Chemistry HT2

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  • Created by: Jess4989
  • Created on: 20-12-17 16:49

Bonding

There are three main types of strong bonds in Chemistry. 

IONIC BONDING - Ionic bonding occurs between a metal and a non-metal. The particles in the ionic bond are oppositely charged IONS. The bond is essentially the attraction between the oppositely charged atoms. 

COVALENT BONDING - Covalent bonding occurs between non-metals. It involves sharing electrons between the atoms. The attraction is between the shared electrons and posotive nucleus of the atoms in the bond. 

METALIC BONDING - Metalic bonding occurs between metals and alloys. The attraction is between the metal ions and the mobile electrons. 

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Atomic Structure

23 (Mass number)

Symbol representation of sodium is                      Na

11(Atomic number)

Atomic number = Number of protons = Number of electrons

Mass number    = Number of protons +  number of electrons

Therefore, Sodium has 11 protons and 11 electrons and 12 neutrons. 

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Ionic bonding

Ionic bonded compounds are made up of IONS. Ions are charged particles, they can be posotively charged and negatively charged. 

Posotive ions (Cations)

Posotive ions are formed by the LOSS of electrons. Electrons are negatively charged particles. When they leave the electrons leave the atom the atom becomes posotively charged. 

Na wants to loose an electron to obtain a full outershell. This gives it stability. All group 1 electrons have 1e- in the outershell so group 1 elements form +1 ions. 

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Ionic bonding 2

All group 2 elements have 2 electrons in their outershell. They all loose 2e- to obtain a full outershell. This gives them stability. All group 2 elements form +2 ions. 

All group 3 elements have 3 electrons in their outershell. They all loose 3e- to obtain a full outershell. This gives them stability. All group 3 elements (if they form ions) form +3 ions. 

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Ionic bonding 3

Negative ions (anions)

Negatively charged ions are formed by GAINING electrons. Electrons are negatively charged making the overall charge on the atom negative. 

Nitrogen also wants a full outer shell, this is acheived by gaining 3- electrons. All group 5 elements, if they form ions form -3 ions. 

All group 6 elements have 6e- in the outershell. They prefer to gain 2e- to obtain a outershell. All group 6 elements form -2 ions.

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Ionic bonding 4

All group 7 elements have 7 electrons in the outershell and therefore will gain 1 electron to obtain a full outershell. They all form -1 ions. 

GROUP 4 DO NOT FORM IONS AND GROUP 8 ALREADY HAVE A FULL OUTER SHELL

Ionic bonding occurs between METALS and NON-METALS forming a compound. During the REACTION, electron transfer occurs FORMING IONS. NEGATIVE and POSOTIVE ions are FORMED. These posotive and negative ions are ATTRACTED to each other. AN IONICALLY BONDED COMPOUND IS FORMED. 

 The sodium needs to loose one electron to obtain a full outershell while the chlorine needs to accept one to gain s full outershell. Sodium therefore gives up its electron to chlorine forming a sodium and chloride ion

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Ionic bonding 5

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Ionic bonding 6

Ions are attracted to each other because of their oppositely charges. ELECTROSTATIC FORCES

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Deducing formulae of ionically bonded compounds

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Giant Ionic Structures

Ionically bonded compounds adopt a GIANT IONIC STRUCTURE. 

THEY DO NOT EXIST AS MOLECULES

(http://www.expertguidance.co.uk/wp-content/uploads/2017/09/image019.png)           

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Giant Ionic Structures

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Giant Ionic Structures 2

Sodium Chloride           Magnesium Chloride

Na+       Cl-                   Mg2+           Cl-

Magnesium Chloride should have the higher melting point compared to sodium chloride. This is because the electrostatic attraction between the magnesium ion with the two posotive charges and the chloride ion will be stronger than between the sodium ion (one posotive charge) and the chloride oin. Mg 2+ ion is also smaller than Na+. (There is more pull power with 2+. The atom with the higher charge will always have the higher melting point.)

