Topic 2- Bonding and Structure
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- Created by: McTighe
- Created on: 09-02-18 22:45
How does Ionic bonding occur?
Where the metal atom loses electrons to a non-metal atom, to produce positive metal ion (cation) and a negative non-metal ion (anion). They are held together by electrostatic attraction between oppositely charged ions
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Why do the ions is a ionic bond become isoelectronic?
They take the same structure as noble gases (much more stable)
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How do you measure the size of electrostatic attraction?
(charge of first ion X Charge of second ion) / DIstance between two charges
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What are the properties of strong ionic bonds?
-Hard, brittle crytalline substances -High melting point/boiling point -Soluable in water -Do not conduct electricity when a solid but do when molten or liquid
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What happens to the ionic bond during electrolysis?
The cations move to the negative electrode (cathode) when the ion gains an electron to form a sodium atom. Chloride anode ions move to the positive electrode whee the ion loses an electron to form an atom, then pair up to produce chlorine molecules
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What does the migration of ions provide evidence for?
Existence of ions (Observed in electrolysis of coloured compounds)
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What produces the strongest electrostatic attraction?
Highest charge and smallest radii
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Why are ionic radii difficult to measure?
They vary depending on the environment of the ion
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What is the trend in radii as you go down a group
The radii increases as the element has more shells with more electrons, this increases the size of the atom, causing the radius to increase
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What is the trend in radii as you go across a period
Postively charged ions have the same electronic structure (ISOELECTRONIC), but number of protons increases in nucleus. This positive charge pulls electrons towards centre of ion, decreasing radii. Negative increase in size due to the extra electron
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What is a covalent bond?
A bond formed between atoms where a shared pair of electrons is held by electrostatic attraction between the positive nuclei and negative electrons
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What are electrons called that are not involved in bonding?
Lone pairs of electrons
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Name three purposes of lone pairs
1.Affect shape of molecules 2.Used to form dative covalent bonds 3.Important in chemical reactions for water and ammonia
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What is a dative covalent bond?
A bonding which two atoms share a pair of electrons being donated by one atom
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Describe how Ammonia uses dative bonds?
Ammonia molecule has a lone pair and a hydrogen ion has a vacant 1s in its orbital. Dative bond formed when ammonia reacts with hydrogen to make an ammonium ion
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Describe how Aluminium Chloride uses dative bonds?
At high temps, it splits into AlCl3 molecules (Electron deficient). Between the molecules contains two dative bonds fomred on lone pairs on chlorine atoms and donated into empty orbital on aluminium atom.
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What is bond length?
The distance between the nuclei of two bonded atoms in a molecule
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What method can be used to obtain value for bond lengths in a molecule in the vapour phase?
Microwave Spectroscopy
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Why do larger atoms forrm longer bonds?
They have more electrons shielding nuclei, reducing attraction for electron cloud
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What forms a longer bond: Single, double, triple bond
Single
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Why are triple bonds the shortest bonds?
More shared electrons in the electron cloud means a stonger attraction between electrons and nucleus so the nucleus is closer.
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What type of bond, LONG or SHORT, has the greatest bond energy?
Short
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What is bond energy?
The energy required to break one mole of the bonds in a substance in a gaseous state
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Describe the properties of a simple molecular strucuture
-Gases, liquids or soft solids at RTP -Low melting/boiling point -Do not conduct electricity as they do not contain free eletrons -More soluable in non-polar solvents
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What is the electron-pair repulsion theory?
The shape of molecule/ion is determined by the electron pairs in the outer shell around the central atom. The electron pairs repel each other to get as far away as possible t
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What is a bond angle?
The angle between two covalent bonds in a molecule
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What is a valence?
The outer shell of electrons
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What bonds does a double bond contain?
One sigma and one Pi bond
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What is the shortest single bond?
Hydrogen Fluoride
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What shape does two electron pairs around the central atom form?
Linear
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What angle is produces when there are two electron pairs around the central atom?
180*
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Give an example of a molecule with two electron pairs around central atom?
Beryillium Chloride- BE has two outer electrons, bond to two chlorine atoms (4 electrons- 2 pairs). NO IONIC CHARGE
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What is the name of the shape of molecule with three electron pairs around the central atom
Trigonal Planar
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What angles are found in trigonal Planar?
120*
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Give an example of a molecule with three electrons around the central atom
Boron Chloride - Boron has 3 outer electrons, bonds to three other hydrogens (6 electrons- 3 pairs)
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What is the shape of Methane?
Tetrahedral
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What angle is found in Methane?
109.5*
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Describe the bonding in methane
Carbon has 4 outer electrons, bonds to four hydrogen atoms ( 8 electrons forms 4 pairs)
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What is the shape of Ammonia?
Trigonal Pyramidal
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What is the angle found in Ammonia?
107.5*
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Describe the bonding in Ammonia
Nitrogen has 5 outer electrons, hydrogen adds three electrons (8 electrons). 3 bonding pairs and 1 lone pair. Lone pair causes bond angle to be reduced
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What is the shape of Ammonium ion?
