Molecules And Compounds - Chemistry Worksheet Page 2
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9Diatomic Molecules: Know these 7 elements exist as diatomic (two-atom) molecules:
H
N
O
F
Cl
Br
I
2
2
2
2
2
2
2
– Consider them the “diatomic seven” since there are seven of them, and six of them form a
7 on the Periodic Table.
molecule: compound of nonmetal atoms held together by covalent bonds (e.g., H
O, CO
, etc.)
2
2
ionic compound: a compound consisting of ions—usually metal cations with nonmetal or
polyatomic anions—held together by ionic bonds (e.g., NaCl, Al
O
, CaBr
, KMnO
, BaSO
)
2
3
2
4
4
5.5 WRITING FORMULAS FOR IONIC COMPOUNDS
5.7 NAMING IONIC COMPOUNDS
+
–
2–
monoatomic ions: from a single atom (eg Na
, Cl
, O
)
–
–
2–
polyatomic ions: consist of 2 or more atoms (eg. OH
, MnO
, SO
)
4
4
cations: positively charged ions
– Metal atoms and hydrogen lose electrons to form cations.
I. Some metals always form the same charge:
+
+
+
+
– Group IA elements form ions with a +1 charge: H
, Li
, Na
, K
2+
2+
2+
2+
– Group IIA elements form ions with a +2 charge: Mg
, Ca
, Sr
, Ba
3+
+
2+
2+
– aluminum ion = Al
, silver ion = Ag
; zinc ion = Zn
; cadmium ion = Cd
→
+
2+
element name + ion
Na
=sodium ion or Ba
=barium ion
II. The Stock system is used to name most transition metals and other metals that can
form more than one charge:
2+
3+
– e.g., iron (Fe), a transition metal, forms 2 different ions: Fe
and Fe
2+
4+
– e.g., lead (Pb), in Group IVA, forms 2 different ions: Pb
and Pb
element name (charge in Roman numerals) + ion
2+
4+
Sn
=tin (II) ion
and
Sn
=tin (IV) ion
CHEM 121: Tro Chapter 5
page 2 of 9
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