AQA Additional Chemistry

Atoms consist of electrons surrounding a nucleus that contains protons and neutrons.

Netrons have no charge

Protons have a relative charge of +1

Electrons have a relative charge of -1

Atoms contain equal numbers of protons and electrons. Therefore the overall charge of any atom is exactly zero.

The number of protons in an atom is called its atomic number. In the periodic table atoms are arranged in atomic number order.

The electrons in an atom are arranged in energy levels or shells. The lowest energy level is nearest to the nucleus.

As electrons are negativley charged they are attracted towards the positvely charged nucleus.

The first energy level can contian a maximum of 2 electrons.The second energy level and above can contain a maximum of 8 electrons.

Atoms with the same number of electrons in their outer shell belong in the same group of the periodic table.

The number of electrons in the outer shell of an atom determines the way that the atom behaves in chemical reactions.

Elements which have full outer shells are very stable and unreactive. They are called Noble gases.

When two or more elements react they make a compound. The compund formed has different properties to the elements that reacted to together to form it. It is very difficult to reverse the reaction when it has taken place chemicaly.

When an atom has a full outer shell it is stable and unreactive. However when an atoms outer shell is not full, the atom tries to achive a full outer shell to become stable by either sharing electrons with another atom ( Covalent Bonding) or by tranfering electrons to or from another atom (Ionic Bonding).

In Ionic bonding, atoms involed either gain or lose electrons to achive a full outer shell. For example: Sodium two full shells and an extra electron = 2,8,1. In ionic bonding it will ose one electron, so it is left with a stable electronic structure = 2,8. But, it now has one more proton than it does electrons, so the particle then becomes charged positivley, a Sodium ion.  The formula of a sodium ion is Na+. The electronic structure of the sodium ion is [2,8]+.

Ionic compounds are usally formed when metals react with non-metals.

Ions formed are held together by extremely strong forces of attraction between opositely charged ions. This electrostatic force of attraction is called the ionic bond. These bonds result in the particles being arragnged in a giant structure.

We can represent the atoms and ions involved in forming ion by dot and cross diagrams.

Covalent bonding normaly takes place between non-metals. When they react together they share electrons to form molecules.

The atoms of no metals normaly need to gain electrons to achieve a stable outer shell .The atoms in the molecules are then held together because they are sahring pairs of electrons. The strong bonds between the atoms are called covalent bonds.

Most substances containing covalent bonds conisist of small molecules e.g water. However, some have giant structures where huge numbers of atoms are held together by a network of covalent bonds e.g Diamonds or Silicon dioxide.

Metals bond to form giant structures. Metals are a lattice of metal atoms (or positively charged ions) arranged in regular layers.

The outer electrons in a metal are free to move from one atom to another. They form a 'sea of delocalised electrons' surrounding positively charged metal ions. Strong electrostatic attraction between electrons and the ions bond the metal ions together.

Metals are made up of a number of small crystals. These are called grains and the place where they join are the grain bounbaries.

Steel is protected from rusting by being dipped in zinc. This process is called Galvanising. Galvanised steel is used to make channels for carrying insulated electric wires.

Ionic compounds consist of gaint structures of ions arranged in a lattice. The attractive electrostatic forces between the oppositely charged ion act in all directions and they are also very strong. This hold the ions together in the lattice tightly.

As the forces between the ions are very strong it takes allot of energy to break the lattice apart. So, Ionic compunds have high melting points and boiling points.

In a liquid, the ions are free to move and are no longer within the lattice. This means that the substance can now carry and electrical charge. A solid ionic substance cannot because the ions cannot move within the lattice.

Also if dissolved in water, ionic compounds can conduct electricity because in the solution the ion are free to move around.

Covalently bonded substances tend to have low melting and boiling points. This means that many of convalently bonded substances are liquids or gases at room temperature. Other solids have low melting points e.g Iodine and sulfur.

Covelent bonds are very strong, so the atoms within each molecule are held very tightly together. However, each molecules have very weak intermolecular forces so breaking these force doesnt require much energy.

A simple molecule will not conduct electricity as a liquid because the subsatnce has no overal charge, so cannot conduct an electrical charge.

Atoms consist of electrons surrounding a nucleus that contains protons and neutrons.

Netrons have no charge

Protons have a relative charge of +1

Electrons have a relative charge of -1

Atoms contain equal numbers of protons and electrons. Therefore the overall charge of any atom is exactly zero.

