Transcript intro to atoms ppt

Atoms and the Periodic Table
• Chemists used the properties of elements to sort the
elements into groups.
– Mendeleev used increasing atomic mass to construct his
table.
– He knew some elements had similar chemical and physical
properties!
– He put each element on a card wit its melting point (MP)
density, color, atomic mass and the # of bonds it would
form.
– He was able to predict undiscovered elements and their
properties after he arranged the cards by atomic mass!!
– Modern periodic table has elements arranged in increasing
atomic number (we needed to identify subatomic particles before
we could use atomic #)
When Mendeleev arranged his cards of elements
he noticed that the pattern was not quite right,
but when he moved a few cards over and left
spaces the pattern worked. He concluded that
the spaces were “yet undiscovered” elements.
He was able to predict the properties of these
elements!
Today the periodic table looks a little different,
more elements have been found and we have
discovered “sub atomic particles” which allowed
scientists to re arrange the elements by atomic
number. The pattern became even more regular!
Atomic number.
Atomic symbol
6
Element name
C
Carbon
12.011
Average atomic mass Review:
*To find the number of protons, see the atomic number.
*To find the number of electrons (see the atomic number)
*To find the number of neutrons, subtract the atomic number from the
atomic mass. Use whole number. Atomic mass -- 12
Atomic #
-6
6 neutrons
V. How Do The Structures of the Atoms Differ?
A. Atomic Number - # of protons in the nucleus
1. Also tells the number of electrons in a neutral
atom
2. Each atom has a unique atomic number; never
changes
3. It identifies the atom
4. Usually the smallest number, always a whole #
B. Mass Number – sum of the protons + neutrons
1. Usually the biggest number, often a decimal
C. Ion – an atom or group of atoms that has lost or gained 1
or more electrons; therefore has a net (overall) charge
D. Isotope – atoms of the element with different numbers of
neutrons Ex: C-12 and C-14
E. Average Atomic Mass – weighed average mass of a
elements isotopes; why the mass is usually not a whole
number
• I: Organization of the Periodic Table
• A. Elements are arranged based upon atomic
number (# of protons). Usually the smallest of
the 2 numbers
• Periodic Law – when elements are arranged the way
there are because of similarities in properties and it
occurs in a regular pattern.
• B. Period (series) – horizontal rows
– Number of protons and electrons increase by 1 as
you move across a period.
• C. Group (family) – vertical columns
– Elements in these groups have the same number of
valence electrons and have similar properties
Because the first
shell is full at 2 it
is at the end of
the period,
Groups
Or
families
instead of
in the
second
group with
the other
elements
with 2
valence
electrons
Periods
(when we write a sentence, we go ACROSS the paper and put a PERIOD at the end.)
Group 2
+2
Looses 2 -e
Group 3
+3
Group
4
Looses 3 -e
Group 5
-3
Group
6
Group 7
-1
Gains 2 -e
Gains 1 -e
Gains 3 -e
Group
8
Group 1
+1
No charge
Looses 1 -e
If you gain an
electron e- you
increase your
(-) charge
Less
(electrons) is
more (+) of a
charge
Transition metals
Variable charges
How Are Elements Classified
• Metals are usually shiny
solids that can be
stretched and shaped
They are ductile (put into
thin wire) and malleable(
hammered into sheets).
They are also good
conductors of heat and
electricity.
Most of the elements are
metals.
They are on the left side of
the periodic table
Form (+) ions
• Nonmetals (except H) are
found on the right side of the
chart. They may be solid,
liquid or gas…solid ones are
usually dull,brittle (shatter if
hit with a hamer)
Form (-) ions.
They are poor conductors of
electricity except for C
• Metalloids (semimetals) have
properties of both metals and
nonmetals. Ex: Boron,
Silicon, Germanium, Arsenic,
Antimony and Tellurium
Alkali Metals - Group 1
• Soft, shiny metals that
react violently with
water and other stuff.
• 1 valence electron in
this group=very
reactive. Will give up
an electron.
• Form 1+ ion
• Ex.: Sodium reacts
quickly with Cl to give
up an electron to it
and become NaCl,
salt.
• Must store in oil
Alkaline Earth Metals- Group 2
• Have two valence electrons,
are not as reactive as alkali
metals, but still reactive
enough to form 2+ ions and
react to form compounds.
• Calcium forms many hard
compounds used to
strengthen organic
structures: shells [become
limestone and marble], coral
and bones and teeth.
• Magnesium- light structural
material, milk of magnesia,
Epsom salts, and flares.
Transition metals
• Much less reactive, but still
can forms ions. Transition
metals can be +2, +3 and
even +4
• Many times you will know
the charge because of
Roman Numerals in () ‘s
• Ex: Cu (III) is Copper with
a +3 charge
Mercury- on metal that is liquid at room temp… useful in
thermometers and thermostats, but has been replaced
due to toxicity.
Gold, Silver, Platinum- very shiny=jewelry use.
Other Nonmetals
• Group 3 – Boron group.
These have +3 charge and
have 3 valence electrons Ex:
Aluminum (Al)
• Group 4 – Carbon group.
These have -4 charge and
have 4 valence electrons Ex:
Carbon (C) – pure state is
found as graphite and
diamonds.
• Group 5 – Nitrogen group.
These have -3 charge and
have 5 valence electrons Ex:
Nitrogen 75% of air is made
of nitrogen
• Group 6 – Oxygen group.
These have -2 charge and
have 6 valence electrons. Ex:
Oxygen 20% of air is made of
oxygen. Sulfur – yellow,
odorless solid, in compounds
give off a terrible smell
Halogens - Group 7
• 7 valence electrons and
have a (-1) charge
• Very reactive; especially with
group 1
• Ex: Bromine (Br) – only
liquid nonmetal at room
temp
• Ex: Fluorine (Fl) – used in
toothpaste
• Ex: Chlorine (Cl) – used in
swimming pools
Nobel gases - Group 8
• All gases. Different from most
elements, because they are very
unreactive.
• 8 valence electrons, so they won’t
react with any other elements.
• Also known as inert.
• Ex: Neon (Ne) - used in neon signs
(mixed with other elements gives
other colors).
• Ex: Helium (He) - is very light
(used in balloons).
• Ex: Argon (Ar) - used in light bulbs
to prevent it from burning up
2
He
This group, the Noble gases (group18)
is usually very unreactive. This is
because they all have full valence
electron shells. Helium (He) has 2e in
the 1st shell (holds 2), Neon (Ne) has
2e in the lst shell, and 8e in the 2nd
shell (full).
10
Ne
18
Ar
36
Kr
54
Xe
86
Rn