Sec 4 Mid-Year Review

Environmental Science

The periodic table

Review of the Atom

Proton (+)

Neutron (o)

Electron (-)

Orbit

How it works

•Each column of the table are called groups/families.

•Each member of a group has the same number of valence electrons

Important Definitions:

• Valence Electron: Number of electrons on the last orbit of

the atom

• A Group corresponds to the columns of the periodic table. All elements of a group share similar properties such as reactivity (they have the same number of valence electrons).

Group 1A : Alkali

• 1st column except hydrogen• They are soft and highly reactive• Must be stored in oil due to their high reactivity and are

never found in their elemental state in nature but always as a compound

Group 2A : Alkaline Earth Metals

• Highly malleable and reactive, they burn easily in presence of heat

• Never found in their elemental state but can be exposed to air (often stored in oil)

• They often form the compound of rocks

Group 7A : Halogens

• Salt creator

• Second to last column

• Non-metals that react easily to form compounds including salts

Group 8A : Noble Gases

• Final column

• Very stable

• Can be found in their elemental state

How does it work?

•Each row is called a period numbered 1 to 7

•Not all periods have the same length

Important Definitions:• A Period corresponds to the rows of

the periodic table. All elements of the same period have the same number of orbits/shells

Other divisions…

•The “staircase” indicates the separation of the metals (under the stair case) from the non-metals (above the stair case).

•The metalloids are located on either side.

Other divisions:Metals

•Generally good conductors of electricity and heat•Ductile and malleable•Usually shiny•All are solid at room temperature (except Hg)•Many react with acids

Other divisions:Non-Metals

•Poor conductors of electricity and heat•Many are gases at room temperature •The solid non-metals can easily be reduced to powder

Other Divisions:Metalloids

•Properties depend on conditions•Seven elements that share properties with the metals and non-metals. •Semi conductors (are good conductors in certain conditions, bad in others

Representing the invisible

General Rules

– Electrons seek to fill the shells nearest the nucleus before occupying a further shell

– The 1st shell contains a maximum of 2 electrons

– The 2nd shell contains a maximum of 8 electrons

– The third shell 18 but after 8 the fourth shell fills up first

Lewis Notation

• Notation in which only the valence electrons (electrons on the last shelf) are represented

Rutherford-Bohr

• Important rules:– the period – indicates the number of shells– the group – indicates the number of

valence electrons– the atomic number – indicates the total

number of protons and electrons in the atom

Simplified Atomic Model

• Clearly shows the number of protons and neutrons in the nucleus– The number of neutron equals the relative mass (rounded to the

nearest whole number) – the atomic number

• The electron and shells are similar to that of Rutherford Bohr’s model

p+

nº

Bonds

Ionic

• Made between a metal and a non-metal or with a polyatomic ion

• Electrons are given to the non-metal

Covalent

• Made between two non-metals

• Electrons are shared

Nomenclature and notation

• Nomenclature (naming)– 1. is it ionic?– 2. is it a polyatomic ion?– 3. What is it, precious?

name 1st

ide ending

Ions

• When an element has more or less electrons than usual

• Depends on its placing in the preriodic table

• Wants to have a complete energy shell

• Loosing electrons = +

• Gaining electrons = -

Notation (writting formulas)

• 1. Write down the symbol for the first element or polyatomic ion

• 2. Write down the symbol for the second element or polyatomic ion

• Add necessary subscript

Chemical Changes

Chemical Reactions

a) Definition:– A reaction that alters the nature and

characteristic properties of matter. – The atoms are rearranged.– New molecules are formed

Chemical Reactions

b) Observable characteristics:– A chemical reaction occurs when:

• A gas is released• Heat is absorbed (endothermic) or released

(exothermic)• Light is emitted• The color changes• A precipitate forms

Chemical Reactions

c) Types of chemical reactions:

i) Basic reactions:• Synthesis

– Two or more reactants become one product

• Decomposition– One reactant is decomposed into two or more products

• Oxidation– A reaction where one of the reactants is oxygen (O2)

• Precipitation– A reaction where two liquid reactants form a solid product

Chemical Reactions

ii) Other chemical reactions– Acid-Base Neutralization

• Reactants: Acid + Base• Products: Water + Salt

– Combustion• Type of oxidation that releases a large amount of energy• Combustion requires

– Oxidation agent

– Ignition temperature

– Fuel

Chemical Reactions

– Cellular respiration:• Takes O2 + glucose to form CO2 +water + energy

– Photosynthesis:• Takes CO2 + water + energy to form O2 + glucose

Balancing Stoich

So far…

• Law of conservation of mass

So far…

• Law of conservation of mass

So far…

• Law of conservation of mass

So far…

• Law of conservation of mass

Law of conservation of mass

• H2 + O2 H2O

2 H2 + O2 2 H2O

Stoichiometry

H2 + O2 H2O

2 H2 + O2 2 H2O

Moles 2 1 2

Mass 4 g 32 g 36 g

?

Representing chemical equations

Synthesis

2 H2 + O2 2 H2O

Decomposition

2 H2O 2 H2 + O2

Oxidation

Fe + O2 2 FeO

Precipitation A (liquid) + B (liquid) C

(solid)

Neutralization

H ___ (acid) + ----OH (base) H2O + salt

HCl + NaOH H2O + NaCl