The number of protons in an atom is called its atomic number. In the periodic table atoms are arranged in atomic number order.

Some covalent substances form large networks of covelent bonds. These are called Giant covalent structures.

Sustances such as diamond, graphite, silicon dioxide and fullerenes have giant covalent structures. These subsatnces tend to be very hard, have high melting and boling points and are very chemicaly unreactive.

Graphite is another example of a giant covalent structure. Graphite is arranged in giant layers. There are only weak forces between the layers so they slide over each other eaisily. It also has free electrons within its structure, so it can conduct electricity. Graphite layers are arranged in hexagons, so each carbon atom in joined to three others, leaving one electron spare on each atom. This electron becomes delocalised.  

The electrons in an atom are arranged in energy levels or shells. The lowest energy level is nearest to the nucleus.

As electrons are negativley charged they are attracted towards the positvely charged nucleus.

The first energy level can contian a maximum of 2 electrons.The second energy level and above can contain a maximum of 8 electrons.

Atoms with the same number of electrons in their outer shell belong in the same group of the periodic table.

The number of electrons in the outer shell of an atom determines the way that the atom behaves in chemical reactions.

Elements which have full outer shells are very stable and unreactive. They are called Noble gases.

We can change the shapes of metals because the layers of atoms in a pure metal are able to slide over easch other easily.

Metals conduct heat and electricity as a direct result of the ability of the delocalised electrons to flow through the giant metallic lattice.

When two or more elements react they make a compound. The compund formed has different properties to the elements that reacted to together to form it. It is very difficult to reverse the reaction when it has taken place chemicaly.

When an atom has a full outer shell it is stable and unreactive. However when an atoms outer shell is not full, the atom tries to achive a full outer shell to become stable by either sharing electrons with another atom ( Covalent Bonding) or by tranfering electrons to or from another atom (Ionic Bonding).

In Ionic bonding, atoms involed either gain or lose electrons to achive a full outer shell. For example: Sodium two full shells and an extra electron = 2,8,1. In ionic bonding it will ose one electron, so it is left with a stable electronic structure = 2,8. But, it now has one more proton than it does electrons, so the particle then becomes charged positivley, a Sodium ion.  The formula of a sodium ion is Na+. The electronic structure of the sodium ion is [2,8]+.

The mass of the proton and a neutron are the same .

The relative mass of a neutron compared to a proton is 1. However, Electrons have a negligible mass.

The mass of an atom is found in the nucleus, so the total number of protons and neutrons in an atom is its mass number.

Mass number =     12

                                    C

 Atomic number =    6

Ionic compounds are usally formed when metals react with non-metals.

Ions formed are held together by extremely strong forces of attraction between opositely charged ions. This electrostatic force of attraction is called the ionic bond. These bonds result in the particles being arragnged in a giant structure.

We can represent the atoms and ions involved in forming ion by dot and cross diagrams.

 Mass numer - atomic number = number of protons

Isotopes:

Atoms of the same element always have the same number of protons but Isotopes are atoms of the same element that have different numbers of neutrons. 

For example: carbon-12 and carbon-14 both have 6 protons but carbon-14 has 8 neutrons and carbon-12 has 6. 

Sometimes, when and isotope has an extra neutron it make the nuleus unstable and become radioactive. However, not all isotopes are radioactive.

Different isotopes have different physical properties but always have the same chemical properties.

Covalent bonding normaly takes place between non-metals. When they react together they share electrons to form molecules.

The atoms of no metals normaly need to gain electrons to achieve a stable outer shell .The atoms in the molecules are then held together because they are sahring pairs of electrons. The strong bonds between the atoms are called covalent bonds.

Most substances containing covalent bonds conisist of small molecules e.g water. However, some have giant structures where huge numbers of atoms are held together by a network of covalent bonds e.g Diamonds or Silicon dioxide.

Chemical equations show how many atoms are need of reactants to make the products. But when the reaction takes place we need to know what amounts to use in grams or cm . A chemical equation may show you that twice as many atoms are needed for a rection than another substance but this does not mean that the substance will be twice the mass of the other substance as all atoms have different masses.

Relative atomic masses (Ar): Instead of working with the real masses of atoms, we focus on the relative masses of atoms.

