Transcript Unit 4: Periodic Table

Dmitri Mendeleev
 Given credit for the periodic table (~1870)
 Arranged the elements by increasing atomic mass
 Left spaces and predicted properties of undiscovered
elements
 Today’s Periodic Table of Elements is arranged by
increasing??
Properties
 Many of the properties of atoms depend not only on
their electron configurations but also on how strongly
their outer electrons are attracted to the nucleus
The Metals of the Periodic Table
 Left side of the table (1 to 3 valence electrons); form
cations
 Properties include:
 Lustrous (shiny)
 Ductile (can pull into wire)
 Malleable (can be hammered into a shape)
 Good conductors of heat and electricity
 Hard
The Nonmetals of the Periodic Table
 Right side of the table (5 to 7 valence electrons); form
anions
 Properties include:
 Good insulators
 Poor conductors
 Gases or brittle solids
 Dull
The Metalloids of the Periodic Table
 Located on the stairs between the metals and
nonmetals
 Properties include:
 Intermediate, meaning they have both properties of the
metals and the nonmetals
 Semiconductors

Si and Ge combing to create computer chips
Group 1: Alkali Metals
 The metals of Group 1 tend to lose an electron,
forming a +1 cation
 Part of the sublevel “s”
Group 2: Alkaline Earth Metals
 Lose 2 electrons forming a cation with a +2 charge
 Part of the “s” sublevel
Groups 3 – 12: Transitions Metals
 These elements lose more than 1 electron to become
cations
 Mercury is the only metal is a liquid at room
temperature
 Part of the “d” sublevel
Group 13 – 15
 They do not have a specific group name
 Part of the “p” sublevel
Group 16: Chalcogens
 Oxygen and Sulfur gain 2 electrons, forming anions
with a -2 charge
 Part of the “p” sublevel
Group 17: Halogens
 Gain 1 electron (except Astatine, which is not part of
this group name) to form anions with -1 charge
 Bromine is the only liquid nonmetal
 Also part of the “p” sublevel
Group 18: Noble Gases
 Every element wants to be a noble, because they are
stable
 Part of the “p” sublevel
Lanthanides and Actinides
 Located under the periodic table
 Part of the “f” sublevel
Periodic Trends
 There are 4 periodic trends of the Periodic Table
 Atomic radii
 Ionic radii
 First Ionization energy
 Electronegativity
 One other property we will look at is reactivity
Size of Atoms and Ions
 One of the important properties of an atom or an ion
is its size
 Atomic radii increases going down a group.
 Atomic radii decreases going to the right.
 Cations are smaller than the parent atom.
First Ionization Energy
 Ionization energy is the minimum amount of energy
needed for an atom or ion to remove an electron from
the ground state
 The greater the ionization energy, the more difficult it
is to remove an electron
 First ionization energy decreases going down a group.
 First ionization energy increases going right.
Electron Shielding (shielding effect)
Reduction of the attractive force between a
positively charged nucleus and its outermost
electrons due to the cancellation of some of the
positive charge by the negative charges of the inner
electrons
Imagine: a magnet (nucleus) with several layers of
iron pieces on it (electrons)
Electronegativity
 Electronegativity is the tendency for a bonded atom to
attract an electron to itself
 Electronegativity decreases going down a row.
 Electronegativity increases going right.
 Fluorine has the highest electronegativity value and
Francium has the lowest electronegativity value
Electronegativity vs Electron Affinity
 Electronegativity (EN): Measure of the ability
of an atom in a chemical compound to attract
electrons
 Electron Affinity (EA): tendency of a neutral
atom to acquire electrons (technically related
to energy changes)
 What’s the difference? For all intents and
purposes, nothing – the trends are the same
Reactivity of Metals
 Increases going down a group.
 Decreases going right.
 Francium is the most reactive metal
Reactivity of Nonmetals
 Decreases going down a group.
 Increases going right.
 Fluorine is the most reactive nonmetal
 Important note: Elements with half-filled sublevels
are more stable than those with empty orbitals!
Allotropes
The three
forms
of the element
carbon:
Diamond.
The three
forms of the
element
carbon:
Graphite.
The three forms of
the element carbon:
Buckminsterfullerene.
Copyright © by Houghton Mifflin Company
Isotopes vs allotropes
 Isotopes are atoms of the same element that are
different in the nucleus (# of neutrons), a sample
of an element will have a proportional number of
atoms of each isotope (C-12, C-14)
 Different at NUCLEAR level
 Allotropes are different forms of the same element
based on the way the atoms are bonded to one
another (structure), this results in different
physical and chemical properties, such as diamond
and graphite (allotropes of carbon)
 Different at STRUCTURAL level
Diatomic Elements
 Naturally occurring elements that contain 2 molecules
of the same element
 7 of them:
 H2
 N2
 O2
 F2
 Cl2
 Br2
 I2