GCSE CHEMISTRY - unit 1 - compounds and bonding

REACTIONS AND COMPOUNDS

New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bonds.

Ionic bonds

Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons:

• metal atoms lose electrons to form positively charged ion
• non-metal atoms gain electrons to form negatively charged ions

The ionic bond is the force of attraction between the oppositely charged ions. 

Covalent bonds

Two non-metals share an electron to form covalent bonds that hold the atoms together to form molecules.

Chemical formulas

The chemical formula of a compound shows how many of each type of atom join together to make the units which make up the compound. For example, in iron sulfide every iron atom is joined to one sulfur atom, so we show its formula asFeS. In sodium oxide, there are two sodium atoms for every oxygen atom, so we show its formula as Na₂O. Notice that the 2 is written as a subscript, so Na2O would be wrong.

GCSE chemistry - unit 1 - extracting metals

Extracting Metals

Metals are very useful as so many thing are made out of it. Metals are found in metal ores (rock with large amounts of the metal of interest; enough metal to make it worth while)

The metal ore contains impurities  and the actual metal is chemically combined with substances (usually oxygen).

First we CONCENTRATE the metal ore (basically get rid of any impurities) by SMELTING (heating) it.

The metal ore without impurities then under goes either DISPLACEMENT or ELECTROLYSIS to remove what it is chemically combined with; mostly oxygen)

All of this will happen only if the metal that is produced is worth more than the cost of getting it out if the ore (A HIGH GRADE ORE). If it is not worth while, they need to find a cheaper way of extraction or one that gets more of the metal out. If not, it's not worth it.

The reactivity series

Potassium              MOST REACTIVE
Sodium
Calcium
Magnesium
Aluminium
-----------------
*carbon*
-----------------
Zinc
Iron
Tin
Lead
Copper
Silver
Gold                      LEAST REACTIVE

If the metal is LESS reactive than carbon they undergo DISPLACEMENT. This means they are reacted with carbon and because the carbon is more reactive than them, it will take away the oxygen the the metal is bonded with to leave the metal and carbon dioxide. This is the cheaper of the two.

If the metal is MORE reactive than carbon they undergo ELECTROLYSIS because carbon is less reactive than theses metal so won't be able to steal the oxygen from them. Electrolysis uses electricity to separate the metal away from the oxygen.

IT IS IMPORTANT TO NOTE THAT GOLD IS SO UNREACTIVE THAT IT IS FOUND NATIVE IN THE GROUND (DOES NOT NEED TO BE EXTRACTED)

E.g. COPPER EXTRACTION

ELECTROLYSIS - a negative and positive electrode are placed in the melted ore solution (IN COPPER'S CASE IT IS CHEMICALLY BONDED WITH SULFUR NOT OXYGEN). The sulfur and copper have bonded ionically so the copper is made up of positive ions and the sulfur, negative ions. The positive copper ions are attracted to the negative electrode so is now separated and can be purified. Salt is left at the positive electrode.

DISPLACEMENT - scrap iron (more reactive than copper) removes the sulfate from the copper sulfate and the copper coats itself around the iron which can be easily removed and purified. This is a lot cheaper

The problem is, there's a shortage of high grade copper ores. We can use PHYTOMINING and BIOLEACHING  to extract copper from low grade ores (containing less than 1% copper) and then use electrolysis and displacement as usual after.

Phytomining

• Grow certain type of plant on land with low grade copper ore in it
• Plants take copper compounds into their body tissue
• Burn plants to leave ash that contains copper which can be extracted by electrolysis or displacement

Bioleaching

• Use certain bacteria to grow on the low grade copper ore to use it as a source of nutrition
• The bacteria produce a byproduct solution containing copper
• The solution goes through electrolysis or displacement to extract the copper

GCSE chemistry - unit 1 - calcium carbonate (limestone)

Calcium Carbonate (Limestone)

Uses of limestone

• Building and statues (strong and durable rock with a nice colour)
• Can be crushed, mixed with clay and heated to make cement
• Can add sand to cement to make mortar (like cement, hard and strong once set and lasts for a long time)
• If you add aggregate (small pebbles) to mortar you get concrete
• So LOTS of uses as BUILDING MATERIALS

Quarrying

• Limestone is a rock so is found in the ground and has to be quarried
• This involves using explosives and heavy mechanical equipment which creates noise dust and pollution
• It spoils the landscape + habitats
• The land is ruined so much that it can't be used again
• It produces a valuable material (limestone)
• Positive economic impact in the area
• Creates employment in the local area

Limestone cycle

Thermal decomposition (seen above)

HAPPENS TO OTHER CARBONATES (CO3)

We see above that Calcium carbonate, when heated, makes calcium oxide and it also makes carbon dioxide.

