Ch 6 Chemistry Notes

Objectives : TEKS 5A: explain the use of chemical and physical properties in the historical development of the periodic table;

TEKS 5C: Use the periodic table to identify and explain periodic trends, including atomic and ionic radii, electronegativity, and ionization energy;

People/Events:

1790’s Lavoisier- listed the 23 known elements

1860-70 known elements with agreed upon masses

1864-Newlands- Law of Octaves (p.152) 1863 Classified known elements into groups, showed periodicity- every 8th element, the properties repeated.

Meyer-created a table, included properties, but didn’t leave space for unknown elements; Published his table just after Mendeleev;

1872 -Mendeleev-“Father of the periodic table”;arranged/developed the 1st useful periodic table that left blank spaces for the unknown elements; Mendeleev arranged the elements by increasing atomic mass and grouped the elements by their properties and was able to predict the existence & properties of undiscovered elements;

Problem- it was discovered that some elements didn’t fall into the correct group when arranged by mass.

Moseley-early 1900’s – because of what was learned about the nucleus of the atom, Mosely arranged elements by increasing atomic number; Problem solved.

Periodic Law (p.153) is a statement that when arranged by increasing atomic #, chem.. and physical properties repeat periodically, every 8th element.

v Others that came after these scientists left their mark by making noticeable changes to the periodic table. This led to the modern periodic table.

Modern Periodic Table p. 156-157

Arranged left to right, by Increasing atomic #

Vertical groups-group number tells us how many valence e- the atom has; there are 18 groups;

horizontal periods-period # tells us how many principal energy levels the atom has; there are 7 periods;

Periods break where the chemical properties repeat (periodicity)

Bold Staircase line separates the metals (left) from the nonmetals (right). Metalloids straddle the line.

Representative elements- groups with the letter “A”-they follow periodic law very closely;

Transition elements - groups with the letter “B”- (or groups 3-12)Transition metals are able to put more than eight electrons in the shell that is one in from the outermost shell. Transition metals can use the two outermost shells/orbitals to bond with other elements. It's a chemical trait that allows them to bond with many elements in a variety of shapes.

The Inner Transition Metals (Lanthanide Series and Actinide Series) were placed below the main body of the table to make it not so wide.

Metals-elements with the following characteristics: they are conductors, malleable (can be pounded into thin sheets, bendable), ductile (can be drawn into wires, stretched;) (Colored blue on PT)

Different groups within the metals:

v 1A Alkali Metals- most reactive p. 181-182

v 2A Alkaline Earth Metals p.183-185

v Inner Transition Metals-Lanthanide Series and Actinide Series

Metalloids- contain properties of both metals and nonmetals (colored in green)

Nonmetals- gases or brittle, dull solids (colored in yellow)

Halogens-7A-highly reactive

Noble Gases-8A-virtually unreactive b/c their valence is full

Synthetic-“man-made”; radioactive.

Radioactive -elements # 43, 61, 84-and up

Transuranium elements- above (across) uranium (# 93 & up )

Hydrogen-in group 1A b/c it has only 1 val. e-; but it’s not a metal, it’s a non-metal;

Ch. 6 section 2:

“s-Block elements”-groups 1A, 2A b/c their val. electron(s) occupy the s-orbital

“p-Block elements”- groups 3A- 8A b/c their val. electron(s) occupy the p-orbital

“d-block elements”- includes all the transition elements

“f-block elements”-includes the Inner transition elements

See page 161 figure 6-10

Elements in the same group have similar properties

Problem Solving Lab: p. 155 (Read)

“Francium-solid, liquid, or gas?”

What we will do: Graph data about the known elements and use extrapolation to estimate the properties of the unknown (Francium).

What is Interpolation  ? 

Interpolation  is  the  process  of  obtaining  a  value  from  a  graph  or  table  that  is located  between  major  points  given,  or  between  data  points  plotted.    A  ratio process is usually used to obtain the value.

What is Extrapolation ?

 Extrapolation  is  the  process  of  obtaining  a  value  from  a  chart  or  graph  that extends beyond the given data.   The "trend" of the data is extended past the last point given and an estimate made of the value.

You can interpolate that your grade will be about __58__ if you study for 1 hour.

You can extrapolate that your grade will be about 80 if you study for 6 hrs.

On your graphs:

Ind. Var. (x)-atomic #

Dep. Var. (y)-mp, bp, radius

Use Pencil to make 3 Graphs

Ø Estimate Francium’s mp, bp, and radius.

Ø Answer Questions #2-4

· All 3 graphs should be about the same size and shape.

· Scale is important- make sure that your scale has the appropriate RANGE and numbers are evenly distributed.