Tetrahedral
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What angles are found in the ammonium ion?
109.5*
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Describe the bonding in Ammonium ion
Nitrogen has 5 outer electron, hydrogen adds 4 more (9 electrons). The positive charge is cancelled out by an electron leaving electrons, 4 pairs (all bonding)
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Why is Methane and Ammonium ion described as isoelectronic?
They have the same number and arrangement of electrons
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How much do lone pairs reduce the angle by?
Approx 2*
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Why do lone pairs create repulsion?
They are closer to the central atom than bonding pairs, so have a stronger repelling effect. The lone pairs only orbit the central atom, so cause repulsion of the bonding electrons
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What is the shape of water called?
Bent/V-shaped
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What angles are found in water?
104.5*
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What is the shape of a molecule with five pairs around the central atom?
Trigonal Bipyramid
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What angles are found in a Trigonal Bipyramid?
120, 180, 90
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Give an example of a molecule with Trigonal Bipyramid?
Phosphorus Chlorine- Ph 5 outer electrons and chlorine adds 5 more electrons (10 electrons- 5 pairs). 3 Chlorines are on a 120* planar, other two at a right angle
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What is the name of shape given to a molecule with 6 electrons around the central atom?
Octahedral
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What angles are found in a Octahedral molecule?
90*, 180*
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Give an example of a Octahedral molecule
Sulfur Hexafluoride- Sulfur has 6 outer electrons, plus 6 from fluorine giving 12 electrons (6 pairs).
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What is a polar bond?
A bond between atoms of different elements. Electrons are drawn to atoms with stronger pull on electrons, creating a positive and negative end
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What is a purely covalent molecule?
WHen a molecule contains the same element so electrons are shares equally, creating a non-polar molecule (e.g. diatomic molecules)
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How does an atom have a stonger pull on the electrons?
A greater effective nuclear charge
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What happens if the electrons move all the way over to another atom?
Ions are produced
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What makes the difference in bond polarity between molecules?
Electronegativity
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Is Ammonia polar or non-polar?
Polar (due to lone pairs)
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What is the bond if there is no electronegativity difference?
Non-polar covalent
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What is the bond is there is a small electronegativity difference?
Polar covalent bond
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What is the bond if there is a large electronegativity difference?
Ionic bond
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What is electronegativity?
The ability of an atom to attract bonding electrons in a covalent bond
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What scale is electronegativity measured on?
The Pauling scale (0-4)
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What is the most electronegative element?
Fluorine
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What are other electronegative elements?
Oxygen, Nitrogen, Chlorine
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Does electronegativity increase or decrease across a period?
Increases
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Why does electronegativity increase across a period?
The nuclear charge increases but the number of shielding electrons remains constant, so attraction of shared pair increases
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Does electronegativity increase or decrease down a group?
Decreases
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Why does electronegativity decrease down a group?
Although nuclear charge increases, the number of shielding electrons also increases. This means the bonding pair of electrons is further from the nucleus, so there is less attraction
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What is a polar molecule?
Contains polar bonds which do not cancel each other out, so the whole molecule is polar
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What are the two opposite charged ends of a molecule called?
Dipoles
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What is the dipole moment?
Measure of the overall polarity of a molecule, where a molecule has several polar bonds, the overall dipole moment is the vector sum of the individual dipole movements taking size and direction into account
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What are London Dispersion forces?
Intermolecular forces that exsist between all molecules. They arise from temporary dipole and fleeting dipole they induce in neighbouring molecules
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When does a temporary induced dipole occur?
Between two non-polar molecules
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How does a temporary induced dipole work?
Repulsions and attractions arround a non-polar molecule occur, causing the temporary induce dipole to induce a dipole in neighbouring molecules
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Does branching make london dispersion forces weaker or stronger?
Weaker
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What is polarisability?
An indication of the extent to which the electron cloud in a molecule can be distorted by a nearby electric charge
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Why do bigger molecules have higher polarisability?
They have more electrons so the possibility for temporary induce dipole is greater, so the boiling point increases
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How does shape of a molecule affect the dispersion forces?
Long, thin molecules develop stronger temporary dipoles due to electron movement. This is because they have a large surface area, and can lie much closer together
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Why do Alkanes boiling point increases with chain length?
There are more electrons so have higher polarisability. This means higher chance of a temporary dipole being formed, so bigger dispersion forces
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Why do Alkanes boiling point decrease with branching?
Chains push the molecules further away, so do not lie closely to each other. This means the chance of temporary dipole being formed is smaller, so dispersion forces are weaker
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What do permanent dipole- permanent dipole interactions occur between?
Polar molecules (In addition to London dispersion forces)
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Why do molecules that have permanent dipoles have higher boiling points
The forces are slightly stronger as its always present. It also has London dispersion forces as well
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What are hydrogen bonds?
A bond that occurs between hydrogens and hydrogens bonded to an electronegative element.
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Why does water have a higher boiling point than hydrogen fluoride?
