Notas

Chemistry

hockeygirl10 Science High School Inglês 1 página

Conteúdo das notas (1)

Página 1

Periodic Table Patterns

Atomic size gradually decreases from left to right across a period of elements.

Atomic size gradually increases going down a group.

Atomic radius decreases from left to right within a period

Atomic radius increases from top to bottom within a group.

Types of Chemical Reactions

Chemical change: any change in which new substance is formed

Evidence of a chemical change

- release of energy as heat

- release of energy as light

- change in colour

- formation of gas

- change in odour

Types of Chemical Reactions

Neutralization: Acid (H) + Base(OH)—> salt + H(OH)

Combustion: AB + Oxygen —> CO2 + H2O

Synthesis: A + B —> AB

Decomposition: AB —> A + B

Single Displacement: A + BC —> AC + B

Double Displacement: AB + CD —> AD + CB

Synthesis Reactions

Synthesis reactions are also known as FORMATION reactions. Two or more reactants (usually elements) join to form a compound

A + B —> AB

where A and B represents elements

-The elements may form ionic compounds, like… sodium metal and chlorine gas combine to form sodium chloride

2Na + Cl2 —> 2NaCl

Elements that form ionic compounds: Magnesium metal reacts with oxygen gas to form magnesium oxide.

2Mg + O2 —> 2MgO

2. Elements that form covalent compounds: Nitrogen gas and oxygen gas join to form dinitrogen monoxide

2N2 + O2 —> 2N2O

Decomposition Reactions

-Opposite of synthesis reactions

A compound breaks down into 2 or more products

—> AB —> A + B

1. Ionic compounds may decompose to produce elements like the following

salt, sodium chloride, can be broken down into sodium metal and chlorine gas be melting salt at 800 degrees Celsius and running electricity through it

A B A

H2 (g) + O2 (g) —> H2O

Synthesis

AB A B

H2O —> H2(g) + O2 (g)

Decomposition

ClNa—> Cl + Na

2. Covalent compounds may decompose into elements like the following 2H2O —> 2H2 + O2

Single Replacement Reactions

-Single replacement reaction replace one element from a compound with another element

a compound and element reacts and an element react and the element switches places with part of the original compound

A + BC —> B + AC Where A is a metal or,

A + BC —> C + BA where A is a non metal

Types: Single displacement

Example

Zn + CuCl2 —> ZnCl2 + 2Cu

General: AB + C —> AC + B

*A metal can only replace a metal*

When A is a metal:

Aluminum foil in a solution of copper (ll) chloride produces solid copper and aluminum chloride

2Al + 3CuCl2 —> 3Cu + 2AlCl3

When A is a non-metal:

When fluorine is bubbled through sodium iodide solution,iodine and sodium fluoride are produced

F2 + 2NaI —> I2 + 2NaF

There are certain elements on the periodic table that only exist as diatomic molecules (you will never see these elements just by themselves) ( also mostly just for gases)

Be able to predict the product from the reactants and what kind of reaction it is

Double Replacement Reactions

Double replacement reactions swap elements between 2 compounds that react together to form two new compounds

Two compounds react, with elements switching places between the original compounds

AB + CD —> AD + CB

eg. MgO + CaS —> MgS + CaO

Two solutions react to form a precipitate (solid) and another solution

Ionic solution + ionic solution —> ionic solution + ionic solid

AB + CD —> AD + CB

When potassium chromate and silver nitrate react, they form a red precipitate, silver chromate, in a solution of potassium nitrate

K2CrO4 + 2AgNO3 —> Ag2CrO4 + 2KNO3

Neutralization Reactions

Neutralization Reactions occur when an acid (most compounds starting with H) and a base(most compounds ending in OH) react to form a salt and water

Neutralization reactions are a type of double replacement

Acid + base —> salt + water

HX + MOH —> MX + H2O

Sulfuric Acid is used to neutralize calcium hydroxide

H2SO4 + Ca(OH) 2 —> CaSO4 + 2H2O

H3PO4 + 3Fe(OH) 2 —> Fe3(PO4)2 + 6H2O

Combustion Reactions

Combustion reactions occur when a compound or element react with oxygen to release energy and produce an oxide

also sometimes referred to as hydrocarbon combustion

CxHy +O2 —> CO2 + H2O

Where x and y represents integers

Natural gas (methane) is burned in furnaces to heat homes

CH4 + O2 —> CO2 + 2H2O + energy

An acetylene torch is used to weld metals together

2C2H2 + 5O2 —> 4CO2 + 2H2O + energy

Carbohydrates like glucose combine with oxygen in our body to release energy

C6H12O6 + 6O2 —> 6CO2 + 6H2O + energy

Exothermic Reactions

These are reactions that use energy as a product of the reaction

Energy is given off to the surroundings, typically as heat or light

The energy needed to make the reaction occur is less than the total energy released

