many things that stink, contain sulfur
(rotten eggs, garlic, skunks, etc.)
 6 valence electrons
 3 nonmetals and 2 metalloids
 Oxygen is most abundant element in Earth’s
The 10 most
abundant elements
by mass in the
earth's crust . All
are main-group
elements except
iron and titanium.
 Elements in group 17 (7A)
 Very reactive, volatile, diatomic,
 Always found combined with other
element in nature .
 Used as disinfectants and to
strengthen teeth.
 7 valence electrons
 Despite physical differences, the halogens have
similar chemical properties
 Highly reactive nonmetals, with fluorine being the
most reactive and chlorine a close 2nd
 React easily with most metals
 Chlorine added to drinking water and swimming
pools to kill bacteria
 Elements in group 18 (8A)
 VERY unreactive,
monatomic gases
 Used in blimps to fix the
Hindenberg problem.
 Have a full valence shell.
 8 valence electrons
 EXCEPTION is Helium, it has 2 valence electrons
 Colorless and odorless
 Used in lighted “neon” signs

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