1.1 + 1.2 Formulae and equations/Basic Ideas about Atoms Flashcards
name of:
positive ions
negative ions
cations
anions
order of balancing
CARBON
HYDROGEN
OXYGEN
relative isotopic mass
weighted average of several iostopes relative to 1/12th mass of a carbon 12 atom
relative atomic mass
weighted average of an atom compared to 1/12 mass of one carbon 12 atom
diatomic
N O F F CL BR I
ammonia
NH3
methane
CH4
hydrogen sulfide
H2S
giant covalent elements
Diamond
graphite
graphine
silicon
giant covalent compounds
silicon dioxide (SiO2
ionic compounds
HCL - hydrochloric acid
H2SO4 - sulfuric acid
HNO3 - nitric acid
H3PO4 - phosphoric acid
hydrogen sulfide
H2S
Positive ions 1+
Li+
Na+
K+
Ag+
NH4+ (ammonium)
H+a
Positive ions 2+
Mg2+
Ca2+
Ba2+
Zn2+
Positive ions 3+
Al3+
Negative 1- ions
F-
Cl-
Br-
I-
NO3- (nitrite)
HCO3 - (hydrogencarbonate)
OH-
MnO4- (Magnate VII)
Negative 2- ions
O2-
S2-
CO3 2-
NO 2-
SO3 2- (sulfate)
Cr2O7 2- (dicromate VI)
Negative 3- ions
PO4 3- (phosphate)
N 3- (nitride)
mass = Mm (Mr) x mol
calculate empirical formula
find out mol using mass/percentage
divide by smallest mol value
give mol ratio
molecular formula from empirical
relative mass of empirical
relative molecular mass (given) divided by empirical formula mass
number of empirical formula units
find formula of hydrated salt
determine mass of water in hydrated salt
determine mole ratio by g divided by Mr
divide by smallest calue
mole
amount of substance that has the same number of particles as there are number of atoms in C12/Avogadros number
empirical formula
the simplest whole number ratio of atoms present in a compound
cm3 to dm3
divide by 1000
dm3 to cm3
multiply by 1000
oxidation number/state
number of electrons that nned to be added or taken away to make an element neutral
oxidation rule 1
All uncombined elements have an oxidation number of zero.
E.g. in O2 gas the oxidation number = 0
oxidation rule 2
The sum of oxidation numbers in a compound is zero.
E.g. in MgO, Mg = +2, O = –2, +2 – 2 = 0
oxidation rule 3
In an ion, the sum equals the overall charge.
E.g. in NO3– the sum of oxidation numbers = –1, Nitrogen = +5, Oxygen = -2, +5 + (–2 x3) = –1
oxidation rule 4
Group 1 metals have an oxidation number of +1; Group 2 metals have an oxidation number of +2.
oxidation rule 5
Group 6 elements usually have an oxidation number of –2; Group 7 elements usually have an oxidation number of –1.
oxidation rule 6
The oxidation number of oxygen is –2, except in peroxides (in H2O2 it is –1) or when combined with fluorine.
oxidation rule 7
The oxidation number of hydrogen is +1, except in metal hydrides. For example, in NaH, hydrogen is –1 because Group 1 metals like Na always have an oxidation number of +1.
