Constructing Atoms Today we’ll go beyond the basics and construct models of atoms. After today, you’ll be able to construct a model of almost any atom through… Sketching (today) Other 3-D models

Constructing an Atom. Starting atomic models Atoms are usually represented as a nucleus surrounded by rings. To start any atomic model, start with the periodic table to find… The number of protons The number of neutrons The number of electrons Once these are found, you’d start with a circle to represent the nucleus. The proton and neutron numbers should be written in the nucleus with the appropriate symbol…

Examples of Nuclei Argon Carbon Potassium

The Rings The nucleus describes the proton and neutron numbers but we also must input where electrons are. There are rules to how the e- are distributed. The first rule is electrons exist in rings outside the nucleus. The rings exist because it’s been found that e- can’t occupy random or the same space at the same time. Every element has a specific number of rings. The row (going from top to bottom) tells you how many rings the atom has. Hydrogen is in the 1st row = one ring Nitrogen is in the 2nd row = two rings Shown to the right. How many rings does iodine have?

Energy Levels: How it looks on an atom. H: 1 ring = 1 energy level Li: 2 rings = 2 energy levels Na: 3 rings = 3 energy levels K: 4 rings = 4 energy levels And so on… It works left to right as well

Reading the Periodic Table The Row tells you how many rings (Energy levels) the atom has.

These rings are the atom’s energy levels, as proposed by Niels Bohr Within energy levels, electrons occupy what are known as orbitals. Orbitals are tracks or regions of space where electrons are likely to be found. The higher the energy level the more orbitals there can be in the particular level. There is a specific MAXIMUM number of orbitals for each energy level that you must remember. What do you notice about the number of orbitals? The number of orbitals in a ring (aka energy level) is the square of the energy level! Atomic Orbitals 2 =

We are not getting too complicated with atoms at this point, but understand that atoms exist in a 3-D world. Though often drawn as 2-D, because it’s easier to do this on paper, electrons are capable of moving in the X, Y, and Z planes. Watch the short video clip next to see the probable regions where electrons exist…

Numbers of Electrons You now know how many energy levels and particular element will have. Based upon the row in the periodic table. You also know how many orbitals it has. Based upon the square of the energy level. You also know how many electrons are in an atom. How? Based upon the number of protons! The electrons are distributed in the energy levels based upon the number of orbitals.

Numbers of Electrons The numbers of electrons is dictated by the number of protons. But where those electrons are distributed is based upon the number of orbitals. The rule is: The maximum number of electrons per orbital is TWO. This would suggest that electrons are paired in orbitals.

Concept Check. Based upon the information you’ve learned so far… Complete this chart in your notes.

Electron Configuration The actual configuration of electrons has another rule. It is based upon stability. The most stable electron configuration in the one in which the electrons are in orbitals with the lowest possible energies. When this happens the atom is in its ground state.

The Numbers Really Matter The numbers in the periodic table represent an atom’s proton, neutron, and electron number when it is un-bounded and electrically neutral. Atoms, however, are rarely like this, stable, in nature. Mainly, it’s because the electrons are always flying around and energy is being transferred everywhere. electron

What Happens to Atoms When There is Energy Applied? When an atom is stable it’s in its ground state with all electrons distributed in their appropriate energy levels and orbitals. What did I say about when energy is applied? Electrons can jump into other energy levels. When an atom gains electrons an atom is in its less stable excited state. When the atom loses energy it emits light as it goes back to its ground state.

STABILITY! Atom Stability So what is the difference between Ground State & Excited State atoms? STABILITY!

The Outer Ring… The Valence Shell Remember, electrons are orbiting the nucleus in the region called the electron cloud... In different energy levels that have specific numbers of orbitals. The outer ring, called the valence shell, is the important one. This holds the valence shell electrons. It’s in the valence shell where bonding, or the interaction between atoms, happens. The Valence Shell

The Outer Ring Another way to say this is: The outer most edges of the electron cloud is called the valence shell. There is a strict rule for how many electrons are in this valence shell. This is called the OCTET RULE: The maximum number of electrons that can exist in the valence shell is 8. For most groups of atoms, you can determine the # of valence shell electrons from the column it’s in. The column determines the valence shell electrons. Group 1A (hydrogen, etc.) has one valence electron. Group 2A (beryllium, etc.) has two. This rule only applies to A groups though. How many valence electrons does phosphorus have? A: 5

Valence Shell Electrons Ignoring the middle transition elements, which have special properties that you’ll learn in chemistry, the periodic table tells you how many electrons are in the valence shell. Starting from left to right, each element increases it’s valence shell by one electron. Hydrogen has 1. Beryllium has 2. Boron has 3. Carbon has 4. & so on. It starts over as you go back to the beginning. So Lithium would also have 1.

Complete the Chart In Your Notes Element Protons Neutrons Electrons Rings Valence e- Hydrogen   Beryllium Boron Carbon Oxygen 1 1-1=0 4 9-4=5 2 5 11-5=6 3 6 8

Summary of the Rules for Constructing Atomic Models Part/Step Rule # of Protons Atomic Number # of Neutrons Atomic Mass - # protons # of Electrons = # Protons # of Rings The row it’s in # of Valence Electrons Based upon it’s ‘A’ column Rest of Electrons Fill inside out, based upon energy level and orbital rule

Concept Check On your handouts (back side of the periodic table), complete the blank atom for the element lithium (practice problem #1). Draw the: Correct # of protons Correct # of neutrons Correct # of electrons Correct # of rings Correct # of electron in the valence shell Put everything in the correct places.

Lithium Atom

Concept Check On your handouts (back side of the periodic table), complete the blank atom for the element carbon (practice problem #2). Draw the: Correct # of protons Correct # of neutrons Correct # of electrons Correct # of rings Correct # of electron in the valence shell Put everything in the correct places.