Bonding and redox Flashcards
Draw a linear shape, include angles
1 atom with 2 electron pairs shared (3 atoms in total.) *Straight line. Angles = 180
Draw a Trigonanal planar molecule
1 atom sharing 3 electron pairs (4 atoms in total.) All atoms on the same plane with one in the middle and three projecting outwards at 120^ angles between them
Draw a tetrahedral
1 atom sharing 4 electron pairs (5 atoms in total.) Not on the same plane. There is an atom in the middle and another pointing upwards from there. The other three are projecting downwards from the centre atom in a triangle shape. The angles between them are 109.5^.
Draw a trigonal bipyramid
1 atom sharing 5 electron pairs (6 atoms total.) There of them form a vertical linear shape through the middle, the the three project out from the middle atom creating a trigonal planar shape with it.
Draw an Octahedral
1 atoms sharing 6 electron pairs (7 atoms total). Similar to a trigonal bipyramid but the centre horizontal plane hosts 4 atoms, not three.
Name the simplest alkanes, in order.
Methane Ethane Propane Butane Pentane Hexane Heptane Octane
What is the bond angle in ammonia?
107^
Name the alkane carbon chains
Methane Ethane Propane Butane Pentane Hexane Heptane Octane
What is an isomer?
A molecule with the same number of atoms but different shape… Same Chemical formula but different structural formula
Two types of structure:
Giant structure
simple molecular structures
Are the bonds in giant molecular structures strong or weak?
Strong.
All the atoms or ions in a giant structure are linked by a network of strong bonding extending throughout the crystal. Strong bonding results in giant structures with high melting and boiling temps.
What kinds of bonds are in simple molecular structures?
Covalent bonds link the atoms in the molecules (intramolecular forces) and are relatively strong.
The intermolecular forces are weak though.
What is a giant structure?
Crystal structures in which all the atoms or ions are linked by a network of strong bonding.
What’s a simple molecular structure?
Groupsof atoms held together by strong covalent bonding within the molecules, but weak forces of attraction between the molecules.
intermolecular forces
weak attractive forces between molecules
Tyoesof giant structures
ionic solids, giant covalent solids and metals
What happens when a compound is formed between a metal and a non-metal?
the metal atoms los electrons to become positively charged ions (cations) while the non-metals gain electrons and become negative ions (anions).
What is an ionic bond?
the strong electrostatic forces between oppositely charged ions in a lattice
Group 2 have a higher melting temperature and lower solubility in water than the corresponding group 1, why?
because there are stronger ionic bonds between the ions of the group 2 atoms than group 1. Ions with the high charges and small radii produce the strongest electrostatic attractions.
Properties of ionic compounds
Hard, brittle crystalline substances
High melting and boiling temps
Often soluble in water and other polar solvents, but insoluble in on-polr solvents
Do not conduct electricity when solid, because their ions cannot move away from fixed positions in the giant lattice
Conduct electricity when they are melted or dissolved in water, because the charged ions are then free to move
What is electrolysis
The decomposition of a compound by electricity. The compound which is decomposed is called an electrolyte and it is described as being electrolysed.
When an atom loses electrons, does the radii increase or decrease?
decreases because electrons are lost from the outer shell.
Covalent bond
The strong electrostatic attraction between two nuclei and the shared pair of electrons between them.
Lone pairs of electrons…
A par of electrons in the outer shell that are not involved in bonding
They can affect thee shape of the molecule
used to form dative covalent bonds
important in the chemical reactions of some compounds including water and ammonia
dative covalent bond
A bond in which two atoms shape a pair of electrons, both the electrons being donated belong to one atoms
What is bond length?
The distance between the nuclei of two bonded atoms in a molecule
What effects bond length?
Number of electron shells present in atom
Number of electrons in electron shells
Single, double or triple bonds (single bonds are larger, then double etc.)
Bond energy is…
The energy required to break one mole of the bonds a substance in the gaseous state.
What state are you likely to find molecular structures at room temp?
liquid or gas
What can be said about the melting temp of molecular structures and why?
They are usually low
Because the intramolecular forces between atoms are weak.
Given an example of non-metal giant structures
diamond
silicon dioxide
Name two giant structure held together by covalent bonding
diamond
silicon dioxide
What about the structure of iodine (I2) makes the it change from solid straight vapor on only dental warming?
It is a giant structure made entirely of intermolecular covalent bonds. These intermolecular forces are weak and require little energy to break.
Properties of simple molecular structures
- Usually gas, liquid or soft solid at RT
- Relatively low melting and boiling temps
- Do not conduct electricity as solids, liquids or gases because they don’t contain ions or free electrons to carry the charge
- Usually more soluble in non-polar solvents, i.e. hexane. Still can not conduct electricity in solvent.
