forming chemical bonds. compounds remember compounds are two or more different elements that combine...
TRANSCRIPT
Compounds
• Remember compounds are two or more different elements that combine chemically –Can be broken down by chemical means
–Have properties different from those of its component element
– Thousands of compounds exist
Chemical Bonds
• A chemical bond is a force that holds two atoms together
• Chemical bonds usually only involve valence electrons
Valence Electrons• Valence electrons are electrons in the highest
occupied s and p energy level.
• The number of valence electrons largely determines the chemical properties of an element.
• To find the number of valence electrons in a representative (group A) element, simply look at its group number.
Why do elements react?
• Noble Gases typically do not react and are chemically stable because they have eight valence electrons called an octet
• Elements tend to react in order to acquire a full octet or “eight is great” (gain stability)
• Octet rule –when forming compounds, atoms tend to achieve the stable electron configuration of a noble gas
Formation of Positive Ions-Cations• A cation is an atom or group of atoms with a
positive charge because of a loss of valence electrons. Ca “+” ion
• Metals only form cations• Reactivity of metals is based on the ease in
which they lose a valence electron to achieve a stable octet.
• Brainiac Alkali Metals Video
Electron Configuration of Positive Ions-Cations
• All of the above metal ions have electron configurations of the noble gas neon, Ne. 8 is great!
Na atom Na 1s22s22p63s1
Na ion (lost 1 electron) Na+ 1s22s22p6
Mg atom Mg 1s22s22p63s2
Mg ion (lost 2 electrons) Mg2+ 1s22s22p6
Al atom Al 1s22s22p63s23p1
Al ion (lost 3 electrons) Al3+ 1s22s22p6
Ne atom (noble gas) Ne 1s22s22p6
Cation Charges
• Group 1A lose 1 electron, making a 1+ ion • Group 2A loses 2 electrons, making a 2+ ion• Group 3A loses 3 electrons, making a 3+ ion
Formation of Negative Ions-Anions
• An anion is a negative atom or group of atoms that gain electrons
• Nonmetals tend to gain electrons
egative
Electron Configuration of Negative Ions-”Anions”
• Cl ion and S ion have the noble gas configuration of argon. 8 is great!
Cl atom Cl 1s22s22p63s23p5
Cl ion (gain 1 electron) Cl- 1s22s22p63s23p6
S atom S 1s22s22p63s23p4 S ion (gain 2 electrons) S2- 1s22s22p63s23p6
Ar atom Ar 1s22s22p63s23p6