Science 3200 Unit 1 Part 2. Bonding Bonding of elements is the attraction between atoms or ions...

Science 3200

Unit 1 Part 2

Bonding

Bonding of elements is the attraction between atoms or ions

Bonds that are formed between two non-metals (i.e. elements found to the right of the ladder on the periodic table) result in molecular compounds

Bonds that are formed between a metal and a non-metal (i.e. one from the left and one from the right of the ladder) result in ionic compounds

Bonding

Ex. State whether each compound is molecular or ionic.

a. NaCl

b. CO2

c. CF4

d. LiBr

Bonding

Some atoms will combine with other atoms of the same element. These atoms are found in nature like this. These are: Hydrogen (H2) - Bromine (Br2)

Nitrogen (N2) - Iodine (I2)

Oxygen (O2) - Astatine (At2)

Fluorine (F2) - Phosphorus (P4)

Chlorine (Cl2) - Sulfur (S8)

Bonding

Covalent Bonding (Molecular Compounds) Sharing of electrons

the two non-metals both want to gain electrons (to be like the noble gases), since both cannot gain electrons at the same time they share.

The unit formed by a covalent bond is called a molecule (it is neutral; it has no charge)

Bonding

Ionic Bonding Gaining and losing electrons to form stable

compound The unit formed by an ionic compound is a

formula unit These form neutral compounds by the number of

electrons lost is equal to the number taken up

Compounds

Molecular Compounds Involve the sharing of electrons resulting in

covalent bonding Composed of two non-metals Exist as individual molecules May or may not be in lowest whole number

ratios

Naming Molecular Compounds

Mono-atomic elements Mono means one, so these are elements that exist on

their own in nature. Namely the noble gases:

He – helium Ne – neon Ar – argon Kr – krypton Xe – xenon Rn – radon

No need to memorize these as they are listed in the periodic table


Diatomic molecular compounds These are non-metals that exist in nature as two atoms

joined together. They are:

H2 – hydrogen

O2 – oxygen

N2 – nitrogen

Cl2 – chlorine

F2 – flourine

Br2 – bromine

I2 - iodine


Polyatomic molecular elements These are non-metals that exist in nature with many

atoms joined together These are:

S8 – sulfur

O3 – ozone

P4 – phosphorus (red)


Trivial names These are names on compounds that do not follow

the guidelines put out by IUPAC. These are:

H2O – water

H2O2 – hydrogen peroxide

NH3 – ammonia

C12H22O11 – sucrose

CH4 – methane

CH3OH – methanol

C2H5OH - ethanol


For binary molecular compounds, we use prefixes to indicate the number of atoms that are present in the compound. These are: Mono – one Di – two Tri – three Tetra – four Penta – five Hexa – six Hepta – seven Octa – eight Nona – nine Deca - ten


When writing the name of a molecular compound start with the first element, not changing the name, except for adding the prefix. Then write the name of the second element with the prefix and changing the ending of the name to –ide.

Note: the prefix mono on the first element only is optional.


For example, name the compound CCl4

The first element is carbon and there is only one of them.

The second element is chlorine and there are 4 of them. Therefore the name would be

monocarbon tetrachloride

or

carbon tetrachloride


Ex 2. Write the name for P4F6.

Sol’n: The first element is phosphorus and there are four atoms.

The second element is fluorine and there are six atoms. Therefore the name of this compound is:

tetraphosphorus hexafluoride


Your turn. Name each of the following.

1. P4F5

2. C2O4

3. NO3

4. Cl2O

5. N3Br2

6. O6I2

Writing Molecular Formulas

When writing molecular formulas you look up each element on the periodic table to determine the chemical symbol for the element. (Don’t forget that the ending on the second element has been changed to –ide)

Use the prefix on each element to determine the number of atoms present. Write this number to the right of the symbol and as a subscript.


Ex. Write the formula for diboron hexahydride.

The first element is boron which is B and di means 2.

The second element is hydride (or hydrogen) which is H and hexa means 6.

