Unit 1 - Chemical Changes And Structure Flashcards
How do metallic bonds form and what properties to they have
?
Lattice Between two metals Delocalised electrons Positive charged ions Conduct electricity Relatively strong bonds
What determines the strength of metallic bonds?
The greater the number of metallic bonds, the greater the charge on the metal ions, the greater the strength of the metallic bond and so increased mp and bp
How do monatomic gases exist?
As separate or discrete atoms.
Held together when cooled by intermolecular forces
e.g. Helium, Neon, Argon - Noble gases
What is an example of a covalent molecular gas?
Diatomic gases that are covalently bonded.
What is the trend for the strength of intermolecular forces down a group?
Down the groups, the atoms increase in size, which increases the number of electrons. This increase in electrons increases the strength of the intermolecular forces between the molecules, as well as the strength of the covalent bonds, thus increases the mp and bp
Give an example of a covalent molecular solid?
Sulphur
Phosphorous
What structure and properties does a diamond have?
Covalent network All bonds are covalent No intermolecular forces Very high mp and bp Very hard substance
Why does graphite conduct electricity but diamonds don’t?
Graphite has free delocalised electrons that allow electricity to pass through while all of diamonds electrons are bonded
What is covalent radius?
Half the distance between two covalently bonded atoms of an element
What is trend for covalent radius down a group?
Down a group, the number of filled electron shells increases, which produces a shielding effect, preventing the outer electrons from being strongly attracted to the nucleus, thus increasing the covalent radius
What is the trend for covalent radius across a period?
Across a period, the number of protons increase, which increases the nuclear charge. This attracts the electrons closer to the nucleus and so decreases the covalent radius.
Why can’t the covalent nucleus be measured for noble gases?
Noble gases are monatomic and so do not bond for the covalent radius to be measured
What is electronegativity?
Electronegativity is a measure of an atoms nuclear attraction for the electrons in a covalent bond - can find on pg12 of data booklet
Trend for electronegativity down a group?
Down a group, the number of filled electron shells increase which increases the shielding effect, preventing the outer electrons from being strongly attracted to the nucleus. This decreases the electronegativity values.
What is the trend for electronegativity across a period?
Across a period, the number of protons increase, increasing the nuclear charge, attracting the outer electrons closer to the nucleus. This increases the electronegativity values.
Why is electronegativity described as a periodic property?
There is a clear trend across a period and down a group
Why aren’t there electronegativity values for the noble gases?
Monatomic as they have full electron shells and therefore have no bonding electrons
What is ionisation energy?
The energy required to removed one electron from one mole of an atom in a gaseous state.
Trend for ionisation energy across a period?
Across a period, the number of protons increase, which increases the nuclear charge that attracts the outer electrons closer to the nucleus. Therefore the ionisation energy increases as more energy is required to remove an outer electron.
Trend for ionisation energy down a group?
Down a group, the number of filled electron shells increase which increases the shielding effect, preventing the outer electrons from being strongly attracted to the nucleus. This decreases the ionisation energy as less energy is required to remove an outer electron.
When are ionic bonds formed?
When there is a large difference in electronegativity values between a metal and a non metal
Properties of ionic compounds?
High mp and bp
Solid at room temperature
Conduct electricity when molten or in solution because ions are delocalised
How do covalent bonds form?
Shared pair of electrons between non metals
Types of intermolecular forces?
London Dispersion Forces (LDF’s) (Also known as temporary dipole to temporary dipole interactions)
Permanent dipole to permanent dipole interactions
Hydrogen bonding
What intramolecular bonds make what intermolecular forces?
Non Polar Covalent Molecules -> London Dispersion Forces
Pure Covalent Molecules -> London Dispersion Forces
Polar Covalent Molecules -> Permanent Dipole to Permanent Dipole Interactions or Hydrogen Bonding
What is defined as pure covalent bonds?
When there is no difference in electronegativity values - e.g. diatomic elements
What determines the overall polarity of a molecule?
If there is symmetry
When do non polar bonds form?
When there is a electronegativity difference between 0 and 0.4
When do polar bonds form?
When the electronegativity difference is between 0.4 and 1.7
When do hydrogen bonds form?
When the electronegativity value is over 1.7
Is oxygen polar or non polar?
Polar
What is the test for polarity?
If it deflects from a charged rod (moves towards rod) it is polar.
How do you work out if a molecule is polar or non polar?
Draw structure Add electronegativity values Count how many polar bonds there are Count how many non polar bonds there are Symmetry? (If polar molecules are devisable by two, cancel out) Can it cancel out? If yes, non polar If no, polar
What increases the strength intermolecular bonds?
The number electrons
Where do hydrogen bonds form?
Between Hydrogen and either Nitrogen, Fluorine or Oxygen. Between molecules, not atoms
What is responsible for the high boiling point of water?
Hydrogen bonds
How would you measure visocity?
Choose alcohols with similar mass
Apparatus -> measuring cylinder, bung, timer, ball bearing
Method -> turn measuring cylinder upside down and time how long it takes for the ball bearing to reach the stopper.
The longer the ball takes, the more viscous the liquid
What does the viscosity of a liquid say about the intermolecular bonds?
How many hydrogen bonds there are in the liquid
What is miscability?
How well a something mixes
What is solubility?
How well something dissolves
What is the best solvents for what?
“Like dissolves like”
Non polar substances are the best solvents for other non polar substances
Polar substances are the best solvents for other polar substances and ionic compounds
How to write Redox Equations?
Write electron equation
Scale up electrons
Combine equations
Score out electrons
What is reduction?
A gain of electrons
What is oxidation?
A loss of electrons.
What is an oxidising agent?
A substance which promotes the oxidation of another substance by accepting electrons - is reduced.
What is a reducing agent?
A substance which promotes the reduction of another substance by donating electrons - is oxidised.
Uses of oxidising agents?
Hydrogen Peroxide and Sulphur Dioxide - bleaching
Potassium Permanganate : antiseptic
Where do you find the best reducing agents?
Top right corner of page 12 of the data booklet
Where do you find the best oxidising agents?
Bottom left corner of page 12 in the data booklet
How to write full REDOX equations?
Write equation (usually given) Balance main element (e.g. Cr, N, F) Balance Oxygens by adding water Balance hydrogen by adding H+ ions Balance charge by adding electrons
How to calculate titrations?
Write equation and balance Write mole ratio Work out one side Use mole ratio to transfer information to other side Scale up if required
Why would a result not be included in the average volume for a titration?
Not concordant
How do you make a standard solution?
Take a substance of known mass and dissolve it in minimal amount of water
Transfer into a volumetric flask
Use deionised water to rinse out beaker and to ensure all remains are transfer into flask
Use deionised water to fill to known volume
How do you perform a titration?
What is an enzyme?
A biological catalyst
