Download Chapter 7.1 Notes

Chapter 7.1 Notes
Atoms are the smallest form of
elements.
Matter is made of what?
• Yes, matter is made up of atoms.
• Everything is made up of atoms.
• Atoms are the smallest particle of an element
that has the chemical properties of that
element.
How many elements were
described at first?
• In 1789 Antoine Lavoisier created the firs tlist
of elements.
• Lavoisier described 33 elements.
• He decided that a substance made 2 or more
elements would be named after the elements
it was made of.
– EX: Carbon + 2 Oxygen = Carbon Dioxide.
Why are the elements given a 1
or 2 letter symbol?
• Many elements are named after people,
places or things.
• Because there are over 100 elements, we
have to use symbols with 1 or 2 letters to
represent each element.
• Some elements have the first letter in the
name as the symbol. The symbol is always
capitalized.
Carbon = C, Hydrogen = H, Oxygen = O
• Other elements use the first letter and an
additional letter in the name as the symbol.
• In two letter symbols, the first letter is always
capitalized and the second letter is always
lowercase.
– EX: Aluminum = Al, Platinum = Pt
• Some symbols do not match the name we
call them.
– EX: Gold = Au, Lead = Pb, Iron = Fe
• This is because the symbol is based on the
Latin name of the element.
Element names and symbols
summarized.
• Element Names: Named after famous
people, places and things.
– Einsteinium (Es) named after Albert Einstein
– Neptunium (Np) named after the planet Neptune
• Symbols: 1st letter always capitalized, 2nd
letter always lowercase.
– Hydrogen (H), Sulfur (S), Nitrogen (N)
– Cobalt (Co), Zinc (Zn), Chlorine (Cl), Silver (Ag)
What is the structure of an atom?
• Every element is made up of atoms.
• Every atom of an element is exactly the
same.
– All oxygen atoms look identical.
• Every element has as different atom.
– Oxygen atoms are different from Carbon atoms.
• So how do they look?
• Atoms are made up of particles called Protons,
Neutrons and Electrons.
• Protons are positively charged particles. (+)
• Neutrons are particles with no charge. (0)
• Protons and Neutrons are located in the center
of the atom. They are bunched together in the
nucleus of the atom.
• Electrons are located on the outside of the
nucleus and move around the protons and
neutrons.
• The electrons in an atom form an “electron
cloud”
• This electron cloud is where the electron are
zipping around the nucleus.
– We never know exactly where an electron is, but
we do know that it is somewhere inside the cloud.
– The positive charge of the proton attracts the
electron so it doesn’t fly away.
Nucleus
Draw
This!!!
So, how big is a single atom?
• A single atom is about 0.0000000001 meters
in diameter.
• You could fit millions of atoms into a period
printed in the textbook!
• It would take you 500 years to count the
number of atoms in a single grain of salt!
How big are protons, neutrons
and electrons?
• Protons and Neutrons are 2000 times the
size of an electron.
• When calculating the mass of an atom, you
only count protons and neutrons.
– Electrons have so little mass you ignore them
when calculating the mass of an atom!
Particle Charge
Mass
Proton
+1
1
Neutron
0
1
Electron
-1
0.0005
What part of an atom determines
what element it is?
• The Atomic Number tells us what
element the atom is.
• The Atomic Number is the number of
protons in the nucleus.
– EX: Hydrogen is atomic number 1.
• That means there is exactly 1 proton in the nucleus
of hydrogen.
• Gold is atomic number 79. Gold has 79 protons in
the nucleus.
• The number of protons in an element
never changes!!!
What do you count to get the
atomic mass?
• To get the atomic mass, you count the
particles in the nucleus. (Count the
protons and neutrons.)
• Remember, the number of protons in an
element never changes… but the number
of neutrons can change.
• Isotopes are atoms of an element with a
different number of neutrons in the
nucleus.
• Isotopes: The # of protons never changes!
• The number of neutrons is the only
difference.
Protons
stay the
same
The # of neutrons changes.
How many neutrons does
Chlorine-37 have?
• The number after the element is the atomic
mass of the isotope.
• Chlorine-37 means 37 total
protons+neutrons.
• Chlorine is atomic number 17.
• Atomic number 17 = 17 protons in chlorine.
• 37-17 = # of neutrons.
• 37-17 = 20 neutrons.
How do atoms form ions?
• First off, what is an ion?
• An ion is an atom with missing or added
electrons.
• The number of electrons an element begins
with is equal to the number of protons…
which is also the same as the atomic number.
Positive Ions
• When an atom loses an electron, it loses a negative
charge.
– There are now more positive charges (protons) than
negative charges (electrons).
• A positive ion is smaller in size than the original
atom. The electron cloud shrinks.
– The protons can pull more on the remaining electrons.
• Positive ions are written with a “+” after the symbol
for each electron lost.
– Na+, Ca2+, Al3+
– The more positive the ion, the smaller the electron cloud
becomes.
Negative Ions
• Negative Ions form when an atom gains
electrons.
• Because there are more negative charges
(electrons) than positive charges (protons)
the electron shell expands/gets bigger.
– The more negative charges, the bigger it gets!
• Negative ions are written with a “-” after the
symbol for each electron gained.
– Cl-, O2-, N3-
Chapter 7.2 Notes
Elements make up the…
Elements can be organized by
similarities.
• One way scientists organized elements in the
past was by their atomic mass.
• To do this, they had to get the mass of a large
chunk of the element and calculate the mass
of a single atom.
• Because there are isotopes of atoms.. (atoms
with a different number of neutrons in the
nucleus) the atomic mass that was calculated
ended up being the average atomic mass of
all the isotopes.
Mendeleev and his periodic table.
• The time is the 1860’s. Mendeleev is working
on figuring out patterns in the physical and
chemical properties of the known elements of
the time.
• Mendeleev used rows of elements to show
similar chemical properties. If the elements
were in the same row, they had similar
chemical properties.
• Next, Mendeleev used columns to show
atomic mass from lightest to heaviest.
• Here is what Mendeleev’s periodic table
would have looked like if written like modern
periodic tables.
• Mendeleev predicted that the holes in his
table were elements that were not discovered
yet.
• Many scientists laughed at this idea of
undiscovered elements.
• But, only 6 years after his periodic table,
scientists began discovering those predicted
elements and the elements had the chemical
and physical properties Mendeleev predicted.
So, why is the periodic table
organized the way it is?
• The periodic table of elements is organized by
the properties of the elements and their
atomic number.
How to read the periodic table.
• Each “cell” on the table
tells us lots of
information.
– Atomic Number
– Chemical Symbol of the
element
– Name of the element
– Average atomic mass of
the element.
How does the periodic table in
your text book look?
• Basically the same,
but with different
colors.
• In your text book, the
color of the chemical
symbol means
something too!
= gas
Blue = liquid
Black = solid
1
Hydrogen
1.008
Groups and Periods
• Groups are the columns
on the periodic table.
(Up/down)
• Groups are also called
“family of elements”
• Elements in the same
group have similar
chemical properties.
• They like to react in the
same way with the same
elements.
• Their physical properties
can be different!
• Periods are the rows
(left/right)
• Periods show electron
energy cloud “shells”
• There are 7 energy
shells.
–
–
–
–
–
–
Shell 1 holds 2 electrons
Shell 2 holds 8
Shell 3 holds 8
Shell 4 holds 18
Shell 5 holds 18
Shell 6 and 7 hold a lot
more.
• Basically, periods of
elements have similar
electron clouds.
Empty shells
Full Shells