# 3.1 Ionic and covalent compounds  (Page 2/13)

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## Composition of ions

An ion found in some compounds used as antiperspirants contains 13 protons and 10 electrons. What is its symbol?

## Solution

Because the number of protons remains unchanged when an atom forms an ion, the atomic number of the element must be 13. Knowing this lets us use the periodic table to identify the element as Al (aluminum). The Al atom has lost three electrons and thus has three more positive charges (13) than it has electrons (10). This is the aluminum cation, Al 3+ .

Give the symbol and name for the ion with 34 protons and 36 electrons.

Se 2− , the selenide ion

## Formation of ions

Magnesium and nitrogen react to form an ionic compound. Predict which forms an anion, which forms a cation, and the charges of each ion. Write the symbol for each ion and name them.

## Solution

Magnesium’s position in the periodic table (group 2) tells us that it is a metal. Metals form positive ions (cations). A magnesium atom must lose two electrons to have the same number electrons as an atom of the previous noble gas, neon. Thus, a magnesium atom will form a cation with two fewer electrons than protons and a charge of 2+. The symbol for the ion is Mg 2+ , and it is called a magnesium ion.

Nitrogen’s position in the periodic table (group 15) reveals that it is a nonmetal. Nonmetals form negative ions (anions). A nitrogen atom must gain three electrons to have the same number of electrons as an atom of the following noble gas, neon. Thus, a nitrogen atom will form an anion with three more electrons than protons and a charge of 3−. The symbol for the ion is N 3− , and it is called a nitride ion.

Aluminum and carbon react to form an ionic compound. Predict which forms an anion, which forms a cation, and the charges of each ion. Write the symbol for each ion and name them.

Al will form a cation with a charge of 3+: Al 3+ , an aluminum ion. Carbon will form an anion with a charge of 4−: C 4− , a carbide ion.

The ions that we have discussed so far are called monatomic ions , that is, they are ions formed from only one atom. We also find many polyatomic ions . These ions, which act as discrete units, are electrically charged molecules (a group of bonded atoms with an overall charge). Some of the more important polyatomic ions are listed in [link] . Oxyanions are polyatomic ions that contain one or more oxygen atoms. At this point in your study of chemistry, you should memorize the names, formulas, and charges of the most common polyatomic ions. Because you will use them repeatedly, they will soon become familiar.

Common Polyatomic Ions
Name Formula Related Acid Formula
ammonium ${\text{NH}}_{4}{}^{+}$
hydronium ${\text{H}}_{3}{\text{O}}^{+}$
oxide ${\text{O}}^{2-}$
peroxide ${\text{O}}_{2}{}^{2-}$
hydroxide ${\text{OH}}^{-}$
acetate ${\text{CH}}_{3}{\text{COO}}^{-}$ acetic acid CH 3 COOH
cyanide CN hydrocyanic acid HCN
azide ${\text{N}}_{3}{}^{-}$ hydrazoic acid HN 3
carbonate ${\text{CO}}_{3}{}^{2-}$ carbonic acid H 2 CO 3
bicarbonate ${\text{HCO}}_{3}{}^{-}$
nitrate ${\text{NO}}_{3}{}^{-}$ nitric acid HNO 3
nitrite ${\text{NO}}_{2}{}^{-}$ nitrous acid HNO 2
sulfate ${\text{SO}}_{4}{}^{2-}$ sulfiric acid H 2 SO 4
hydrogen sulfate ${\text{HSO}}_{4}{}^{-}$
sulfite ${\text{SO}}_{3}{}^{2-}$ sulfurous acid H 2 SO 3
hydrogen sulfite ${\text{HSO}}_{3}{}^{-}$
phosphate ${\text{PO}}_{4}{}^{3-}$ phosphoric acid H 3 PO 4
hydrogen phosphate ${\text{HPO}}_{4}{}^{2-}$
dihydrogen phosphate ${\text{H}}_{2}{\text{PO}}_{4}{}^{-}$
perchlorate ${\text{ClO}}_{4}{}^{-}$ perchloric acid HClO 4
chlorate ${\text{ClO}}_{3}{}^{-}$ chloric acid HClO 3
chlorite ${\text{ClO}}_{2}{}^{-}$ chlorous acid HClO 2
hypochlorite ClO hypochlorous acid HClO
chromate ${\text{CrO}}_{4}{}^{2-}$ chromic acid H 2 Cr 2 O 4
dichromate ${\text{Cr}}_{2}{\text{O}}_{7}{}^{2-}$ dichromic acid H 2 Cr 2 O 7
permanganate ${\text{MnO}}_{4}{}^{-}$ permanganic acid HMnO 4

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x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
Need help solving this problem (2/7)^-2
x+2y-z=7
Sidiki
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-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
An investment account was opened with an initial deposit of \$9,600 and earns 7.4% interest, compounded continuously. How much will the account be worth after 15 years?
lim x to infinity e^1-e^-1/log(1+x)
given eccentricity and a point find the equiation
12, 17, 22.... 25th term
12, 17, 22.... 25th term
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20/(×-6^2)
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oops. ignore that.
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The eyes of some reptiles are sensitive to 850 nm light. If the minimum energy to trigger the receptor at this wavelength is 3.15 x 10-14 J, what is the minimum number of 850 nm photons that must hit the receptor in order for it to be triggered?
A teaspoon of the carbohydrate sucrose contains 16 calories, what is the mass of one teaspoo of sucrose if the average number of calories for carbohydrate is 4.1 calories/g?
4. On the basis of dipole moments and/or hydrogen bonding, explain in a qualitative way the differences in the boiling points of acetone (56.2 °C) and 1-propanol (97.4 °C), which have similar molar masses
Calculate the bond order for an ion with this configuration: (?2s)2(??2s)2(?2px)2(?2py,?2pz)4(??2py,??2pz)3
Which of the following will increase the percent of HF that is converted to the fluoride ion in water? (a) addition of NaOH (b) addition of HCl (c) addition of NaF