College Preparatory Chemistry Unit 10 –The Periodic Table

The Periodic Table Electron Configurations- continued We have previously learned the order for filling orbitals for the first eighteen elements: 1s2s2p3s3p. Where do we go after 3p? Since there is one more sublevel on the 3rd PEL, one would expect to fill in 3d next. However, experiments have shown that this is not the case. For example, tests have shown that potassium has chemical properties similar to the other elements in its group (column). Similar properties would indicate they have the same number of valence electrons (the electrons found in the highest energy level).

Examples H = 1s1 1 valence electron Li = 1s2 2s1 1 valence electron Na = 1s2 2s2 2p6 3s1 1 valence electron If 3d was filled in next, potassium’s electron configuration would be: K = 1s2 2s2 2p6 3s2 3p6 3d1 9 valence electrons! (which doesn’t make sense to the octet rule and would mess up everything!)

So What Is Going On Here? Scientists believe that 4s fills in after 3p. That would give potassium 1 valence electron, the same number as lithium and sodium, other metals in the same column. This makes sense since many chemical properties are based on the element’s valence electrons. The correct electron configuration for potassium would be:   K = 1s2 2s2 2p6 3s2 3p6 4s1 1 valence electron

Remember The complete order of filling orbitals: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d …   Reminders: The s sublevel holds ___2__ electrons The p sublevel holds ___6__ electrons The d sublevel holds __10___ electrons The f sublevel holds __14___ electrons

Example Ex. Write the electron configuration for scandium (Z= 21) and determine the number of valence electrons. Sc = 1s2 2s2 2p6 3s2 3p6 4s2 3d1 Valence electrons = 2 (Look carefully at highest energy level)  

Examples Ex. Write the electron configuration for zinc (Z= 30) and determine the number of valence electrons. Zn = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 Ex. Write the electron configuration for gallium (Z= 31) and determine the number of valence electrons. Ga = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1

Periodic Table Observations: Valance electrons are only in the s and p sublevels. So there can be a maximum of 8 valance electrons. The number of the column corresponds to the number of valance electrons. The row corresponds to the highest principal energy level (PEL).

Observations: How many columns to the left of the transition metals? _____2_____ We call this the _s__ block. How many columns to the right of the transition metals? ______6____ We call this the _p__ block. How many columns wide are the transition metals? _____10_____ We call this the __d__ block. How many columns are in the rows down on the bottom?___14_____ We call this the __f__ block.

Examples Ex. Where would the last electron be for strontium (Z= 38)? 5s2 because Sr is in the s block of the table, 5th row, 2nd column   Ex. Where would the last electron be for tin (Z= 50)? 5p2 because Sn is in the p block of the table, 5th row, 2nd column

Examples Ex. Where would the last electron be for titanium (Z= 22)?   3d2 because d doesn’t show up until the 3rd energy level, so the first row of d is 3d and it is in the 2nd column of 3d Ex. Where would the last electron be for promethium (Z= 61)? 4f4 because f doesn’t show up until the 4th energy level, so the first row of f is 4f and it is in the 4th column of 4f

Exceptions There are four exceptions that you are responsible for know; Cr, Mo, Cu, and Ag.

Examples Ex. Where would the last electron be for krypton (Z= 36)? 4p6 Ex. Where would the last electron be for cesium (Z= 55)? 6s1 Ex. Where would the last electron be for uranium (Z= 92)? 5f3 Ex. Where would the last electron be for platinum (Z= 78)? 5d8

Noble Gas Abbreviation – a shortcut representing the core electrons How to write an electron configuration using the Noble Gas abbreviation: For a given atom, start with previous noble gas (the core electrons through its valence electrons (s and p orbitals) are filled). Put the noble gas symbol in a bracket. This represents that many core electrons, Next write energy level for valence e- n = ? : count rows down from top of periodic table Read left to right across table until you get to given atom. Write down orbitals and electrons in those orbitals along the way. Double check by adding electrons

Ex. Sulfur – atomic number 16 Last noble gas is neon: [Ne] - This represents 10 core electrons. Sulfur is 3rd energy level down: 3 Left side of the table is s orbitals – pass through 2 columns: 3s2 Right side of table – p orbitals - pass through 4 columns: 3p4 Noble gas abbreviation is [Ne] 3s2 3p4 Double check: 10 + 2 + 4 = 16 electrons

Ex. Scandium – atomic number 21 Last noble gas is argon: [Ar] - This represents 18 core electrons. Scandium is 4th energy level down: 4 Left side of the table is s orbitals – pass through 2 columns: 4s2 The next section is the d orbitals – must remember they are delayed filling – this is the 3rd energy level d - pass through 1 column: 3d1 Noble gas abbreviation is [Ar] 4s2 3d1 Double check: 18 + 2 + 1 = 21electrons

