Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond?
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Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond? As Ga Ge Se. Topic: Writing Binary Ionic Formulas. Empirical Formulas. = smallest whole-number ratio of elements in compound Ionic compounds have empirical formulas only.

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Do Now: An atom of which element has the greatest attraction for electrons in a chemical bond?

As

Ga

Ge

Se

Topic: Writing Binary Ionic Formulas


Empirical formulas
Empirical Formulas for electrons in a chemical bond?

= smallest whole-number ratio of elements in compound

  • Ionic compounds have empirical formulas only


Identify the empirical formulas
Identify the empirical formulas for electrons in a chemical bond?

  • H2O

  • H2O2

  • CaF2

  • NaCl

  • CH4

  • C2H6

  • NiO

  • FeCl3

Empirical – NOT ionic

Molecular – NOT ionic

Empirical, Ionic

Empirical, Ionic

Empirical – NOT ionic

Molecular – NOT ionic

Empirical, Ionic

Empirical, Ionic


Formula unit
Formula Unit for electrons in a chemical bond?

= simplest ratio of ions in ionic compound

Examples:

  • KBr is formula unit

    • potassium ions & bromide ions are in a 1-to-1 ratio

  • Al(NO3)3 is formula unit

    • Aluminum & nitrate ions in 1-to-3 ration


Binary ionic compounds
Binary Ionic Compounds for electrons in a chemical bond?

  • Composed of two different elements

    • Positive monatomic metal ion

    • Negative monatomic nonmetal ion

Note: A binary compound may contain more than 2ionsbut only 2kindsof ions like Al2O3


Oxidation number or state

Na for electrons in a chemical bond?+1

Ca+2

O-2

Fe+2 and Fe+3

Al+3 and Ag+1

Oxidation Number or State

  • charge of monatomic ion

  • has right superscript

  • Some elements form only 1 ion

  • Some elements can form more than 1 ion


Oxidation states
Oxidation States for electrons in a chemical bond?

  • Group 1 ions always +1

  • Group 2 ions always +2

  • MOST group 13 ions are +3

  • Groups 14, 15, 16, and 17 have multiple oxidation states

    • both (+) and (-)

  • Transition metals (Group B) can have more than 1 oxidation state

    • but are always (+)


Writing formulas for binary ionic compounds
Writing Formulas for for electrons in a chemical bond?Binary Ionic Compounds

  • first rule in writing formulas for ionic compounds is

    POSITIVE ION FIRST

But how do you get the subscripts?

start by writing formulas from the ions



Equal but opposite charges
Equal but Opposite Charges for electrons in a chemical bond?

  • Na+1 and Cl-1: NaCl +1 + (-1) = 0

  • Mg+2 and O-2: MgO +2 + (-2) = 0

  • Al+3 and P-3: AlP +3 + (-3) = 0

  • Rule: write symbols, (+) FIRST!


Try a few formulas
Try a few formulas: for electrons in a chemical bond?

  • Li+1 and I-1

  • Ca+2 and O-2

  • Al+3 and N-3

  • K+1 and F-1

  • Ba+2 and S-2

LiI

CaO

AlN

KF

BaS


Criss cross method
Criss-Cross Method for electrons in a chemical bond?

  • When the charges don’t cancel out immediately:

  • Mg+2 and Cl-1, CROSS and DROP!

    (# only, forget signs!)

  • Mg1Cl2 but if subscript is 1, forget it!

  • MgCl2 means 1 Mg+2 and 2 Cl-1


Check the math
Check the Math for electrons in a chemical bond?

  • MgCl2 means 1 Mg+2 and 2 Cl-1

    (1 x +2) + (2 x -1) = +2 + -2 = 0

  • charges MUST add up to zero!


Try a few formulas1
Try a few formulas: for electrons in a chemical bond?

CaCl2

  • Ca+2 + Cl-1

  • Na+1 + O-2

  • Cs+1 + S-2

  • Al+3 + Cl-1

  • Al+3 + Se-2

  • Mg+2 + F-1

  • K+1 + N-3

Na2O

Cs2S

AlCl3

Al2Se3

MgF2

K3N


Of course it gets more difficult
Of course, it gets more difficult for electrons in a chemical bond?

KF

  • Potassium (K) and Fluorine (F)

  • Zinc (Zn) and Iodine (I)

  • Sodium (Na) and Oxygen (O)

  • Magnesium (Mg) and Oxygen (O)

  • Aluminum (Al) and Oxygen (O)

  • Calcium (Ca) and Bromine (Br)

  • Cesium (Cs) and Iodine (I)

  • Silver (Ag) and Sulfur (S)

ZnI2

Na2O

MgO

Al2O3

CaBr2

CsI

Ag2S


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