1.2 Basic ideas about atoms Flashcards
in terms of an atomic nucleus, what is radioactive decay?
process that takes place when an unstable atomic nucleus loses energy by emitting radiation
what is alpha decay?
alpha decay is a type of radioactive decay, during which an atomic nucleus loses two protons and two neutrons. An alpha particle is equivalent to a helium nucleus. it reduces the atomic number by two and the mass number by four, making the element more stable.
what is beta decay?
beta decay is a type of radioactive decay, during which a beta particle is lost, which is equivalent to an electron, and a neutron turns into a proton or a proton turns into a neutron. This changes the atomic number by one, but the mass number remains the same.
what is positron emission?
positron emission, also known as beta plus decay, is a subcategory of beta decay. A beta plus particle is the antiparticle to an electron, meaning it has the same mass but opposite charge. Therefore, when released, it increases a nucleus’ proton number by one and has no effect on the mass number
what is electron capture?
electron capture is a process that can be used by unstable atoms to make them more stable. The process involves an electron being drawn into the nucleus where it reacts with a proton to form a neutron and a neutrino.
compare the ionising power of alpha, beta and gamma radiation
Alpha - very strong ionising power
Beta - medium ionising power
Gamma - weak ionising power
Compare the penetrating strength of alpha, beta and gamma radiation.
Alpha - stopped by thin paper
Beta - stopped by thin metal
Gamma - stopped by thick lead
Compare the range in air of alpha, beta and gamma radiation.
Alpha - less than 5cm range
Beta - less than 1m range
Gamma - infinite range
How are alpha, beta and gamma particles affected by electric fields?
Alpha particles are positively charged and beta particles are negatively charged so alpha and beta radiation can be deflected by an electric field. Gamma radiation is neutral so is not affected by an electric field.
what is radioactive half life?
half life is the time it takes for the radioactivity of the number of unstable nuclei to halve
why should people limit the exposure they have with certain types of radiation?
when radiation interacts with molecules in living cells, it can damage them and cause a mutation in DNA. The cell can become cancerous if the DNA in the nucleus of a cell is damaged.
give some uses of radioisotopes
used to examine metal structures like piping to identify any defects
used in tracers for diagnostic purposes
radio-dating (used to date materials like rocks)
medically to treat cancerous tumours
define first ionising energy
the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions.
is ionisation energy exothermic or endothermic?
endothermic
what factors influence ionisation energy?
the number of protons in the nucleus.
the sub-shell from which the electron is removed.
electron shielding.
how do successive ionisation energies tell you which group an element belongs to?
a large increase between two different successive ionisation energies, e.g. between 7th and 8th ionisation energy, suggests 8th electron is being taken from a new, full, stable shell (hence this requires more energy to remove).
there are therefore 7 electrons in its outer shell to the element belongs to group 7 (new group 17)
what is the trend in ionisation energy across a period?
ionisation energy increases across a period because the number of protons increases and electron shielding remains very similar. This means across the period the electrons require more energy to overcome one the strengthening nuclear attraction.
what is the trend in ionisation energy down a group?
ionisation energy decreases down a group. This is because the atomic radius and electron shielding increases so the nuclear attraction with the electron gets increasingly weaker making the electron easier to remove.
what is an orbital?
a region within an atom that can hold up to two electrons with opposite spins.
what is a sub shell?
a division of electron shells separated by orbitals.
Sub shells are called s, p, d, and f
what rules do electrons follow when filling up orbitals?
electrons always enter the lowest energy orbital available.
Electrons prefer to occupy orbitals on their own and will only pair up if there is no empty orbital of the same energy available.
how many orbitals (max no. electrons) are there in each type of subshell?
s-subshell: 1 orbital (2 electrons)
p-subshell: 3 orbitals (6 electrons)
d-subshell: 5 orbitals (10 electrons)
f-subshell: 7 orbitals (14 electrons)
which electron shells, from 1-4, contain which sub shells?
shell/subshell(s)/max no. electrons present
1 / s / 2
2 / s, p / 8
3 / s, p, d / 18
4 / s, p, d, f / 32
why are the 4s orbitals generally filled before the 3p orbitals?
the 4s orbitals are at a lower energy level so they are filled first.
what is the electron configuration of calcium?
a calcium atom has 20 electrons
1s²2s²2p⁶3s²3p⁶4s²
1 means first shell
s means subshell
little number means number of electrons in that subshell
what determines the chemical properties of an element?
the electron configuration
what shapes are the s- and p- orbitals?
s-orbital → spherical
p-orbital → dumbbell shaped
explain the origin of emission and absorption spectra in terms of electron transitions
when an electron experiences a change in energy do that it moves down an energy level, a photon is released to help conserve energy. When an electron gains energy to move up an energy level, photons are absorbed to provide the energy for this. The specific wavelengths and energies or photons that are involved in the interactions can be seen using emission and absorption spectra.
What is the difference between absorption spectra and emission spectra?
Emission spectra - displays lines at the specific frequencies of emitted photons.
Absorption spectra - displays an entire spectrum with black lines for the ‘missing’ frequencies of the absorbed photons.
what is the equation that links energy and frequency?
Energy (J) =
Planck’s constant (m²kgs⁻¹) x Frequency of photon (Hz)
(E = hv)
what is the equation that links frequency and wavelength?
Frequency (Hz) =
Speed of light (m/s)/Wavelength (m)
put in order of increasing energy:
UV light, visible light and infrared radiation
Infrared radiation < visible light < UV light
What is the significance of the frequency of the convergence limit of the Lyman series when related to the ionisation energy of the hydrogen atom?
The frequency of the convergence limit of the Lyman series can be used in the equation E=hv to calculate the first ionisation energy for hydrogen.
