ELECTRON CONFIGURATION MAKING SENSE OF THE PERIODIC TABLE

Why are electrons so important? Electrons determine how an atom behaves; what it will or won’t bond with. Neutral Atoms Electrons = Negative Protons = Positive This means that neutral atoms have equal numbers of protons and electrons So the atomic number not only tells you the number of protons in the atom, but also the number of electrons EX) How many electrons does a neutral atom of iron have?

Layers are called “shells” or “energy levels” Bohr’s idea of layers Bohr’s idea that electrons orbit in layers of the atom is very useful to help us visualize the chemistry of atoms. Think of the layers as “regions” of the electron cloud. Layers are called “shells” or “energy levels”

Electron Configuration Visualize each energy level split into sub- layers, called “subshells” or “orbitals” They are named the “s”, “p”, “d”, and “f” orbitals Each Layer contains certain orbitals Each orbital can hold a certain number of electrons before it is “full” s orbital = 2 electrons p orbital = 6 electrons d orbital = 10 electrons f orbital = 14 electrons

THE Electron Configuration Hotel Imagine the atom as a seven-story hotel: Each floor of the hotel represents a layer of the atom Each floor has a certain number of rooms Each room represents an orbital within that layer Each room type can hold a certain number of guests (s=2, p=6, d=10, f=14) The number of guests in each room represent the electrons in that orbital

The Electron Configuration Hotel Blueprints 7d - 10 7f - 14 6s - 2 6p - 6 6d – 10 6f – 14 5s - 2 5p - 6 5d – 10 5f – 14 4s - 2 4p - 6 4d – 10 4f – 14 3s - 2 3p - 6 3d – 10 Parking Garage 2s - 2 2p - 6 Restaurant 1s - 2 Lobby Room Types: s (1 bed), p (3 beds), d (5 beds), f (7 beds) – 2 guests per bed

Electron Configuration Sometimes, the orbitals in different layers overlap each other This causes the orbitals to fill up in a certain order: Electrons always fill up orbitals of lower energy first.

Electron Configuration

Why is the periodic table shaped so weird?

Electron Configuration Electron Configuration is a way to mathematically represent an element Layer (1-7) Orbital (s, p, d, or f) Number of Electrons (superscript) (s1-2, p1-6, d1-10, or f1-14) EX) Hydrogen (atomic # = 1)  1 electron H: 1s1 EX) Nitrogen (atomic # = 7)  7 electrons N: 1s22s22p3

Electron configuration practice Sodium (atomic # = 11) Na: 1s22s22p63s1 Calcium (atomic # = 20) Ca:1s22s22p63s23p64s2 Bromine (atomic # = 35) Br: 1s22s22p63s23p64s23d104p5

Shows the total number of electrons on each energy level. EX) Boron Bohr Diagram Shows the total number of electrons on each energy level. EX) Boron

Be Drawing a Bohr Diagram Draw the Nucleus (element symbol) Draw the layers Use the electron configuration Start filling up the layers with electrons Follow the electron configuration EX) Beryllium Be: 1s22s2 Be

Bohr Diagram PRactice EX) Chlorine Cl: 1s22s22p63s23p5 Cl

Each element has a specific number of valence electrons Valence Electrons are the electrons located on the outer shell They are important in determining how elements react with one another

Determining the Valence Electrons A trick to using the periodic table to learn how many valence electrons an element has: Look at the group number (ones digit) Group 1 = 1 valence electron Group 2 = 2 valence electrons Group 13 = 3 valence electrons Group 14 = 4 valence electrons Group 18 = 8 valence electrons Only used for groups 1-2 & 13-18 S and P block elements D and F orbitals are “overlapped” by S and P orbitals

Octet Rule Octet Rule: An atom’s outer shell is full when it has 8 valence electrons Atoms want a full outer shell (fill s and p orbitals = 8 valence e-) Noble Gases have 8 valence electrons  they do not react often Other elements react in order to fill their outer shell NOTE: Helium is full with only 2 valence electrons (s orbital only holds 2) Periods 4-7 must fill up the previous d/f orbitals To simplify, we’ll focus on elements 1-18 (periods 1-3)

Shows the number of valence electrons Electron Dot Diagram Shows the number of valence electrons Useful in predicting/visualizing chemical bonds Dots surrounding the element symbol represent valence electrons If an element is surrounded by 8 valence electrons, it is a noble gas (except helium which only has 2)

F Electron Dot Diagram Write the symbol of the element EX) Fluorine Determine the number of valence electrons Draw the first two on the right of the symbol These represent the s orbital – 2 Draw the remaining dots one at a time going counter-clockwise until you finish top, left, and bottom represent the p orbital – 6 Note, each of the four sides has room for two valence electrons EX) Fluorine F

Electron Dot Diagram EX) Nitrogen N

Electron Dot Diagram EX) Beryllium Be

Putting it All Together EX) Aluminum Electron Configuration 1s22s22p63s23p1 Bohr Diagram Electron Dot Diagram Al Al