For example, an atom of carbon as a standard atom is given a mass of 12 units because it has 6 protons and 6 neutron. All the other masses of other atoms are compared to this standard carbon atom. The relative atomic mass is normaly the same as the elements mass number.

The relative ionic mass of an ion is the same as the relative atomic mass of that element.

Metals bond to form giant structures. Metals are a lattice of metal atoms (or positively charged ions) arranged in regular layers.

The outer electrons in a metal are free to move from one atom to another. They form a 'sea of delocalised electrons' surrounding positively charged metal ions. Strong electrostatic attraction between electrons and the ions bond the metal ions together.

Metals are made up of a number of small crystals. These are called grains and the place where they join are the grain bounbaries.

Steel is protected from rusting by being dipped in zinc. This process is called Galvanising. Galvanised steel is used to make channels for carrying insulated electric wires.

Relative formula masses ( Mr ) :

The relative formula mass of chemical compunds is simply the elements involed atomic masses added together. E.g soduim clhoride's atomic mass is:

23 + 35.5 = 58.5

Ar + Ar = Mr

In water its: (Ar x 2) + Ar = Mr

Moles = relative atomic mass in grams or relative formula mass in grams

The Ar of an element is one mole. One mole of any substance always contains the smae number of particles.

Ionic compounds consist of gaint structures of ions arranged in a lattice. The attractive electrostatic forces between the oppositely charged ion act in all directions and they are also very strong. This hold the ions together in the lattice tightly.

As the forces between the ions are very strong it takes allot of energy to break the lattice apart. So, Ionic compunds have high melting points and boiling points.

In a liquid, the ions are free to move and are no longer within the lattice. This means that the substance can now carry and electrical charge. A solid ionic substance cannot because the ions cannot move within the lattice.

Also if dissolved in water, ionic compounds can conduct electricity because in the solution the ion are free to move around.

Working out the amount of a element in a compound.

To calculate the percentage of a element in a compound, you: divide the relative atomic mass of the element by the relative forumla mass of the compund.

We can work out the ratio of the number of atoms by dividing the mass of each element by it relative atomic mass

Covalently bonded substances tend to have low melting and boiling points. This means that many of convalently bonded substances are liquids or gases at room temperature. Other solids have low melting points e.g Iodine and sulfur.

Covelent bonds are very strong, so the atoms within each molecule are held very tightly together. However, each molecules have very weak intermolecular forces so breaking these force doesnt require much energy.

A simple molecule will not conduct electricity as a liquid because the subsatnce has no overal charge, so cannot conduct an electrical charge.

The mole mass of water is

Ar of hydrogen = 1  ....so mass of 1 mole of H2 = 2 x 1 = 2g

Ar of oxygen = 16 .... so mass of 1 mole of O2 = 2 x 16 = 32g

Mr of water = (16+2)= 18 .... so mass of 1 mole of water is = 18g

Calculations:

100g of sodium hydroxide is 100 divided by the mass of one mole of sodium hydroxide (40g) = 2.5 moles.

If in a chemical equation we were told that for every 2 moles of sodium hydroxide we need 1 mole of chlorine.  So, we need 2.5 divide by 2 = 1.25 moles of chlorine. 1 mole of chlorine has a mass of 71g so we need 1.25 x 71 = 88.75g of chlorine to react with 100g of sodium hydroxide.

Some covalent substances form large networks of covelent bonds. These are called Giant covalent structures.

Sustances such as diamond, graphite, silicon dioxide and fullerenes have giant covalent structures. These subsatnces tend to be very hard, have high melting and boling points and are very chemicaly unreactive.

Graphite is another example of a giant covalent structure. Graphite is arranged in giant layers. There are only weak forces between the layers so they slide over each other eaisily. It also has free electrons within its structure, so it can conduct electricity. Graphite layers are arranged in hexagons, so each carbon atom in joined to three others, leaving one electron spare on each atom. This electron becomes delocalised.  

Percentage yield = (amount of product produced divided by the maximum amount of product possible) X 100

Atom economy: The amount of starting products that end up as useful products is called the atom economy.

Percentage atom economy = ( relative formula mass of the useful product divided by the relative formula mass of the reactants) X 100

We can change the shapes of metals because the layers of atoms in a pure metal are able to slide over easch other easily.

Metals conduct heat and electricity as a direct result of the ability of the delocalised electrons to flow through the giant metallic lattice.

