States of Matter

The Particle Theory of Matter:

1. Matter is made up of tiny particles (Atoms & Molecules) 2. Particles of Matter are in constant motion. 3. Particles of Matter are held together by very strong electric forces 4. There are empty spaces between the particles of matter that are very large compared to the particles themselves. 5. Each substance has unique particles that are different from the particles of other substances 6. Temperature affects the speed of the particles.  The higher the temperature, the faster the speed of the particles.

Chemical Equations

A chemical equation summarizes what happens to substances during a chemical reaction.

For example, the combustion of methane (in oxygen) is depicted as: CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)

Periodic Table of Elements

The periodic table of elements arranges elements into periods (horizontal rows) and groups (vertical columns) according to their atomic numbers. The atomic number is the number of protons in an atomic nucleus. The entire table can be separated by metals (green), metalloids (pink) and non-metals (blue).

Predicting Chemical Reactivity

Electron shell diagrams are useful because they show the numbers of electrons in the shells of atoms. Knowing the number of outer shell electrons helps you predict the formation of compounds, and write their chemical formulas. A chemical bond forms between two atoms when electrons in the outer shell of each atom form a stable arrangement together. The outer shell is called the valence shell. The electrons that occupy it are called valance electrons.

Positively Charged: Cations

Any atom or group of atoms that carries an electrical charge is called an ion. When a neutral atom gives up an electron, the positively charged ion that results is called a cation. Alkali metals form cations easily and are chemically very reactive.

When elements gain one electron they become negatively charged particles called anions.

Electron Dot Diagrams (Lewis Structures)

In any group, all the elements have atoms with the same number of valence electrons. You can use a simple model called an electron dot diagram or Lewis diagram, to represent an atom and its valence electrons.

Forming Compounds

Atoms may share electrons between other atoms creating bonds. Substances that are composed of cations and anions are called ionic compounds. The attraction between the oppositely charged ions is called an ionic bond. Nearly all ionic compounds involve bonds between metal cations and non-metal anions.

- Ionic compounds tend to have relatively high melting points because a large of amount of energy is needed to break the strong forces of attraction in ionic bonds.

- Ionic compounds conduct electricity when they are molten or when they are dissolved in water. This is because the ions are able to move freely.

- Ionic compounds in the solid state are not electrical conductors since the ions are not able to move

Forming Compounds

Atoms that share a pair of electrons are joined by a covalent bond. A neutral particle that is composed of atoms joined together by covalent bonds is called a molecule. Substances that are composed of molecules are called molecular compounds. Molecular compounds are formed when atoms of non-metals are joined by covalent bonds. Although the bonds between atoms within the molecule are strong, the force of attraction between the molecules is weak.

- Molecular compounds have relatively low melting points because little energy is needed to break the forces of attraction between molecules.

- Molecular compounds tend not to conduct electricity when they are in the solid or liquid state, or when they are dissolved in water, because they do non contain ions.

Chemical Names and Formulas

The system for naming an ionic compound is different from that for naming a covalent compound, so before a compound can be named, it must be classified as ionic or covalent.

Classifying a compound is not an easy task, but for the purposes of naming them, we employ a simple test:

Is there a metal or a polyatomic ion present?

A polyatomic ion consist of two or more different non-metal atoms, which are joined by covalent bonds.

If the answer is yes, use the system for naming ionic compounds. If the answer is no, use the system for naming covalent compounds.

Naming Ionic Compounds (continued)

If a Roman numeral is required, the charge on the metal ion must be determined from the charge on the negative ion.

Helpful Rules to Remember

Formula Reasoning Name

FeCl2Cl has a 1- charge, and there are 2 of them for a total of 2-, so the Fe must be 2+ iron (II) chloride

Fe2O3

O has a 2- charge, and there are 3 of them for a total of 6-, so the Fe must have a total charge of 6+ split equally between the two iron atoms, so each must have a 3+ charge

iron (III) oxide

PbS2S has a 2- charge, and there are 2 of them for a total of 4-, so the Pb must be 4+ lead (IV) sulfide

Cu3NN has a 3- charge, so the Cu must have a total charge of 3+ split equally between the 3 copper atoms, so each must have a 1+ charge

copper (I) nitride

Examples

A metal ion is always positive. The Roman numeral indicates the charge, not the subscript.The positive and negative charges must cancel (total charge must = 0).Nonmetals are always negative & can never form more than one monatomic ion.