Ginat ionic structures DONT conduct electricity in the solid state, but can conduct electricity in the molten (liquid) or aqueous state(dissolved in water)

-ions cannot move in the solid state 

-ions can move in the molten (liquid) state

-Ions can move in the aqueous (dissolved in water) state. 

FOR THE IONICALLY BONDED COMPOUNDS TO CONDUCT ELECTRICITY THE IONS MUST BE ABLE TO MOVE. 

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Electrolytes

An electrolyte is a substance which does not conduct electricity in the solid state but does conduct electricity in the molten (liquid) or aqueous state. 

Common electrolytes are ionially bonded compounds e.g. Sodium chloride, acids and alkalis. These compounds are made up of IONS. Ions are charged particles. Ions can be nagatively or posotively charged. 

Why do electrolytes conduct electricity in the molten or aqueous state. 

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Electrolytes 2

The posotive ions move for the negative electrodes.

The negative ions move for the posotive electrodes. 

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Building Molecules

Hydrogen 

Water

Methane

Hydrogen Chloride

Oxogen

Carbon Dioxide

Ethanol

Ammonia

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Molecules and covalent bonding

Molecules are groups of atoms joined together by sharing pairs of outer electrons. The bonds are called COVALENT BONDS. A single line (-) is a SINGLE BOND. A double line (=) is a DOUBLE BOND. Triple bonds are possible.

Some simple molecules

Water,H O           H-O-H                                       Methane,CH                H-C-H

Ammonia,NH     H-N-H                                         Carbon dioxide,CO        O=C=O

Hydrogen Chloride,HCl    H-Cl                             Oxygen, O                  O=O

Nitrogen, N      N=N                                              Ethanol, C H O         H-C-C-O-H

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Dot and Cross diagrams -covalent bonding

Covalent bonding occurs between non-metals and it involves sharing  electrons to obtain a full outershell. 

Hydrogen, H

Each H atom has 1e- in its 1st shell. Both need an extra electron to complete their outershell. The two electrons are shared between the two H atoms to produce a covalent bond. i.e. 2 electrons sharing between two atoms. 

H-H, single line represents 1 electrom pair i.e. 2 electrons shared between the two atoms.

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Dot and Cross diagrams -covalent bonding 2

Oxogen, O

Each O atom has 6 electrons in its outershell. They each need 2e- to complete their outershells. Therefore 2 electron pairs i.e. 4 electrons are shared between the  two oxogen atoms. A DOUBLE bond exists. O=O

Methane, CH

Due to the sharing of electrons between carbon and hydrogen, both carbon and hydrogen have a full outershell. 

                                H-C-H (2 electrons are being shared between the two atoms)

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Dot and Cross diagrams -covalent bonding 3

Water, H O

Electrons are shared between each atom soe ach obtains a full outer shell.

   O            (2 electrons shared between O and H)

Ammonia, NH

Both N and H obatain full outershells by sharing electrons. 

N-H (two electrons sharing)

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Dot and Cross diagrams -covalent bonding 4

Hydrogen Chloride, HCl

Full outershells for chlorine and hydrogen are acheived by sharing 1 pair of electrons (2e-) between the two atoms

H-Cl

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Structures adopted by covalently bonded compounds

There are two types of structure adopted by covalently bonded compounds. 

-SIMPLE MOLECULES

-GIANT COVALENT STRUCTURES 

Simple Molecules

Simple molecules have LOW melting points and boiling points. Hence they are usually liquids or GASES at room temperature. If they are solids then they will melt very EASILY. Examples of solids which are molecules are, SULFUR and IODINE.

The covalent bonds WITHIN the molecules are STRONG and these bonds are not BROKEN when the substance melts or boils. It is the forces BETWEEN the molecules which are broken. These forces are called INTERMOLECULAR FORCES and are WEAK. They do not require a lot of energy to break. This is why molecules have low MELTING POINTS and boiling points.

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Structures adopted by covalently bonded compounds

Cl                   Cl          Strong covalent bond.

                                    Weak intermolecular forces between molecules.

Cl                   Cl

As the molecule gets larger the intermolecular forces between the molecules increase, so they have higher melting points compared with small molecules. Therefore, a molecule like C H  will have stronger intermolecular forces betwee its molecules compared with C H

Simple molecules do not conduct electricity because they do not have any mobile ELECTRONS. They are involved in bonding.

