LOGO

Course lecturer :

Jasmin Šutković

11th March 2015

Chemistry - SPRING 2015

Lecture 2:Molecules, Ions and Chemical formulas

Contents International University of Sarajevo

1. Chemical Compounds 1.1 Covalent Compounds 1.2 Ionic Compounds 1.3 Molecular structure

2. Chemical formulas 3. Hydrcarbons4. Acid and Bases 5. Industry important Chemicals

1. Chemical Compounds

Atoms in all substances that contain more than one atom are held together by electrostatic interactions—interactions between electrically charged particles such as protons and electrons.

Chemical Compounds cont.

Electrostatic attraction between oppositely charged particle species (positive and negative) results in a force that causes them to move toward each other.

Electrostatic repulsion between two species that have the same charge (either both positive or both negative) results in a force that causes them to repel each other

When the attractive electrostatic interactions between atoms are stronger than the repulsive interactions, atoms form chemical compounds and the attractive interactions between atoms are called chemical bonds.

1.1 Covalent compounds

Covalent compounds consist of molecules, which are groups of atoms in which one or more pairs of electrons are shared between bonded atoms.

Each covalent compound is represented by MOLECULAR FORMULAExp: H2O , 2 hydrogen atoms and 1 oxygen atom or CO2 ,NO2

….

Some pure elements also exists as covalent molecules .Exp:H2, N2, O2,F2, Cl2,Br2 and I2.

Covalent compounds cont…

Covalent compounds that contain mostly Carbon and Hydrogen's are called ORGANIC COMPOUNDS

Compounds that consist primarily of elements other than Carbon and hydrogen are called INORGANIC COMPOUNDS , include ionic and covalent compounds Formulas are written when the component elements

are listed beginning with the one farthest to the left in the periodic table with those in the same group listed alphabetically

Representations of Molecular Structures

Molecular formula – Gives the elemental composition of molecules

Structural formula Shows which atoms are bonded to one another and the approximate

arrangement in space Enables chemists to create a three-dimensional model that provides

information about the physical and chemical properties of the compound A single bond, in which a single pair of electrons are shared, is

represented by a single line (–) A double bond, in which two pairs of electrons are shared, is indicated

by two lines (=) A triple bond, in which three pairs of electrons are shared, is indicated

by three lines (≡)

Representations of Molecular Structures

Figure 1: Molecular structures

1.2 Ionic Compounds

· Ions are atoms or assemblies of atoms that have a net electrical charge.

· Ions that contain fewer electrons than protons have a net positive charge and are called cations.

· Ions that contain more electrons than protons have a net negative charge and are called anions.

Ionic Compounds cont…

Ionic compounds contain both cations and anions in a ratio that results in no net electrical charge.

Ionic compounds are held together by the attractive electrostatic interactions between cations and anions.

Cations and anions are arranged in space to form an extended three-dimensional array that maximizes the number of attractive electrostatic interactions and minimizes the number of repulsive electrostatic interactions.

Ionic Compounds cont…

· The electrostatic energy of the interaction between two charged particles is proportional to the product of the charges on the particles and inversely proportional to the distance between them:

electrostatic energy = (Q1) (Q2)

rQ1 and Q2 are electrostatic charges and r is the distance between them.

· If the electrostatic energy is positive, the particles repel each other.

· If electrostatic energy is negative, the particles are attracted to each other.

Ionic Compounds cont…

Many elements have a tendency to gain or lose enough electrons to attain the same number of electrons as the noble gases, which are the closest to them in the periodic table.

Monatomic ions contain only a single atom. Charges of most monatomic ions derived from the main group elements

are predicted by simply looking at the periodic table and counting how many columns an element lies from the extreme left or right.

Usually form hard crystalline solids that melt at high temperatures and are very resistant to evaporation

Covalent compounds – Can be gases, liquids, or solids at room temperature and

pressure, depending on the strength of the intermolecular interactions

– Covalent molecular solids tend to form soft crystals that melt at low temperatures and evaporate easily

– Consist of discrete molecules held together by comparatively weak intermolecular forces (the forces between molecules) even though the atoms within each molecule are held together by strong intramolecular covalent bonds (the forces within the molecule)

Physical Properties of Ionic and Covalent Compounds cont….

Chemical bonds

Ionic bonds : between elements of metals and nonmetals.... (Anions and Cations)

Covalent bonds: only between nonmetal elements ... Valence electrons : outermost shell

electrons ...electrons in the last shell...they are essential for bonds....

Three ways to find the valence electrons: http://www.wikihow.com/Find-Valence-Electrons

Figure 2: Samples of ionic and covalent bonds

Ionic bonds ...

Energy attraction between oppositely charged ions(cations and anions)

Metals have small energy of ionization..therfore they are electron donors .

Nonmetals are having high affinity to electrons so they accept electrons .

Example : K and S .... How do we know that this compound in nature can be found as K2S..? K has 19 electrons and S has 16 ...two ways to check the valence electrons ...via groups in PSE and via electron configuration ... K has 1 v.e and S has 2 v.e....so 1 electron is missing to have a neutral charge ... So we just add one more K and we get K2S ...

