how do we draw atoms? bohr models lewis dot diagrams
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How to draw a Bohr Model1. Draw a nucleus & put protons and neutrons inside.
(may use a square shape so you don’t draw any electrons on it)
2. Remember the p=e in a neutral atom, so begin putting electrons on the energy levels until you use them all up.
Fill energy levels in order (can’t put any in 2nd shell until you’ve filled the first)
Drawing Bohr models, cont…Helpful hints: 1. Draw electrons at each of the four “corners”,
then double up2. Write the number of electrons you drew (in
parentheses) on each energy level to help you keep track.
But…that can be a pain…Most of the time we only really care about
the valence electronsValence Electrons- electrons in the outermost
shellAlso the GROUP NUMBER!!!
Valence Electrons-Find the number of valence electrons by
counting over the rows (skipping transition metals) See next slide
How to draw a Lewis Dot Structure1. Find the group # (top of the row on the PT)2. Write the symbol.3. Draw dots around the symbol equal to the
group number (if group 2- draw two dots)1. Place dots one at a time around the top,
right, bottom and left side of the atom before you double any up.
How to draw a Lewis Dot Structure1. Find the group # (top of the row on the
PT) Let’s do Phosphorus2. Write the symbol. P3. Draw dots around the symbol equal to
the group number (if group 2- draw two dots)
1. Place dots one at a time (clockwise) around the top, right, bottom and left side of the atom before you double any up.
Octet rule exceptions…(octet rule=Most atoms want to have 8 electrons in their outer shell)
Helium- What is its group number?Why doesn’t it make sense to draw that many
dots?Because it is easier for it to fill that first shell
which only needs two electronsOther- Exceptions:
___H__ , __Li___ , __Be___
Atomic Mass Mystery…Look at the average atomic mass for Oxygen.
What does it say (exactly?)15.9999
What is the mass number?P + N = whole number
So what the heck!?!?!Average of the actual isotopes’ mass
numbers and abundance on Earth!!!
How can we change the mass of an element?We can’t mess with protons, but what CAN
we “mess with?”Neutrons…
What would that change about the atom? Changes the MASS Get an ISOTOPE
IsotopesIsotopes are different atoms of the same
element that contain the same number of protons but different number of neutrons.
Examples Cl-35 vs. Cl-37 17P 17P 18N 20N
How to write isotopes…Mass/Hyphen Notation:
Especially important for a form of the isotope that is NOT the “usual”
Write the symbol, a dash, and the mass # for that isotope
Ex’s C-14 C-12
How to write isotopes…Nuclear Symbol Notation
Includes the symbol, atomic #, and the mass # for that isotope
Ex’s 14
6C
Mass #
Atomic # (=p)
What else CAN we “mess with?”Already know…Neutrons…
Get an ISOTOPE, changes the mass
But what if I mess with Electrons…What would that change about the atom?Changes the CHARGEGet an ION
How are these ions made?Can you mess with protons?Would messing with neutrons
do anything to the charge?What must you mess with???What charge does an
electron have?So what would happen to the
atom if they LOSE one? Would they get more positive or more negative overall???