In a reversible reaction the products of the reaction can react to make the original reactants.

In a closed system the rate of the foward and backward reactions are equal at equilibrium. Equalibrium = Th point at which a eversible reaction takes place at exactly the same rate in both directions.

When starting with the reactants in a reversible reaction, the rate of the foward reaction is greater than the rate of the backward reaction. As the rate of the foward reaction builds the amount of products produced and the foward rate begins to slow, the rate of the backward reaction begins to increase. Untill eventualy the rates equal out and become the same.

Changing the conditions of the reaction can change the amounts of products and reactants in a reaction mixture.

The mass of the proton and a neutron are the same .

The relative mass of a neutron compared to a proton is 1. However, Electrons have a negligible mass.

The mass of an atom is found in the nucleus, so the total number of protons and neutrons in an atom is its mass number.

Mass number =     12

                                    C

 Atomic number =    6

 Mass numer - atomic number = number of protons

Isotopes:

Atoms of the same element always have the same number of protons but Isotopes are atoms of the same element that have different numbers of neutrons. 

For example: carbon-12 and carbon-14 both have 6 protons but carbon-14 has 8 neutrons and carbon-12 has 6. 

Sometimes, when and isotope has an extra neutron it make the nuleus unstable and become radioactive. However, not all isotopes are radioactive.

Different isotopes have different physical properties but always have the same chemical properties.

Chemical equations show how many atoms are need of reactants to make the products. But when the reaction takes place we need to know what amounts to use in grams or cm . A chemical equation may show you that twice as many atoms are needed for a rection than another substance but this does not mean that the substance will be twice the mass of the other substance as all atoms have different masses.

Relative atomic masses (Ar): Instead of working with the real masses of atoms, we focus on the relative masses of atoms.

For example, an atom of carbon as a standard atom is given a mass of 12 units because it has 6 protons and 6 neutron. All the other masses of other atoms are compared to this standard carbon atom. The relative atomic mass is normaly the same as the elements mass number.

The relative ionic mass of an ion is the same as the relative atomic mass of that element.

Relative formula masses ( Mr ) :

The relative formula mass of chemical compunds is simply the elements involed atomic masses added together. E.g soduim clhoride's atomic mass is:

23 + 35.5 = 58.5

Ar + Ar = Mr

In water its: (Ar x 2) + Ar = Mr

Moles = relative atomic mass in grams or relative formula mass in grams

The Ar of an element is one mole. One mole of any substance always contains the smae number of particles.

Working out the amount of a element in a compound.

To calculate the percentage of a element in a compound, you: divide the relative atomic mass of the element by the relative forumla mass of the compund.

We can work out the ratio of the number of atoms by dividing the mass of each element by it relative atomic mass

The mole mass of water is

Ar of hydrogen = 1  ....so mass of 1 mole of H2 = 2 x 1 = 2g

Ar of oxygen = 16 .... so mass of 1 mole of O2 = 2 x 16 = 32g

Mr of water = (16+2)= 18 .... so mass of 1 mole of water is = 18g

Calculations:

100g of sodium hydroxide is 100 divided by the mass of one mole of sodium hydroxide (40g) = 2.5 moles.

If in a chemical equation we were told that for every 2 moles of sodium hydroxide we need 1 mole of chlorine.  So, we need 2.5 divide by 2 = 1.25 moles of chlorine. 1 mole of chlorine has a mass of 71g so we need 1.25 x 71 = 88.75g of chlorine to react with 100g of sodium hydroxide.

Percentage yield = (amount of product produced divided by the maximum amount of product possible) X 100

Atom economy: The amount of starting products that end up as useful products is called the atom economy.

Percentage atom economy = ( relative formula mass of the useful product divided by the relative formula mass of the reactants) X 100

In a reversible reaction the products of the reaction can react to make the original reactants.

In a closed system the rate of the foward and backward reactions are equal at equilibrium. Equalibrium = Th point at which a eversible reaction takes place at exactly the same rate in both directions.

When starting with the reactants in a reversible reaction, the rate of the foward reaction is greater than the rate of the backward reaction. As the rate of the foward reaction builds the amount of products produced and the foward rate begins to slow, the rate of the backward reaction begins to increase. Untill eventualy the rates equal out and become the same.

Changing the conditions of the reaction can change the amounts of products and reactants in a reaction mixture.