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Transcript
Democratis – the founder of
atoms

Early Greek-early philosopher who came
up with the term atom. Described the
building block of all substances

2 Laws govern these atoms, the Law of
definite proportion, and the Law of multiple
proportions
Definite and Multiple proportion

Definite- says that a
compound has a fixed
ratio of atoms

H20- H weighs 2 for
every 16 O

Same two atoms can
combine in multiple
ways

PbO, PbO2
FeO, Fe2 O3
Carbon dioxide,
carbon monoxide
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If H weighs 4, the O
has to weigh 32,
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Dalton and his law
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Atoms are the smallest set of matter
Atoms of same element are the same,
atoms of different elements are different
Atoms can’t be created or destroyed
Atoms combine into compounds
In compounds, atoms are always in whole
number ratios
Modern atomic theory, was Dalton
correct?
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Atoms are the smallest
set of matter
Atoms of same element
are the same, atoms of
different elements are
different
Atoms can’t be created or
destroyed
Atoms combine into
compounds
In compounds, atoms are
always in whole number
ratios

1 protons, neutrons and
electrons, quarks, lepetons,
Change mass numbers,
changes properties, called
Isotopes!!!

Fission, Fusion

Yes

Yes
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Atoms! What they are made of

Electrons

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– the negative part of atoms, roam around the
exterior of atoms.
Mass negligible. Weigh 1/1832th of the atom.
Nucleus
Houses protons. Positive charge, very heavy,
make up a lot of the mass.
 Neutrons- have no charge, but mass = to protons.
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Other good info
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If the atom were size of a football field ,
the nucleus would be a dime in the center.
( it would weigh more than a semi truck)
Rest of field would be space for electrons,
which would weigh no more than a fly.
In an atom, the number of protons is = to
the number of electrons.
The periodic table and how it
helps

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Atomic number is the number of protons. This
defines an element
Atomic weight- the weight of protons+ neutrons
in atomic mass units

Round that to a whole number, it counts protons +
neutrons.

Try some, write p+, N, and e- for the following
C, H, N, O, Ne, He, B, Na
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What if the atom is active?
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Atoms do gain or lose electrons.
Called an ION!!!!!! Has a positive or negative
charge.
Na with 11 p+ and 10 e-. Na+1
S have 16 p+ and 18 e-. S -2
How many electrons does Mg +2 have?
How about O-2?
Does their proton number change? Their mass?
What happens if the neutron
number is different?

All atoms come in different varieties. They
have the same number of protons, but the
neutron number changes.

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That means the mass number changes and
so do the properties.
Usually the change makes the less common
varieties radioactive
Isotope is the name for atoms with same
atomic number but different mass number
Isotopes

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The atomic mass on the periodic table is
an average of all the types of that
elements, with weight given for how much
of each there is
Usually in here we are referring to the
most common, so the numbers off the
periodic table are fine.
•If you want to refer to a specific isotope, there
are 2 ways to write it.
•Isotope notation. Use the name of the
element- mass number ( rounded atomic mass
•You try some
•Sodium that weighs 22.99
• Calcium that weighs 41.33
Nuclear notation

This looks like the block of the periodic table.
Use mass number over atomic number
55
26
Fe
84
or
36 Kr
You try, write the isotope that is silver with
a mass of 109, and Nickel that has 28
protons and 32 neutrons.
Nuclear reactions!!!
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Nuclear reactions- change in nucleus.
Most atoms have stable nucleus that doesn’t
change,
There is a force in the nucleus that ties protons
and neutrons together.
but a few atoms are radioactive, which means
their nucleus’s do change, and give off radiation.
.
Types of atoms that are
radioactive
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Neutrons have no force, so they do not repel,
they are like the glue helping hold together.
When get too many protons ( above 83) not
enough neutrons to hold. So all elements above
83 are radioactive. (state some)
Also isotopes of stable atoms that have too
many neutrons makes an atom unstable!
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Hydrogen –2 and Hydrogen –3, also Carbon -14
What is radioactivity?
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Radioactivity- first discovered when uranium
sample was put on photographic film
Radioactivity is the spontaneous emission of
radiation from an element.
Not necessarily dangerous! There are 3 types
1st 2 types of radioactivity- not
dangerous

Alpha particles
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have double the charge of an electron with opposite
charge so +2. Very low penetrating power. Can’t hurt
you!!!! Lots of this given off all the time all over the
place!!
Stopped by paper they have 2p and 2n.
just like He-4.

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write with an “”
Can also write 4/2 He or 4/2
Beta particles write with a “”
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0/-1 are high speed electrons -1 charge
stronger penetrating, stopped by heavy clothing can
penetrate light clothing or skin.
The dangerous type of radiation!
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Gamma radiation
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Write “ ” is similar to X rays, and has no
charge/ particles. High, have to be stopped by
lead.
How to write nuclear equations
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The proton and neutron numbers must
add up, so write it like a math equation

Try Xe + alpha
U 238 = alpha + __________
Th233 = beta + ___________
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