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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 - PowerPoint PPT Presentation
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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 moleculesAdd to Vocabulary Log!
Familiar Compounds and Their Formulas
VinegarAcetic acidCH2COOH
Grain AlcoholEthanolC2H5OH
Cane sugarSucroseC12H22O11
Stomach acidHydrochloric acidHCl
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
• Remember! Electrons do all the work in chemical bonds!
• Atoms do 3 things with electrons:
1. Give them away
2. Take them3. Share them
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)
Chemical Formula 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.
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)
RATIO2 Na : 1 C : 3 O
Chemical Formula Practice Determine the number of each
atom in the following compounds.1. N2
2. CO3. H2CO3
4. KOH5. CaCO3
6. 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)Element Electronegativity
(Paulings)Hydrogen 2.20Lithium 0.98Sodium 0.93
Potassium 0.82Rubidium 0.82Cesium 0.79
Francium 0.70
Elements and their Electronegativity (2)
Element Electronegativity (Paulings)
Lithium 0.98Beryllium 1.57
Boron 2.04Carbon 2.55
Nitrogen 3.04Oxygen 3.44Fluorine 3.98
What trend(s) doyou 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
Cl, Si, Al, S, PRadon, Strontium, Magnesium, BerylliumAluminum, 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
ELECTRONEGATIVITY
ATOMIC SIZE
As electronegativity increases, atomic size decreases!
Why is this relationship true? Atoms with HIGH
ELECTRONEGATIVITIES hold their electrons very close!
Sooooo, the atomic size decreasesHigh or low
electronegativity?
Large or small atomic size?
Practice Time! (15min)1. T or F? Electronegativity decreases as you move left across the
periodic table.2. T or F? As you move down the Periodic Table, atoms get more
electronegative.3. Rank the following sets of elements in order of increasing
electronegativity (small big). Set A: Bh, Mn, Re, Tc Set B: Sb, I, Ag, Ru Set C: Y, Ti, Sg, Ta
4. Rank the following sets of elements in order of decreasing electronegativity (big small).Set A: Cl, At, I, F, Br Set B: Te, Xe, Sn, InSet C: Rb, K, Sr, Ca
5. Why do Alkali metals have a lower EN then Halogens?6. Why don’t the Noble Gases have an EN?7. What is the relationship of atomic size to electronegativity?8. Why does this relationship exist?9. What are the oxidation numbers for the following elements?
A. Fluorine, Barium, Francium, Helium, Arsenic