Download Valence Electrons

Periodic Table and
Periodic Law
Chapter 6
Chapter Big Idea
Periodic trends in the
properties of atoms
allow us to predict
physical and chemical
properties!
SECTION 1: DEVELOPMENT
OF THE MODERN PERIODIC
TABLE
Essential Questions & Vocabulary
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How was the periodic table developed?
What are the key features of the periodic table?
Vocabulary
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Period law
Group
Period
Representative element
Transition element
Alkali metal
Alkaline earth metal
Transitional metal
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Inner transition metal
Lanthanide series
Actinide series
Nonmetal
Halogen
Noble gas
metalloid
Section 1: Main Idea
The periodic table evolved
over time as scientists
discovered more useful
ways to compare and
organize the elements.
Lavoisier

In the 1700s, Lavoisier compiled a list of all the known
elements of the time.
John Newlands (1864)
•
The 1800s brought large amounts of
information and scientists needed a
way to organize knowledge about
elements.
•
John Newlands proposed an
arrangement where elements were
ordered by increasing atomic mass.
•
Newlands noticed when the elements
were arranged by increasing atomic
mass, their properties repeated every
eighth element (law of octaves).
Meyer and Mendeleev (1869)
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Meyer and Mendeleev both demonstrated a connection
between atomic mass and elemental properties.
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Mendeleev is given more credit because he published his
information first.
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Arranged elements in order of increasing atomic mass
into columns with similar properties.
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Mendeleev was able to predict the existence and
properties of undiscovered elements (blank spaces).
Mendeleev’s Periodic Table
Moseley - 1913
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A few elements were discovered and the
atomic masses of the known elements
were not accurately determined.
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Several elements in Mendeleev’s table not in
the correct order.
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Moseley discovered that each element
contain a unique number of protons in
their nuclei – atomic number

Moseley rearranged the table by
increasing atomic number, and resulted in
a clear periodic pattern.
Moseley’s Periodic Table
Periodic Law

Periodic repetition of chemical and
physical properties of the elements when
they are arranged by increasing atomic
number

Periodic comes from the Greek word “periodos”,
meaning way around, circuit
The Modern Periodic Table
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The modern periodic table contains boxes that contain
the element's name, symbol, atomic number, and atomic
mass.
Modern Period Table
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Groups - Columns of elements
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Periods - Rows of elements
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Representative Elements - Elements in groups 1,2, and
13–18 possess a wide variety of chemical and physical
properties
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Transition Elements -Elements in groups 3–12
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Elements are classified as metals, nonmetals, and
metalloids.
Metals

Metals are elements that are generally shiny when smooth
and clean, solid at room temperature, and good conductors of
heat and electricity.
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Alkali metals are all the elements in group 1 except hydrogen, and are very
reactive.
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Alkaline earth metals are in group 2, and are also highly reactive.
The transition elements are divided into transition metals
and inner transition metals.
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The two sets of inner transition metals are called the lanthanide series and
actinide series and are located at the bottom of the periodic table.
Nonmetals & Metalloids
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Nonmetals are elements that are generally gases or
brittle, dull-looking solids, and poor conductors of heat
and electricity.
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Halogens – elements in Group 17 which are highly reactive
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Noble Gases – elements in Group 18
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gases at room temperature and are extremely unreactive
Metalloids, such as silicon and germanium, have
physical and chemical properties of both metals and
nonmetals.
SECTION 2: CLASSIFICATION
OF ELEMENTS
Essential Questions & Vocabulary

Why do elements in the same group have similar
properties?
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Based on their electron configurations, what are the four
blocks of the periodic table?
Vocabulary
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Valence electron
Section 2: Main Idea
Elements are organized
into different blocks in
the periodic table
according to their
electron configurations.
Electron Configuration

Recall electrons in the highest principal energy
level are called valence electrons.
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Only s & p orbital electrons count as valence electrons
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All group 1 elements have one valence electron.
Valence Electrons - Practice

How many valence electrons are in the
following elements?
Element
Na
Mg
H
He
Cl
Al
# Valence Electrons
Valence Electrons – Practice
Solutions
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How many valence electrons are in the
following elements?
Element
# Valence Electrons
Na
1
Mg
2
H
1
He
2
Cl
7
Al
3
Lewis Dot Structures

Draw the Lewis dot structures for each of
those elements
Na
He
Mg
Cl
H
Al
Lewis Dot Structures of
Representative Elements
The s-, p-, d-, and f-Block
Elements
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The shape of the periodic table becomes clear if it is
divided into blocks representing the atom’s energy
sublevel being filled with valence electrons.
S- block
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Chemically reactive metals
Group #1= alkali metals
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Slippery appearance and can be cut with a knife!

