C4- Structure and Bonding Revision

1. What is the charge of an electron? 

2. What is the charge of a neutron?

3. What is the overall charge of an atom?

4. Which particle is the heaviest: proton or neutron?

5. Where are the metals located on the periodic table?

6. Name an element that is a gas at room temeperature?

7. What is the name of the elements located in group 1?

8. What is the middle section of the Periodic table called?

When two or more elements chemically react together they form a compound.

This can be achieved through ionic bonding, which involves an atom losing or gaining electrons. When this happens the atoms become charged forming ions.

The atoms that lose electrons become positivey charged and the atoms that gain electrons become negatively charged.

The atoms within the compound are more stable because they have a complete outer electron shell. 

Why do ionic substances have high melting points?

Ionic substances have high melting points because there are stong electrostatic attractions between oppositely charged ions. 

1. Ionic bonding occurs between what type of elements?

2. What type of ions are formed when an atom looses an electron?

3. Statement: Group 6 elements want to gain 2 electrons.

4. Why do group 0/8 elements(noble gases) not gain/loose electrons to form ions?

5.Being able to conduct electricity is a property of ionic structures. A) What is the name of these structures? B) Do ionic substances conduct electricity when solid? Explain.

6. What is the other property of ionic substances? 

All solid salts do not conduct electricity.

All molten salts do conduct electricity. 

All solutions of soluable salts do conduct electricity. 

Salts such as sodium chloride are made up of ions. An ion is a charged atom. Sodium Chloride is made from Na+ ions and Cl- ions. These oppositely charged ions attract eachother.

A crystal of sodium chloride is made from millions of sodium and chloride ions packed tightly together. In the solid, these ions cannot move towards the electrodes and so the compound cannot coduct electricity.

When the solid is molten or dissolved the ions in the structure seperate close together. This means that the ions are now free to move and so can conduct electricity.

During electrolysis the negative electrode attracts the positive ions and the positive electrode attracts the negative ions. This is because oppositely charges attract eachother. 

Properties of metals

• High melting and boiling point
• Malleable
• Shiny
• Conduct Electricity
• Conduct heat
• Expand when heated 
• Hard
• Strong(tensile strength)
• Dense 
• Ductile

Metals are made up of atoms that are: 

• arranged in a regular pattern
• packed closely together

 Particles  in a metal are held together by strong metallic bonds. It takes alot of energy to seperate the particles. This is why they have high melting and boiling points.

The Proccess

• In a solid metal the atoms lose their free electrons from their outer shell amd become positively charged atoms.
• a sea of free(delocalised) electrons drift freely between metal atoms.
• The attraction of the 'sea' of negative electrons and positively charged metal ions hold the structure together. 
• Overall, the metal crystal is not charged because the total negative charge on the electrons balances the total charge on metal ions.
• The electrons can move freely through the structure which allows an electric current to flow from one end to another.

Why are metals such good electrical conductors? 

Metals contain electrons that are free to move in the metal structure, carrying charge from one place to another and allowing metals to conduct electricity well.

Why are metals shiny?

Metals are shiny because they contain free electrons that vibrate when they come in contact with light. When the electrons vibrate, they produce their own light. This is reflected back and is what creates the shiny appearance.

Malleability: the physical property of metals which defines their ability to be hammered, pressed or rolled into thin sheets or different shapes without breaking. Saying something is malleable, it means the particles od an object can slide onto eachother.

Ductility: the ability of a solid to deform under tensile strength(the amount of strain a material can withstand). This means it can be stretched out into a wire.

A covalent bond is formed between non metal atoms, which combine together by sharing electrons. Covalent compounds have no free electrons and no ions so they don't conduct electricity.

When two or more atoms bond together by sharing electrons we call it Covalent bonding. This type of bonding occurs between non metal atoms. It caused the atom in the molecule to  be held together very strongly but there are weak forces between individual molecules. This is why covalently bonded molecules  have low boiling and melting. (i.e. they are usually liquid or gas). 

