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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

Stability and Ionic Bonding

Section 20.1 & 20.2


Sc standards covered
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
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



Chemical formulas
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
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



- 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
Ionic Bonding begin to get attracted to other atoms and form

  • 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-


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? begin to get attracted to other atoms and 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
Using electron dot structure to show ionic bonds begin to get attracted to other atoms and form

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 begin to get attracted to other atoms and form

  • 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



Lets try aluminum and oxygen!! how many of each element it took

Al

O

2

Al+3

[ O ]-2

3

O

Al

Al2O3

O


Your turn
Your Turn!! how many of each element it took

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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