Other carbonates do exactly the same thing:

• Copper carbonate, when heated, makes copper oxide and carbon dioxide
• Zinc carbonate, when heated, make zinc oxide and carbon dioxide 
• Magnesium carbonate, when heated, makes magnesium oxide and carbon dioxide
• Etc.

GCSE chemistry - unit 1 - covalent bonding

Covalent Bonding

A chemical bond between two or more non-metal atoms (these can be from the same element or from different elements as long as they are both non-metals.)

It involves the sharing of an electron. If both atoms need on electron to get a full outer shell they share an electron and become joined. They share a pair of electrons and now both have a full outer shell.

More than one other atom can join to one atom; if an atom need two electrons, two other atoms will join to share two pairs of electrons. In this case the two atoms will be different to the atom needing two electrons. See above right.

These are all now SIMPLE MOLECULAR COMPOUNDS with strong bonds. However covalent bonding can also form giant covalent structures such as diamonds or graphite.

Chemistry AQA - unit 1 - ionic bonding

Ionic Bonding

A chemical reaction between a metal and a non-metal.

Atoms from group 7 in the periodic table are very reactive because they have 7 electrons in their outer shell and need just one more to become stable; because all atoms want to become stable. Similarly atoms in group one and two are very reactive because they are so close to a full outer shell they just need to loose one electron.

Therefore if one needs and electron and the other wants to get rid of an electron a transfer of electron happens. The non-metal (e.g halogen) always gains the electron because it it so close to a full shell and the metal always looses because it needs to get rid of one to show the full shell underneath.

METAL ALWAYS LOOSES THE ELECTRON
NON-METAL ALWAYS GAINS THE ELECTRON

Because the metal has lost an electron, it overall charge is now positive because it has more protons than electrons. And because the non-metal has gained an electron it has an overall negative charge. We say they've formed negative/positive ions. An ion is an atom that's lost or gained an electron.

METAL BECOMES POSITIVE ION
NON-METAL BECOMES NEGATIVE ION

This can happen with one or more electron. If the metal looses one electron it has a charge of +1 and if it looses two it has a charge of +2. And the same for the non-metal but with a minus charge.

The positive and negative ions then attract (opposites attract) and this creates strong bonds into a ionic lattice and structure formed by strong attraction.

The new structure is stable as there is no need for it to react because both of its substances have full outer shells.

CHEMISTRY - unit 1 - the periodic table

CHEMISTRY - UNIT 1

The periodic table - shows the elements in order of increasing atomic number

Elements in the same group in the periodic table have similar chemical properties. This is because their atoms have the same number of electrons in their outer shells.

GROUP 1 - alkali metals

• Low melting and boiling points
• Low densities
• React quickly with water and oxygen to produce hydroxides and oxides
• Their hydroxides and oxides dissolve in water to form strong alkali solutions.

GROUP 0 - noble gasses

• Very unreactive because they have full outer shells

All atoms want complete outer shells. Atoms in group 1 are very reactive because they want to get rid of their single outer electron (this would be easier than trying to get seven more). They are more reactive than transitional metals because they are closer to a full shell. Halogens are equally very reactive because they only need one electron to get a full outer shell. Noble gasses are very unreactive because they have a full outer shell so don't need to react. They are stable.

CHEMISTRY - unit 1 - basic ideas of chemistry

CHEMISTRY - UNIT 1 ATOMS

Atoms consist of ELECTRONS surrounding a nucleus containing PROTONS and NEUTRONS.

• NEUTRONS are neutral
• PROTONS have a charge of +1
• ELECTRONS have a charge of -1

The number of electrons is equal to the number of protons so atoms have no overall charge.

All substances are made up of these tiny particles called atoms.

• An element is made up of only one type of atom.

Structure of atoms

ATOMIC NUMBER is the number of protons an atom contains (therefore the number of electrons)

MASS NUMBER is the total number of protons and neutrons in the nucleus (usually the bigger no.)

