The Periodic Table

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Transcript The Periodic Table

The Periodic Table
• Substances containing only ONE kind of atom
are ELEMENTS
• CANNOT be broken down into smaller pieces
(by normal laboratory processes)
Inside an Atom
• In the early 1900s, scientists began to identify
the particles that make up atoms (subatomic
particles
• Every atom has a core called a nucleus, where the
majority (99.9%, to be exact) of an atom's mass is
held.
• Although the nucleus contains the majority of the
mass of the atom, the nucleus is very small
compared to the size of the whole atom, because
most of the atom is empty space surrounding the
nucleus.
• Within the nucleus are two types of smaller particles
called protons and neutrons.
• The third type of particle that makes up the atom,
electrons, orbit around the nucleus in the electron
cloud
PROTONS
• Positively charged particles found inside the
nucleus of an atom. Every atom of a particular
element contains the same number of protons.
• Number of protons is unique to each element.
Each element has a unique atomic number,
or a unique number of protons in its nucleus.
• Never changes for any given element.
– example, oxygen has an atomic number of 8. That
tells us that oxygen always has 8 protons.
NEUTRONS
• Other particle found in the nucleus of an atom.
• Unlike protons and electrons, neutrons carry no
electrical charge. neutrons are "neutral.”
• Atoms of a given element do not always contain
the same number of neutrons.
– Atoms of an element that have a different number of
neutrons in the nucleus are called isotopes of each
other.
ELECTRONS
• Electrons are negatively charged particles that
orbit around the outside of the nucleus in
electron cloud.
• The mass of an electron is about 1/2000th of the
mass of a proton or a neutron.
• The sharing or exchange of electrons
between atoms forms chemical bonds, which
is how new molecules and compounds are
formed.
ATOMIC Number
• How many protons are in that atom's
nucleus.
For example, oxygen has an atomic number of 8,
meaning that there are 8 protons in the nucleus of an
atom of oxygen. Copper's atomic number is 29,
meaning that there are 29 protons in the nucleus of
an atom of copper.
– Later, you'll see how the periodic table conveniently
tells you each element's atomic number.
ATOMIC MASS
• Because atoms are so small, their masses
cannot be measured in grams or milligrams.
• Instead, scientists have created the atomic mass
unit (amu) to measure mass of subatomic
particles. The mass of a proton or a neutron is
about 1 amu. The mass of an electron, however,
is about 1/2000 amu.
• To find the atomic mass of an atom, add the
number of protons and neutrons in the
nucleus.
– Example: If an atom has 3 protons, 4 neutrons, and
3 electrons, the atomic mass is 7 amu, because you
do not count the very small mass of the atom's
electrons (1/2000 amu). Only add the number of
protons and neutrons (each has a mass of 1 amu) in
the nucleus.
• Question: Find the atomic mass of an atom that
has 10 protons, 8 neutrons, and 10 electrons.
• Answer: 18 amu. Just add the protons and
neutrons.
Why is the Periodic Table important
to me?
• The periodic table is the
most useful tool to a
chemist.
• You get to use it on
every test.
• It organizes lots of
information about all the
known elements.
Pre-Periodic Table Chemistry …
• …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.
Dmitri (men duh LAY ef) Mendeleev:
Father of the Table
SOME PROBLEMS…
HOW HIS WORKED…
• Put elements in rows by • He left blank spaces for
what he said were
increasing atomic weight.
undiscovered elements.
• Put elements in columns
(Turned out he was
by the way they reacted.
right!)
• He broke the pattern of
increasing atomic weight
to keep similar reacting
elements together.
The Current Periodic Table
• Mendeleev wasn’t too far off.
• Now the elements are put in rows by increasing
ATOMIC NUMBER!!
• 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.
Think Inside the Box
•When you look at the periodic table, you should notice that each
box represents a different element, and each box contains vital
information about the element, including its name, symbol, atomic
number, and atomic mass.
»
6
»
»RR
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C
Carbon
»
»Bolbol
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12.011
ATOMIC NUMBER
# of Protons
The element's symbol
Element’s name
ATOMIC Mass
Periods
• ROWS- Horizontal
• Contains different types of elements from
different families NOT alike in properties
• Gradually change properties as you go across
left to right.
