E LECTRON C ONFIGURATIONS Niels Bohr The way electrons are arranged around the nucleus. 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 4p 6 5s 2 4d 10 5p 6 6s 2 4f 14 5d 10 6p 6 … Chapter 12, page 364

Energy Levels and Sublevels The emission spectrum for each element has a characteristic set of spectral lines. This means that the energy levels within the atom must also be characteristic of each element. When scientists investigated multi-electron atoms, they found that their spectra were far more complex than would be anticipated by the simple set of energy levels predicted for hydrogen. These spectra have many more lines than the spectrum of hydrogen.

Some lines are grouped close together, and there are big gaps between these groups of lines. Energy Levels and Sublevels The big gaps correspond to the energy released when an electron jumps from one energy level to another. This suggests that sublevels—divisions within a level—exist within a given energy level. The interpretation of the closely spaced lines is that they represent the movement of electrons from levels that are not very different in energy.

If electrons are distributed over one or more sublevels within an energy level, then these electrons would have only slightly different energies. The energy sublevels are designated as s, p, d, or f. Energy Levels and Sublevels Each energy level has a specific number of sublevels, which is the same as the number of the energy level. For example, the first energy level has one sublevel. It’s called the 1s sublevel. The second energy level has two sublevels, the 2s and 2p sublevels Within a given energy level, the energies of the sublevels, from lowest to highest, are s, p, d, and f. The third energy level has three sublevels: the 3s, 3p, and 3d sublevels; and the fourth energy level has four sublevels: the 4s, 4p, 4d, and 4f sublevels.

The Distribution of Electrons in Energy Levels A specific number of electrons can go into each sublevel. SublevelNumber of Atomic Orbitals Maximum Number of Electrons s12 p36 d510 f714

Electron Configurations This most stable arrangement of electrons in orbitals and sublevels is called an electron configuration. Electrons fill orbitals and sublevels in an orderly fashion beginning with the innermost sublevels and continuing to the outermost.

Get out your PERIODIC TABLES and highlighters / color pencils of different colors

Sections of Periodic Table to Know f-block s-block d-block p-block

E LECTRON C ONFIGURATIONS Electron Configurations represent the location of the electrons in an atom or ion. 1s 2 2s 2 2p 5 the energy level of the electron (n) the sublevel the number of electrons

N OTATIONS OF E LECTRON C ONFIGURATIONS Standard Shorthand Orbital Diagrams

W RITING E LECTRON C ONFIGURATIONS 1. You always start at the beginning of the periodic table. 2. Use the row number on the periodic table to give you the energy level (or coefficient) to use. 3. Use the block on your periodic table to tell you the sublevel (or letter) to write on your electron configuration. 4. Count across your periodic table until… a. You reach the end of a block or a row. b. You reach your desired element. This tells you the number of electrons to write (or the exponent).

Write the ground state electron configuration for hydrogen. 1s 1

Write the complete electron configuration for beryllium. 1s 2 2s 2

Write the electron configuration for chlorine. 1s 2 2s 2 2p 6 3s 2 3 p 5

E LECTRON C ONFIGURATIONS You try these on your own! Fluorine Potassium 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1

E LECTRON C ONFIGURATIONS ( CONTAINING THE D - SUBLEVEL ) The energy level of d-sublevel will ALWAYS be one less than the row or period number.

Write the electron configuration for titanium (Ti). s1s p 6 3s 2 3 p 6 4s 2 3 d 2

Write the electron configuration for iron (Fe). s1s p 6 3s 2 3 p 6 4s 2 3 d 6

Write the electron configuration for bromine (Br). s1s p 6 3s 2 3 p 6 4s 2 3 d 10 4p 5

You try these on your own! Tellurium (Te) Silver (Ag) 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 10 5p 4 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 2 4d 9

S HORT -H AND N OTATION [Ne]3s 2 3p 2 Uses a noble gas (Group 18) to represent the innermost electrons. Outermost electrons are represented the same way. Hint: To find the noble gas, look at the noble gas from the previous row or the row above the element.

Shorthand Electron Configuration (S.E.C.) To write S.E.C. for an element: 1. Put symbol of noble gas that precedes element in brackets. 2. Continue writing e – config. from that point.

Write the noble gas electron configuration for silicon. [Ne] s 2 33p 2

Write the noble gas electron configuration for zinc. [Ar] s 2 43d 10

N OBLE G AS E LECTRON C ONFIGURATIONS You try these on your own! Barium (Ba) Antimony (Sb) [Xe]6s 2 [Kr]5s 2 4d 10 5p 3

O Orbital Diagrams …show spins of e – and which orbital each is in 1s 2s 2p3s 3p 1s 2s 2p3s 3p P

O RBITAL D IAGRAMS /E LECTRON C ONFIGURATION hydrogen helium carbon 1s 1 1s 2 2s 2 2p 4

V ALENCE E LECTRONS Valence electrons are electrons found on the highest energy level. They are always “s” or “s” and “p” electrons. There can be no more than eight valance electrons. 1s 2 2s 2 2p 6 3s 2 3p 2 What is the highest energy level? n =3 or third energy level How many electrons are on the highest energy level? 4 electrons How many valence electrons are in this element? 4 electrons

S AMPLE Q UESTIONS Write the electron configuration (the long way or short hand notation) for the following elements. For each element, determine the number of valence electrons. 1. Calcium 2. Nitrogen 3. Arsenic 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 or [Ar]4s 2 2 valence electrons 1s 2 2s 2 2p 3 or [Ne] 2s 2 2p 3 5 valence electrons 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 3 or [Ar] 4s 2 3d 10 4p 3 5 valence electrons

L EWIS D OT D IAGRAMS Element Symbol One Dot for Each Valence Electron

L EWIS S TRUCTURES 1) Find your element on the periodic table. 2) Determine the number of valence electrons. 3) This is how many electrons you will draw.

L EWIS S TRUCTURES Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons.

G ROUPS - R EVIEW Each column is called a “group” Each element in a group has the same number of electrons in their outer orbital, also known as “shells”. Except for He, it has 2 electrons The electrons in the outer shell are called “valence electrons”

N

L EWIS S TRUCTURES 1) Write the element symbol. 2) Carbon is in the 4 th group, so it has 4 valence electrons. 3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol.

L EWIS S TRUCTURES

S AMPLE Q UESTIONS How to Place the Dot on Any Symbol Draw the Lewis dot diagrams for the following elements. Silicon Sodium Iodine X Si Na I