E.g          35

                   Cl    has 17 protons and 35 protons                    ...............................and neutrons.

                17

    

      Chlorine therefore has 18 neutrons (35-17)

Periodic table - shows the elements in order

(part of the periodic table)

• The horizontal rows are periods and show the number of shells an atom has
• The vertical columns are groups and show how many electrons an atom has in its outer shell

Therefore all elements in period 4 have atoms that have 4 occupied shells and all elements in group 3 have atoms that have 3 electrons in their outer shell.

Electronic structure

The shells around atoms are energy levels.

The innermost shell can hold 2 electrons and the rest can hold 8, so we write 2,8,8,8 etc. depending on how many electrons an atom has (shown by the atomic number)

If sodium (Na) has an atomic number of 11, it has 11 electrons. We show it's electronic structure as 2,8,1 

• 2 electrons in the first shell (can only hold 2)
• 8 electrons in the second shell (can only hold 8)
• And 1 electron in the third shell (only 1 electron left)

Sodium will be found in group 1 because it has 1 electron in its outer shell.

The electronic structure diagram for sodium will be:

           

Use the periodic table to work out electronic structures:

1. Work out the period (rows) and draw that many circles (shells)
2. Look at the atomic number (bottom one) and draw on dots.  2 in the first and 8 from then on.

chemistry test on friday... all about bonds and structures

So 10M have a chemistry test next Friday on structures and bondings; you might find this a bit long but it has everything you need to know about structures and all that other stuff and I’ve kept it to a bare minimum so you don’t have to learn loads.

Chemistry

The different types of structure considered here are:

• Metallic (two metals)
• covalent bonds (two non-metals)
• ionic (non-metal and metal)

--------------------------------------------------------------------------------------------------------------------------

Metallic structure

A metallic structure consists of a giant lattice of positively charged ions and delocalised outer electrons.

Metals are malleable - they can be bent and shaped. This is because they consist of layers of atoms. These layers can slide over one another when the metal is bent, hammered or pressed.

Metals - Higher tier

Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.

Metals are good conductors of electricity and heat. This is because the free electrons can move throughout the metal.

 

 

 

 

--------------------------------------------------------------------------------------------------------------------------
 

 

A COVELANT BOND - is a strong bond between two non-metal atoms. It consists of a shared pair of electrons. A covalent bond can be represented by a straight line or dot-and-cross diagram.

Covalent molecular structure (between two non-metals)   A covalent molecular structure consists of discrete molecules held together by weak intermolecular forces, such as hydrogen bonds.

Covalent network structure

 

A covalent network structure consists of a giant lattice of covalently bonded atoms.

 

Covalent bonds form between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong. Covalently bonded substances fall into two main types:

1.    Simple molecules

2.    Giant covalent structures

PROPERTIES

Properties of simple molecular substances

·         Low melting and boiling points - This is because the weak intermolecular forces break down easily.

·         Non-conductive - Substances with a simple molecular structure do not conduct electricity. This is because they do not have any free electrons or an overall electric charge.

Properties of giant covalent structures

·         Very high melting points - Substances with giant covalent structures have very high melting points, because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600ºC.

·         Variable conductivity - Diamond does not conduct electricity. Graphite contains free electrons, so it does conduct electricity. Silicon is semi-conductive - that is, midway between non-conductive and conductive.

 

 -------------------------------------------------------------------------------------------------------------------------

 

 

IONIC BOND - An ionic bond is formed between metals and non-metals. The metal donates one or more electrons to the non-metal. This causes the metal to become positively charged (as it has lost at least one electron) and the non-metal to become negatively charges (as it has gained at least one electron). This attraction between the positive metal ions and the negative non-metal ions causes a bond (ionic bond) to be formed.

 

Ionic structure

An ionic structure consists of a giant lattice of oppositely charged ions.

An ionic bond is between a metal and a non-metal.

 

PROPERTIES

Melting points and boiling points

Ionic bonds are very strong so a lot of energy is needed to break them. Ionic compounds contain many of these strong bonds so they have high melting and boiling points.

Conduction of electricity

Ionic compounds conduct electricity when they are dissolved in water or when they are melted. This is because their ions are free to move and carry the current. However, ionic compounds do not conduct electricity when they are solid. This is because their ions cannot move around in their lattice structure.