• BUT there is a pattern
• From very reactive metals to metalloids to
nonmetals to unreactive gas.
The two at the bottom
• Still a part of the table
• Separated out to make the table less wide and
more user friendly!
Groups…Here’s Where the Periodic
Table Gets Useful!!
• Elements in the
same group
have similar
chemical and
physical
properties!!
•
(Mendeleev did that on purpose.)
Why??
• They have the same
number of valence
electrons.
• They will form the same
kinds of ions.
Families on the Periodic Table
• Columns are also grouped
into families.
• Families may be one column,
or several columns put
together.
• Families have names rather
than numbers. (Just like your
family has a common last
name.)
Elements
Are arranged in
The Periodic table
Organized in order of increasing
Atomic number
made up of
Rows
called
Columns
called
Periods Families or Groups
Hydrogen
• Hydrogen belongs to a family
of its own.
• Hydrogen is a diatomic,
reactive gas.
• Hydrogen was involved in the
explosion of the Hindenburg.
• Hydrogen is promising as an
alternative fuel source for
automobiles
Alkali Metals
• 1st column on the
periodic table (Group 1)
not including hydrogen.
• Very reactive metals,
always combined with
something else in nature
(like in salt).
• Soft enough to cut with a
butter knife
Alkaline Earth Metals
• Second column on the
periodic table. (Group 2)
• Reactive metals that are
always combined with
nonmetals in nature.
• Several of these
elements are important
mineral nutrients (such
as Mg and Ca
Transition Metals
• Elements in groups 3-12
• Less reactive harder
metals
• Includes metals used in
jewelry and construction.
• Metals used “as metal.”
Boron Family
• Elements in group 13
• Aluminum metal was
once rare and expensive,
not a “disposable metal.”
Carbon Family
• Elements in group 14
• Contains elements
important to life and
computers.
• Carbon is the basis for
an entire branch of
chemistry.
• Silicon and Germanium
are important
semiconductors.
Nitrogen Family
• Elements in group 15
• Nitrogen makes up over
¾ of the atmosphere.
• Nitrogen and phosphorus
are both important in
living things.
• Most of the world’s
nitrogen is not available
to living things.
• The red stuff on the tip of
matches is phosphorus.
Oxygen Family or Halogens
• Elements in group 16
• Oxygen is necessary for
respiration.
• Many things that stink,
contain sulfur (rotten
eggs, garlic, skunks,etc.)
Halogens
• Elements in group 17
• Very reactive, volatile,
diatomic, nonmetals
• Always found combined
with other element in
nature .
• Used as disinfectants
and to strengthen teeth.
The Noble Gases
The Noble Gases
• Elements in group 18
• VERY unreactive,
monatomic gases
• Used in lighted “neon”
signs
• Used in blimps to fix the
Hindenburg problem.
• Have a full valence shell.
Metals, Nonmetals &
Metalloids
• Most periodic tables contain a stair step line
which allows you to identify which elements are
metals, nonmetals, and metalloids. Following are
descriptions of each of the three types of
materials.
Metals
• Most elements are metals. 88 elements to the
left of the stair step line are metals or metal like
elements.
• Chemical Properties of Metals:
• Easily lose electrons
• Corrode easily. Corrosion is a gradual wearing
away. (Example: silver tarnishing and iron
rusting)
Physical Properties of Metals:
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Luster (shininess)
Good conductors of heat and electricity
High density (heavy for their size)
High melting point
– Solid at room temperature
– Some require temperature increase of 3,400 C to melt them
• Except Mercury Hg, which is liquid at room temperature
• Ductile (most metals can be drawn out into thin wires)
• Malleable (most metals can be hammered into thin sheets)
• Several are attracted to magnets and can be made into magnets
(iron Fe, cobalt Co, and nickel Ni)
Metals Mixed Together= ALLOYS
• Mixture= two or more substances mixed together
• Alloy= mixture of metals
– Combine the best properties of two or more metals
– Iron= rusts easily but mix with carbon, chromium,
and vanadium = stainless steel
– Cooper= thin and malleable but mix with tin=
Bronze (last hundreds of years)
Nonmetals
• Many of the very common elements
• Nonmetals are found to the right of the stair step
line. Their characteristics are opposite those of
metals.