balance equations with oxidising and reducing agents
Oxidising agents - O
Reducing agents - H
then balance
mol = conc x dm3
conc (mol/dm3)
atoms = mol x avo
vol = mol x 24
radioactive emission
occurs when unstable nucleus becomes more stable
via giving out energy
eg electrons
alpha particles
two protons, two neutrons
helium neclei
beta particles
electrons
deflection of radioactive particles in an electric field
alpha - positive, slowmoving, weakly attracted to negative plate of electric field
beta - light, fastmoving, deviation towards positive plate of electric field
gamma - short wavelenth, therefore unaffected by an electric field
positron - more attracted to negative plate than alpha, as lower mass
penetrating power of radioactive particles
alpha - least penetrating, paper
beta - thin layer of foil
gamma - stopped thick plate of lead
ionising power of radioactive particles
alpha - most ionising, remove electrons from atoms, high positive charge, strongly attracts electrons
beta - less ionising, collide with electrons in atoms, knock them out, ionise the atom
gamma - least ionising, ionises atoms if electron absorbs energy of gamma unlikely due to short wavelength
positrons
anti electrons
same mass but positive charge
positron + electron
when positrons and electron come in contact, they annihilate, creating gamma radiation
gamma radiation
high energy EM radiation
short wavelength
high frequency
emited after electron capture (proton rich nucleus absorbs inner electron, which combines with proton to form a neutron)
alpha equation
bottom number determines element
beta equation
positron equation
electron capture equation
atomic number
atomic mass
atomic mass - bigger, top
atomic number - smaller, bottom
half life
time takes for the mass of a radioactive substance to fall to half its original value
ionising radiation
radiation absorbed by a neutral atom
electron is removed
atom is ionised
Radiation affect on living cells
Late Effect of Ionising Radiation:
DNA of a cell is damaged
becomes cancerous
divides uncontrollably
tumors
Acute Effect:
Large doses of radiation can cause cell death
Kill cancer cells, harmful bacteria, and other microorganisms
Effects on the body INSIDE
Inside the body:
alpha - most ionising, most damage to living cells
beta and gamma - less ionising, more likely to pass through
Effects on the body OUTSIDE
Outside the body:
alpha - least penetrating, can’t reach living cells under dead cells
beta and gamma - more dangerous, can penetrate dead cells on surface and damage living cells beneath
uses of radiation:
tracers
radioactive materials injected, radiation detectors, beta or gamma used, short half-life, easily pass through body, not easily absorbed as alpha by cells
uses of radiation:
radiotherapy
beam of gamma focused on tumor, kills cancer cells, radiation can damage/kill healthy cells, rotating gamma source focus on tumor, minimise exposure to healthy cells
uses of radiation:
radio dating
eg carbon 14, long half-life
carbon 14 decays
by counting remaining carbon atoms
uses of radiation:
thickness of metal eg foil
beta source and detector, rollers move depending on level of radiation recieved
ionisation energy
measure of energy required to remove one or more electron from an atom
first ionisation energy
energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
Second ionisation energy
the energy required to remove one mole of electrons from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.
large increase in successive ionisation energies
change in principle energy level
electron removed from an energy level closer to the nucleus (less shielding)
so more energy required
eg if large jumpe between group 2 and 3
Element is in group 2
factors affecting ionisation energy
- atomic radius - greater radius, e- easier to remove, outer e- feels reduced nuclear charge
- number of protons - increase protons, increase force of attraction to nucleus
- shielding - repulsion by electrons in shells between electron and nucleus, outershell electrons are held less tightly
The screening effect or shielding effect refers to the decrease in the nucleus’s force of attraction on valence electrons due to the existence of electrons in the inner shells.
SO
weaker force of electrostatic attraction between nucleus and outer shell electron
nuclear charge
Nuclear charge refers to the total positive charge found in the nucleus of an atom
the higher the nuclear charge, the higher the ionisation energy
the greater the positive charge of the nucleus, the stronger the attraction for the outer electrons.
IE
trend down groups
first IE decreases down groups
increasing atomic radius, increasing shielding, reduces electrostatic attraction
IE
trend across groups
generally increases, number of protons in nucleus increase, increases nuclear charge
Each electron in an energy level is not identical
shape of S orbital
shape of P orbital
shell and subshell table
How to write electron configuration
Order of orbitals increasing energy
and exception
The 4s is filled before the 3d because it is lower in energy.
watch out for chromium and copper
the 3d orbital becomes lower in energy than the 4s orbital when filled
4s electrons are removed before the 3d electrons when transition metals are ionised
Copper reduced electron electron repulsion in d shell
Eg of orbitals
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
explain increase in IE across period
increased nuclear attraction
distance to nucleus is constant, shielding is constant, number of protons steadily incrasing
chromium
expected configuration (based on the Aufbau principle) would be:
Ar 3d4 4s2
However, the actual configuration is:
Ar 3d5 4s1
This is because having a half-filled 3d subshell provides extra stability due to reduced electron repulsion
noble gas electron configuration
configuration
2p6
meaning it is a noble gas with a completely filled outer shell, which is the most stable electron configuration in nature.
2p1
This lone electron is less stable because it is far from the nucleus and not part of a stable full or half-full configuration.
C has a greater effective nuclear charge (ENC) than A, which means its electrons are pulled closer to the nucleus and are harder to remove.