Ex. Cerium – atomic number 58 Look carefully - Last noble gas is xenon: [Xe] - This represents 54 core e– . Cerium is 6th energy level down: 6 Left side of the table is s orbitals – pass through 2 columns: 6s2 The next section is the d orbitals – must remember they are delayed filling – this is the 5th energy level - pass through 1 column: 5d1 The next section is the f orbitals – must remember they are two energy levels of delayed filling – this is the 4th energy level f - pass through 1 column: 4f1 Noble gas abbreviation is [Xe] 6s2 5d1 4f1 Double check: 54 + 2 + 1 + 1 = 58 electrons

Write the Noble Gas abbreviation for manganese (Z= 25) Last noble gas is ____argon_____ : - This represents __18_ core electrons. Manganese is ____4th ___ energy level down: Left side of the table is s orbitals: 4s2 The next section is the d orbitals – must remember they are delayed filling this is the 3rd energy level d: 3d5 Noble gas abbreviation is: [Ar] 4s23d5 Double check: 18+2+5 = 25

Examples Ex. Write the Noble Gas abbreviation for iodine (Z= 53). [Kr] 5s23d105p5 Ex. Write the Noble gas abbreviation for mercury (Z= 80). [Xe] 6s24f145d10

Periodic Table Development J.W. Dobereiner- classified elements into sets of 3 called triads - Early 1800s Elements in a triad have similar chemical properties Properties of the middle element are approximate averages of the first and third Ex. Element Atomic mass Density Cl 35.5 amu 1.56 g/L Br 79.9 amu 3.12 g/L I 126.9 amu 4.95 g/L

Periodic Table Development J.A.R. Newlands- law of octaves - 1865 Arranged elements in order of increasing atomic mass Properties repeated every 8 elements; properties of 8th were like 1st; 9th like 2nd; 10th like 3rd; etc.

Periodic Table Development Dmitri Mendeleev- 1st periodic table - 1869 Arranged elements in order of increasing atomic mass Placed elements with similar properties in the same column Switched the increasing atomic mass order of some elements, such as Co & Ni because he thought grouping in columns according to properties was more important. Predicted the existence and properties of undiscovered elements, such as germanium. When they were discovered, his property predictions were accurate

Periodic Table Development Henry Moseley- 1910 discovered atomic number; changed periodic table to now be in order of increasing atomic number.

NOTE: Mendeleev had the right pattern but the wrong property As Atomic Number Increases So Does The Atomic Mass Most Of The Time

Periodic Law- (basis of the periodic table) when elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern Current Periodic Table Arranged in order of increasing atomic number Rows are called periods or series Columns are called groups or families   NOTE: Columns go _____Vertically__________; Rows go ______Horizontally__________

Groups with Special Names: Group 1 - ______Alkali Metals______________ (Except: ___H___!!) Group 2 - ______Alkaline Earth Metals __________ Group 7 - ______Halogens____________________ Group 8 - ______Noble Gases__________________ Middle section - __Transition Metals ______________

Periods with Special Names: 4f- ____Lanthanides ________________ 5f- ____Actinides ___________________

Periodic Trends Periodic trend- a pattern a particular property demonstrates in a group or period All trends are based on the distance and attractions between the nucleus and the valence electrons.   HINT: Read questions involving trends carefully and explain the trend given to you. NOTE: When explaining why a trend occurs, it is NOT ENOUGH of an answer to merely state the location of elements on the periodic table! You must address the number of protons in the nucleus, the valence electron energy levels and attractions between the two.

Atomic Radius (Size) Atomic Radius (Size) - distance from center of nucleus to valence electrons ↓ Why? ____Increases___ → Why? ____Decreases ___ As PEL increases so does the distance between the nucleus and the valance electrons. More protons – increase in the positive charge – pulls electrons closer to the nucleus.

Example Which atom is larger: Ca or Ba? Barium: Its valence electrons are in the 6th energy level and calcium’s are in the 4th energy level. The 6th energy level is farther from the nucleus.

Example Which atom is smaller: Mg or S? Sulfur: Both have valence electrons in the 3rd energy level, but S has 16 protons to attract the valence electrons while Mg only has 12 protons. The 16 protons can attract the valence electrons closer that the 12 protons will.

Examples – You Try It Ex. Which atom is larger: K or Ca ? Ex. Which atom is smaller: B or Al ?

Ionization Energy Ionization Energy- energy required to remove an electron from an atom Why? ↓ Why? __Decreases__   → Why? _Increases___ Larger Radius (e- further away ) More PEL shield e- from nucleus Smaller radius (e- closer) Greater columbic attraction – More protons

Example Which has a higher ionization energy: F or N? Fluorine: Both have valence electrons in the 2nd energy level, but F has 9 protons and N has 7. The 9 protons will pull the electrons closer and the radius will be smaller. In addition to the radius being smaller, the 9 protons will attract the valence electrons more tightly and it will be harder to remove one.

Example Which has a lower ionization energy: K or Fr? Francium: Since its valence electrons are in the 7th energy level vs. the 4th energy level for K, the nucleus is less able to attract the valence electrons and its easier to remove one of them. In addition, since there are more energy levels shielding the nucleus from the valence electrons, it is easier to remove one of them.

Examples – You Try It Ex. Which has a higher ionization energy: H or Na ? Ex. Which has a lower ionization energy: C or O ?