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For real?
They all have one valence electron
Combine readily with the halogens to form salts
Group #2- Alkaline Earth Metals
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Harder, denser and stronger than group #1
metals
Have 2 valence electrons
d- block - Transition Metals
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Lowest quantum # = 3
Maximum # of electrons = 10
There are exception to the electron
configuration rules
Some metals may form several different ions
They are all metals and good conductors of
heat and electricity and have high luster.
Properties vary greatly.
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Some metals are highly reactive
Other metals not so much- Au, Pt, Pd
p-block – Groups 13-18
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Group 13- 3 valence electrons
Group 14 – 4 valence electrons
Group 15- 5 valence electrons etc. etc.
Contains metals, non-metals and metalloids.
Important group- #17- Halogens
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Most are gases- most reactive with metals
Main Group elements aka
Representative Elements
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Elements found in the s block and p block
Only elements that can be used in Lewis Dot
Structures
Practice Problem
Strontium, which is used to produce red
fireworks, has an electron configuration of
[Kr]5s2. Without using the periodic table,
determine the group, period, and block of
strontium.
SECTION 3:PERIODIC TRENDS
Essential Questions & Vocabulary
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What are the period and group trends of different
properties?
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How are period and groups trends in atomic radii related
to electron configuration?
Vocabulary
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Energy level of an atom
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Octet rule
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Ion
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electronegativity
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Ionization energy
Section 3: Main Idea
Trends among elements
in the periodic table
include their sizes and
their abilities to lose or
attract electrons.
Atomic Radius
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Atomic size is a periodic trend
influenced by electron
configuration.
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For metals, atomic radius is
half the distance between
adjacent nuclei in a crystal of
the element.
Atomic Radius
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For elements that occur as
molecules, the atomic radius
is half the distance between
nuclei of identical atoms
that are chemically bonded
together.
Atomic Radius Trend
Shielding/Screening
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Electrons have an attraction or pull towards the nucleus of the
atom (opposite charges attract)
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Electrons are also repelled away from the inner electrons (like
charges repel)
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Shielding/ Screening: the attraction of valence (outer-shell)
electrons is counterbalanced by the repulsion of the inner-shell
electrons.
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The inner-shell electrons “screen” or “shield” the outer-shell
electrons from full attraction
Effective Nuclear Charge
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Effective nuclear charge is the net
positive charge experienced by valence electrons.
Atomic Radius Decreases
From Left to Right
Why?
•
Increasing positive charge in nucleus
•
Valence electrons are not shielded from the increasing
nuclear charge
•
Increasing effective nuclear charge
Atomic Radius Increases
Down a Group

Why?
Additional
electron
shells make
the atom
larger.
I
n
c
r
e
a
s
e
s
Atomic Radii – Practice I
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Rank the following atoms in increasing
atomic radius.
• Carbon
• Beryllium
• Fluorine
• Lithium
Fluorine < Carbon < Beryllium < Lithium
Ions
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An ion is an atom or bonded group of atoms with a positive or
negative charge.
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Atoms become charged by either gaining or losing electrons.
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Cations: atoms lose electrons and become positively charged
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Anions: atoms gain electrons and become negatively charged
Cations are smaller than the
neutral atom
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Smaller than the neutral atom
1.
The loss of a valence electron can leave an empty outer orbital,
resulting in a smaller radius.
2.
Electrostatic repulsion decreases allowing the electrons to be
pulled closer to the nucleus
Anions – Bigger than the
neutral atom
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Why?
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The addition of an electron increases electrostatic
repulsion.
Ionic Radius
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The ionic radii positive ions (cations) generally decrease
from left to right.
The ionic radii of negative ions (anions) generally decrease
from left to right, beginning with group 15 or 16.
Both positive and negative ions increase in size moving
down a group.
Ionic Radius
Ionic Radii – Practice
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Arrange the following ions in order of
increasing ionic radii:
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Na+, Ti3+, Mg2+
Mg2+
Na+
Ti3+
Atomic & Ionic RadiiMixed Practice
A
A.
B
C
If the figure represents the atoms helium, krypton, and
radon, match the letter to the correct atom.
A – Radon
A.
B – Krypton
C - Helium
If the figure represents a cation, an anion, and a neutral
atom from the same period, match the letter to correct term.
A – Anion
B – Atom
C - Cation
Ionization Energy
Ionization energy is defined as the energy required to
remove an electron from a gaseous atom.
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First Ionization Energy - the energy required to
remove the first electron
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Increases from left
to right across a
period.
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Decreases from
top to bottom in a
group
Second Ionization Energy
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Second Ionization Energy – the energy required to
remove a second electron
Each successive ionization requires more energy, but it
is not a steady increase.
Ionization Energy
WHY?
•
Electrons are attracted to the nucleus. The closer they are to
the nucleus, the stronger the attraction and the higher the
energy needed in order to remove the electron.
Opposite trend of Atomic Radius
Smaller radii – higher ionization energy
Ionization Energy - Practice
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Arrange the following elements in order of
decreasing Ionization Energy.
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Al, Mg, Na, Si
Si
Al
Mg
Na
Interesting IE Pattern
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The ionization at which the large increase in energy
occurs is related to the number of valence electrons.
Octet Rule
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Octet rule - states that atoms tend to gain, lose or share
electrons in order to acquire a full set of eight valence electrons.
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The octet rule is useful for predicting what types of ions an
element is likely to form.
Electronegativity
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Ability for an atom to attract electrons
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When it is chemically combined with another
atom.
Elements with high electronegativities
(nonmetals) often gain electrons to form
anions.
Elements with low electronegativities (metals)
often lose electrons to form cations.
Electronegativity
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Increases from left to right
Decreases from top to bottom
Fluorine has the
highest
electronegativity
Opposite trend of Atomic Radius. Smaller radii – higher
electronegativity (closer electron can get to the nucleus)
Electronegativity Visual
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Which visual representation best describes
electronegativity?
The ability of a nucleus of one atom to attract an
electron from another atom in a chemical bond.
Electronegativity - Practice
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Arrange the following in increasing order of
electronegativity:
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Na, Li, K
K
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Na
Li
Se
Br
Ca, Br, Se
Ca
Review of Periodic Trends