Give an example of a molecular substance that can dissolve in water to conduct electricity
hydrogen chloride
Dissolves into H+ and Cl- ions and can conduct electricity due to the presence of these ions.
Bond angle is…
The angle between two covalent bonds in a molecule or giant covalent structure
What is the electron pair repulsion theory?
Electron pairs in the outer shell of atoms repel one another and so try to get as far apart as possible.
What is the bond angle of a tetrahedron?
109.5^
What molecular shape adopts a 109.5^ angle?
Tetrahedron
What is the bond angle of a linear molecule?
180^
What molecular shape adopts a 180^ angle?
Linear
Valence shell electron-pair repulsion (VSEPR) is another acronym for…
The electron-pair repulsion theory.
What is the bond angle of a trigonal planar molecule?
120^
What molecular shape adopts a 120^ angle?
Trigonal planar
What is an isoelectronic molecule
Atoms that have the same number and arrangement of electrons
What is the octet rule?
Any atom in Period 2 of the periodic table can not form more than 4 bonds because the maximum number of electrons these atoms can have is eight in 4 pairs. Therefore only 4 atoms can be covalently bound to a period 2 molecule.
By how many degrees (roughly) does an extra lone pair increase or decrease the angles between covalent bonds?
~2.5 degrees
The angle between the two hydrogens in H2O is approximately what? And why?
104^
Because lone pairs of electrons are held closer to the central atom and have a stronger repulsion than bonded electrons. The four electron pairs should form a tetrahedron and a normal tetrahedron is 109.5^ but the O has two lone pairs which repel the hydrogens and results in a V-shape.
What is the bond angle between two hydrogens in NH3? Why?
107^
Because lone pairs of electrons are held closer to the central atom and have a stronger repulsion than bonded electrons. But there is only one set of unpaired electrons therefore the bonds are larger than that of the Hs in H2O, but smaller than a normal tetrahedron.
Between the repulsion effects of the”lone pair- lone pair”, the “lone pair - bonding pair” and the “bonding pair - bonding pair” which is the strongest and which is the weakest?
Strongest: “lone pair - lone pair” repulsion
Weakest: “lone pair - bonding pair” repulsion
Define electronegativity
The ability of an atom to attract the bonding electrons within a covalent bond.
In a polar bond, the electrons are drawn towards the more electronegative atom.
Used to predict polarity
In a water molecule, which atoms have a slightly positive and which have a slightly negative charge? Why?
Oxygen is slightly negative because it is more electro negative
Which is the most electronegative element?
Fluorine
Where in the periodic table do the most electronegative elements sit?
top right
intermolecular forces
Weak attractive forces between molecules.
What is a london force?
A type of intermolecular force
The intermolecular forces that exist between all molecules. They arise from the temporary instantaneous dipoles and the fleeting dipoles they induce in neighbouring molecules.
What is the weakest type of intermolecular force?
Temporary induced dipole moments
What is polarisability?
An indication of the extent to which the electron cloud in a molecule (or ion) can be distorted by an electric charge.
Use the theory of polarisability to describe why the group 7 elements have increase boiling temperatures further down the group.
Bigger molecules with more electrons have higher polarisability. Therefore, the possibility for temporary induced dipoles is greater.
Do branched alkanes have higher london forces or lower london forces than linear alkanes?
lower. Because there is less electrically charged surface area for another molecule to attract.
Is hydrogen bonding inter- or intra- molecular?
intermolecular
Is hydrogen bonding stronger or weaker than covalent bonding?
~10x weaker
Does a hydrogen bond effect the reactivity of a molecule?
no, it only effects the physical properties
What shape forms from the three atoms associated with a hydrogen bond?
Linear (180^ angle)
What is a hydrogen bond?
A strong intermolecular force between the lone pair of electrons on either N, O or F when bound to H, and the delta + effect of the H on an adjacent molecule. Occurs because O, N and F atoms are highly electro-negative.
Hydrogen bonding accounts for:
- The relatively high boiling temperatures of ammonia, water and hydrogen fluoride
- The open structure and low density of ice
- solubility of simple alcohols
- pairing of bases in the DNA double helix
What does “like dissolves like” mean?
Water (highly polar) dissolves ionic compounds and compounds with an -OH group.
Non-polar solvents dissolve hydrocarbons
What is a solute?
A chemical which dissolves in a solvent
What is a saturated solution
A solution which has dissolved as much of the solute s possible d a particular temperature.
When dissolving a solute in a solution, what three interactions are involved?
Intermolecular interactions between the molecules of the solute
Intermolecular interactions between the molecules of thee solution
Intermolecular interactions between the molecules of the solute and the solution.
What governs how soluble a molecule is?
A molecular substance dissolves if the energy needed to break intermolecular forces and to separate the molecules in the solute and in the solvent is about the same and the energy released s the new solute forms new intermolecular forces with the solvent.