Metallic Bonding: A metallic bond is the electostatic force between free electrons and metal ions. Metallic bonds are strong which is why metals maintain their regular lattic structure and have high melting and boiling points ( because lots of energy is required to break the bonds holding the particles together). 

Ionic Bonding: Occurs between non metals and metals. It is when the atoms lose or gain electrons in order to have a complete outer shell and be more stable. 

Covalent Bonding: The sharing of a pair/pairs of electrons between atoms and only occurs between non metals, it causes the atom in the molecule to be held together very strongly but there are weak forces between individual molecules.

Allotropes - structurally different forms of the same element.

Diamond

• made from only carbon atoms
• every carbon makes four covalent bonds to acheive a full outer shell
• every carbon atom is bonded to four other carbon atoms
• therefore the structure carries on growing

Properties

• Hard to scratch
• very high melting and boiling points
• when diamonds are cut light can be reflected of the diamond to make them shiny
• doesn't conduct electricity.

Graphite

Graphite is made only from carbon atoms. Every carbon atom makes four covalent bonds to achieve a full outer shell. Every carbon atom is bonded to three other atoms.

The covalent bonds form a hexagon pattern. The hexagons are flat forming sheets which stack in layers. Between the sheets are delocalised electrons ( which are free to move ) allowing the thin layers to slide over each other making the substance soft and slippery ( also so as a pencil it can make marks on paper).

Properties

• high melting and boiling points
• insoluble
• conducts electricity due to free moving electron
• soft (used as pencil)
• slippery (used as lubricant for machinery)

Atoms:

• have a tiny nucleus which contains Protons and Neutrons ( also known as nucleons)
• have electrons which orbit around the outside of the nucleus arranged in shells ( energy levels)

The closer the electron shell is to the nucleus the lower the energy level.

The first shell arranged around the nucleus can only hold two electrons the other shells after that can hold 8 electrons.

The nucleus is the centre of mass of an atom and has a positive charge.

The overall charge of the atom is neutral as the proton ( + ) and electron ( - ) cancel eachother out.

• The metals are located on the left hand side all the others are non-metals.
• Ther periodic table is split into groups along the top from 1-8(0) and into periods going down from 1-7.
• The Group number tells you how many electrons there are in the outer shell.
• The Period number tells you how many shells the element has.

When looking at the individual elements : 

• top number = relative atomic mass ( which is the total number of protons and neutrons in the nucleus)
• Bottom number = atomic (proton) number ( which determines the number of protons and electrons).

Number of Protons + number of neutrons = relative atomic mass

Number of protons = number of protons

relative atomic mass - proton number = number of neutrons

Properties e.g melting points, change across a period.these changes are called  trends.

• Elements in group 0 have full electron shells and are inert ( they are very unreactive)
• Group 1 - The alkali metals
• Group 2 - The alkaline earth metals
• Group between 2 and 3 - The transition metals
• Group 7 - Halogens
• Group 0 - The noble gases ( Helium)

All elements in group 1 :

• are metals
• have one electron in their outer shell of their atoms
• soft ( easily cut with a knife)
• react with water ( the reaction gets more violent as you move down group 1)
• flammable
• their hydroxides are harmful and corrosive

The physical properties of Group 1 e.g melting point, boiling point and density show trends down the group.

Therefore when handling group 1 metals keep them away from water and naked flames.

During the reaction with water hydrogen gas is formed (which pops when lit) and makes a metal hydroxide which is an alkali ( turning the pH indicator blue ).

Metal + water ---> metal hydroxide + hydrogen

Group 7 elements: 

• contain diatomic molecules ( meaning they have 2 atoms joined together in each molecule)e.g

  F₂ , Cl₂, Br₂ , I₂ , At₂ - elements going down order

• corrosive and toxic elements (so are kept in a fume cupboard)
• group 7 elemnts react with alkali metala and  with other metals such as iron to form metal halides.
• melting and boiling points increase down the group whilst reactivity decreases.
• All have 7 electorns in the outer shellwhen a more reactive halogen takes the place of a less reactive halogen in a compound it is called a displacement reaction.e.g. when chlorine water solution is added to bromide solution the chlorine displaces the orange-coloured bromine.For non-metals the smaller the atom (the fewer the electron shells) the more reactive the element is.

Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds. The atoms are usually arranged into giant regular lattices- extremely strong structures because of the many bonds involved.

Examples of giant covalent structures and their properties

Silicon dioxide (Sio₂) - commonly known as glass. Silicon and oxygen are both non-metals so they make covalent bonds.

• cannot conduct electricity
• insoluble
• high melting and boiling points
• hard

Simple covalent molecules only contain a few atoms held together by strong covalent bonds. An example is carbon dioxide (CO2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen.

Simple covalent substances have low melting and boiling points.This is because although they have strong bonds between the atoms ; there are weak forces holding the molecules together.When the simple substance melts or boils the weak intermolecular forces break, not the strong covalent bonds therefore they have low melting and boiling points.

Graphite is soft whereas diamond is hard because graphite has covalent  bonds which joins each carbon atom to three of its neighbours.The three bonds are distributed in two dimensions, making flat sheets of hexagons. Each atom has one outer shell electron which has not been used to make a covalent bond. This free electron can drift between the gaps in the layers.Therefore there is a weak bond holding the layers together so that it is soft. ( the weak forces allow layers to slide of each other allowing it to conduct electricity but diamond has no charged particles that are free to move so it is an insulator diamond has strong covalent bonds holding its carbon atoms together - this makes it hard to break and cut.

In 1828, Dobereiner put the elements into group based on their chemical properties. He put the elements into groups of three called, which he called triads.  The middle element of each trade had a relative atomic mass that was the average of the other two. E.g.: 7 of lithium plus 39 of potassium divided by two was 23 the RAM of Sodium.

In 1864,Newlands noticed that when you arranged the elements in order of relative atomic mass, every eighth element had similar properties.These sets of eight were called "Octaves".He left no gaps for new elements to be discovered so his work was ignored.He mixed up metals and non-metals e.g.: oxygen and iron and his group contained elements that didn't have any similar properties, e.g.: carbon and titanium. 

Dmitri Mendeleev was a Russian chemist and inventor and was born near Tobolsk in Siberia in 1834. In 1869, Dmitri Mendeleev in Russia, armed with about 50 known elements, arranged them into his Table of Elements- with various gaps. He put the elements in order of atomic mass (like Newlands did), left gaps in order to keep elements with similar properties in the same vertical groups and was prepared to leave some very big gaps in the first two rows before the transition metals come in on the third row. The gaps were useful as they predicted the properties of so far undiscovered elements. When they were found out, the elements did fit the pattern and helped confirm Mendeleev's ideas.Through the use of the table, he predicted the properties of elements yet to be discovered.

Mendeleev found he could arrange the 65 elements then known in a grid or table so that each element had:

1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0).

2. Similar chemical properties to other elements in the same column - in other words similar chemical reactions. Magnesium, for example, is placed in the alkali earths' column.

The modern Periodic Table is based on Dmitri Mendeleev’s ideas. Data about properties of elements can be used to work out trends and make predictions.  

Ionic bonding is the complete transfer of electrons. Unstable atoms (atom's without a full outer shell) lose or gain electrons to complete their outer shell so they are stable.

• Ionic bonds form when a metal reacts with a non-metal.
• Metals form positive ions whilst non-metals form negative ions.
• Ionic binds are the electrostatic forces of attraction between oppisitely charged ions.
• They form Ionic compounds with charged ions which are arranged in a regular pattern called a giant ionic crystal lattice.

• Litosphere- land
• Hydrosphere - water
• atmosphere - air

Useful materials we extract  from the Lithosphere are : coal, oil, gas , aluminium ,zinc, iron, copper,diamond , graphite and building materials such as clay , stone and gravel.

Relative atomic mass = the mass of a atom compared to the mass of an atom of carbon which is giventhe value of 12.

Relative formula mass = the sum of the realtive atomic masses of all the atoms or ions shown its formula.

e.g. hydrogen atomic mass = 1 and oxygen = 16

so formula mass = 2 x 1 + 16 = 18