CHEMISTRY Trends and Configurations

Electron Configurations and the Periodic Table Valence electron configurations repeat down a group

Ground state electron configurations Example: Li atomic number = 3 nucleus has 3 protons neutral atom has 3 electrons 2 electrons in 1s orbital, 1 electron in 2s orbital 2s 1s

Different ways to show electron configuration Energy level diagram Box notation   2s 1s 2s 1s Spectroscopic notation Li 1s2 2s1 Read this “one s two” not “one s squared” Write the superscript 1. Don’t leave it blank

Using the Periodic Table The last subshell in the electron configuration is one of these (row #) s (row # – 1) d (row #) p (row # – 2) f

The f-block is inserted into to the d-block

Electron configuration of O Atomic number of O = 8 so neutral atom has 8 e–

Electron configuration of Co Atomic number of Co = 27 so neutral atom has 27 e–

Simplifying electron configurations Shorthand Noble Gas Configuration      Build on the atom’s noble gas core He 1s2 O 1s22s22p4 O [He]2s22p4 Ar 1s22s22p63s23p6 Co 1s22s22p63s23p64s23d7 Co [Ar]4s23d7 1s 2s 2p                1s 2s 2p 3s 3p 4s 3d

Noble Gas electron configurations What is the electron configurations for Neon Abbreviated way to write configurations Start with full outer shell then add on Br Ba

Why are we doing all of this? Properties of atoms correlate with the number and energy of electrons Electron configurations are used to summarize the distribution of electrons among the various orbitals

Electron configuration of ions What is an ion? How many electrons does Cl1- have? What is the electron configuration for the chloride ion? How many electrons does Ca2+ have? What is the electron configuration for the calcium ion? What do you notice?

Why is this important Valence electrons Electrons in the outermost energy level Where all the action occurs

The f-block is inserted into to the d-block

Find the electron configuration of Au Locate Au on the periodic table

Find the electron configuration of Au Au [Xe] The noble gas core is Xe

Find the electron configuration of Au Au [Xe]6s2 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row  6s2

Find the electron configuration of Au Au [Xe]6s24f14 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row  6s2 Then detour to go 14 spaces across the f-block  4f14 note: for the f-block, n = row – 2 = 6 – 2 = 4

Find the electron configuration of Au Au [Xe]6s24f145d9 The noble gas core is Xe From Xe, go 2 spaces across the s-block in the 6th row  6s2 Then detour to go 14 spaces across the f-block  4f14 note: for the f-block, n = row – 2 = 6 – 2 = 4 Finally go 9 spaces into the d-block on the 6th row  5d9 note: for the d-block, n = row – 1 = 6 – 1 = 5

Practice Draw the orbital diagram for sulfur. What ion does sulfur want to form and why? Draw the orbital diagram for Potassium.

Periodic Trends http://www.chem1.com/acad/webtext/atoms/atpt-6.html

Preview 4 Periodic Trends 2 main factors affect periodic trends Atomic Size/Radius Ionic Size (**) Ionization Energy Electronegativity 2 main factors affect periodic trends Number of electron shells (group) Effective Nuclear Charge (period)

Periodic Trends Atomic radius The distance from the center of an atoms nucleus to it’s outermost electron Measure of atomic size

Periodic Trends

Atomic Radius Group Trend Period Trend Increases from top to bottom More energy levels or quantum levels (or “shell”) as you go down a group – atomic radius increases Period Trend Decreases from left to right All electrons in the same energy level. Increased # of protons holds them closer to nucleus.

Table of Atomic Radii

Period Trend: Atomic Radius

Periodic Trends Size of an atom when electrons are added or removed. Electrons removed atom becomes smaller. Electrons added atoms become larger Why? Electron-Electron Repulsion Ionic Size

Ionic Size Cations Anions Positively charged ions formed when an atom of a metal loses one or more electrons Cations Smaller than the corresponding atom Negatively charged ions formed when nonmetallic atoms gain one or more electrons Anions Larger than the corresponding atom

Table of Ion Sizes

Ionic Size Group Trend Period Trend Increases from top to bottom More energy levels as you go down a group – ionic size increases Period Trend Decreases as atoms lose more electrons Increases dramatically as atoms start gaining electrons, decreases as atoms gain fewer electrons.

Periodic Trends Ionization Energy Energy needed to remove one of the electrons on an atom’s outer shell. How strongly does an atom hold it’s outermost electron.

Graph the first 20 elements. What is the trend down a group Graph the first 20 elements. What is the trend down a group? Across a Period?

Ionization Energy Group Trends Period Trend Decreases from top to bottom. Shielding makes electrons easier to remove. Period Trend Increases from left to right. Increased Effective Nuclear Charge makes it harder to remove electrons.

Periodic Trend: Ionization Energy

Periodic Trends Electronegativity Is a measure of the level of attraction (pull) an atom exerts on the electrons of another atom. Ability of an atom to attract electrons Which elements want to gain electrons the most?

Graph the first 20 elements. What is the trend down a group Graph the first 20 elements. What is the trend down a group? Across a Period?

Periodic Table of Electronegativities

Electronegativity Group Trend Period Trend Decreases from top to bottom. As radius increases, electrons are farther to the nucleus (increase in number of electron shells, Shielding effect) Period Trend Increases from left to right Increased Effective Nuclear Charge means the atom wants to attract more electrons. Exception: Trend does not apply to Noble Gases

Periodic Trend: Electronegativity

Summary of Periodic Trends

Practice Se and Br P, S, Se Cl, Cl1-, Br, Br1- Mg, Mg2+, Na, Na1+ Smallest atom Lowest Ionization Energy P, S, Se Largest atom Highest Ionization Energy Cl, Cl1-, Br, Br1- Largest ionic size Mg, Mg2+, Na, Na1+ Smallest ionic size

Atomic Properties Definitions Ionization Energy: Energy needed to remove an electron from an atom or molecule. The higher the effective core charge and lower the number of electrons shells, the greater the ionization energy Atomic size How big (e.g., radius) an atom is Atomic radius is measured from the center of the nucleus to the valence electron shell. The higher the effective core charge and lower the number of electron shells, the smaller the atom. Electronegativity Measure of the level of attraction (pull) an atom exerts on the electrons of another atom. The higher the effective core charge and lower the number of electron shells, the greater the electronegativity