Topic 1- Elements Of Life Flashcards
What is the relative mass, charge and location of a neutron?
Relative mass= 1
Charge= 0
Location= nucleus
What is the relative mass, charge and location of an electron?
Relative mass= 0.00055
Charge= -1
Location= energy levels around the nucleus
What is the relative mass, charge and location of a proton?
Relative mass= 1
Charge= +1
Location= nucleus
What are the atomic number and the mass number of an element?
Atomic number= the number of protons (and electrons)
Mass number= the number of protons and neutrons
What is an isotope?
Atoms of the same element that have the same atomic number (proton number) but different mass numbers (numbers of neutrons)
How can you work out the relative mass of an element from all of its isotopes?
100
What does radioactive mean?
When the nucleus of an atom is unstable and breaks down (decays) randomly emitting radiation. (Either alpha, beta or gamma)
What is alpha decay?
A helium nucleus (2 protons and 2 neutrons)
Range in air: few cm
Stopped by: paper
Deflection by an electrical field: low
What is beta decay?
An electron, a neutron is converted into a proton and a electron, the electron is ejected from the nucleus.
Range in air: a few m
Stopped by: aluminium foil
Deflection by electrical field: high
What is gamma decay?
An imparticulate high frequency electromagnetic wave.
Range in air: very long
Stopped by: lead sheet
Deflection by electrical field: nil
What is nuclear fusion?
2 light atomic nuclei fuse together to form a single heavier nucleus of a new element. This releases large quantities of energy.
Large amounts of energy are needed because at normal temperatures the 2 positive nuclei repel at high temperatures nuclei move with more energy and so collide with enough energy to overcome the energy barrier
What is half life?
The time taken for half of a radioactive nuclei to decay.
How can you use radioisotopes in geology?
Geological clocks- if the original isotope decays to eventually form a stable daughter product then measuring the ratio of parent:daughter we can predict the age of the rock.
What criteria must be filled to predict the age of a rock using radioisotopes?
- half life of the radioisotope must be known accurately
- there must have been no movement of parent/daughter into/out of the rock
- must be no ‘resetting’ of the radioactive clock e.g. Melting and reforming
How can radioisotopes be used to date archeological remains?
The ratio of C12 to C14, when an organism dies the ratio of C12 to C14 gradually increases. This makes it useful for dating remains up to about 50,000 years old. Beyond this the amount of C14 remaining is so small that measurements become difficult
What are radioactive tracers used for? What should be their properties?
Radioactive isotopes can be injected into the body to locate problems e.g. Cancerous tumours.
They should be gamma emitters- to enable detection and minimise ionisation of cells.
They should have a short half life to allow detection but minimise harm to the patient
Why do all atoms react to gain a full outer shell?
Because this is the most stable and low energy arrangement.
What is ionic bonding?
When electrons are transferred from metal atoms to non-metal atoms to create 2 charged particles, or ions. This charge radiates over the entire surface of the ions and so a 3-D arrangement called a lattice is formed.
What is covalent bonding?
Electrons are shared as outer energy levels overlap.
As 2 atoms approach there is a shared attraction by the nuclei for the pair of electrons. However there will also be a force of repulsion as the 2 nuclei get so close they repel. The bond is made when there is an overall distance where attraction= repulsion.
What is dative covalent bonding?
When the bonding pair of electrons comes from only one of the atoms, it is represented by an arrow.
What is the atomic core of an atom?
Nucleus + inner full shells. The atomic core is the charge that you are left with. From group 1-7 the atomic core increases from +1 to +7
The atomic core shows the ‘power’ of an atom to attract a pair of electrons in a bond
What is electronegativity?
When an atom has the ability, because of its nucleus radiating positive charge, to attract incoming electrons we say it is electronegative.
What causes an atom to be more electronegative?
- if it is smaller (fewer shells) shielding the nucleus
- if it has a more positive atomic core
What are the most electronegative elements?
Most electronegative= fluorine
F, O, N, Cl
What is a polar covalent bond?
When an element that is more electronegative bonds with an element less electronegative covalently and attracts the bonding pair of electrons closer to itself giving it a d- charge and the other a d+ charge.
What is metallic bonding?
The outer electrons are lost from the metal atoms, leaving positive ions in a sea of delocalised electrons.
Metals are solid at room temperature because an electrostatic attraction exists between the ions and electrons. This requires large amounts of energy to overcome.
What is the electron pair repulsion theory?
The electrons around the outer shell exist in pairs and these pairs of electrons repel each other so that they are as far apart from each other as possible.
What shape and bond angle do 2 electron pairs create?
A linear shape with a bond angle of 180 degrees.
What shape and bond angle do 3 pairs of electrons create?
A trigonal planar shape is created with a bond angle of 120 degrees.
What shape and bond angle do 4 pairs of bonding electrons create?
A tetrahedral shape is created with a bond angle of 109 degrees
What shape and bond angle do 3 bonding pairs and 1 lone pair of electrons create?
Trigonal pyramidal shape is created with a bond angle of 109 (107) degrees
What shape and bond angle do 2 bonding pairs and 2 lone pairs of electrons create?
A bent shape is created, which a bond angle of 109 (104.5) degrees.
What shape and bond angles do 5 bonding pairs of electrons create?
A trigonal bipyramidal shape is created with a bond angle of 90 degrees (@the top) and 120 degrees (@the bottom)
What shape and bond angle do 6 bonding electron pairs create?
An octahedral shape with a bond angle of 90 degrees is created.
What is the mole concept?
Number of moles= mass of substance
———————–
Ar/Mr
1 mole= 6.02 x 10^23
What are the 2 theories of light?
- Wave theory- treats light as one continuous wave
c= f x wavelength - Particle theory- treats light as a particle- photons.
E= h x f
What is an emission spectrum?
When a sample of a substance is given energy the electrons become excited as they absorb energy and move out of ground state. After a period of time the electrons ‘lose’ this energy and EMIT it to the surroundings, this emitted energy can be detected and create an emission spectrum which can be observed as a series of lines.
Why does each element have a different emission spectrum?
Every element will absorb and re-emit different energies and therefore different frequencies of em waves and so we will see different lines. This makes it possible to identify atoms in different EM emitting sources e.g stars
What is the difference between emission and absorption spectrums?
Emission spectrum is a series of coloured lines on a black background, this shows only frequencies of radiation emitted by an atom
Absorption spectrum is a series of black lines on a coloured background so you see the frequencies of radiation the element has absorbed
What is periodicity?
When similarities in trends in properties are seen as you go across a period.
Give an equation for the reaction of a group 2 element with water
M(s) + H2O —-> M(OH)2 (aq) + H2 (g)
The reactivity increases as you go down group 2
Give an equation for heating a group 2 metal carbonate.
MCO3(s) —-> MO(s) + CO2(g)
They become more difficult to decompose as you go down the group, thermal stability increases.
What are the solubilities of compounds of group 2 metals?
Hydroxides, as you go down the group the solubility increases
Carbonates, as you go down the group the solubility decreases
