How do we Draw Atoms? Bohr Models Lewis Dot Diagrams

How to draw a Bohr Model 1. 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 2 nd shell until you’ve filled the first)

Drawing Bohr models, cont… Helpful hints: 1. Draw electrons at each of the four “corners”, then double up 2. 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 electrons Valence Electrons- electrons in the outermost shell Also 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 Structure 1. 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 Structure 1. Find the group # (top of the row on the PT) Let’s do Phosphorus 2. Write the symbol. P 3. 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 electrons Other- 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?) 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

Isotopes Isotopes 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 6 C 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 CHARGE Get 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???

IONS If 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 charge Means you added an electron! Cation- has a positive charge Means you lost an electron