Na and F ionic bond example

Na has 1 v.e and F has 7 v.e ...

Covalent bonds ...

Bond of electron pairs...can be represented with dots ...Lewis dots ..

Exp: , where two electrons (one electron pair) make a covalent bond, represented as two dots or one line ( B ).

Again ; OCTATE rule (8 electrons)....very important !!!!

One-valent, double and tri valent bonds!

Example with H2

A covalent bond forming H2 where two hydrogen atoms share the two electrons

Lewis Octate rule ...

Lewis proposed that an atom forms enough covalent bonds to form a full (or closed) outer electron shell. In the methane (CH4) diagram shown here, the carbon atom has a valence of four and is therefore surrounded by eight electrons (the octet rule); four from the carbon itself and four from the hydrogens bonded to it.

Lewis representation of electrons ....

Example .... Compound between N and H !!

Show the bonds of the following elements ...(Lewis law and representation)!!

1. Define the elements valence electrons. N has 5 v.e and H has 1 .v.e.... Octate law is

not satisfied...so we add then two more H atoms (2 more electrons ) to get 8 electron and the perfect compund.. NH3

2. Chemical Formulas

When scientists make a new compound they may do not know its molecular or structural

formula. Empirical formula

– The relative numbers of atoms of the elements in the compound, reduced to the smallest whole numbers

– Shows only the ratios of the numbers of the elements present

– Empirical formulas are used to indicate the composition of ionic compounds since they do not contain discrete molecules

ALSO known as the SIMPLEST FORMULA of a chemical compund...

The difference between empirical and molecular formulas can be demonstrated with butane C4H10.....

Butane (C4H10) example

Ration between atoms (carbon and hydrogen) is 4:10, which can be reduced to 2:5….so the empirical formula of butane would be C2H5.

So Butane contains 2 C2H5 formula units resulting in the molecular formula of

C4 H10

Binary IONIC compounds

An Ionic compound that contains ONLY 2 elements, one present as a CATION and other as ANION .

Exp: NaCl, MgCl2 , MgO , Na2O…etc.… In such cases the empirical formula can be

also determined as follows … All elements (ionic or covalent) must be

electrically neutral to be a compound !

Examples ….

Na + Cl NaCl .....why?• Na (in PSE) has 11 electrons (1 valence electron )• Cl (in PSE) has 17 electrons (1 v.e)• Na 1+ and Cl 1- = NaCl

Na + O Na2O .....why? Na has 1 v.e (metalic element = donor) and O

has 2 v.e (nonmetal = acceptor )... Na + and O2- ions ....so to satisfy the octate rule we need 1 more electron ...adding 1 Na atom to the compound we get Na2O !!

Example 2 …

Write the empirical formula for the following binary ionic compound! Ga and As 1. You ca determine the formula via electronic configuration

method !

Ga (31 electron)

1- 1s2 2- 2s2 2p63- 3s2 3p6 3d104- 4s2 4p1

Ga can give 3 electrons

As (33 electron)

1- 1s2 2-2s2 2p63-3s2 3p6 3d104- 4s2 4p3

As can take 3 electron

Ga3+ and As3-

GaAs

Electron configuration ...

Define the net charges of elements ....

The definition of net charge is the total charge an ion has. Ions can be either positive (+) or negative (-) charge. If you look on the periodic table, there are 8 groups going across, from left to right. Each group has it's own specific charge!

Define the net charges of elements ....

So, left to right...

Group 1 starts with H has a charge of +1Group 2 starts with Be has a charge of +2Group 3 starts with B has a charge of +3Group 4 starts with C has a charge of +4Group 5 starts with N has a charge of -3Group 6 starts with O has a charge of -1Group 7 starts with F has a charge of -1Group 8 noble gases has a ZERO charge -- they mostly don't bond

Polyatomic Ions

Polyatomic ions are electrically charged molecules of more than one atom. The term "polyatomic" itself is derived from the Greek word "poly" meaning "many."

For example, nitrate (NO3-) has an overall negative charge by having one more electron than the total number of protons in the molecule.

Method used to predict empirical formula for ionic compounds that contain monatomic ions can be used for compounds containing polyatomic ions. Overall charge on the cations must balance the overall charge on the anions in the formula unit.

http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html

3. Hydrocarbons

One third of all compounds produced industrially are Organic compounds .

The simplest class of Org.Comp. Are Hydrocarbons which entirely consists of carbon and hydrogen.

Four major classes of Hydrocarbons are :

1. Alkanes

2. Alkenes

3. Alkynes

4. Aromatic compounds Alkanes are saturated whereas alkenes (single bonds),

alkynes and aromatics are unsaturated (double and tripple bonds).

Alkanes

Names of all alkanes end in –ane, and their boiling points increase with more carbon atoms present.

The simplest alkane is methane(CH4)

In larger alkanes, carbon atoms are joined in an unbranched chain (straight-chain alkanes) where each carbon atom is bonded to two other carbon atoms.

