module 2 - foundations in chemistry Flashcards
relative mass and charge of a proton
mass - 1
charge - +1
relative mass and charge of a neutron
mass - 1
charge - 0
relative mass and charge of an electron
mass - 0 (negligible)
charge - -1
definition of an isotope
an atom of the same element with different number of neutrons and different masses
what is the atomic number
the number of protons and electrons
what is the mass number
number of protons and neutrons (take atomic number away from mass number)
how many protons, neutrons and electrons are there in the element Beryllium
protons - 4
neutrons - 5
electrons - 4
relative isotopic mass definition
mass of an atom of an isotope compared with 1/12 mass of carbon -12
relative atomic mass definition
weighted mean mass compared with 1/12 mass of carbon -12
how many protons, neutrons and electrons are in an ion of potassium
protons - 19
neutrons - 20
electrons - 18
relative atomic mass equation
[(% abundance x mass isotope 1) + (% abundance x mass isotope 2)] / 100
how can you guess the charge of an element
the group that the element is in
name the following ions:
NO3 -
CO3 2-
SO4 2-
OH -
NH4 +
Zn 2+
Ag +
nitrate ion
carbonate ion
sulfate ion
hydroxide ion
ammonium ion
zinc ion
silver ion
ammonium ion formulae
NH4 -
hydroxide ion formulae
OH -
nitrate ion formulae
NO3 -
nitrite ion formulae
NO2 -
hydrogencarbonate ion formulae
HCO3 -
carbonate ion formulae
CO3 2-
sulfate ion formulae
SO4 2-
sulfite ion formulae
SO3 2-
phosphate ion formulae
PO4 3-
difference between ammonia and ammonium
ammonia - NH3
ammonium - NH4
how to identify a compound containing metal + non metal + oxygen
ends in ‘ate’
how to identify a compound containing a metal + non metal
ends in ‘ide’
what does the bohr model tell us about atomic structure
electrons exist in energy levels around the nucleus
how many electrons are in the first 4 shells
2 , 8 , 18 , 32
how many electrons are in each subshell
s - 2
p - 6
d - 10
f - 14
what are the 4 orbitals that are within each subshell
s , p , d , f
what is an orbital
a region that can hold up to two electrons with opposite spins
what is the shape of s- orbitals
spherical
what is the shape of p- orbitals
elongated dumbells
electronic structure order?
1s,2s,2p,3s,3p,4s,3d,4p,4d,4f
electronic configuration of the atom Ni (28)
1s2,2s2,2p6,3s2,3p6,3d8,4s2
avagadro’s constant
3.02 x10 23
empirical formula definition
simplest whole number ratio of atoms of each element present in a compound
where is the s block
left side
where is the d block
middle
where is the p block
right
where is the f block
bottom
molecular formula definition
the number and type of atoms of each element in a molecule
how to write an ionic equation
write full balanced symbol equation using state symbols
rewrite the equation ionically
identify and cancel spectator ions
rewrite ionic form of equation
what compounds are soluble
nitrates
hydroxides if in group 1 or 2
sulphates if group 1 or 2
carbonates if lithium or sodium
number of particles equation
number of particles = avagradros constant (NA) x moles
water of crystallization definition
amount of water inside a hydrated salt
hydrated definiton
contains molecules of water
hydrochloric acid formulae
HCl
sulfuric acid formulae
H2SO4
nitric acid formulae
HNO3
acetic acid formulae
CH3COOH
sodium hydroxide formulae
NaOH
potassium hydroxide formulae
KOH
ammonia formulae
NH3
difference between strong acid and weak acid
- strong acid fully dissociates in aq solution
- weak acid partially dissociates in aq solution
difference between alkali and acid in water
Alkali: base that dissolves in water releasing OH-
ions into solution
Acid: acid that dissolves in water releasing H+ ions into solution
preparing standard solution
- Solid weighed + dissolved in beaker using less distilled water than needed to fill volumetric flask
- Transfer to volumetric flask + last traces rinsed into flask with distilled water
- Add distilled water drop wise until bottom of meniscus matches up with mark
- Flask inverted slowly several times to mix, if not titration results will be
inconsistent
acid-base titration procedure
- use pipette to add set volume of unknown solution to conical flask
add a few drops of indicator (methyl orange or phenolphthalein) to conical flask - fill burette with known solution and make sure it’s levelled off at exactly 0ml
- slowly add solution from burette to unknown solution in the conical flask
- swirl the conical flask whilst solution from burette is being added
- stop adding when reaction is complete (when there is an appropriate colour change)
- record final volume on burette (tells us the volume of the solution added – titre)
- repeat experiment for accuracy
percentage yield calculation
(actual yield/theoretical yield) x 100
atom economy calculation
Mr of desired product/ Mr of all products
why aren’t yields ever 100%
- product can be lost during filtration, evapouration, transferring etc
- reversible reaction may not go to completion
- impure starting chemicals
- reaction incomplete
why is it better to use a reaction with a higher atom economy
- it uses fewer natural resources, produces less waste, and is better for the environment
rules for assigning oxidation numbers to elements
- the oxidation number of an element is always 0 as it isn’t bonded to another element
rule for assigning oxidation numbers to compounds
each atom in a compound has an oxidation number, and it must always cancel out each other
rule for assigning oxidation numbers to ions
the oxidation number must always add up to give the overall charge of the ion
what does it mean when the name of an compound has a roman numeral
the element has that charge
e.g sodium chlorate (V)
this means that the sodium has a charge of 5
what is oxidation
the loss of electrons
