Element

1
Cutting up matter
14 cm strip of aluminum foil
Element
Atom
1 atom of aluminum
Its not aluminum anymore!
2
Parts of an atom
Proton
Neutron
Electron
- (nothing else left!)
(positive)
0 (neutral)
Charge
Mass (mg)
1.6726 x 10-21
1.6749 x 10-21
9.1094 x 10-25
Which part(s) of the atom is the lightest?
the electrons! They weigh 2000 times less than
protons and neutrons
3
Putting the atom together
1. Where do the different pieces go?
2. How many of each part do we use?
Well start with Carbon which has
4
Putting the atom together
1. Where do the different pieces go?
The protons and neutrons are at the center of the
atom.
This is called the nucleus.
The nucleus is about 10-13 cm in size.
Do you think the electrons are located in the
nucleus?
Nope, otherwise, size of atom size of nucleus
5
Where the electrons hang out
The electrons are mobile and they move around the
nucleus.
Description 1 single orbit model
the good shows electrons surrounding the
nucleus the bad puts electrons on the same path
around the nucleus
6
Where the electrons hang out
The electrons are mobile and they move around the
nucleus.
Description 2 Bohr model
the good shows electrons surrounding the nucleus
and places electrons into different paths (like
planets) the bad electrons dont actually
travel in circles around the nucleus
7
Where the electrons hang out II
The problem We can only define the volume in
space where the electrons are located (we call
this an atomic orbital).
(Think of putting a bee in an opaque balloonwe
know the bee has to be somewhere inside the
balloon but we dont know exactly where at any
given time)
The shape of the orbital depends on its energy
and the number of electrons we have.
8
Where the electrons hang out II
For carbon (6 total electrons)
2 electrons hang out in a spherical atomic orbital
2 electrons hang out in a slightly larger
spherical atomic orbital
2 electrons hang out in the barbell shaped atomic
orbitals
The more electrons you have, the more interesting
the shapes of the orbitals get!
9
Visualizing the atom
If we start stacking atomic orbitals on top of
each other, it gets messy pretty fast
electrons 1 2
electrons 5 6
electrons 3 4
10
Visualizing the atom II
easy
Its ok to use the Bohr model as long as we
remember that it is an imperfect model!
11
Visualizing the atom II
Putting the atom together
1. Where do the different pieces go?
2. How many of each part do we use?
12
Protons electrons
This number tells me the number of protons (and
electrons) in the atom. It is called the atomic
number.
Why does protons electrons?
An atom is not positively or negatively charged
6x(1) 6x(-1) 0
13
Neutrons
What do we know about the mass of a proton
relative to the mass of a neutron?
mass of proton mass of neutron
How about the mass of the electron?
2,000 times smaller
Therefore
mass of atom mass of protons mass of neutrons
Lets say that 1 proton has a mass of 1 atomic
mass unit (amu)
What is the mass of carbon in amu?
(6 protons)x(1 amu) (6 neutrons)x(1 amu) 12
amu
14
Neutrons II
Anyone see the mass of carbon in amu on the
periodic table entry for carbon?
so, we can use the atomic mass and the atomic
number to find the number of neutrons in an atom!
15
Lets practice sodium
of protons
11
of electrons
11
of neutrons
23 11 12
What is the mass of the sodium nucleus?
nucleus contains protons and neutrons ? 11 12
23
Where are the electrons in the sodium atom?
moving around the nucleus in different atomic
orbitals
16
The periodic table