The systematic name for branched hydrocarbons uses the

lowest possible number to indicate the position of the branch along the longest straight carbon chain in the structure

Alkanes ...cont ...

Formed of C atoms ...go from C 1 to C 60.

C1 to C5 – gases C5 to C17– liquids C17 to C 60 solid waxes

All Alkanes are flammable, Ph 7 and insoluble in water (hydrophobic)

non polar bonds (similar electronegativity of C and H) colorless, tasteless, nearly odorless boiling points increase with increasing MW, and decrease

with branching (C1-C5 are gases) narcotic and irritant effects increase with MW ( C5-C9)

ONLY SINGLE BOND !!!

Alkenes

The simplest alkenes are ethylene and propylene.

Names of alkenes that have more than three carbon atoms use the same stems as the names of alkanes but end in –ene.

DOUBLE BONDS ...DO NOT HAVE METHANE ( CH4) not soluble in water (= hydrophobic) nonpolar bonds (similar electronegativity of C

and H) low boiling points – lower than alkanes of the

same length (C1-C4 are gases) double bond consist of 1 and 1 bond the double bond does not permit free rotation geometric isomerism exists!!!

Examples of geometric isomerism....

Alekenes cont....

If alkenes have 2 double bonds: ALKADIENS

2-methyl-1,3-butadiene

= isoprene

Alkynes

boiling points slightly higher than that of alkanesand alkenes

specific gravity higher in comparision to alkenes

the triple bond = 1 and 2 bonds

C2H2 =ethyne

Aromatic Hydrocarbons

Alkanes, alkenes, alkynes, and cyclic hydrocarbons are called aliphatic hydrocarbons.

Aromatic hydrocarbons are also called arenes and are obtained by the distillation and degradation of highly scented resins from tropical trees.

The simplest aromatic hydrocarbon is benzene (C6H6)• The chemical behavior of aromatic compounds differs from the

behavior of aliphatic compounds.• Groups of atoms derived from aromatic hydrocarbons are aryl

groups

• Cyclopropane (C3H6), Cyclopentane, Cyclobutane ,Cyclohexane!

Examples ...

5. Acid and Bases

Acids

– A substance with at least one hydrogen atom that can dissociate to form an anion and an H+ ion (a proton) in aqueous solution, thereby forming an acidic solution

Bases

– Compounds that produce hydroxide ions (OH–) and a cation when dissolved in water, thus forming a basic solution

Neutral

– Solutions that are neither basic nor acidic

What is an acid ?

An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour".

The more H + ions, the more acidic the solution.

• Acetic Acid = Vinegar• Citric Acid = lemons, limes, & oranges. • Ascorbic acid = Vitamin C which your body needs to

function.• Sulfuric acid is used in the production of fertilizers, steel,

paints, and plastics.• Car batteries

If H+ is attached to a polyatomic ion these acids are called OXOACIDS or OXYACIDS

Exp:HCL...hydrochlor acid

If an acid contain more than 1 H+ it becomes a derivative of oxyacids.

Exp: SO4 2- ...sulfate , NO3- ...nitrate Name of some common acids in table 2.9 (page

71)

What is a base?

A base is a solution that has an excess of OH- ions.

Another word for base is alkali. Bases are substances that can accept

hydrogen ions

Bases give soaps, ammonia, and many other cleaning products some of their useful properties.

The OH- ions interact strongly with certain substances, such as dirt and grease.

Chalk and oven cleaner are examples of familiar products that contain bases.

Our blood is a basic solution.

pH scale

pH is a measure of how acidic or basic a solution is.

• The pH scale ranges from 0 to 14.

Acidic solutions have pH values below 7

A solution with a pH of 0 is very acidic.

A solution with a pH of 7 is neutral.• Pure water has a pH of 7.

• Basic solutions have pH values above 7

5. Industry important Chemicals

Many chemical compounds are prepared industrially in huge quantities and are used to produce foods, fuels, or plastics and other materials.

PETROLEUM Mixture of several thousand organic compounds (alkenes, alkanes,

cycloalkanes,,,,) Petroleum is converted to useful products such as gasoline's, kerosene,

lubricants …etc…through several steps such as :

destilationm, cracking and reforming. (page 76)

Octane ratings

– Indicates quality of a fuel – A measure of a fuel’s ability to burn in a combustion engine without

knocking or pingingThe benzin we use today consists of isooctane and n-heptane.The better quality the higher isooctane .Exp: benzin 85, (85% isooctane +15% n-heptane)

Sulfuric Acids – H2SO4

Compound produced in the largest quantity in the industrial world and is one of the oldest chemical compounds known

Production — starts with elemental sulfur obtained through a technique called the Frasch process, in which very hot water forces liquid sulfur out of the ground in nearly pure form.

Sulfuric acid is produced by the reaction of sulfur dioxide with oxygen in the presence of vanadium(V) oxide (the contact process), followed by the absorption of the sulfur trioxide in concentrated sulfuric acid to produce oleum.

Uses — to make fertilizers and potash, one of the major ingredients in fertilizers. Used in drying textiles .

Readings …

Chapter 2 ! Pages (46-81)

Good luck …