ENC increases as the number of protons increases and the outermost electrons are shielded less by inner electrons.
In C, the electrons are evenly distributed in filled subshells, minimizing electron-electron repulsion.
In A, the single electron in the
2
p
2p orbital experiences less stability because it is less shielded and subject to greater interactions.
EM spectrum
radio waves (at the lowest frequency and longest wavelength) to gamma rays (at the highest frequency and shortest wavelength).
E = hf
E=J h=Js f=Hz
h is Planck’s constant and has a value of 6.63 × 10-34 Js. This constant is given on the AS examination data sheet.
Since h is a constant, then E α f. Therefore, if the frequency increases, the energy increases.
c = fλ
c=ms-1 f=Hz wvleng=m
c is the speed of light and is a constant, with a value of 3 × 10^8 ms-1.
nm to m 1x10^-9
As c is a constant, when frequency increases, wavelength decreases.
To calculate energy in kJ mol-1, you must:
calculate the frequency using the given wavelength
use the wavelength to calculate the energy in J
multiply the energy in joules by Avogadro’s number (NA, 6.02 × 1023 mol-1) to get the energy in J mol-1
divide the energy value by 1000 to convert from J mol-1 to kJ mol-1.
absorption spectrum
certain specific energy has been absorbed, then only a specific frequency of light is absorbed from the electromagnetic spectrum - this appears as a “missing” line or frequency in the spectrum.
emission spectrum
An emission spectrum is a series of lines which correspond to particular frequencies of energy emitted by an excited species.
why do atoms absorb or emit certain frequencies of light
the gap between energy levels is fixed
where is the majority of ligh absorbed or emitted by atoms and molecules found
in ultra violet and visable regions of the EM spectrum
The Balmer Series
If the excited electron falls back into the n=2 energy level (second shell), then the energy of light emitted is in the visible region of the electromagnetic spectrum and appears as coloured lines.
You need to remember the origin of the first four lines in the visible emission spectrum.
when drawring, n=3 to n=3 for first line in visable region
The Lyman Series
If the excited electron falls back into the n=1 energy level (first shell), then the energy of light emitted is in the ultraviolet part of the electromagnetic spectrum and thus can only be detected electronically, such as with a UV-Vis spectrometer.
Examination of the Lyman series gives us information about two key features of the hydrogen atom:]
Convergence Limit
The Convergence Limit
-spectral lines become closer and closer as frequency of radiation increases until they converge to a limit
-Within the Lyman series, the frequency of this convergence limit corresponds to the energy required to remove the electron (i.e. the ionisation energy).
-The lines get closer together toward the convergence limit because the energy levels get closer together the further away they are from the nucleus.
Examination of the Lyman series gives us information about two key features of the hydrogen atom:]
Ionisation Energy
Transition between n=1 level and the convergence limit, where the energy levels are so far from the nucleus that they are effectively the same energy. At this point, the electron is effectively removed from the atom and therefore corresponds to ionisation.
Therefore, the transition from n=1 to n = ∞ corresponds to the atom losing the electron completely. The ionisation energy of the hydrogen atom corresponds exactly to the highest frequency line in the Lyman series of the hydrogen atom spectrum since they both refer to exactly the same process.
Measuring the convergent frequency allows the ionisation energy to be calculated from E = hf.
When the energy levels in hydrogen get closer in energy as they get further from the nucleus, it is known as the
convergence limit
The frequency associated with the convergence limit in the Lyman series can be measured and used to calculate the
ionisation energy
The series of lines produced when the electron in hydrogen drops down to the n = 1 energy level is known as the
Lyman Series
The series of lines produced when the electron in hydrogen drops down to the n = 2 energy level is known as the
Balmer Series
effect of bond energy (KJ mol -1) on absorbtion wavelentgh (nm)
lower bond energy, bond can absorb lower energy photons, correspond to longer wavelentghs
absorbtion range relation to colour
if absorbtion within visible range
will absorb specific wavelengths of visible light
unabsorbed wavelengths of visible light will be transmitted or reflected
Explain how the Lyman series can be used to calculate the ionisation energy of
hydrogen
The ionization energy of hydrogen is the energy required to completely remove an electron from the hydrogen atom, i.e., to transition the electron from the ground state (n=1) to n=∞, where the electron is no longer bound to the atom.
hydrogen emission spectrum frequency and wavelength
