Elements of Life Flashcards
How do we weigh atoms?
We weigh atoms by mass spectrometry
What is mass spectrometry?
Mass spectrometry is an accurate way to measure (instrumental technique) used to find the relative abundance and relative mass of an isotope.
How does mass spectrometry work?
Ionisation - An electron gun removes electrons from the sample material (positive ions)
Acceleration - Ions are attracted to negatively charged plates (opposites attract)
Deflection - The direction of ions is changed by an electromagnetic field
Detection - Ions strike a counter plate which causes a current to flow, this is then recorded on a computer
What does mass spectrometry tell us?
The mass spectrometry graphs peaks tells us the atomic mass in the form of mass:charge ratio (usually called the M/Z value).
The peak intensity gives the relative abundance
The highest abundance is scaled up to 100% and the other values are adjusted accordingly.
Empirical formula
Empirical formula is the simplest ratio of atoms in a compound
Molecular formula
The actual number of each atom in a compound
Spectrometry
Under certain conditions a substance can either emit or absorb EM radiation and spectrometry is the study of how light and matter interact.
As frequency increases the energy also increases, but wavelength decreases.
Absorption Spectrometry
In absorption spectrometry atoms absorb EM radiation (energy). This promotes an electron in the shell of an atom to be promoted from its ground state to a much higher excited rate with an increased amount of energy. This results in black absorption lines in a coloured spectrum (these lines are where frequencies of light have been absorbed by the atom.
Emission Spectrometry
In order to lose the extra energy produced from absorbing energy (EM radiation), the electron falls back to its ground state - this emits light energy. This results in a black spectra covered with coloured emission lines of emitted light from the atom.
Spectrometry of stars in space
white light contains all the visible wavelengths and its spectra is continuous. The light from stars is non-continous - it consists of lines, corresponding to the absorption or emission of specific frequencies of light.
Spectrometry for specific elements (Bohr’s energy levels)
Each element shows specific absorption and emission lines which are specific to the atom of that element.
His theory was:
Electrons exist in certain discreet energy levels.
A photon of light is emitted/absorbed when an electron changes from one energy level to another.
The photon energy is the energy difference - and therefore only certain frequencies are emitted/absorbed so they’re not continuous.
Flame Tests
When metal compounds are placed in a bunsen burner flame, the electrons in the metal atoms absorb energy from the flame and are promoted to higher (excited) energy levels. The electrons then emit energy as they fall back to their lower energy levels.
FLAME TEST - LITHIUM
BRIGHT RED
FLAME TEST - SODIUM
YELLOW
FLAME TEST - POTASSIUM
LILAC
FLAME TEST - BARIUM
APPLE GREEN
FLAME TEST - CALCIUM
BRICK RED
FLAME TEST - COPPER
BLUE/GREEN
Electron Configurations
Each energy shell is designated a principle quantum number (N), the higher the value of ‘N’ the greater the energy and we fill up from the lowest energy levels.
ELECTRON SHELL
An electron shell is the amount of energy as designated by the principle quantum number
SUBSHELL
A subshell is a sub division of an electron shell
ATOMIC ORBITAL
An atomic orbital is a further divided orbital
ORBITAL
An orbital is a region in space where one is likely to find an electron, electrons can only occupy the same orbital if they have opposite or paired spins. EACH ORBITAL CAN HOLD UP TO TWO ELECTRONS AS LONG AS THEY HAVE OPPOSITE SPIN
ORBITAL ELECTRON SPIN
Electrons in an atom have a spin (in one of two directions), every electron spins at the same rate in either a clockwise of anti-clockwise direction.
HOW ELECTRON’S ARE FILLED
1S, 2S, 2P, 3S, 3P, 4S, 3D, 4P, 4D, 4F, 5S, 5P, 5D, 5F, 6S, 6P, 6D, 7S, 7P
what were Hunds rules?
Every orbital in a sublevel is singly occupied before any orbital is doubly occupied .
All of the electrons in a singly occupied orbital have the same spin.
Orbitals are filled according to HUND’S LAW
AUFBAU PRINCIPLE
Electrons orbiting one or more atoms fill the lowest available energy levels before filling the highest energy levels.
ATOMIC RADIUS
The non-bonded atomic radius of an atom is half of the distance between two unbounded atoms of the same element when the electrostatic forces are unbalanced.
As you move along a period, the proton number increases and this means that the atomic radius decreases, this is because the electrostatic force between the outer electrons and nucleus increases.
FIRST IONISATION ENERGY
The first ionisation energy of an atom is the minimum energy required to remove an electron from a neutral atom in its ground state.
As protons increase, the atoms get smaller and therefore there’s a stronger attraction from the nucleus to the electrons in the outer shell.
EXAM DEFINITION - The first ionisation energy is the energy needed to remove one electron from one mole of gaseous atoms to form one mole of gaseous 1+ ions.
ELECTRONEGATIVITY
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
As you go from the bottom left corner of the PT to the top right corner the electronegativity increases - this means its easier for the the nucleus to attract electrons, more easily creating covalent bonds. ‘THE ABILITY OF AN ATOM TO ATTRACT THE ELECTRON PAIR IN A COVALENT BOND TO ITSELF’.
ELECTRON SHEILDING
The more shells there are, the greater the shielding so the outer electrons feel less of the positive protons attraction.
CHEMICAL BOND
A chemical bond is a strong force of electrical attraction (electrostatic attraction) between atoms and or ions in a structure. It involves the sharing or transferring of electrons in the highest occupied electron shells (the most stable arrangement of electrons).
COVALENT BOND
Electrostatic attraction of two atoms due to a pair of electrons being shared
MULTIPLE BOND
More than 2 pairs of electrons being shared
DIFFERENT SHAPES
LEWIS STRUCTURE - Dot and cross diagram
STRUCTURAL FORMULA - Drawn as a single line
COORDINATE/DATIVE BOND - Shared pair of electrons, both being supplied by one atom - drawn as an arrow.
VSEPR (Valance shell Electron Pair Repulsion Theory)
Molecules contain covalent bonds and because covalent bonds consist of pairs of electrons, each bond will repel other bonds. When bonds are closer together the repulsive forces are greater and when bonds are further apart/equal distance apart then the repulsive forces are less. Bonds will therefore push each other as far apart as possible in order to reduce the repulsive forces and when repulsions are equal the bonds are equally spaced apart.
“THE SHAPE ADOPTED BY A SIMPLE MOLECULE OR ION IS THAT WHICH KEEPS REPULSIVE FORCES TO A MINIMUM”
LONE PAIRS
If a molecule/ion has lone pairs in the CENTRAL ATOM then the shapes are slightly distorted away from the regular shape - this is because of the extra repulsion caused by lone pairs.
ELECTRON CONFIGURATION
The arrangement of electrons in shells and orbitals
explain how the spectrum for each element is unique
each element has a different electron arrangement, so the frequencies of radiation absorbed and emitted are different, this means the spectrum for each element is unique.
