# 3.1 Ionic and covalent compounds  (Page 5/13)

 Page 5 / 13

Because an ionic compound is not made up of single, discrete molecules, it may not be properly symbolized using a molecular formula. Instead, ionic compounds must be symbolized by a formula indicating the relative numbers of its constituent ions. For compounds containing only monatomic ions (such as NaCl) and for many compounds containing polyatomic ions (such as CaSO 4 ), these formulas are just the empirical formulas introduced earlier in this chapter. However, the formulas for some ionic compounds containing polyatomic ions are not empirical formulas. For example, the ionic compound sodium oxalate is comprised of Na + and ${\text{C}}_{2}{\text{O}}_{4}{}^{2-}$ ions combined in a 2:1 ratio, and its formula is written as Na 2 C 2 O 4 . The subscripts in this formula are not the smallest-possible whole numbers, as each can be divided by 2 to yield the empirical formula, NaCO 2 . This is not the accepted formula for sodium oxalate, however, as it does not accurately represent the compound’s polyatomic anion, ${\text{C}}_{2}{\text{O}}_{4}{}^{2-}.$

## Molecular compounds

Many compounds do not contain ions but instead consist solely of discrete, neutral molecules. These molecular compounds (covalent compounds) result when atoms share, rather than transfer (gain or lose), electrons. Covalent bonding is an important and extensive concept in chemistry, and it will be treated in considerable detail in a later chapter of this text. We can often identify molecular compounds on the basis of their physical properties. Under normal conditions, molecular compounds often exist as gases, low-boiling liquids, and low-melting solids, although many important exceptions exist.

Whereas ionic compounds are usually formed when a metal and a nonmetal combine, covalent compounds are usually formed by a combination of nonmetals. Thus, the periodic table can help us recognize many of the compounds that are covalent. While we can use the positions of a compound’s elements in the periodic table to predict whether it is ionic or covalent at this point in our study of chemistry, you should be aware that this is a very simplistic approach that does not account for a number of interesting exceptions. Shades of gray exist between ionic and molecular compounds, and you’ll learn more about those later.

## Predicting the type of bonding in compounds

Predict whether the following compounds are ionic or molecular:

(a) KI, the compound used as a source of iodine in table salt

(b) H 2 O 2 , the bleach and disinfectant hydrogen peroxide

(c) CHCl 3 , the anesthetic chloroform

(d) Li 2 CO 3 , a source of lithium in antidepressants

## Solution

(a) Potassium (group 1) is a metal, and iodine (group 17) is a nonmetal; KI is predicted to be ionic.

(b) Hydrogen (group 1) is a nonmetal, and oxygen (group 16) is a nonmetal; H 2 O 2 is predicted to be molecular.

(c) Carbon (group 14) is a nonmetal, hydrogen (group 1) is a nonmetal, and chlorine (group 17) is a nonmetal; CHCl 3 is predicted to be molecular.

(d) Lithium (group 1) is a metal, and carbonate is a polyatomic ion; Li 2 CO 3 is predicted to be ionic.

Using the periodic table, predict whether the following compounds are ionic or covalent:

(a) SO 2

(b) CaF 2

(c) N 2 H 4

(d) Al 2 (SO 4 ) 3

(a) molecular; (b) ionic; (c) molecular; (d) ionic

## Key concepts and summary

Metals (particularly those in groups 1 and 2) tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. By this means, a positively charged ion is formed. Similarly, nonmetals (especially those in groups 16 and 17, and, to a lesser extent, those in Group 15) can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table. Thus, nonmetals tend to form negative ions. Positively charged ions are called cations, and negatively charged ions are called anions. Ions can be either monatomic (containing only one atom) or polyatomic (containing more than one atom).

Compounds that contain ions are called ionic compounds. Ionic compounds generally form from metals and nonmetals. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules (uncharged groups of atoms that behave as a single unit), are called covalent compounds. Covalent compounds usually form from two nonmetals.

## Chemistry end of chapter exercises

Using the periodic table, predict whether the following chlorides are ionic or covalent: KCl, NCl 3 , ICl, MgCl 2 , PCl 5 , and CCl 4 .

Ionic: KCl, MgCl 2 ; Covalent: NCl 3 , ICl, PCl 5 , CCl 4

Using the periodic table, predict whether the following chlorides are ionic or covalent: SiCl 4 , PCl 3 , CaCl 2 , CsCl, CuCl 2 , and CrCl 3 .

For each of the following compounds, state whether it is ionic or covalent. If it is ionic, write the symbols for the ions involved:

(a) NF 3

(b) BaO,

(c) (NH 4 ) 2 CO 3

(d) Sr(H 2 PO 4 ) 2

(e) IBr

(f) Na 2 O

(a) covalent; (b) ionic, Ba 2+ , O 2− ; (c) ionic, ${\text{NH}}_{4}{}^{+}\text{,}$ ${\text{CO}}_{3}{}^{2-};$ (d) ionic, Sr 2+ , ${\text{H}}_{2}{\text{PO}}_{4}{}^{-};$ (e) covalent; (f) ionic, Na + , O 2−

For each of the following compounds, state whether it is ionic or covalent, and if it is ionic, write the symbols for the ions involved:

(a) KClO 4

(b) MgC 2 H 3 O 2

(c) H 2 S

(d) Ag 2 S

(e) N 2 Cl 4

(f) Co(NO 3 ) 2

For each of the following pairs of ions, write the symbol for the formula of the compound they will form:

(a) Ca 2+ , S 2−

(b) ${\text{NH}}_{4}{}^{+}\text{,}$ ${\text{SO}}_{4}{}^{2-}$

(c) Al 3+ , Br

(d) Na + , ${\text{HPO}}_{4}{}^{2-}$

(e) Mg 2+ , ${\text{PO}}_{4}{}^{3-}$

(a) CaS; (b) (NH 4 ) 2 SO 4 ; (c) AlBr 3 ; (d) Na 2 HPO 4 ; (e) Mg 3 (PO 4 ) 2

For each of the following pairs of ions, write the symbol for the formula of the compound they will form:

(a) K + , O 2−

(b) ${\text{NH}}_{4}{}^{+}\text{,}$ ${\text{PO}}_{4}{}^{3-}$

(c) Al 3+ , O 2−

(d) Na + , ${\text{CO}}_{3}{}^{2-}$

(e) Ba 2+ , ${\text{PO}}_{4}{}^{3-}$

how can chip be made from sand
is this allso about nanoscale material
Almas
are nano particles real
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
no can't
Lohitha
where is the latest information on a no technology how can I find it
William
currently
William
where we get a research paper on Nano chemistry....?
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
how do you find theWhat are the wavelengths and energies per photon of two lines
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