We have B2H6


Ex. Write the formula for nitrogen triiodide.

The first element is nitrogen which is N and since there is no prefix there is only one.

The second element is iodide (or iodine) and tri means 3.

We have N1I3 or NI3.


Your turn. Write the formulas for each of the following.

a. Carbon disulfide

b. Dinitrogen pentabromide

c. Silicon trifluoride

d. Hexaphosphorus pentachloride

Ionic Compounds

Ionic Compounds: Involve the transfer of electron(s), i.e gaining

and losing electrons, resulting in ionic bonding Made up of two oppositely charged ions (metal

and non-metal, or combination involving a polyatomic ion)

Are always written as empirical formulas (lowest whole number ratio)

Naming Ionic Compounds

There are two categories of ionic compounds that we will deal with.

1. Binary ionic Simple ions (only single charges)

2. Polyatomic ions (complex ions)


Binary ionic compounds are composed of a metal ion (+) and non-metal ion (-). Binary simply means that only 2 ions are involved.

Ex. NaCl – the combination of a sodium ion and a chloride ion.


Rules for naming simple binary ionic compounds (meaning a compound with only two elements):

1. Name the metal (+) by writing the full name of the metal.

2. Name the non-metal (-) by shortening the name of the atom and adding the –ide ending.


Ex. NaCl sodium chloride

CaF2 calcium fluoride

K2O potassium oxide

**Note: Do NOT use prefixes – they are for molecular compounds only (i.e. two non-metals)


Your turn. Name the following:

1. LiBr

2. AlCl3

3. Rb2S

4. Mg3P2

5. CaO

Writing Ionic Formulas

Rules for writing binary ionic formulas:

1. Write down the symbols of the ions involved.

2. Cross over the charges and write as subscripts.

3. Determine the lowest whole number ratio of ions that will give a net charge of zero.

4. You do not need to write 1’s.


Ex. 1) Write the chemical formula for potassium bromide.

2) Write the chemical formula for calcium oxide.

3) Write the chemical formula for magnesium iodide.


Your turn. Write the chemical formula for each compound:

1. Sodium sulfide

2. Aluminum bromide

3. Barium iodide

4. Magnesium nitride

5. Aluminum nitride

Naming Compounds with Polyatomic Ions

A polyatomic ion is two or more atoms covalently bonded together that carry an overall charge. Since they have a charge they can gain or lose electrons to form ionic compounds.

These ions are listed on your sheet but this list is not exhausted, i.e. There are more polyatomic ions than what’s listed.


To identify these compounds look at the elements involve. If you have more than two elements in the compound and the compound is not in your trivial names list than it contains a polyatomic ion.

You name these the same way you name ionic compounds: look up the element/polyatomic ion and write the names down changing the second name to have the ending –ide.


Ex 1. (NH4)3PO4

Ex 2. Cr(NO3)3


Your turn. Write the name of the following compounds.

1) Zn(OH)2

2) Pb(NO3)2

3) Mg(CH3COO)2

4) Na3BO3

5) K2Cr2O7

Writing Compounds with Polyatomic Ions

When writing the formulas for compounds containing a polyatomic ion(s), you treat the ion as a single unit, not as individual elements.

If you need to write a subscript for a polyatomic ion, then you must enclose the ion in brackets.

Remember to use the charges on the polyatomic ions to determine how many you need to have a balanced compound, NOT the subscripts!!!


Ex 1. sodium chlorite

Ex 2. iron (III) sulfate

Ex 3. ammonium permanganate


Your turn. Write the formula for each of the following.

1. Sodium hydroxide

2. Potassium bicarbonate

3. Potassium carbonate

4. Magnesium hydroxide

5. Ammonium sulfate

Science 3200 Unit 1 Part 2. Bonding Bonding of elements is the attraction between atoms or ions...

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Transcript of Science 3200 Unit 1 Part 2. Bonding Bonding of elements is the attraction between atoms or ions...