Chemistry

Properties of Metals

Properties of Metals

• Malleable

• Conduct electricity

• Conduct heat

• Ductile (can be stretched)

• Shiny

Properties of Non-Metals

• Low melting and boiling points

• Do not conduct heat

• Do not conduct electricity

• Brittle

• Dull

Metalloids

Both physical properties of metals and non-metals

Periodic table patterns

• The period is the row and is determined by the number of energy levels (shells)

• The group is the column down and it is determined by the number of valence electrons

Ionisation energy

The amount of energy required to remove and electron from an isolated atom or molecule

Atomic Radius

The total distance from an atom's nucleus to the outermost orbital of an electron

Electronegativity

A measure of an atom's ability to attract shared electrons to itself

Relationships down the groups of the PT

Ionisation is less, the electronegativity is less, but the atomic radius is more.

Relationships across the periods of the PT

Ionization is more, the electronegativity is more, but the atomic radius is less.

Formation of an ion

• An atom has an equal number of protons and electrons so they are electrically neutral

• The number of electrons can change in an atom and a chemical reaction can change the number of electrons in the outer shell (valence shell)

• Atoms will generally follow the octet rule where they are more stable when they have a full valence shell

Formation of a cation

• When an atom loses electrons they are losing negative charge and therefore become positive

• A positive ion is called a cation

  • E.g., Magnesium goes from 2.8.2 and loses 2 electrons to form 2.8

Formation of an anion

• When an atom gains electrons into the outer shell it is gaining negative charge so it becomes a negatively charged ion

• A negative ion is called an anion

  • E.g., Sulphur has an electron configuration of 2.8.6 and it becomes 2.8.8

Polyatomic ions

Polyatomic Ions are an ion that contains two or more atoms joined together and it has an overall positive or negative charge

Ionic compounds

• Ionic compounds contain oppositely charged ions which are organised in a regular 3 dimensional lattice

• Each ion is held in the crystal lattice by strong electrostatic attraction between the oppositely charged ions around it

• These are called ionic bonds

Naming ionic compounds

CATION FIRST

• Potassium fluoride

• Copper oxide

• Magnesium hydroxide

• Barium carbonate

• Iron chloride

• Aluminium bromide

Writing ionic fomulae

• Identify the positive and negative ions

• Look at the charges they need to cancel out

• Swap them over and place at the bottom or if a ration of one to one put together

Physical properties of ionic compounds

• Hard

• Brittle

• Non-conductors of electricity as a solid

• Conductors of electricity in solution or molten

• High melting and boiling points

Isotope

Two or more forms of the same element that contain equal number of protons but different number of neutrons in their nuclei

Relative atomic mass definition

A weighted average of the masses of atoms of the isotopes

Carbon isotopes

• Almost all carbon atoms found in living things, and in the rocks, seas, and atmosphere of our planet have the number symbol 12C6

  • The is called Carbon-12

• A fraction of the carbon atoms on Earth have the nuclear symbol 14C6

  • This is called Carbon-14

Relative atomic mass

The relative atomic mass we see written on the periodic table is an average.

• E.g., Only a tiny fraction of carbon atoms have a mass number of 13 or 14. All the rest have a mass number of 12.

• This means that the average mass of carbon atoms is 12.01

  • This is called the relative atomic mass of carbon

Relative atomic mass calc

1. Multiply the mass number of each isotope by its % abundance

2. Add these values together

3. Divide by 100 to get the average

   • E.g., Boron

   1. 10x20=200, and 11x80=880

   2. 200+880=1080

   3. 1080/100=10.8

Properties of an Acid

• Corrosive

• Taste sour

• Turn blue litmus red

• React with active metals

• React with bases

• Contain hydrogen ions

Properties of a Base

• Corrosive

• Taste bitter

• Turn red litmus blue

• Feel soapy or slippery (react with fats to make soap)

• React with acids

• Alkalis = soluble base

• Contain hydroxide ions

Acid + Base → __________

Acid + Base → Salt + Water

E.g, Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water

Oxidation

Loss of electrons

• Element gains oxygen

Reduction

Gain of electrons

• Element loses oxygen

A successfull collision means a chemical reaction occurs, two things must be true:

Controlling rate of reaction

• Temp

• Concentration

• Surface area

• Agitation

• Catalysts

Temp

• Increased temp = increased ROR

Reasons:

1. Increased speed of particles in liquids and gases leads to particles colliding more frequently

2. Gives particles more energy, when ,molecules collide, chemical bonds are more likely to break (activation energy)

Rate of Reaction

How fast a chemical reaction occurs

Concentration of the reactants

• Concentrated - more solute to solvent

• Dilute - less solute to solvent

• Increased concentration = increased ROR

Reason:

1. Reactant particles are more likely to collide if there is a lot of them in a small space

Surface area

• Increased SA = increased ROR

Reason:

1. More reactant particles are exposed

Agitation

• Mixing and stirring

• Increased agitation = increased ROR

Reason:

1. More reactant particles are exposed

Catalysts

• Chemicals that speed up reactions but are not consumed (used up) during the reaction

• Catalysts = increased ROR

Reasons:

1. Reduce the activation energy that is required to convert the reactants into products

2. Provides an alternate pathway for reaction

3. Easier for reactant molecules to collide

E.g., Enzymes are biological catalysts

Mole

Avogadros number, 6.022 x 10^23

• Used to count atoms, molecules, ions etc.

The mole equation

• n = number of moles (mol)

• m = mass of the sample (grams, g)

• M = molar mass of the sample (grams per mole, g/mol)

• Molar mass is the no. of grams making up 1 mole of a substance

n=m/M

When is a substance said to be soluble?

If it dissolves in solution

Metal + Acid → ________

Metal + Acid → Salt + Hydrogen

Metal carbonate + Acid → _________

Metal carbonate + Acid → Salt + Water + Carbon dioxide

Types of Chemical Reactions

1. Decomposition

2. Single displacement

3. Double displacement

4. Combination (synthesis)

5. Combustion

Precipitate reactions

• Reaction occurs when two soluble reactants combine to form an insoluble product known as the precipitate

• Particles from two soluble compounds mix together and some stick to form an insoluble solid

• Solid precipitates out of the solution, making it murky

• Usually the solution clears as the precipitate settles on the bottom or rests at the top