what is reduction
gain of electrons
ideal gas equation
pV= nRT
oxidation in terms of electron transfer and changes in oxidation number
- loses electrons
-oxidation number increases
reduction in terms of electron transfer and changes in oxidation number
- gains electrons
- oxidation number decreases
redox reaction of acid with metal
metal + acid = salt + water
ionic bonding definition
- electrostatic attraction between positive and negative ions
explanation of solid structures of giant ionic lattices
- oppositely charged ions held together by strong ionic bonds in a huge three-dimensional structure
how does ionic bonding affect the physical properties of ionic compounds
- high mpt and bpt, electrostatic forces holding ionic lattice together are strong so require lots of energy to break
- conduct electricity when molten, ions free to move and have delocalised electrons and mobile charge carriers that can conduct
covalent bonding definition
strong electrostatic attraction between a shared pair of electrons and the nuclei of bonded atoms
bond angle and number of lone pairs/bonding pairs of a linear molecule
180
bp = 2
lp = 0
bond angle and number of lone pairs/bonding pairs of a bent molecule
104.5
bp = 2
lp = 2
bond angle and number of lone pairs/bonding pairs of a trigonal planar molecule
120
bp = 3
lp = 0
bond angle and number of lone pairs/bonding pairs of a triangular pyramidal molecule
107
bp = 3
lp =1
bond angle and number of lone pairs/bonding pairs of a tetrahedral molecule
109.5
bp = 4
lp = 0
bond angle and number of lone pairs/bonding pairs of a trigonal bipyramidal molecule
180 and 120
bp = 5
lp = 0
bond angle and number of lone pairs/bonding pairs of a octahedral molecule
90
bp = 6
lp = 0
electronegativity definition
atom’s ability to attract the bonding electrons in a covalent bond
why does electronegativity increase across a period and decrease down a group
period - atomic radius decreases and charge density increases
group - shielding increases and atomic radius increases so charge density decreases
hydrogen bonding definition
intermolecular bonding between molecules containing N,O,F or H
anomalous properties of water
- low density, open structure due to hydrogen bonded lattice
- in liquid state, H bonds are constantly breaking and re-forming so a lattice structure isn’t created
- bpt of water is high due to hydrogen bonds
- hydrogen bonding = strongest intermolecular bonds
why are simple molecular lattices solid structures
- they are covalently bonded molecules attracted by intermolecular forces
average bond enthalpy as a measurement of covalent bond strength
the amount of energy needed to break a covalent bond into gaseous atoms averaged over different molecules.
how does electron pair repulsion affect shapes of molecules and ions
- electrons are negatively charged and will repel other electrons when close to each other
- in a molecule, bonding pairs of electrons will repel other electrons around the central atom, forcing the molecule to adopt a shape to minimise these repulsive forces
how is a polar bond formed
- in a covalent bond between 2 atoms of different electronegativities, bonding electrons are pulled towards more electronegative atom. this makes a polar bond
- in a polar bond, difference in electronegativity between the two atoms causes a permanent dipole.
- greater the difference in electronegativity, the more polar the bond.
dipole definiton
= difference in charge between the two atoms caused by a shift in electron density in the bond.
polar molecule and overall dipole in terms of permanent dipole and molecular shape
- polar molecules have an overall dipole. arrangement of polar bonds in a molecule determines whether or not molecule will have a overall dipole.
- in simple molecules, e.g hydrogen chloride, the one polar bond causes a single permanent dipole, which gives whole molecule an overall dipole.
- more complicated molecules might have several polar bonds. shape of the molecule will decide whether or not it has overall dipole and so whether or not it will be polar. if polar bonds are arranged symmetrically so that the dipoles cancel each other out, e.g in carbon dioxide, then the molecule has no overall dipole and is non-polar.
- if polar bonds are arranged so that they all point in roughly same direction, they won’t cancel each other out and charge will be arranged unevenly across whole molecule. molecule will have an overall dipole and so it will be polar.
formation of temporary dipole-dipole forces
a result of the present of electrons in the molecule and the formation of temporary dipoles:
- sudden displacement of electrons in one atom to one side causes atom to have a temporary dipole
-Once temporary dipole is formed, it induces temporary dipoles in neighbouring atoms and molecules (like a domino effect).
-the two temporary dipoles are attracted towards each other by induced dipole- dipole forces also known as London or Van der Waals forces.
effect of structure and bonding on the physical properties of covalent compounds with simple molecular lattice
- simple molecules held together by weak intermolecular forces.
- atoms within a molecule are held together by strong covalent bonds but individual molecules are held together by weak intermolecular forces of attraction.
- compounds with simple molecular structure have low mpts and bpts.
- when in its solid state, the simple molecules that make up the compound are arranged in a regular lattice held together by weak intermolecular forces.
- as these interactions are very weak, not much energy is required to overcome them, which results in simple molecular structures usually being gaseous or liquid at room temperature.
- can’t conduct electricity. This is because there are no mobile ions or electrons to carry the current.