It has two hydrogen bonds per molecule
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Give examples of water hydrogen bonds are responsible for
-Higher temperatures of water, ammonia, hydrogen fluoride -Open structure and low density of ice -Solubility of alcohols in water -Base pairing in DNA
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What is an Isomer?
Same molecular formular, different structure
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Why do alcohols have lower volatility (and higher BP) than alkanes?
The alcohol contains -OH. The oxygen is more electronegative than hydrogen, making hydrogen slightly positive. The hydrogen bonds to a slightly negative oxygen form hydrogen bond. These are strong bonds so require lots of energy to break
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Why does pentane have a higher boiling point than 2,2-dimethylpropane?
Pentane is a straight chain so pack together easily and large surface area to electrons are exposed to form london forces. The other one is more globular, branches cause steric hindrane so cannot pack together as easily
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What is soluablility?
The concentation of a saturated solution of a solute at a specified temperature
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What is a saturated solution?
A solution that contains as much of the solute as possible at a particular temperature
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Why do non-polar substance not dissolve in water?
The molecules are easily separated by intermolecular forces, but the hydrogen bonds between water molecules act as a barrier so molecules that cannot form hydrogen bonds are kept out.
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Why do alcohols dissolve in water?
They can break hydrogen bonds of water, and form new hydrogen bonds between the alcohol and the water
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What is a Miscible liquid?
Liquids that mix with each other e.g. water and ethanol
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Why are salts soluable in water?
The ions are strongly hydrated by polar water molecules. The water molecules cluster around them and bind to them. Energy release when water binds to ion is enough to overcome electrostatic attraction holding lattice together, and break it up
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Why are some salts insoluable in water?
The hydration energy is not large enough to overcome the electrostatic forces in the lattice
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What is water a good solvent for?
Ionic compounds (hydrating the ions) and simple alcohols (hydrogen bonds)
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What is water a poor solvent for?
Compounds unable to form hydrogen bonds
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What are non-aqueous solutions good solvents for?
Compounds that have similar intermolecular forces to those in the solvent
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What is a giant structure?
Crystal structures in which all atoms and ions are linked by a network of strong bonding extending through the crystal. They have high melting/boiling points
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Give three examples of Giant structures
Ionic solids, giant covalent solids, giant metallic lattices
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What are simple molecular structures?
Small groups of atoms held together by strong intermolecular covalent bonds, but weak forces between molecules. These forces allow molecules to be seperated easily. They have low melting/boiling points
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What are Allotropes?
Different forms of the same element in the same physical state, held together by strong covalent bonds
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Describe the structure of Diamond
4 carbon atoms to one atom; no free electrons (localised)
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What are the properties of Diamond?
-Does not conduct electricity -COnducts thermal energy (when rubbed the atoms vibrate and produce kinetic energy) -High boiling/melting point -Insoluble in water
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Describe the structure of Graphite
Atoms held together in hexangon layers; each atom bonds to three others -Delocalised electrons found between sheets
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How does Graphite conduct electricity?
The delocalsied electrons form a cloud. They move around to form temporary dipoles
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Why is graphite used as a lubricant?
It is greasy and soft, due to weak bonds between layers so the layers can slide over each other
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What are the properties of Graphite?
-High melting/boiling point -Low density -Insoluble in water
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What are fullerenes?
Small molecules of carbon within a sphere of molecules
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Are fullerenes soluble or insoluble in water?
Insoluable, but soluble in other olvens due to weak van der waals attractions between carbon and water
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Is Buckminsterfulleren a molecular or giant strucutre?
Molecular
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What is Graphene?
A single layer of graphite (2D as one atom thick). It is one of thinnest materials but also very strong
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Describe the structure of metals
Giant lattices with delocalised electrons (free to move)
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Describe the bonding in metals
Occurs due to the electrostatic attraction between the positive metal ions and the 'sea' of delocalised electrons
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What are the general properties of metals?
-High melting/boiliing point -High density -Good conductors of heat/electricity -Malleable
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Why do metals have high melting/boiling point?
Metal atoms are closely packed with strong electrostatic forces between the positive ions and delocalised electrons. Lots of energy is needed to overcome the attraction to move metal ions from their place
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Why do metals have high density?
Atoms are closely packed together with little space between them
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Why are metals good conductors of heat?
When heated, kinetic energy is transferred to electrons, causing them to move faster and conduct heat to other parts of the metal
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WHy are metals good conductors of electricity?
When a voltage is applied, the electrons are attracted to the positive electrode and flow through metal to produce a current. They are able to move around and carry the current
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Why are atoms malleable?
When a force is applied, they are able to slide over each other
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Other cards in this set
Card 2
Front
Why do the ions is a ionic bond become isoelectronic?
Back
They take the same structure as noble gases (much more stable)
Card 3
Front
How do you measure the size of electrostatic attraction?
Back
Card 4
Front
What are the properties of strong ionic bonds?
Back
Card 5
Front
What happens to the ionic bond during electrolysis?
Back
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