Naming Ionic Compounds (continued)

II. Polyatomic ions each have specific names which must be memorized so they can be recognized on sight.

(At this point, if you are asked to name any compound that contains more than two elements, it will contain at least one polyatomic ion.)

Formula Name

C2H3O21- acetate

CO32- carbonate

HCO31- bicarbonate

NH41+ ammonium

A few of the more common polyatomic ions

Formula Name

NO31- nitrate

OH1- hydroxide

PO43- phosphate

SO42- sulfate

Naming Ionic Compounds: Examples

Na2SO4 sodium sulfate

Fe(NO3)2 iron (II) nitrate

AlCl3 aluminum chloride

PbI4 lead (IV) iodide

(NH4)3PO4 ammonium phosphate

Mg3N2 magnesium nitride

C2H3O21- acetate

CO32- carbonate

HCO31- bicarbonate

NH41+ ammonium

NO31- nitrate

OH1- hydroxide

PO43- phosphate

SO42- sulfate

* Groups I & II, Al, Zn, Cd, and Ag need no Roman numeral.

AgC2H3O2 silver acetate

Naming Covalent Compounds

Covalent compounds are named by adding prefixes to the element names.

The compounds named in this way are binary covalent compounds.

‘Binary’ means that only two atom are present.

‘Covalent’ (in this context) means both elements are nonmetals.

A prefix is added to the name of the first element in the formula if more than one atom of it is present. (The less electronegative element is typically written first.)

A prefix is always added to the name of the second element in the formula. The second element will use the form of its name ending in ‘ide’.

Naming Covalent Compounds

Prefixes

Subscript Prefix

1 mono-

2 di-

3 tri-

4 tetra-

5 penta-

Subscript Prefix

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

Note: When a prefix ending in ‘o’ or ‘a’ is added to ‘oxide’, the final vowel in the prefix is dropped.

Naming Binary Covalent Compounds: Examples

N2S4 dinitrogen tetrasulfide

NI3 nitrogen triiodide

XeF6 xenon hexafluoride

CCl4 carbon tetrachloride

P2O5 diphosphorus pentoxide

SO3 sulfur trioxide

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 heptaa

8 octa

9 nona

10 deca

* Second element in ‘ide’ from

* Drop –a & -o before ‘oxide’

Naming Compounds: Practice

SiF4 silicon tetrafluoride

Na2CO3 sodium carbonate

N2O dinitrogen monoxide

K2O potassium oxide

Cu3PO4 copper (I) phosphate

CoI3 cobalt (III) iodide

Analysis If “Yes”

* Is the cation a metal? (If so, does it need a Roman numeral?

The compound is ionic: name

each ion present

(DO NOT USE PREFIXES)* Is there a

polyatomic ion present?

* Are both elements nonmetals?

The compound is covalent:

use prefixes (NO

CHARGES EXIST) PI3 phosphorus triiodide

two nonmetals covalent use prefixes

metal present ionic no prefixesNa group I no Roman numeral

two nonmetals covalent use prefixes

metal present ionic no prefixesK group I no Roman numeral

metal present ionic no prefixesCu not group I, II, etc. add Roman numeral (PO4 is 3-, each Cu must be 1+)

metal present ionic no prefixesCo not group I, II, etc. add Roman numeral (I is 1-, total is 3-, Co must be 3+)

two nonmetals covalent use prefixes

NH4Cl ammonium chlorideNH4 polyatomic ion present ionic no prefixes

Writing Chemical Formulas: A Review

I. Ionic Compounds

II. Covalent Compounds

Classifying Compounds

Classifying a compound using its name is not as difficult as using its formula.

The names of covalent compounds will be easily recognized by the presence of the prefixes (mono-, di-, tri-, etc.).

If no prefixes are present in the name, the compound is ionic. (Exception: some polyatomic ion names always contain prefixes (such as dichromate) but those will be memorized and recognized as ions.)

Writing Formulas for Ionic CompoundsFormulas for ionic compounds are written by balancing the

positive and negative charges on the ions present.

The total positive charge must equal the total negative charge because the number of electrons lost by one element (or group of elements) must equal the number gained by the other(s).

Polyatomic ion names must still be recognized from memory (e.g. ammonium nitrate), but metals will have a Roman numeral associated with them if there is the possibility of more than one ion (e.g. copper (I) chloride or copper (II) chloride). The Roman numeral indicates the charge on the ion not the number of ions in the formula.

