Chemistry Chapter 5 & 6

Page 1

5.1 Atoms and Elements:

Atoms:

Particles that make up all the substances in the universe.

Made up of protons, electrons and neutrons.

Can't be seen with an STM (Scanning tunnelling microscope) because they're too small.

Indirect evidence - Evidence that does not involve direct observation.

The Nucleus:

Located in the centre of each atom.

Tight, dense bundle of protons and neutrons.

Neutrons are slightly heavier than protons, and both are about 1800 times heavier than electrons.

The positive charges of protons give the nucleus a positive charge too.

Electrons:

Spin around in the space surrounding the nucleus.

Attracted to protons.

Number of electrons in an atom = Number of Protons

Elements:

Building blocks of matter.

Atoms are the smallest unit of an element

The number of protons in the nucleus determines the element.

118 elements

Most earth substances are compounds

Atomic Number = Number of protons

Mass Number = Number of protons + neutrons

Isotopes: The element with the same atomic number, but with different mass numbers.

5.2 Arranging the Elements

The Periodic Table:

Lists all the known elements in order of increasing atomic number.

Every box within the table represent a different atomic number and therefore a different element.

Periods and Groups:

Horizontal rows are periods

Vertical columns are groups

Special Blocks:

Three blocks on the periodic table known as the transition elements, lanthanides and actinides

Group Number- Number of Electrons in outer shell

Period Number- How many shells it has

5.3 -

Alkali Metals - Group 1

- Most reactive

- Found as compounds

- Form ions with a form of +1

Alkaline Earth Metals - Group 2

- Less reactive than group 1

- 2 electrons in the outer shell

- Lose two electrons

Atoms get larger as we go down a group because there are more shells it goes down so it becomes further away from the nucleus.

As we go down a group the atoms become more reactive

Allotropes: Different forms of the same element

Carbon --> Diamond, Graphite and Charcoal

5.4 - Family Groupings

Electron Configuration: How electrons are arranged in the shells of an atom

- Electrons spin around the nucleus known as electronic shells

- Charges of group 1 and 2: Positive (getting rid of the ions)

Page 2

Chapter 6 - Chemical Reactions

Atoms --> Molecules --> Compounds

(O,N,C) (O2, H2O, CO2) (Proteins, Lipids and Carbs)

Balancing Equations: Making the chemical equations equal on both sides

2Ca + O2 --> 2CaO

How to write Formulas:

E.g. Hydrogen Sulfide

Find the group numbers for each element

H +1 S -2

(Cris Cross)

= H2S

Law of Conservation of Mass:

- The mass of the products in a chemical reaction must equal to the mass of the reactants

- Matter can neither be destroyed or created. the mass of an object or collection of objects never changes, no matter how the parts are rearranged.

Worded to chemical equations:

Dilute Sulphuric Acid = H2SO4

6.2 - Energy in Chemical Reactions

Endergonic- When energy is required to make a reaction happen.

Exergonic- When energy is released

Endothermic- Heat energy taken in. E.g. Photosynthesis

Exothermic - Heat energy is released. E.g. Cooking on a stove

Catabolic- Breaking of a complex molecule into simpler ones

Anabolic- Joining of simple molecules to make complex ones.

Combustion- Burning of substances in the presence of oxygen.

Corrosion - When a metal reacts with oxygen to produce a metal oxide but doesn't produce a significant amount of heat and light.

During a chemical reaction, if the amount of energy stored in the reactants is greater than energy stored in the products, then the energy will be released as heat or light (Exothermic).

If the amount of energy stored in the reactants is less than the energy stored in products, energy will need to be absorbed from the environment.

6.3 Classifying Chemical Equations:

Decomposition: Complex molecules break down into simpler ones

XY-->X+Y

Thermal Decomposition: Substances that decompose when heated

2NaHCO3 --> Na2CO3 + CO2 + H2O

Combination Reaction: When two reactants combine form a single product

X+Y-->XY

Precipitation Reaction: When two clear solutions are mixed, they react to form an insoluble solid.

Neutralisation Reaction: When an acid reacts with a base. Acid + Base --> Salt and Water

Acids and Metals: Acid +Metal --> Salt and Hydrogen

Acids and Carbonates: Acid + Carbonate--> Salt + Water + Carbon Dioxide

How to write the formula of a compound:

E.G- MgCl

Mg +2 (group 2)

Cl -1 (group 17)

Mg2Cl-1

(criss cross) -->MgCl2

6.4- Rates of Chemical Reactions

Factors that create faster reactions:

Temperature

Heat Energy --> Kinetic Energy --> Movement --> Move Collisions --> Faster Reactions

pH Levels

- Each reaction needs an optimum pH level and temperature.

- If the pH is too high or low it changes the structure of the molecules.

Concentration

- As the concentration of a reaction increases, the reaction speeds up, but to a certain level.

- Increasing the concentration of reactants generally increases the rate of reaction because more of the reacting molecules or ions are present to form the reaction products.

Catalyst

- An enzyme that speeds up the rate of reactions

A + B --> C + D

(catalyst)

- A catalyst speeds up a chemical reaction, without being consumed by the reaction. It increases the reaction rate by lowering the activation energy for a reaction.

Surface Area

- Surface area can be increased by crushing the substance so that it has many pieces.

- Increasing the surface area of a solid reactant exposes more of its particles to attack. This results in an increased chance of collisions between reactant particles, so there are more collisions in any given time and the rate of reaction increases.