CHEMISTRY YEAR 9

What is a group in the periodic table?

A vertical column of elements in the periodic table.

How are groups in the periodic table identified?

Groups are identified by numbers from 1 to 18.

What do elements in the same group have in common?

Elements within the same group share similar chemical properties because they have the same number of valence electrons.

Name and describe some important groups of the periodic table.

1. Group 1: Alkali Metals

   • Highly reactive metals.

   • Tend to lose one electron.

2. Group 2: Alkaline Earth Metals

   • Reactive metals, but less so than alkali metals.

   • Tend to lose two electrons.

3. Group 17: Halogens

   • Highly reactive nonmetals.

   • Tend to gain one electron.

4. Group 18: Noble Gases

   • Very unreactive (inert) gases.

   • Have a full outer electron shell.

Types of Acids

Citric-oranges/lemons

Hydrochloric-stomach acid

Nitric-fertilisers

sulfuric-batteries

ethanoic-vinegar

Salts

• ionic compounds with high melting/boiling points 

• soluble in H₂O

• solutions of soluble salts [electrolytes→ conduct electricity and decompose

Indicators

substances which are used to detect the presence of acidic, alkaline or neutral substances.

Colour change given by acids and alkalis with indicators

Methyl orange

Acid-pink

Neutral-orange

Alkaline-yellow

Litmus

acid-red

neutral-purple

alkaline-blue

Phenolphthalein

acid-colourless

neutral-colourless

alkaline-pink

Universal indicator

series of colour changes

not all acids/alkalis have the same strength

basics

• All acids have a pH less than 7

• A solution that has a pH of 7 is neutral

• All alkalis have a pH greater than 7

most common acid formulas in lab

HCl_(aq) / hydrochloric acid

H₂SO_4(aq) /sulfuric acid

HNO_3(aq) / nitric acid

Acids

a substance which releases H⁺ when dissolved in water

strong acids

high concertation of H⁺ ions and ionised completely

• hydrochloric acid

• nitric acid

• sulfuric acid 

liquid-concentrated

aqueous-dilute 

weak acids

low concertation of H⁺ ions and partially ionised

• ethanoic acid

• citric acid

• carbonic acid

Hydrated salts

are salts that contain water molecules in their structure. This water is referred to as water of crystallisation. When hydrated salts are heated the water of crystallisation is removed to form an anhydrous salt.

Homogenous mixtures

are mixtures where the parts of the mixture are all in the same phase or state of matter.

Heterogenous mixtures

are mixtures where its parts are in different states of matter.

Production of salt from seawater in Malta

1. salt pans are built next to the sea.

2. they are filled with seawater.

3. the water evaporates due to the sun heating up the rocks.

4. as the water evaporates, crystals of salt form in the salt pans [crystallisation] .

Filtration

used to separate an insoluble solid from a liquid or aqueous solution.

Evaporation to dryness

used to obtain a soluble solid from a liquid solvent.

• the slower the rate of evaporation, the larger the crystals formed because they have more time to form properly.

Crystallisation

used to obtain a soluble solid from the liquid solvent.

• a water bath should be used

• a hydrated salt is required

• the salt required is not thermally stable [ do not decompose on heating]

• large crystals are required.

• remaining solution becomes super saturated

Salt

a chemical substance that is made of metal and nonmetal ions which are chemically combined together and are solid at RTP. The bond that exists between the metal and nonmetal ions is very strong and is called an ionic bond.

Sodium chloride [NaCl] / common salt

• ionic solid.

• salts form giant ionic lattices which are large structures of cations[positive ions] and anions[negative ions] held together by strong electrostatic forces of attraction

Ionic [electrovalent] bonding

• metals can combine chemically with nonmetals to form compounds

• this means that metals lose one or more electrons while the nonmetals gain these electrons

• during the reaction between metals and nonmetals, metals form positively charged metal ions[cations] while the nonmetal atoms form negatively charged ions[anions[

Ions are charged particles since the number of protons is not equal to the number of electrons.

The ionic bond that forms between these ions is an electrostatic force of attraction between oppositely charged ions.

polyatomic ions

a group of covalently chemically combined atoms that is charged and exists in several compounds

Endings

-ide presence of a nonmetal ion

-ate a polyatomic ion containing oxygen

-ite a polyatomic ion that also has oxygen in it but when there are two polyatomic ions of the same nonmetal that have different number of oxygen atoms, the one that has the lowest amount gets its name ending in -ite and the higher amount of oxygen gets the -ate.

SOLVENT ACTION OF WATER, SOLUTIONS AND SOLUBILITY

The solubility of a solute is the max quantity of solute that can dissolve in a certain quantity of solvent at a a specific temp.

Main factors that influence solubility:

• the nature of the solute and solvent

• temperature

• pressure

Factors determining how fast a substance dissolves in a solvent:

• size of particles

• stirring

• amount of solute already dissolved

• temperature

Hard and soft water

in areas where sedimentary rock is present, the rocks contains limestone will react with naturally slightly acidic rainwater resulting in dissolved calcium hyrogencarbonate[hard water]. Ground water also contains any other soluble salts that may be present in the bedrock.

Water Hardness

Hard water contains dissolved calcium/magnesium ions

Soft water does not have calcium/magne4sium ions dissolved in it

Temporary Hardness

• caused by the presence of dissolved calcium/magnesium hydrogen carbonate

• calcium/magnesium hydrogen carbonate is formed by the reaction of acidified rainwater with limestone/dolomite.

• removed by boiling since calcium/magnesium hydrogen carbonate thermally decompose.

Permanent Hardness

• caused by the presence of dissolved calcium/magnesium ions

• contains gypsum that dissolves calcium/magnesium sulfate.

• cannot be removed by boiling but can be removed by other methods.

