October 15 th 2009
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October 15 th 2009. Objectives SWBAT Identify oxidation numbers for given ions SWBAT State the definition of electronegativity SWBAT explain electronegativity trends on the periodic table Catalyst

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October 15 th 2009

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October 15th 2009

Objectives

  • SWBAT Identify oxidation numbers for given ions

  • SWBAT State the definition of electronegativity

  • SWBAT explain electronegativity trends on the periodic table

    Catalyst

  • Write down the stable ion that will form for the following elements: Be able to explain why…

    • Na, Ar, O, Mg

  • Label the ions above as cations or anions


Catalyst Review

  • Na+1, because sodium needs to lose 1e- to be stable

  • Ar, because Argon is already stable, it does not lose or gain any e-.

  • O2-, because Oxygen needs to gain 2e- to be happy

  • Mg2+, because magnesium needs to lose two electrons to be happy


Agenda

  • Catalyst Review (15min)

  • Welcome to Unit 4 (5min)

  • Compounds and Chemical Bonds (10min)

  • Oxidation numbers (5min)

  • Electronegativity (20min)

  • Practice (25min)

  • Exit Ticket (10min)


New word

  • Oxidation Number – the positive or negative charge on an ion

    • What is the oxidation number of Sodium?

    • Argon?

  • Na+1

  • Ar

  • O2-

  • Mg2+


What to expect in Unit 4

  • You will learn about…

    • Compounds (ionic and covalent)

    • Chemical formulas

    • Electronegativity, ionization energy, polarity

    • Naming compounds

    • Valence electrons continued

    • Lewis structures

  • You will get to…

    • Make Ionic Personal Ads!

    • Speed Date!


Atom - the smallest particle of an element


What is a compound?

  • A compound is a pure substance

  • A compound is a combination of two or more different elements that are chemically combined

Water molecules

Add to Vocabulary Log!


Vinegar

Acetic acid

CH2COOH

Familiar Compounds and Their Formulas


Grain Alcohol

Ethanol

C2H5OH


Cane sugar

Sucrose

C12H22O11


Stomach acid

Hydrochloric acid

HCl


What is a compound?

  • Remember! Electrons do all the work in chemical bonds!

  • Atoms do 3 things with electrons:

    • Give them away

    • Take them

    • Share them

  • A compound is a pure substance

  • A compound is a combination of two or more different elements that are chemically combined


What is a chemical bond?

  • A chemical bond is the force that holds two atoms together in a compound (attractive force)

  • There are two main types of bonds:

    • Ionic

    • Covalent


Chemical Bond Spotlight: NaCl (table salt)

2 different elements:

  • Sodium (Na)

  • Chlorine (Cl)

    1 compound:

  • Sodium chloride (NaCl)

Na

Cl

NaCl


Chemical Bond Spotlight: NaCl (table salt)


A chemical formula is a combination of chemical symbols used to represent a compound.

A chemical formula contains the number of each atom in the compound.

Chemical Formula


Ratio Examples

  • KBr has 1 atom of K and 1 atom of Br

  • H2O has 2 atoms of H and 1 atom of O

  • CO2 has 1 atom of C and two atoms of O


Subscript Numbers

  • Subscript numbers are small numbers placed to the lower right of element symbols and are used to show how many atoms of each element are present

H2O

CO2


Chemical Formulas

  • What is a chemical formula?

  • What is a subscript number?

  • What does the subscript number tell us?

    If there is no number, it is an implied ONE

  • Example: Na2CO3

    • 2 atoms Na (sodium)

    • 1 atom C (carbon)

    • 3 atoms O (oxygen)

    • 6 total atoms (2 + 1 + 3 = 6)

RATIO

2 Na : 1 C : 3 O


Chemical Formula Practice

  • Determine the number of each atom in the following compounds.

    • N2

    • CO

    • H2CO3

    • KOH

    • CaCO3

    • KNO3


What is electronegativity?

  • Electronegativity is…

    • The ability of an atom to attract electrons to itself in a chemical bond

    • How much an atom wants electrons

  • Electronegativity is expressed in numerical values of 4.0 or less

    • These numerical values are called Paulings

    • Higher number means the atom will attract electrons in a chemical bond


  • Rb has an electronegativity value of .82 Paulings

  • Br has an electronegativity value of 2.96 Paulings

    • Which one wants an electron more?


Graphing Electronegativity

  • On two white boards in your groups:

  • Draw a line graph

    • X-axis: Element

    • Y-axis: Electronegativity

  • Part 1 – points = dots

  • Part 2 – points = squares


Elements and their Electronegativity (1)(Logistics manager copy down the chart for your group)


Elements and their Electronegativity (2)


What trend(s) do

you notice?


Electronegativity

Electronegativity decreases as you go down the periodic table and increases as you go left to right across the periodic table.


Practice Problems

  • Rank the following elements in order of increasing electronegativity based on location on the periodic table (smallest to biggest)

  • Mg, Sr, Be, Ra

Radon, Strontium, Magnesium, Beryllium

Cl, Si, Al, S, P

Aluminum, Silicon, Phosphorus, Sulfur, Chlorine


Let’s Think about the Trends…

  • Discuss the following question with your group…10 class points if you come up with the right answer.

    • Why do Alkali metals have such low Electronegativities and Fluorine such a high electronegativity?

    • Why aren’t electronegativities listed for the Noble gases?


The Answer…

  • Electronegativity tells us how much an atom wants to TAKE an electron. (- charge)

  • The alkali metals have low electronegativities because in order to be stable (happy) they need to GET RID of an electron. (+ charge)

  • Halogens have a high electronegativity because in order to be stable (happy) they need to GAIN an electron (- charge)

  • Noble gases are already happy, so they do not want to gain or lose an electron (EN of zero)


How does atomic size related to electronegativity?

Atomic size is indirectly related to electronegativity

ATOMIC SIZE

As electronegativity increases, atomic size decreases!

ELECTRONEGATIVITY


Why is this relationship true?

  • Atoms with HIGH ELECTRONEGATIVITIES hold their electrons very close!

  • Sooooo, the atomic size decreases

High or low electronegativity?

Large or small atomic size?


Practice Time! (15min)

  • T or F? Electronegativity decreases as you move left across the periodic table.

  • T or F? As you move down the Periodic Table, atoms get more electronegative.

  • Rank the following sets of elements in order of increasingelectronegativity (small  big).

    Set A:Bh, Mn, Re, TcSet B:Sb, I, Ag, Ru

    Set C: Y, Ti, Sg, Ta

  • Rank the following sets of elements in order of decreasingelectronegativity (big  small).

    Set A: Cl, At, I, F, BrSet B: Te, Xe, Sn, In

    Set C:Rb, K, Sr, Ca

  • Why do Alkali metals have a lower EN then Halogens?

  • Why don’t the Noble Gases have an EN?

  • What is the relationship of atomic size to electronegativity?

  • Why does this relationship exist?

  • What are the oxidation numbers for the following elements?

    A. Fluorine, Barium, Francium, Helium, Arsenic


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