Bohr, isotopes, and ions, Oh My!!

How do we Draw Atoms?Bohr Models Lewis Dot

Diagrams

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.

Electron configurations (Bohr Models)

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

Valence Electrons are what react and bond!

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-Most atoms want to have 8 electrons in their

outer shell.

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___

Elements with a full outer shell naturally (Noble Gases)

Lewis Dot Structures

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

Intro to Ions

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???

IONSIf you mess with the electrons you change the

overall charge of the atom…an atom that is no longer neutral is called an ION.

Anion- has a negative chargeMeans you added an electron!

Cation- has a positive chargeMeans you lost an electron