Mixed Example: Ex. Which is the smallest atom: O or F or Cl? HINT: If the elements are not all in the same column or same row, you might want to sketch how they are related to each other on the periodic table.

Answer Ex. O F Cl Comparing atoms in the same row- F is smaller than O since they are both in the 2nd energy level but F has 9 protons vs. 8 protons so it has a greater attraction and pulls the valence electrons closer, making a smaller radius. Comparing atoms in the same column- F is smaller than Cl since its valence electrons are in the 2nd energy level vs. the 3rd, so it has a smaller radius. Since F < O and F < Cl, F is the smallest atom.

Hints HINT: Read questions carefully – make sure you are answering the question that you are asked. Shielding is never a factor in a row.

HINT: If you are asked about a trend on a test or quiz, you will be expected to do the following: Define the trend Say what the trend does as you go down a column and explain why Say what the trend does as you go across a row and explain why Give an example using elements that illustrate the trend. Your answers will need details about protons, valence electron energy levels and attractions (as the examples given to you have included).

Metal Reactivity Physical properties of metals: luster, malleable, ductile, good conductors, mostly solid, most silver in color Physical properties of nonmetals: lack properties of metals Chemical Differences: Metals-  Lose electrons to form positive ions Nonmetals- Gain electrons to form negative ions

Metal Reactivity Metal Reactivity- how reactive a metal is; how easily it forms a positive ion by losing an e- ↓ Why? Why? __Increases_ → Why? Why? __Decreases__ Greater dis. from nucleus More shielding Smaller radius Greater columbic attraction – more protons

Example Which is the more reactive metal: K or Ca? Potassium: Both K and Ca are in the 4th energy level. Since K is a larger atom, it will have less attraction for the valence electrons and will lose it more easily. Also, since Ca has 20 protons and K has only 19 protons, Ca has a greater attraction for its valence electrons and will not lose them as easily.

Example Which is the less reactive metal: Li or K? Lithium: Li’s valence electrons are in the 2nd energy level vs. the 4th for K, the nucleus has more control over its valence electrons and will not lose them as easily. Also, since K has two more levels of electrons shielding its valence electrons from the nucleus, it is easier for K to lose its valence electrons.

Examples - Ex. Which is more reactive: Na or Mg ? Ex. Which is less reactive: Sr or Ba ?   Ex. What is the most reactive metal overall? Fr

Nonmetal Reactivity Nonmetal Reactivity- how reactive a nonmetal is; how easily it forms a negative ion by gaining an e- ↓ Why? Why? __Decreases__ → Why? Why? __Increases__ Greater dis. from nucleus More shielding Smaller Radius increases e- att. Greater columbic attraction – more protons

Example Which is the more reactive nonmetal: Cl or I? Chlorine: Since the nucleus is trying to attract an electron to the valence shell, it is easier for Cl to attract because its valence electrons are in the 3rd energy level and I has its valence electrons in the 5th energy level. In addition, I has 2 more levels of electron shielding and this decreases the amount of attraction between the nucleus and the valence electrons.  

Example Ex. Which is the less reactive nonmetal: Si or S? Silicon: Since Si is the larger atom, it is harder for the nucleus to attract electrons over the larger radius. In addition, it has only 14 protons to attract an electron vs. 16 protons for S.

Examples Ex. Which is the more reactive nonmetal: N or O?   Ex. Which is the less reactive nonmetal: Cl or Br? Ex. What is the most reactive nonmetal overall? F

Hints HINT: Be able to tell the difference between a metal and a non-metal Some people call this activity and some call it reactivity so be aware that you might hear it either way

Ionic radius Ionic radius- radius of an ion; atoms gain or lose electrons to be “electronically like” a noble gas (stable) (Remember, all the noble gases have complete valence shells- means the s and p orbitals are filled). The fancy term for this is isoelectronic. Positive ions lose electrons becoming smaller than the parent atom Why? They lose an electron level   Same number of protons pulling on less electrons

Example Ex. Which is larger: Na vs. Na+1? (Electron configuration for Na is [Ne] 3s1) Sodium atom: Na has one valence electron in the 3rd energy level. It loses 1 electron when it becomes an ion, so the valence shell becomes the 2nd energy level, so it is a smaller radius. In addition, the ion has the same 11 protons pulling on only 10 electrons, so they can be pulled closer which decreases the radius.

Ionic radius Negative ions gain electrons becoming larger than the parent atom Why? Electrons in orbits repel one another Same number of protons pulling on more electrons

Example Which is smaller: F vs. F-1? (Electron configuration for F is 1s2 2s2 2p5) Fluorine atom: When an electron is added to the ion, the electrons repel more and the radius gets larger. In addition, since there are the same 9 protons in both cases, the nucleus can attract 9 electrons tighter than 10 electrons, so the atom is smaller

Examples- You Try It Ex. Which is smaller: calcium atom or calcium ion? Ca+2 Ex. Which is larger: chlorine atom or chloride ion? Cl-1 Ex. Which is larger: O or F-1 or Cl? Cl