Boiling

only temporary hardness can be removed by boiling

Ca(HCO₃)_2(aq) → CaCO_3(s) + H₂O_(l) + CO_2(g)

Distillation

separates the solvent from any dissolved solutes, removes all soluble ions to produce pure water

100^oC

Washing soda

both temporary and permanent hardness can be removed by adding washing soda to hard water

the addition of sodium carbonate would remove such hardness because the carbonate ions from the washing soda react with the calcium/magnesium ions to form a precipitate.

Testing for water hardness

One method to show the difference between hard and soft water is too add soap to it.

Soft water readily forms lather with soap

hard water does not form lather readily but forms scum.

Advantages of hard water

• the calcium salts in the water help form healthy teeth and bones

• calcium carbonate is important for shell and egg formation in many animals

Disadvantages of hard water

• soap wastage increases since all dissolved salts have to be precipitated before soap can function.

• the scum produced is difficult to remove from fabrics.

• formation of limescale in pipes

mixture

made up of two or more substances mixed together that can be separated by physical means

percentages of gases in air

Nitrogen 78%

Oxygen 21%

Carbon dioxide 0.03%

Noble gases approx 1%

Nitrogen

• most abundant gas in air

• colourless and odour less

• pH7

• slightly soluble in water

• very unreactive

• combines with oxygen to form oxides

• liquid nitrogen boils at 196^oC

• used to produce ammonia when combined with hydrogen under special conditions

Oxygen

• colourless and odourless gas

• neutral gas

• slightly soluble in water

• slightly denser than air

• very reactive and supports combustion

carbon dioxide

• colourless and odourless gas

• acidic gas

• slightly soluble in water forming carbonic acid, H₂CO₃

• denser than air

• taken up by plants during photosynthesis

noble gases

• colourless and odourless gases

• monoatomic [ exist as single atoms ]

• very unreactive due to full outer electron shell

• become denser on going down the group

• boiling points increase on going down the group

Helium is used in weather balloons and in mixtures with oxygen for deep sea diving tanks.

Argon is used for filament bulbs.

Neon is used for advertising signs and lasers since it produces a bright red colour.

Krypton and xenon are used in lighthouse lamps and lasers.

Elements

a pure substance which cannot be further divided into simpler substances by chemical methods and contain only one type of atom.

Compounds

a pure substance which is made of two or more elements that are chemically combined together

Isotopes

atoms of the same element that have the same number of protons but a different number of neutrons

Relative Atomic Mass

the average mass of isotopes of an element compared to a 1/12^th of the mass of an atom of ¹²C.

RAM =

average mass of isotopes of an element—————————————————

1/12 x mass of 1 atom of carbon12

Relative molecular mass RMM

used for covalently bonded substances

Relative Formula Mass RFM

used for ionically bonded substances

Monoatomic elements

Formation of molecules

when a group of atoms are held together by covalent bonds.

covalent bonding

two atoms of the same element joined together by a bond and happens only between nonmetal atoms

valency

of an element is the number of electrons its atoms lose, gain, or share to obtain a noble gas configuration.

a single covalent bond

forms when two atoms each contribute one electron to a shared pair of electrons.

a double covalent bond

forms when two atoms each contribute two electrons to have 2 pairs of shared electrons.

a triple covalent bond

forms when two atoms each contribute three electrons to have 3 pairs of shared electrons.

simple covalent molecules

• are gases or liquids at RTP

• have low melting and boiling points at RTP due to weak intermolecular forces of attraction which exist between simple molecules and require low energy to break.

• do not dissolve in water but dissolve very easily in organic solvents.

• do not conduct electricity since they have neither free electrons nor free ions.

Diffusion

happens when the molecules move from a high conc to a low conc until all of the space is evenly occupied.

GREEN HOUSE GASES

absorb heat in the atmosphere and prevents heat from escaping into space , keeping the Earth warmer.

hydrocarbon + oxygen → carbon dioxide + water vapour

Increasing Global temperatures causes

• polar ice caps melt causing sea levels to rise

• some lands will be submerged under water

• a change in climate and weather patterns all over the world

• frequent extreme weather events

• some agricultural areas will cease to produce crops and become desserts due to climate change.

• some species that cannot adapt with a change will die out.

combating climate change

• less consumption of fossil fuels

• using renewable sources of energy

• reduce reliance on cars

• have energy efficient buildings

• improved power plant efficiency

• planting more trees

carbon monoxide CO

• colourless odourless gas

• poisonous but non-irritating

• product of incomplete combustion of fuel

• vehicular exhaust is a major source of CO

• readily combines with haemoglobin in RBCs , preventing the uptake of oxygen.

• Catalytic converters oxidize CO in the exhaust gases to carbon dioxide.

complete combustion

when there is a plentiful supply of oxygen

incomplete combustion

limited supply of oxygen

particulates

are tiny particles of solid or liquid suspended in a gas.

sulfur dioxide SO₂

sulfur + oxygen → sulfur dioxide

S_(s) + O_2(g) → SO_2(g)

• colourless gas with an irritating smell

• poisonous

• creates acid rain ( sulfuric acid)

sufur dioxide + water + oxygen → sulfuric acid

nitrogen oxides NO_x

NO

• comes into contact with oxygen in the air, it oxides to form nitrogen dioxide

NO₂

• reddish-brown toxic gas with a characteristic sharp, irritating odour

• most prominent air pollutants

• causes acid rain.

N_2(g) + O_2(g) → 2NO_(g)

2NO_(g) + O_2(g) → 2NO_2(g)

Chlorofluorocarbons and ozone

CFCs are harmful to the ozone layer

The Ozone Layer O₃

acts as a protective screen against excessive UV radiation reaching the Earth’s surface.