• Chemical Properties of Nonmetals:
• Tend to gain electrons
• From compounds easily
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Physical Properties of
Nonmetals:
Opposite of metals
No luster (dull appearance)
Poor conductor of heat and electricity
Brittle (breaks easily) low density
Not ductile
Not malleable
Low density
Low melting point
Low boiling points
– Many are gases at room temperature
Metalloids
• Elements on both sides of the zigzag line have
properties of both metals and nonmetals.
• Varying ability to conduct electricity
• Most common is Silicon Si
• Combines with Oxygen, O, to form familiar substances
including sand, glass and cement
Physical Properties of
Metalloids:
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Solids
Can be shiny or dull
Ductile
Malleable
Conduct heat and electricity better than
nonmetals but not as well as metals
Valence Electrons- Why the table
works
• valence electrons are the electrons contained
in the outermost, or valence, electron shell of an
atom.
• Based on the understanding of protons, neutrons
and electrons, scientists are able to explain and
predict how atoms will behave in interactions
• Modeled on the transferring of electrons
BETWEEN atoms
VALENCE Electrons
• Electrons involved in transferring or sharing
• The number of electrons available determines if
element: gives up, shares or accepts electrons
from other elements during reactions
– The fewer valence electrons an atom holds, the less
stable it becomes and the more likely it is to react.
• Increase from left to right across period (row) of
periodic table.
•
Stability
Hydrogen, helium, lithium, beryllium, and boron need 2
valence electrons in their outer energy level to be stable
• Others need 8 to be stable – usually.
• Electron dot diagrams- include the element symbol and
dots to represent valence electrons
• Can use electron dot diagrams to help us determine
stability– H is less stable than He because it has only 1 valence electron
while He has 2 valence electrons
How do atoms become stable?
• They share, gain, or lose electrons to become
stable
• Chemical bond- force that holds atoms together
in a compound – caused by either exchanging or
sharing electrons
Valence Electrons in Groups
• Elements in same groups have same number
and arrangement of valence electrons and have
similar properties.
• # of valence electrons help determine an
element’s properties
Periodic table group
# Valence electrons
Group 1 (I) (alkali metals)
Group 2 (II) (alkaline earth metals)
Groups 3-12 (transition metals)
Group 13 (III) (boron group)
Group 14 (IV) (carbon group)
Group 15 (V) (nitrogen group)
Group 16 (VI) (oxygen halogens)
Group 17 (VII) (halogens)
Group 18 (VIII or 0) (noble gases)
1
2
1 or 2*
3
4
5
6
7
8**
* Valence electrons are not generally useful for transition metals.
** Except for helium, which has only two electrons.
BONDING
• Since metals tend to lose electrons and
nonmetals tend to gain electrons,
– metals and nonmetals like to form compounds
with each other. These compounds are called
ionic compounds.
Ionic Bonding
• Chemical bond
• Attraction between opposite charges of ions of in an
ionic compound
– The metal donates one or more electrons, forming a
positively charged ion with a stable electron configuration.
– These electrons then enter the non metal, causing it to form a
negatively charged ion or anion which also has a stable
electron configuration.
– The electrostatic attraction between the oppositely charged
ions causes them to come together and form a bond.
• For example, common table salt is sodium chloride.
When sodium (Na) and chlorine (Cl2) are combined,
– The sodium atoms each lose an electron, forming a cation
(Na+),
– The chlorine atoms each gain an electron to form an anion
(Cl-).
– These ions are then attracted to each other in a 1:1 ratio to
form sodium chloride (NaCl).
– Na + ½Cl2 → Na+ + Cl- → NaCl
Covalent Bonds
• When two or more nonmetals bond with each
other, they form a covalent compound.
• Chemical bond
• Atoms share pairs of electrons
• Produces molecules
Chemical Formulas
• Chemical Formula- tells how many of each element
are present in a compound
– Consists of element symbols and subscripts
– Water has 2 hydrogen atoms and 1 oxygen atom
What do the formulas mean?
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SiO2
silicon- 1 Oxygen-2
C12H22O11
Carbon- 12 Hydrogen-22 Oxygen-11
N2O
Nitrogen- 2 Oxygen-1