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Giant Covalent Structures

Substances like DIAMOND, GRAPHITE and SILICON DIOXIDE all adopt a giant structure. These giant lattices contain ATOMS which are covalently bonded. These atoms are in a giant lattice with strong covalent bonds holding them in position. 

  • They dont conduct electricity (exept graphite)
  • They have hight melting and boiliing points
  • They are insoluble in water

DIAMOND                   

-Diamond is a very hard substance. This is because its carbon atoms are bonded to four other carbon atoms. These atoms are bonded together with strong covalent bonds in a giant structure.

-Diamond does not conduct electricity as they do not have any mobile electrons or ions in its structure.

-It has a high melting point because alot of energy is needed to break the strong covalent bonds.

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Giant Covalent Structures 2

SILICON DIOXIDE

-Like diamond, silicon dioxide does not conduct electricity as it has no mobile electrons or ions in its structure.

- Its melting point is high due to alot of energy needed to break the strong covalent bonds between the atoms in the giant covalent structure.

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Graphite

GRAPHITE

Graphite is another form of carbon. It is a giant structure, but the atoms are ARRANGED DIFFERENTLY to diamond. (forms something different)

-Graphite is an example of a giant covalent structure which CAN conduct electricity. It does not contain ions, but instead is made up of carbon atoms. Not all of the carbon's electrons are tied up in covalent bonds. Some are DELOCALISED i.e. they are able to move throughout the whole structure.

-Graphite has a giant structure made up of carbon atoms arranged in hexagonal rings. Each carbon atom in this layer uses three of its electrons to form covalent bonds with its closests neighbours. The fourth electron in each carbon atom becomes delocalised i.e. MOVES OVER THE WHOLE STRUCTURE. It is no longer associated with a particular carbon atom. As graphite has mobile electrons it can conduct electricity.

-The carbon layers in graphite are held together by WEAK forces. Theses layers are able to SLIDE OVER EACH OTHER as these forces are easily overcome. Hence graphite is soft and slippy. It is used in pencils and as a lubricant.

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Graphene

GRAPHENE

Graphine is a single sheet of carbon atoms from graphite. It is a layer of interlocking hexaagonal rings made up of CARBON atoms. It is only ONE ATOM THICK.

This is graphite                                   This is graphene

Image result for graphite giant covalent structures (http://userscontent2.emaze.com/images/21c8fd64-6898-4c3e-8f3c-644f839b0ce2/ecd65c96-f5f9-41d7-8ca0-d4d5913f16c1.png)                                    Image result for graphene giant covalent structures (http://cnx.org/resources/bac5ec5fc6a10f049e0f85c5470c7d24/graphene.jpg)

Graphene is

  • An excellent conductor of heat and electricity
  • The most reactive form of carbon
  • Strong in relation to its mass
  • Has a very low density
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Fullerenes

FULLERENES

Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms, but may also contain rings with five or seven carbon atoms. The first fullerene to be discovered was Buckminsterfullerene C   which has a spherical shape.

Image result for buckminsterfullerene

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Giant covalent structures 3

Graphine-

Scientists can now make many new molecules based on graphine. They can make football shapes, rugby ball shapes, anion (spheres within spheres), cones and tubes which can be open or closed at the ends. The general name for all these hollow shapes molecules of carbon is fullerenes.

The structure of these fullerenes are called NANOTUBES. (1 x 10  m). These nanotubes form extremely thin cylinders whose length is much greater than their diameter. They have useful properties such as, High tensile strength which is used in composite materials used in making                                              tennis racquets. High thermal and electrical conductivity, due to them having mobile                   electrons. This property will be useful in the electronics industry. 

Fullerenes can also be used to deliver drugs to specific parts of the body. Scientists now place other molecules inside carbon cages. This can help to treat cancer by targeting and delivering drugs to very specific sites.  This is very useful in the treatment of cancer.

Fullerenes can also be used as lubricants and as catalysts because of their large surface area to volume ratio.

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