Reactants —> Products + Energy (NRG)

EXO = Exit

Endothermic Reactions

These are reactions that absorb energy as part of the reaction

Energy is taken in as heat from the surroundings

The energy needed to make the reaction occur is more than the energy that is released

Reactants + Energy (NRG) —> Products

ENDO = Enter

Counting Atoms

Rules for counting atoms

subscripts only refer to the atom that they are behind.

For example H2S (subscript only refers to Hydrogen) There are two atoms of Hydrogen and one atom of sulfur

Coefficients apply to the entire compound. You multiply the coefficients and subscripts

For example 2H2S Atoms of Hydrogen: 4 Atoms of Sulfur:2

If there isn’t a subscript behind an element, assume there is only one atom of that element

If elements or compounds are inside of parenthesis, then the subscript behind the parenthesis applies to everything inside

For Example Ba(OH)2 Atoms of Barium: 1 Atoms of Oxygen: 2 Atoms of Hydrogen: 2

Naming Covalent Compounds

To name compounds that have formed using covalent bonds, you must name both non-metals as they appear in the formula, adding prefixes to indicate the proportions of atoms participating in the complex.

Example- CO2 = mono carbon dioxide, or carbon dioxide

Example- CO = mono carbon monoxide or carbon monoxide

(note that ‘mono’ can be dropped from the name only if it is the first element)

Remember your prefixes!

1- mono

2- di

3- tri

4- tetra

5-penta

6- hexa

7- hepta

8- octa

9- nona

10- deca

Simple (monatomic) Binary Ionic Compounds

These are compounds that contain only two elements that share an ionic bond

Example- MgCl2

To name the compound using the formula, simple name the metal first, then the non-metal. Change the last few letters of the metal name to end in ‘ide’

Example- MgCl2 = magnesium chloride

Naming Binary Ionic Compounds with Multivalent (variable charge) Ions

Some transition metals can have more tun one ionic charge (see table 2)

Example- Lead can exist as Pb 2+ or Pb 4+

To name the compound properly, you must know and identify the charge on this ion

To name the compound, name the transition metal first, then indicate the charge on the metal using roman numerals. Then name the non-metal in the usual format

Example- PbCl2 = lead (II) chloride

PbCl4 = lead (IV) chloride

Naming Ionic Compounds with Polyatomic Ions

Polyatomic ions are atoms that have formed a complex using covalent bonds, but have an overall ionic charge. Most of these ions are negative, and replace the simple anions in a formula

Example: Sulfate = SO4 2- , Cyanide = CN 1-, phosphate = PO4 4-

To name compounds with polyatomic ions, you must name the metal first, then use the common name of the polyatomic ion

Example: NaSO4 = sodium sulfate

‘Ate’ stands for oxygen

Balancing Chemical Equations

What goes in must come out

Balancing a chemical equations is much like the work of an accountant who has to show every penny that comes in and were it has gone to

Law of Conservation of Mass (you need to remember this law)

The Law of conservation of Mass states: that mass is neither created nor destroyed in any chemical reaction.

Therefore balancing of equations requires the same number of atoms on both sides of a chemical reaction

The number of atoms in the reactants (what we start with) must equal the number of atoms in the products (what we end up with)

Because of the principle of the conservation of mass, an equation must be balanced.

It must have the same number of atoms of the same kind on both sides

Adam Lavoisier (1788) is the founder of the theory: The Conservation of Mass

The mass of all the reactants must equal the mass of the products

Reactant + Reactant = Product

example: iron (II) Sulfide

Iron + sulfur —> Iron (II) Sulfide

Fe + S —> FeS

Note that in a chemical equation, by convention, we use the arrow ‘—>’ instead of the equals ‘=‘

The last stage is to put in state of matter symbols (s, l, g, aq), as appropriate (solid, liquid, gas, aqueous or dissolved in water)

example

Fe(s) + S(s) —> FeS(s)