Chapter 5 “Electrons in Atoms”

What you should know about electrons… They are negative, about 1840 times smaller than proton… The area around the nucleus where you can find an electron is called the electron cloud and this cloud is divided into smaller areas called energy levels. Electrons fly around the nucleus in energy levels. NOT all flight paths are circular (like orbits). Each energy level can hold a certain amount of electrons 1st energy level (closest to nucleus)- hold 2 electrons 2nd energy level – can hold a max of 8 3rd energy level – can hold up to 18

Location of the Electrons Are located in an area around the nucleus known as the Electron Cloud. The Cloud is broken down into smaller areas that hold Fixed amounts of energy called Energy Levels. An amount of fixed energy separates one level from another The electron cannot exist between energy levels With-in each energy level They fly In specific paths, or orbits, at different levels. The paths are called sublevels or orbitals. A quantum of energy is the amount of energy required to move an electron from one energy level to another

Energy Levels Energy levels- (aka: Principal quantum number) are fixed amounts of energy located in a specific region around the nucleus. 1st energy level- located closest to the nucleus and has the least amount of energy. Can hold 2 electrons. 2nd energy level- located higher than the 1st level. Holds more energy and up to 8 electrons. As you go farther from the nucleus, the energy levels hold more electrons and more energy. Within each energy level, there are sublevels depending on the amount of energy it can hold. The sublevels (orbitals) are named, s, p, d and f. As you go farther from the nucleus, more energy is held in the energy levels and there are more sublevels (orbitals) in each. You can find how many energy levels an atom has by which row it is located in on the periodic table. Example: Calcium is in row 4, therefore it has 4 energy levels.

Sublevels (orbitals) The sublevels are s, p, d and f. There is one s sublevel in each energy level. It holds 2 electrons. The p sublevel has 3 orbitals each holding 2 electrons. (total 6 electrons) The d sublevel has 5 orbitals, each holding 2 electrons (total 10 electrons) The f sublevel has 7 orbitals, each holding 2 electrons (total 14 electrons) The sublevels are named due to the shape of the travelling path of the electrons in those orbitals. See next slide.

S d p S S d p p p p d p d d

Location of the sublevels on the periodic table Energy level=each row. There are 7 rows What sublevels do each energy level contain: Energy level 1- s Energy level 2= s, p Energy level 3= s,p,d Energy level 4= s,p,d,f Energy level 5= s,p,d,f Energy level 6= s,p,d, Energy level 7= s,p

Rules for how electrons fill up the energy levels. Three rules tell us how: Aufbau principle - electrons enter the lowest energy first. Pauli Exclusion Principle – Only 2 electrons max can fill an orbital- with different spins Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. This means that if there are 3 p orbitals one electron will go in each first, and then they will finish filling up with 2 electrons. Three rules tell us how: Aufbau principle - electrons enter the lowest energy first. Pauli Exclusion Principle – Only 2 electrons max can fill an orbital- with different spins Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. This means that if there are 3 p orbitals one electron will go in each first, and then they will finish filling up with 2 electrons.

Electron Filling Diagram Used to determine electron configuration. Sublevel (flying path)= s,p,d 6p_____ _____ _____ 5d_____ _____ _____ _____ _____ orbitals (holds 2 electrons) 4f_____ _____ _____ _____ _____ _____ _____ 6s_____ energy level 5p_____ _____ _____ 4d_____ _____ _____ _____ _____ 5s_____ 4p_____ _____ _____ 3d_____ _____ _____ _____ _____ 4S_____ 3p_____ _____ _____ 3s_____ 2p_____ _____ _____ 2s_____ 1s_____ start here Three rules tell us how: Aufbau principle - electrons enter the lowest energy first. Start 1s and go up Pauli Exclusion Principle – Only 2 electrons max can fill an orbital- with different spins. Each blank can have 2 arrows up arrow (clockwise spin) down arrow (counter clockwise spin) Hund’s Rule- When electrons occupy orbitals of equal energy, they don’t pair up until they have to. This means that if there are 3 or more blanks, put one arrow in each blank 1st then pair up.

Using Orbital filling diagram to write electron configuration https://youtu.be/jTI-ZkrVvE4

Using the Periodic Table to Write the electron configuration. Click Here if this video will not play Rules: Start on row one write the last one in each color on each row until you get to the color your element is in. Then write that element.

Exceptions to electron Configuration Some elements that need one more electron to have a completely filled or ½ filled “d” or “f” sublevel. What happens is that they borrow an electron from the “s” below and move it to the level that needs one more. Watch these 2 Videos: Element Should be: Actually is (more stable) Cr 4s23d4 4s13d5 Mo 5s24d4 5s14d5 Cu 4s23d9 4s13d10 Ag 5s24d9 5s14d10 1-See Mrs. Maddox Explain This!!! 2- Youtube video on electron configuration exceptions

Energy levels and the sublevels it contains: Energy level 2= s, p Energy level 3= s,p,d Energy level 4= s,p,d,f Energy level 5= s,p,d,f Energy level 6= s,p,d, Energy level 7= s,p Below: shows the order that the electrons fill the orbitals. The d orbitals fill after the higher level s orbitals.

Writing Nobel Gas Configurations Write the noble gas symbol in brackets from the row before that element. The write the configuration for the row that the element is on. Example: Bromine e- configuration: 1s22s22p63s23p64s23d104p5 Noble gas config: Ar 4s23d104p5

Valence Electrons Valence electrons= the electrons that are located in the highest energy level Valence configuration: It is the highest energy level s orbital or s and p orbitals. Examples: Bromine : 1s22s22p63s23p64s23d10 4p5 Valence configuration: 4s24p5 # of valence electrons = (2 +5) = 7

Electrons can move energy levels Ground state- the lowest energy level that an electron belongs to. Quantum leap- when an electron absorbs energy it will move to a higher energy level for a short period of time. An electron is known to be in the “excited state”, when it absorbs energy and takes a quantum leap. The electron will eventually release the extra energy as light and return to its ground state. The light release by different electrons have color to them depending on how much energy the light wave contains. Examples: Flame test, Fireworks

Electrons and how they release light…

Flame Test Colors

Checking for understanding: What happens when an electron moves to a higher energy level? What happens when an electron moves to a lower energy level? Are energy levels with lower amounts of energy closer or farther from the nucleus of the atom??