Stability and ionic bonding
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Stability and Ionic Bonding. Section 20.1 & 20.2. SC Standards Covered. Standard PS-4.1 Explain the role of bonding in achieving chemical stability. Standard PS-2.5

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Stability and Ionic Bonding

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Stability and Ionic Bonding

Section 20.1 & 20.2


SC Standards Covered

  • Standard PS-4.1

  • Explain the role of bonding in achieving chemical stability.

  • Standard PS-2.5

  • Predict the charge that a representative element will acquire according to the arrangement of electrons in its outer energy level.

  • Standard PS-4.6

  • Predict the ratio by which the representative elements combine to form binary ionic compounds, and represent that ratio in a chemical formula.

  • Standard PS-4.4

  • Classify compounds as crystalline (containing ionic bonds) or molecular (containing covalent bonds) based on whether their outer electrons are transferred or shared.


Combined Elements

  • Most elements are not found by themselves in nature

  • Usually they are found combined with other elements

  • Two or more elements chemically combined is called a compound

  • The properties of a compound are very different from the properties of the elements that make up the compound


Consider Table Salt…


Chemical Formulas

  • Chemical formula – tells what elements and how many of each element are in a unit of that compound

  • H2O – water; contains two atoms of hydrogen and one atom of oxygen

  • NH3 – ammonia; contains one atom of nitrogen and 3 atoms of hydrogen

H

H

O

N

H

H

H


  • Mg(OH)2 – milk of magnesia – contains one atom of magnesium, two atoms of oxygen, and two atoms of hydrogen

Mg

O

O

H

H


Atomic Stability

Why do Elements Form Compounds?

- the noble gases are extremely stable atoms that do not combine with other elements.

- it is the eight valence electrons that make the noble gas atoms stable


  • An atom is chemically stable when its outermost energy level is complete

    • 1st level – 2 electrons

    • All other levels – 8 electrons

  • All elements combine with other elements by losing, gaining or sharing electrons so that they will have eight valence electrons!!


- When atoms begin to lose, share, or gain electrons they begin to get attracted to other atoms and form chemical bonds - a force that holds atoms together in a substance.

x5


Ionic Bonding

  • Atoms that gain or lose electrons become charged forming an ion.

What ion will Sodium form?

Since sodium has 1 valence electron it can lose that electron and then have eight valence elect.

1 e-

8 e-

11 p+

12no

2 e-


  • This will give the sodium atom a +1 charge

  • 11p+ + 10e- = +1Na+1

Superscript – written above line; gives the charge of ion

Group 1 → 1 valence e- → +1

Group 2 → 2 valence e- → +2

Group 13 → 3 valence e- → +3


What ion will fluorine form?

7e-

Fluorine needs to gain 1e- in order to become stable

2e-

9p+

10n0

- This will give fluorine a -1 charge

F-1

Group 17 → 7 valence e-→ -1

Group 16 → 6 valence e- → -2

Group 15 → 5 valence e- → -3

x6


Using electron dot structure to show ionic bonds

Explain the formation of the ionic bond between sodium and chlorine

Na

Cl

Na+[ Cl ]-1

NaCl

Electron dot struct.

Formula unit


Steps to draw electron dot structures for ionic compounds

  • Draw the electron dot structures of the elements

  • transfer electrons from the metal to the nonmetal

  • add elements as needed

  • continue transferring until all atoms are stable


5. Write out the chemical formula using subscripts to show how many of each element it took


Lets try aluminum and oxygen!!

Al

O

2

Al+3

[ O ]-2

3

O

Al

Al2O3

O


Your Turn!!

Use electron dot structures to write chemical formulas for the following combination of elements:

  • potassium and fluorine

  • Magnesium and fluorine

  • Aluminum and nitrogen

  • Magnesium and phosphorous


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