Writing Formulas for Ionic Compounds (continued)

Helpful Rules to Remember

Name Reasoning Formula

ammonium sulfateNH4 has a 1+ charge & SO4 has a 2- charge, so 2 ammonium ions are required for each sulfate.

(NH4)2SO4

zinc chloride Zn has a 2+ charge & Cl has a 1- charge, so 2 chloride ions are required for each zinc ion.

ZnCl2

copper (II) phosphate

Cu has a 2+ charge & PO4 has a 3- charge, so 3 copper (II) ions are required for every two phosphate ions.

Cu3(PO4)2

Examples

A metal ion is always positive. The Roman numeral indicates the charge, not the subscript.The positive and negative charges must cancel (total charge must = 0).If more than one polyatomic ion is needed, put it in parentheses, and place a subscript outside the parentheses.

Writing Formulas for Covalent Compounds

The names of covalent compounds contain prefixes that indicate the number of atoms of each element present.

Remember: The compounds named in this way are binary covalent

compounds (they contain only two elements, both of which are nonmetals).

When in covalent compounds, atoms do not have charges. Subscripts are determined directly from the prefixes in the name.

If no prefix is present on the name of the first element, there is only one atom of that element in the formula (its subscript will be 1).

A prefix will always be present on the name of the second element. The second element will use the form of its name ending in

Writing Formulas for Binary Covalent Compounds: Examples

nitrogen dioxide NO2

diphosphorus pentoxide P2O5

xenon tetrafluoride XeF4

sulfur hexafluoride SF6

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 heptaa

8 octa

9 nona

10 deca

* Second element in ‘ide’ from

* Drop –a & -o before ‘oxide’

Writing Formulas: Practice

carbon tetrafluoride CF4

Na3PO4sodium phosphate

Cu2SO4copper (I) sulfate

Analysis If “Yes”

The compound is covalent: the prefixes give

the subscripts.

* Are there prefixes present

The compound

is ionic: subscripts must be

determined by

balancing charges

prefixes covalent prefixes indicate subscripts

metal ionic balance charges 3 Na1+ needed for 1 PO43-

metal present ionic balance charges 2 Cu1+ needed for 1 SO42-

Al2S3aluminum sulfidemetal present ionic balance charges 2 Al3+ needed for 3 S2-

N2O5dinitrogen pentoxideprefixes covalent prefixes indicate subscripts

NH4NO3ammonium nitratepolyatomic ion present ionic balance charges

1 NH41+ needed for 1 NO3

1-

PbO2lead (IV) oxidemetal present ionic balance charges 1 Pb4+ needed for 2 O2-

Fe2(CO3)3 iron (III) carbonatemetal present ionic balance charges 2 Fe3+ needed for 3 CO3

2-

Chemical Equations and Chemical Reactions

During the late eighteenth century, Antoine Lavoisier conducted numerous experiments that involved chemical reactions. His belief in the need to make accurate measurements resulted in precise values for the masses of the substance in his experiments. Based on numerous observations of the same results, Lovoisier wrote his version of the law of conservation of mass: in every chemical reaction, there is an equal quantity of matter before and after the reaction.

Chemical Equations and Chemical Reactions

A chemical equation describes what happens in a chemical reaction. The equation identifies the reactants (starting materials) and products (resulting substance), the formulas of the participants, the phases of the participants (solid, liquid, gas), and the amount of each substance. Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products. The quantities are expressed as grams or moles.

Writing Chemical Equations

It takes practice to be able to write balanced equations. There are essentially three steps to the process:

1. Write the unbalanced equation. Chemical formulas of reactants are listed on the left-hand side of the

equation. Products are listed on the right-hand side of the equation. Reactants and products are separated by putting an arrow between

them to show the direction of the reaction. Reactions at equilibrium will have arrows facing both directions.

H2 + O2 → H2O

Writing Chemical Equations

2. Balance the equation. Apply the Law of conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product. Once one element is balanced, proceed to balance another, and another, until all elements are balanced. Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

.

2H2 + O2 → 2H2O

Writing Chemical Equations

3. Indicate the states of matter of the reactants and products. Use (g) for gaseous substances. Use (s) for solids. Use (l) for liquids. Use (aq) for species in solution in water. Write the state of matter immediately following the formula of the substance it describes.

2H2(g) + O2(g) → 2H2O(l)