· To find the correct scale, Read p. 903 or follow these steps:

1. Determine the smallest and largest numbers for that axis.

2. Determine if zero must be included.

3. Find the range of required numbers by subtracting the smallest number from the largest number.

4. Count how many divisions there are on the graph paper.

5. Divide the numbers required by the divisions available.

6. Round up to the nearest appropriate number.

section 6.3

Define & describe the trends (from left to right on the PT, and from top to bottom)

· Atomic Radius

· Ionic Radius

· Ionization Energy

· Electronegativity

Atomic Radius

Definition: half of the distance between the nuclei of two atoms of that element that are just touching each other.

· atomic radius decreases across a period from left to right

· atomic radius increases down a given group

The atoms with the largest atomic radii are located in Group I and at the bottom of groups.

· This information applies to the representative elements only (not the transition elements)

Here’s Why:Moving from left to right across a period, electrons are added one at a time to the outer energy shell. Since the number of protons is also increasing, the nucleus is exerting an increasing attraction on the valence e^- ‘s. As this happens, the electrons of the outermost shell experience increasingly strong nuclear attraction, so the electrons become closer to the nucleus and more tightly bound to it. This causes the electrons to be pulled closer to the nucleus and the atomic radius to decrease.

Moving down a group in the periodic table, the number of electrons and filled electron shells increases, but the number of valence electrons remains the same. The electrons are found farther from the nucleus as the number of filled energy shells increases. The filled energy levels shield the valence e- from the increasing charge of the nucleus. Therefore, the atomic radii increase.

Ions- atoms (or groups of atoms) that are charged (not neutral)

How are ions formed? Atoms tend to gain or lose valence electrons to achieve stable octet formation. (Stable octets are seen in the noble gases) “Stable Octet”- full valence (octet means 8)

Ionic Radius-trend across a period:

When atoms lose electrons the radius gets smaller

Why?

1.The loss of a valence e- may leave a completely empty valence resulting in a smaller radius

2. The electrostatic repulsion between the e’s decreases allowing them to be pulled closer to the nucleus.

When atoms gain e’s they become larger

Why?

When e’s are added, the electrostatic repulsion between the e’s increases forcing them to be pushed outward. Therefore, larger radius.

Group 5A gains 3 e’s

Group 6A gains 2 e’s

Group 7A gains 1e

Trend down the group- increases

(Same for both + and – ions)

Why? Same reason that atomic radius increases downward

Ionization Energy

The ionization energy, is the energy required to completely remove an electron from a atom or ion.

Increases left to rt.

Why? b/c the nuclear charge increases L to R, it becomes harder to pull off the e’s

Decrease as you move down a group.

Why? The e’s are farther from the nucleus & the inner Energy levels shield the valence e’s from the + force of the nucleus. Therefore, the val. e’s are easier to remove.

Electronegativity:

• Electronegativity is “a number that describes the relative ability of an atom, when bonded, to attract electrons”.

• EN plays a role in determining which type of chemical bond forms (ionic or covalent)

• Values range from .7 to 3.98 (unit is “Paulings”)

• The periodic table has electronegativity values. See p. 169 fig 6-18;

• Trends: increases left to right

Decreases top to bottom

In chemical Bonding, the atom with the highest EN value is the one that more strongly attracts the bonding electrons.

• We can determine the nature of a bond based on DEN (electronegativity difference).

• DEN = higher EN – lower EN

Basically: a DEN below 1.7 = covalent, above 1.7 = ionic

Example: H₂O DEN = 3.44-2.20=1.24 (covalent)

LiF DEN = 3.98-.98=3.00 (ionic)

How is Ionization Energy related to Electronegativity?

Atoms with High IE will have High EN (due to the strong pull exerted on electrons by the nucleus.)

Atoms with Low IE will have Low EN (because their nuclei do not exert a strong attractive force on electrons)

Summary of Periodic Table Trends

Moving Left --> Right Moving Top --> Bottom

Atomic Radius Decreases Atomic Radius increases

Ionic Radius Decreases Ionic Radius Increases

Ionization Energy Increases Ionization Energy Decreases

Electronegativity Increases Electronegativity Decreases

Electron Affinity Electron affinity reflects the ability of an atom to accept an electron; it’s related to electronegativity; atoms with stronger nuclear charge have greater electron affinity.

Cation- a positively charged ion such as Na⁺

Anion- a negatively charged ion such as Cl^-

This is a GREAT practice/review of the trends we have learned. Try it here

http://www.sciencegeek.net/Chemistry/taters/Unit2PeriodicTrends.htm

End of Ch. 6 Notes